MAPUG-Astronomy Topical Archive in PDF Format

Last update on April 17, 2006
Copyright © by Ed Stewart
Download a PDF copy of the Topical Archive with a searchable index
as of January, 2004 by clicking here.
Tips for new LX200 owners (GPS click here)
What Model of LX200?; Selecting Best Focal Length
Considering CCD Astrophotography?
Eyepiece Recommendations (also see Eyepiece
Topics in right column)
Sources of Information for Beginners
Choosing Between LX90 vs. LX200
LX200 Checklist for Starting-Up (Classic)
LX200GPS Checklist for Starting-Up (GPS)
DVD--"A Beginner's Guide to the Meade LX200GPS"
Accessory Suggestions; Aperature Fever; Top 10 Books
Pointing Accuracy...The Real Story
Also see: "LX200 Initial Alignment" under Aligning-AltAz Concerns, below.
Eyepiece/Accessory Case Hints; Tips Web Page
Light Pollution & Nebula Filters Recommendations
Dealers Rating URL; Warning!!--Check Bolts
Checklist for Starting-Up (Classic); Initial Alignment
Backlash-Aware 2-Star Alignment
LX200 Classic Longitude Calculator
Choosing Stars & Slew Speeds for 2-Star Alignment
Enter Key Problem During Alignment Routine
How close is "close enough" OTA alignment?
Solar & Lunar Tracking URLs
Polar Aligning--see separate topic below
Daytime Observing/Alignment --see topic below
Polar Alignment Procedures--Drift & Iterative
Polar Alignment and PEC Accuracy?
Leveling Accuracy and Polar Alignment?
Southern Polar Alignment Suggestions
Better Alignment Accuracy; Polar Alignment with CCD?
Polar Axis Balance/Tracking; RA Tracking Issues
Dec Blocking Autoguiding Device; Meade Align Method
Resync'ing a Polar Aligned Wedge-Mounted Scope
Polar Drift Alignment Described; Using a Tripod
Best Polar Alignment Routine, Polar GoTo Adjustment
Polaris is Visible -- 2nd Alignment Star Isn't
Polar alignment When Polaris is not Visible
Avoid database errors in Classic v3.30 when aligning
Mount upgrading advice; Mounts for Large OTAs
Initial Reactions to Announcement; Yahoo Groups
Review URL; Photos — RCX400 20" & Maxmount
Magellan II Accuracy & Alignment Issues
Magellan: Building RS232 Cable; Power Cord/Supply
LX50 Connector Pin-Out; Connecting to Computer
Dec Test Results--Chips, Motors, & Gears
Fixing LX50 Dec Axis Stiffness; LX50 Dec Fix Kit
LX50 Dec Wobble Fix; LX50 Dedicated Web Site
Reinstalling LX50 RA Fine Adj. Knob
Fix for LX50 RA Adj. Knob Looseness
Magellan II Digital Setting Circles for LX50
LX50 Mods URL / RA Drive Solution; Drive Upgrade
LX90 Discussion Group link; LX90 vs. LX200
Differences in LX200 vs. LX90 OTA;
LX90-- Pitfalls to Avoid; Miller's Everything LX90 Website
Links to LXD55 websites; Discussion Group Link
LXD650 Mount Good for Imaging?
Mount Mods/Hyper-tuning & Adding Teflon Bushings
ETX Info Site URL; ETX/EC Repair & Tune-Up Page
ETX Collimation; Repair Service; Computer Control
Upgrading Starfinder Dobs; Starfinder Mods
Polar Alignment; Magellan ROM Version Numbers
StarFinder Laser Collimation Setup
Magellan II Operation Hints; Star Charting Software
Starfinder Rotating Rings Source
Starfinder 16" Discussion Group Link
For Pictor cameras & CCD topics see furthur down-LX200 Good for Astrophotography?
Can the LX200 Mirror Mount Allow Precision Tracking
for Imaging?
Switching from LX200 Fork Mount to an Equatorial?
Dew Shield, 2-D, & 3-D Counterbalances; Max Wt-Carrying
Homemade Symmetrical Balancing Device
Balance at High Declinations
Battery Power Boxes; EE101--Basic Electricity Concepts
Battery Power Supply Design; Measuring Remaining Charge
Battery Tester, Inverters, Capacity & Power Cautions
Battery Connectors, Parallel Battery Charging
Battery Resource Site; Reverse-Power Protection
12v Gel Cell Battery Charging/Restoring Tips
Operating the Classic on 15v or 12v; Reducing 18v to 15v
Voltage Regulator Primer; 12v Battery Charger Recom
Fried 18V Converter; 12V to 18V Converter Found
Adjusting Meade 18V Supply; 1812v Converters
Meade 12v to 18v Converter Alternative
DC Power Source & Inverter; Power Supply Issues
Standard LX200 Fuses; Blowing a Fuse--Solved!
120V-12V Power Supply Recommendations
Power Supply (DC>AC vs DC>AC>DC)
Cables and Connectors/Treatise on LX200 Plugs
Electronic Improvement--Resister Upgrade
Grounding the LX200 & Computer/Camera -Sep page
PC-LX200 Serial Connector Diagram
Dual Serial Ports & USB Laptops; Easy Serial Cable
Serial Cable Pin Out; RS232 Tester, Aux RX232 Port
Wiring Control Panel Aux Plug-In to Power Accs
Power Panel/Cable Problem Solved
LX200 Schematics URLs; Installing Ceramic Resistors
Power Connectors / Cable Management
AC Power Supply Voltage Reduction
See: Running Power to Remote Site:
(Observatory topic in right column)
Set-up procedures developed by list members
Carrying Cases for LX200s, 90s & 50s (also in Europe)
Mod to Military Case; Desert Storm Scope Covers
*Star Testing the LX200; Collimating with a Cheshire?
Simple Collimation Method; New Collimation Page
Daytime Alignment; Collimate With or Without Diagonal?
Advanced Optical Adjustments; Cool Down Times
Maintaining SCT Collimation; SCT Collimation Article
Secondary Mirror Rotating?/Optical Alignment
Tri-Lobed Stars Fixed?; LX200 Corrector Plate Glass?
Laser Collimators? --Stay with Star Test
Using the Kendrick Laser Collimator
SCT Laser Collimation Ep?; Collimation On Symmetry Axis?
Collimation Using Two Telescopes?
Bob's Knobs Collimation Screws/Replacement Procedure
Field Flattener Requires Re-Collimation?
Procedures for aligning & finding objects safely
*See Field Rotation Issues topic below
Modification to Use NGF-S; Derotator Advise
Dew
Dew
Dew
Dew
Controller Schematic; Homemade Dew Zappers
Formation & Prevention; DewBuster
Inside Corrector Plate;
Shield Construction & Proper Color
LX200 & Beginning Astrophotography Questions
Getting Started in Astrophotography & CCD Imaging
Piggy Back AstroPhotography; Guiding Techniques Articles
Where to Process Film Images?
Helpful Hints for Astrophotography
LX200 Astrophotography URLs
Film Camera Selection Criteria; Exposure Calculator
Calculating f/ratio with eyepiece projection
FOV in 35mm Camera?
Back focus/JMI/Van Slyke Slide Mirror
New Evaluation Page of Filters
ETX as Guidescope, w/Autoguider, & Info URL
Guidescope Scope Focal Length Calculations
Guidescope URLs; Guidescope vs. Off-Axis Choice
When Autoguiding, Does the Guidescope Have to be
Pointing in same Area as Main Scope?
Economical Classic Autoguiding?
SCT Guidescope Issues, Adapter for Flip-Mirror?
Guidescope Mounting and C-5 Operation
Pros & Cons: Flip mirror, Guidescope, Parfocal Tube
Meade Off-Axis Guider Adjustments, OAG
Finding Stars for Off-Axis Guiding
Lumicon Giant Easy Guider (Off-Axis Guider)
Meade f/3.3 vs. Optec Maxfield; f/6.3 Spacing
Mosaic Image How-To URL; FITS Image Viewers
Deepsky Imaging and Alt/Az?
Astrophotography Math; Tokai Light Pollution Filter
FocalPoint Focuser Source
MAPUG Observatory Site for Posting Member Images
Lens/Camera/Imager Adapters; Opp. of T-Adapter
Eyepiece Projection Imaging & Calculations URL
Homemade Knife-Edge Camera Focuser
Camera Mount for LX200 URL
Review of "CCD Imaging Techniques" Video
What are the Definitive Books about CCD?
Pixels per ArcSec Calculation; Image Size in Microns
Anti-Blooming, Flat Field/Dark Frame
CCD Selection Questions; Pollution Filters for CCD
LX200 8" f/6.3 + CCD Questions
Equipment & Software for Imaging; Useful Adapter
SAC WebCam For Starting CCD Imaging
Internal Mounting a Barlow; LX200 Rear Cell Adapter
Pictor Manuals Comparisons; ETX & Autoguider Primer
CCD Focusing Aid; CCD Camera Diffraction Focuser
Improved CCD Focuser Mask; Tricolor Filters for CCD
Color Filters, Thicknesses, & 3-C Imaging
Filter Wheel Recommendations; Seeing vs. Pixel Size
Camera Connections to Avoid Vignetting
Video Camera for Real-Time Imaging
Anti-blooming Considerations Photometry & Astrometry
Depth of Focus at F/10, F/6.3, & F/3.3
Optimizing a CCD Imaging System--Pixels and FL
Hartman Mask Focus URL; Hartman Mask Focuser
Cable Pin-Out for ST-4; Dark Frames & Flat Fields
Operation in Warm Temps; Camera Desiccant
Color Imaging Concepts; True Technology Flip Mirror
Google Astro Image Search;
Yahoo Groups: Digital SLR (DSLR) & 3D-AstroPics
Image Processing Freeware/Software URLs
SBIG ST-4 vs. Pictor 201XT; ST-4 Autoguiding Tips
AO-7 Benefits (adaptive optics); Using a Guidescope
LX200 7" Mak & Large CCD Chips
MX5-C Color CCD Imaging; Starlight Xpress Camera
LX & Starlight Connection; Mac and Pictor Connection
LX200 Dual Serial Ports; FOV/Plate Scale Calculator
CCD--Min. Sampling Calculation;
Second Laptop Serial Port via USB;
Role of CCD Cameras in Amateur Astronomy
CCD University URL; CCD Unguided Time on a LX200?
CCD Calculator Freeware URL; Getting Started Website
CCD Image Processing & Photometry Tutorial URLs
Narrowband Imaging Resource Site
Narrowband Emission Line Imaging of Nebulae
Field Rotation Program in Basic; Calculator
Field Rotation from Misalignment
Rotational Movement in the Image Field
AutoStar User Friendliness Opinion
AutoStar II Updating Problems/Solutions
Autostar Version and Age of LX200GPS
Autostar Sync to Selected Star; Computed Bodies
Autostar Command Set; Low Level Autostar Debug
AutoStar II Commands/Programming Set
AutoStar with Dead Flash ROM; Parking the GPS
Autostar Update Problem-- Missing Named Stars
Undocumented Command--Guide Speed Slewing
Autostar to PC cable; External Antenna in a Dome?
GPS Firmware Posted; Remote Handbox via AutoStar
Computer Interface / Autostar Update Problems
SMT Software & Lost of Contact with TheSky
Updating Satellite Orbital Elements
14" Base Casting Beefed Up?; First Light Reaction
Accurate Time Necessary?; Bolt Holes Same as Classic?
Scope Certification by Independent Company
Schematic Diagrams Sources
Avoiding the Hard Stops; Internal Componet Photos
GPS Model Loses Dates!, RA Motor Stalled
Does GPS Internal Battery Holds Ephemeris Data?
GPS Alignment Stars Not in FOV
Owner's Manual (PDF) link; GPS Tips Source
GPS & Giant EasyGuider; Worth upgrading to GPS? OpticalMechanical Alignment, Yahoo GPS Group
GPS Starting-Up Checklist; Focuser Speeds/Control
GPS Only Runs on 12v; RS232 to USB Possible?
RS-232 Cable - GPS same as Classic?; Parking
UHTC Coatings vs Classic Multi-Coatings?
Going to 2" Diagonal Worth It Visually Or Not?
Is SMT Worth It?; GPS Mirror Lock Like Classic?
Focuser Lock Issues; Focus Lock Adjustment
Lining OTA with Black Flocked Paper/Flat-Black Paint
How-To Webpage
Baffling in Regards to Rear Aperture & Diagonals
For the Classic
Analysis, Long Cables, Multiple Keypads, Repairs
Classic Keypad Codes & Hot Plugging/Unplugging & Mods
Beep Elimination; Experimental Handcontroller
Classic Keypad Replacement Source; Panic Stop?
Button Membrane Repair
See LX200 Miscellaneous topic below
Controlling the LX200 and SBIG ST7/ST8 with CCDOPS
Creating a Mosaic in Photoshop
Luminance Layering using Photoshop
Multiple Luminance Layering Color Enhancement
Color Imaging of Nebulas with Hydrogen Alpha Data
Processing Flow for LLRGB, Ha/RGB, & Solar Images
How Unsharp Masking and Laplacian Sharpening Work
Making CCD Flats w/Light Box; Photons per ADU
AstroStack Software
Stacking CCD Images vs. Longer Exposures
LX200 Image Magnification; ST-7E/ST8E Guide Chip
F/3.3 Focal Reducer Lessons; Re-Assemble f/3.3 FR
CCD Imaging-- Single Exposure vs. Stacking
SBIG STV Experiences; Lightbox Drawings & Details
CCD Purchase Recommendation; CCD Astrophoto Site
Calculating CCD Pixel Size & Pixel Size Needed
STI-201 Autoguider Focuser for 201XT
Suggested Powering Up/Down Sequence
Buying a CCD Camera Advice
Which LX200 Scope Best for Imaging?
Best for Guiding: ST-4 or Pictor 216XE?
Questions-- FWHM? & OAG w/Focal Reducer
ST-8E vs. Apogee AP47p CCD
Note: see Software/Computer topics in left column
IR Filter On Web Cams; Web Cam Advice & Links
WebCam Acquisition Technique with AstroSnap-Pro
LPI as an Autoguider?; Installing LPI Software
Digital Camera Hacks; Video Camera Advice
Canon 20Da Digital SLR for Astro Imaging
Webcam vs. Digital Camera vs. CCD
DSLR-Focus Software
DSI Blooming Images; LPI as an Autoguider?
Experiences in Installing LPI Software
Using the DSI with the Classic LX200
Using the Pictor 201XT; Pictor Autoguider Flow Chart
216XT--Getting Started; 201XT Instruction Chart
Pictor 201XT-Description of the Calibration Process
Solving 201XT Guiding Problems
Using the 201XT URL; Pictor 201 Killing Motherboard?
STI-201 Autoguider Focuser for Meade 201XT
Pictor 201XT and Other Guider Focus
ETX and 201XT, 208XT, or 216XT Autoguider Primer
Pictor 201XT-- Guidescope or OAG?
208XT Manual Correction--Shutting Down Camera
in Standalone Mode; Frustration Vented!
Pictor 208/216 With Maxim for Autoguiding?
208/216 Autoguider.exe Software Link
Safe Procedures for manual lifting of the scope
Quick & accurate leveling methods
Thermal Effects in SCTs; Stuck Focuser--Classic
Focus Shift Over Long Sessions; Classic Focuser Removal
Re-Attaching the 12" Classic Focuser Mechanism
Mirror Stabilizing Bolt & Its Effects on Collimation
Mirror Cell Mod; Forcing Mirror Flop; Flop Explained
Reducing Mirror Shift and Improving SCT Focuser
Action Updated, Kit available
Focuser Bearing Mod; Removing Focuser Backlash
Field of View Definition; Connecting FocusMax
Loss of Focus--Resolved; Grease for Baffle Tube
Hartman Focusing Mask vs. Diffraction Focusing
Optimum LX200 Primary/Secondary Spacing
Can the LX200 Mirror Mount Allow Precision Tracking
for Imaging?
Getting Started; Setup and Focus; Pin-out
416XTE & SCSI Problems; 416XT + Laptop + SCSI
Pictorview 7.14 & SCSI Advice; Contents of Pictor.ini
SCSI to USB Converter to Connect the Pictor?
RA & Dec Calibration Times of Meade Guiders
Pictor 416/1616 Control Box Description
416XT with Taurus Tracker III; 416XT Vs SBIG ST-7
Supplementary Fan Cooling; 416 Warm-up Update
Cleaning 416XT Article Link; 416XT/ST-7 Desiccant
Baking the 416XTE Dessicant
416XT RGB Exposures / Icing Fix / Focusing
Cooling the 416XT /Pictor Temperature Numbers?
Continuous Frames with Pictor 416XTE
Note: see LX200 Software/Computer topics
in left column
Best Focuser?; Building Your Own Electric Focusser
Focusers Compared--JMI, Optec, Aproge, VanSlyke
Focuser Pinouts for Optec TCF-Focuser
Control Panel Package for the Optec TC-Focuser
PCFocus AutoFocus System & FocusAide
Focusing Controller Kit -- LazyFocus
Advice on RoboFocus & FocusMax; Stepper Focuser
Making Artifical Test Stars, Spherical Aberration
Calculating Actual FLs; Optical Defects Simulation SW
Optical Quality Testing: Ronchi Lines?
How PEC Works, Training Experiences, etc.
PEMPro-- Program Reduces PEC (see Software Page 3)
Polar Alignment and PEC Accuracy?
First Pass PEC Graphs After Cleaning
PEC as Related to Drift Align; Elongated Images
PEC and Long-Term RA Drift Solution
PEC Training w/CCD or Manually?
PEC Problem Caused by RA Worm Damage
Difference Between Periodic & Pointing Errors
PEC Training--Constructing Guiding Keypad
Effective Use of PEC with an Autoguider
Guide Correction Speeds?; Training on Different Teeth?
Selected specs including: Weights of OTAs
& Mounts, Giant Tripod Specs; 12" Max Height
Rear Cell Tread Specs; Fork Arm Weights; Baffle tube
When LX200 Made Switch to Metal Dec Bearings, etc.
Eyepiece & Diagonal Recommendations
Light Pollution & Nebular Filter Recommendations
Lumicon Filters Detoriate Over Time?
Wireless/Wired Reticle Guiding Ep; Best Reticle Ep
Meade Reticle Eyepiece; Astrometric Ep Instrs.
Making a Parfocal Ep, Filter Thread Specs
9mm Reticle Eyepiece; Wired Reticle EP or Battery
TV 2" Rich Field Kit with 55 mm Plossl vs.
TV 2" Diagonal w/35mm Panoptic
Secondary Shadow to Calculate Lowest Power Ep
Eyepiece/Telescope Reviews URL
Meade 2" Eyepiece Filter Threads
How Much More Can You See with a Wide FOV Ep
Choosing a Wide Field Ep; Screw-bolt Ep Cases
Calulating Ep Actual FOV; Apparent vs. True FOV
Maximum Field of View Calculations --separate page
Re-centering Reticle Eyepiece; 8mm-24mm Zoom Ep
LX200 + Eyeopener + Eyepiece; Eyeopener Review
Eyeopener Benefit Wide-Field Eps?; SCT Vignetting
Magnification -- What Does It Really Mean?
*Also see "LX200 Mirror Shift & Focusing Issues"
in left column.
Motor Focuser Issues; Focusers Compared
Meade f/6.3 Focal Reducer/NGF-S Focuser
Optec Maxfield f/3.3 Considerations
Focal Reducers vs. Low Pr Ep; Meade's 1209 Focuser?
Field Flattener Without Focal Reduction Available?
Focal Reducer Adapter; focuser grease recmd
Robo-Focus (Remote Focusing)
Advice on dealing with aperture fever.
Power Connector Replacement
Firmware & Keypad Version #s
Powering the Telrad, Hardwiring Telerad to LX200
1x Finder Suggestions; Accurate Finder Registration
Touch-Up Paint; Washer for 2" Diagonal Rotation
Adding a Cooling Fan; Explanning Setting Circles
OTA Moisture Removal; Adapting 12" Forks to 10" OTA
Spiral Search Function for LX200 Classic?
Accessory Attachment Screws, OTA Bolt Removal
Rusting Screws -- Replace or Recondition?
LX200 ScopeSaver /Mounting Assistant/Website
LX200 Saddle Mount; GPS Attachment for Classic
SCT Cooler Review; Internal Mounting of a Barlow
LX200 12" vs. Celestron 14" - Comparsion
Will Meade Upgrade Optics to UHTC?
Supercharging (rebuilding) Service Available
LX200 Scope Repair Service;
Canadian & UK LX200 Repair Services
OTA Removal from Forks
Vibration Suppression Pad Orientation
Lens Cover as Accessory Tray
How to Subscribe/Unsubscribe to MAPUG-Astronomy
Unsubscribing Quick Links; Email Virus Issues
Links to Regular Archives Sorted by Date
Searchable Archive for MAPUG & other Astro Lists
Five MAPUG Archive Locations; Mother of All Archives
MAPUG-Astronomy Archives: How to Get Back Issues
MAPUG-Astronomy Abbreviated Astro Terms
A page that includes designs and manufactured items by list
members for battery power boxes, 2-D counterweight systems,
scope transporters, scope covers, RA/Dec drive upgrade/fix
kits, observatories, wedges, wedge/tripod stablizers,
permanent piers, & miscellaneous items.
Contact Numbers, Email Address & Suggestions;
Meade's Repair Policy & Options; Extended Warranty?
Replacement Parts Now Available from Meade
LX200 Manual URL; PDFs of Operating Manuals,
Advice in Dealing With Meade About Problem Scope
LX200 Control Software; LX200 Control Commands
LX200 & ST-7 Remote Control; Telescope Control SW
Communicating with LX200; Remote Hi-Precision Slew
Remote LAN & Cables Construction; Wireless vs. Cable
Proper Cable Routing Through Conduit
Lightning Danger; Running Power to Remote Observatory
LX200 Control with Palm; Simple Laptop Connection
Autostar Suites Remote Control Experiences
Remote dome/Scope/Imager control - IP Address?
Lumicon Giant Rich Field Viewer Experiences
Magnitudes, Mirror Sizes, & Reflectivities
Spectrographs Sources; Home-Made Spectroscope
Language Translator URL; Gear Vendors
Eyeglasses for Observing; Laser Vision Correction
Dec Mods to Meade 500 Mount; Java-Based Optical Design
Parking Tips, Park Software URL, Advice
Parked LX200 in Remote Obs. Know Its Position?
See right colum for general Observing,
Planning, & Time/Lat/Long Setting SW
See for Computer/Remote Control SW
LX200 Alignment Stars w/StarryNight Software
LX Star Databases--Software to Download
LX200 Database Cross Reference Files
SAO Catalog Cross-Refer To Other Star Catalogs
TheSky Database; Earth Centered Univ Object Files
USB/Serial Adapter; COM Port Checkout
MaxIm DL Updated to v4/CCD Controls Pictor 416XT
Image Management SW; ASCOM Platform 3.0
LunarGOTO SW; Best Pair Alignment Freeware
FITS Photoshop Plugin URL
SCSI Explained; Adaptec Alternatives
Pictor 416/SCSI/WinXP Connection; Deepsky 2000 SW
Substitute for Red Plastic on Laptop Display
Astro Software Collection by Platform URLs
ATC (Advanced Telescope Control); Skymap 6 Utilities
ACP Observatory Control Software;
LX200 Control Centre Software
ScopeDriver Shareware Updated
MaxPoint Software Explained; AstroStack Software
Satellite Observing SW & Tracking Power Supply
Satellite Transits of Moon & Sun Resources
Sky View Cafe planetarium site
Linux in Astronomy; Telescope Programming Group
KStars Planetarium Software under Linux
Double Serial Cable; Alignment Stars & TheSky
UTC Display & NightVision Freeware Updated
Moon Pointing & Tracking SW; AstroArt
RS232 Grounding & Connection Problems
Dual RS232 Wiring (Classic)
TPoint-- software to correct for mount errors
PEMPro -- Must Have Program to Reduce LX200 PEC
Astroart CCD Control Driver for 416XT/XTE
Selecting Astronomy Software - Final Decision
Best Pair II Freeware; Meade Autoguider SW
USB/Serial Port Adapters; Adding Serial Ports
AstroPlanner (Mac & PC); RS232 Troubleshoot Tool
Virtual Atlas of the Moon Software Link
Experiences in Installing LPI Software
DSLR-Focus Software
TheSky (Mac OS), Cable, and the LX200
Mac Astronomy Software; Software by Platform
Connecting the Mac and LX200; AstroStack Software
ScopeDriver Shareware for Mac-- updated
UTC Display & NightVision Freeware Updated
Lat/Long Converters for Mac OS; Best Pair II Freeware
USB/Serial Adapter for Macs; Desktop Space Images
AstroPlanner SW; Terrabrowser SW; Solscape
Firewire camera control software
Sky View Cafe planetarium site
Image Stacking SW; OpticsCalc--Optical Calculator
Astro Software for the PalmPilot & Handspring Visor
Palm/GPS Use; Palm/WinCE Astro & Control Software
Used SCT Buyers Guide and History of the SCT
Is Lunar Observing Better with Larger Meade SCTs?
Cold Weather Observing Gear; Dressing Cool(er)
Chart Illuminator; "FAKE" Lumicon Filters?
Green Laser Pointer Advice & Safe Use
Green Vs. Red Lasers
Testing for Diagonal Rotation Positioning Error
Question & Answer discussion with Doc G
Mapugger of the Times Awardees
Article by Robert Preston
--select from below:
List 1:
105 Finest Objects
List 2:
52 Finest Objects for Public Nights
Lists 3:
Messier Marathon List URL
Star Charts Vs. Burham's Recommendation
Current Visible Comet, Meteor Shower, Occulation,
and Minor Planet URLs
SkyCharts 2000 (from Sky Atlas 2000)
Meade Catalog Stars Spreadsheet URLs
Excel Astronomy Info File URLs
Astronomical League's Double Star Club--SAO numbers
NGC and IC Catalogs--Text Files
Caldwell Catalog Numbers to NGC/IC URL
Double Star "33" Website
Sources for Efficiently Viewing the Messiers?
Lunar Eclipse Calculator URL; Wood's Lunar 100 list
Online Observing List and Catalog Cross Reference
Professional & Amateur Astronomer Collaborations
List 4:
Double Star List by David Abrams
List 5:
List of Interesting Objects (by size) by Doc G
Star charts organized to minimize slewing.
Solar Spectra Discussion; 1000 Oaks Solar Filters
Slewing to the Sun; H-alpha Filter Observing; Telrad Filter
Setting GMT & Local Time; Local/GMT Time Offset
Time Setting Software & URLs--PC & Mac
Magnetic Declination Calculator
Co-Ordinates for UK; US & Worldwide Long/Lat URLs
See: Lat/Long Converters for Mac OS
in LX200 Software--Mac OS
See Fuses in Battery topic; Water Damaged Electonics
No N, S, E, W Slew, Inconsistant Boot-Up Problem
RA Initialization Sequence Info; Stopped clocks
"MEADE" Only Display on Hand Controller
List of Common Failures (Classic)
Canadian & UK LX200 Repair Services
Slewing, Finding Home, Hand Paddle, Dec Binding,
Componet Temps, OTA Dimensions, Max load, etc.
Purchase Advise; 16" GPS & ST-9 with Derotator?
16" Mirror Removal, EZ Focus Kit, Focuser Fix/Mods
16" CCD Connector Pin Out; Disassemble Drive Base
Motion Limiting System / PEC Retraining & Problems
RA Drive Problem & Photos; 1 or 2 RS232 Ports?
Observatory Designs; Dome Recommendations
Domes vs: Roll-Off Roof; HomeDome Advice
Roll-Off Observatory Based on a Utility Trailer
Plastic Shed Observatories; Controlling Insects
See: Dome Automation Freeware in Remote Control
Pier Location?; "Off the Grid" Power in Remote Control
Design Considerations, Cost Estimating; Wall Height?
Observatory Ventilation?;
Plans & Issues for an Observatory on a House
Zoning, Covenants, and Deed Restrictions Concerns
Observatory Design Books & Other Sources
Determining Observatory Dimensions
Gear Grease Recommedations; Cleaning Procedures
Repair suggestions for Classic keypad
Sources for circuit board schematics on-line
Mirror Removal/Installing; Baffle Tube Off-Center
Removing/Replacement Corrector Plate Procedures
Select from below:
Improving LX200 Pointing Accuracy-Original OTA/Fork Alignment Procedures
Alternate 1, OTA/Fork Alignment Procedures
Alternate 2, OTA/Fork Alignment Procedures
LX200 Fork Mis-Alignment Solution
OTA Bolt Removal
Also see "Pointing Accuracy & 'GoTo' Issues" below.
Tests for Pointing Accuracy; Fork Flexing Issues
Centering Test; Best stars for Polar Iteration
TPoint Software and the LX200
Excellent Pointing Accuracy Detailed
RA Runaway Condition; RA Slewing Overshooting
RA Drive Noise Fix, Drive Repair & How It Works
RA Motor Problem Erratic Slewing- FIXED
Tracking/Noise Problem Solution--Metal Chips in RA
RA Disassembly/Removing Lower RA Bearing
RA Drive Binding Problem; RA Runaway Repair Webpage
Analysis and Repair of Dec & RA Drives URL
LX200 Base Construction & Limitations
Removing Dec/RA Motor Clutch Plates
Image Vibration Solved (Jittery/Jerky Tracking)
Replacing Worm Gear Spring/Mod for Adjusting
Atmospheric Refraction Adj; RA Setting Circle Use
Bias Weighing the OTA vs. Elastic Pulling
Loose RA Motor?; Worm Wheel Lapping
Dec Axis Assembly Adjustment/Repair Procedure
Motor Failures & Study; Backlash/Slop, Some Fixes
Dec Overshooting; Retrograde Motion Fixes
Aligning/Adjusting Dec Setting Circle
Dec Backlash Compensation South of the Equator?
Drive Photos; Rebuild/Bearing Replacement
Dec Tweaking & Mods; Dec Runaway Causes
Dec Runaway Motor Problem (see LX200 Dead!
Dec Runaway Repair Webpage
Dec Encoder Wiring Repair; cable replacement URL
Description, Analysis, & Repair of Dec & RA Drives
List of Resource Links for Piers & Wedges
Proper Material to Fill Steel Pier; Grounding?
Permanent Pier--Dampening Vs. Stiffness
LeSeuer Pier Recommendation, Pier-Tech URL
Enlarging/Extended/Initial Orienting a Pier
Permanent Pier Designs & Considerations
Portable Pier/Wedge Design URL; Wooden Piers
Concrete to Pier Bolts, Concrete Questions
Pier Mounting Plates: One vs. Two; Pier Design URLs
SuperWedge Problems, Cures & Modifications
Superwedge Thrust Bar & Alt. Adjuster Mods
Superwedge Strength & Use of the Central Bolt
Two-Plate Pier Adapter for the SuperWedge
Standard Wedge Modifications & Stabilizer
Mettler Wedge--Alternative to Meade & Milburn
Base Mounting Bolt Pattern URL
Homemade SuperWedge Knob Wrench
Best Wedge for LX200?
Using Giant Tripod with 10" & Superwedge
Meade Superwedge vs. Milburn Wedge
Also see Member Designs for Wedges Available
for purchase--Milburn, Superior, and Ulti-Wedge
Tripod Leg Refinishing/Protecting/Removal
Reducing Tripod Height
Tripod Threaded Rod Component Order
LX50/200 Tripod/Wedge Modifications
Maintaining Polar Alignment (& on a tripod)
Leveling-- Wedge or Mounting Plate?, Necessary?
Mounting with Center Bolt on Wedge
Homemade Wedge Plans URLs; Tripod/Pier Bearing
Wedge Measurements to Determine Pier Height
Wedge Adjustments on a Permanent Pier
Use Central Bolt to Attached Base to Wedge?
DEC Cable Repair/Source for replacement
Loose Dec Clutch Fix; Melting Tantalum Capacitor
Reading the LX200 Dec Scale; Dec Drive Test Points
Eliminate of Hi-Freq. Vibrations, Image Vibrations-Jittery / Jerky Tracking, AO-7 & Sensor
Instruction sheet on installing the Classic service kit
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For New or Prospective LX200 Owners
Tips for new LX200 Owners
What Model of LX200? Recommendation
Selecting Best Focal Length for New Scope
Eyepiece Recommendations --separate page
Using Max Exit Pupil to Determine Lowest Power Eyepiece --separate page
LX200: Choosing Between 8" Vs. 10"
Sources of Information for Beginners
LX200--7" Maksutov Vs. 8"SCT
Accessory Recommendations for the New Owner
LX200 Newbie - Top 10 Books
Aperture Fever...Need Advice
Pointing Accuracy...The Real Story
Eyepiece/Accessory Case Hints
Light Pollution Filters Recommendations
Nebular Filters URL
Telescope Dealers Rating Webpage
Tips Web Page
Warning!! New LX200 Owners -- Check Bolts
Subject: Tips for New LX200 Classic Owners
From: Ralph Pass
Since last year, I have learned a few tips on the LX200 that all of you new users may not be aware of. These really make
observing a greater pleasure. Heres some of what I have learned, feel free to add to this list:
1. In performing the 2-star alignment, its only necessary to know exactly where one star is. Follow the keypoard prompts till you
come to choosing the second star. When you know which star is going to be your second star, find the stars name and press
enter. Then, instead of centering the second star in the eyepiece, just hit the "GoTo" button and the telescope will slew to that
star as best it knows. If your last alignment was done in the same general area, the star will probably at least be viewable in the
finder. This helps if you don't know exactly which star is the one in Orion or Gemini as an example, just give it your best shot and
press "GoTo" instead of centering. This works great! Its not listed in the manual.
If you set up level and pointing south it gets even easier. All you really need is the name of a star that is up. Power up. Press the
STAR key. Press ENTER twice and select the star name. Press GoTo. The scope will slew near to where that star is. It is most
likely the brightest in the area. How close it comes depends on the accuracy of the clock, Lat & Long, level and pointing south.
Once you have the star centered you can perform the above process.
2. When you have hit the "GoTo" comand and the telescope is slewing, you can stop the slew by just hitting the "GoTo" button
again. It will stop the slewing of the scope. To resume slewing, just hit "goto" again and the slew will continue to its destination.
This is a nice feature if you have a fear of maybe the eyepiece or your camera hiting the fork or bump into another part of the
scope. Its nice to know how to stop a slewing scope.
This is not in the manual either. These next few are just ways to make the night viewing more comfortable.
3. Take a comfortable chair with you. Even a bar stool is probably OK as long as you can sit at the eyepiece and view. An
adjustable one is better. Sometimes, objects or details will become much more apparent once you have viewed thru the eyepiece
for a few minutes. This is also great on tired feet or backs as the night lingers on.
Adjustable is very important. A comfortable height can mean the difference between relaxed viewing and back strain. A few
inches can make a difference.
4. Make yourself a Rob Roy Pizza pan. This is one of the greatest simplest ideas ever. Buy your self a 16" pizza pan for 10 bucks
or so and cut out an offset hole in it to slide over your tripod. Place your telescope on the tripod as usual and you now have a
very nice tray to hold a eyepiece, filter, flashlight, a sandwich, twinky, cigar or what every you have that you need to sit down for
a minute as you make adjustments. But most of all, this is a terrific place to hang your key pad anywhere around your telescope,
the full 360 degress around the tripod. You will never leave home without this! I guarantee this! Ask the group for more details
on this Pizza pan idea.
**Archive Editor: check-out the Meade Tripod Shelf Design on the AstroDesigns Home page (click the Home button on this page)
for a shelf that also aligns the scope base to the tripod's center bolt--it eliminates a major frustration of setting-up the scope.
5. Get the Rob Roy Joystick for your keypad. Its the most natural looking option you could get for your keypad and like all
joysticks, it will give joystick control over your telescope. This will also work on LX-50's also. This along with the pizza pan are the
two items that any LX200 owner should always have. This is another one of those "don't leave home without it" items.
6. An extended Keypad coiled cord. I bought a 20 foot black coiled telephone cord at Radio shack for about 5 or 6 dollars. It has
the correct plugs to plug right into your keypad and control panel. You can test it by removing the coiled cord on your telephone
and trying out this one. This gives lots more mobility for you without giving up the keypad. The cord hangs about a foot from the
ground so things dont get tangled into a mess.
**Make sure you get the right kind of phone chord. There are two kinds. One works, and one can be disastrous. I'm not sure
whether the reciever type or the phone to wall type is correct.
7. A JMI Motofucus NGF-S focuser. This is a $250. item so I included it last. This is in my opinion the only way to get rid of image
shift focusing. Without this focuser, very high power viewing is very difficult to focus. This unit is well made and fits the telescope
perfectly. Its expensive, but then, so was the telescope.
Don't forget Bill Arnett's Jiffy Focuser. See his web page: <http://nineplanets.org/>
These are items that I found are very useful to know about and use and makes operating the LX200 much more pleasurable and
comfortable. With the number of new telescope owners out here, I thought it would be good to share this information.
Subject: Which LX200? Recommendation
From: Doc G
Recommendation:
I have had in the past three years all three of the Meade LX200 classic telescopes, the 8", 10" and 12". I have found all three
excellent optically. The 8" was sturdy and easy to set up. A friend still has it and is still very pleased with it. I consider this to be
high praise since he may be even more fussy than I am and an expert at making things break.
I got the 12" next and found it excellent optically. It was too large and heavy for me to set up without help. I mounted it in a
trailer but still found it hard to lug about. I had a building built for it at a dark site belonging to the Madison Astronomical Society
and donated it to the Society. It is now mounted solidly and I use it regularly.
I then purchased a 10" which I found to be the best of the three optically and just right for my imaging interests. (the middle one
was just right as in the story) The point of telling this is that I feel you get a lot of optics and a fairly good mechanism for your
money. I would buy a Meade telescope again. However, there is another consideration. When you purchase a telescope you
should if possible think about the uses you will make of the instrument.
The 8" is from an imaging point of view a really nice long telephoto with a mechanical mount that is more than adequate to point
it. The 12" is large and heavy and has a focal length that is so long that for much CCD imaging the field of view is rather small.
Additionally the mount for the 12" and the 10" are almost identical in terms of the motors, the gears and so forth. I believe the
mechanism is fine for the 10" but a bit undersized for the 12". I also got the 10" which is the f6.3 version to get a larger field of
view for CCD imaging. It is clear that the 10" mount gives good stability while the 12" mount is under stress. I believe this relates
directly to the marginal sizing of the gears and cetera for the 12".
In all of the telescopes the electronic pointing mechanism is very good and it is a joy to wander about the sky looking finding the
dimmest objects at the press of a few keys. I remember distinctly the first night I had the 12" out and aligned properly. I
thought, "Well, Uranus must be out there somewhere high in the South." I keyed in STAR 907, GOTO and Bingo the nice little
blue-green disk appeared right in the middle of the finder. The scope proved itself that night and ever since.
When you purchase your LX200 it is wise to try to get the one most suited to your viewing interests. They are all very good and
they all have essentially identical electronics and good and bad points. Any one telescope will probably not satisfy all your
astronomical needs.
Knowing what I now know, I would get the 10" f/6.3 as the first choice. I really like the LX200s. There are better and much more
expensive telescopes out there if money is no object. Meade gives you a lot of telescope and a basically good telescope for the
money in my opinion. Almost all of the remaining problems I am having with my instruments are fundamental to the fork mount
design. But that is a big topic not appropriate to this message.
Subject: Selecting Best Focal Lengths for New Scope
From: Doc G
For telescopes of the amateur type, say up to 14", the focal lengths are of course just the apertures times the focal ratio. Looking
at a few numbers, we get 120" for a 12" f/10 scope, 100" for your 10" f/10, 63" for a 10" f/6.3 and so forth down to shorter focal
lengths for refractors which are usually 4" to 6" in diameter but a bit faster at F5 to F10. That would give, for example, for a 5"
f/6 refractor a focal length of 30".
Thus there is a considerable difference between amateur scopes. In general however they run from 20" for smaller refractors to
120" for the larger SCT scopes. So the answer to your question might well be that scopes with a focal length of 20" to 50" are
short (small) those in the 40" to 90" range are medium and those longer than 90" are long (large).
This rather arbitrary set of ranges however only answers the questions of how large a real field of view you can get. Get with
what? The field of view depends on the size of the field stop in an eyepiece or the size of the chip you are using for imaging.
I have felt that it is important when selecting a telescope to choose a focal length that will allow you to see the object you are
viewing fully. For planets, you would want to use a barlowed long focal length so as to get a large enough image of the planet to
be useful. On the other hand if you want to view many nebula, you need a short focal length telescope and a 2" eyepiece to get a
large real field of view.
So armed with your needs in the first place you can judge what would be the best focal length for your viewing habits. You can
see immediately that no one scope focal length will satisfy all of the large range of needs. As it turns out, many persons purchase
10" or 12" scopes only to find that they cannot image a large range of interesting objects. Thus they use focal reducers to
effectively shorten the focal length of the base telescope. On the other hand the same telescope will need to have a focal
extender (barlow) to effectively increase the focal length for things like planet viewing.
So you see, this is a dilemma. I feel that no one telescope will do it all and I think a lot of people agree with this assessment. A
folded design like an SCT in the range of 100" focal length is a good choice. Then for very large objects a focal length of 40" is a
reasonable choice. These scopes can then be extended or reduced with an optical element of reasonable construction.
So while the designation of short, medium and long is rather arbitrary, the practical application of focal length as a primary
characteristic of the telescope is not.
Subject: LX200: Choosing Between 8" Vs. 10"
From: David Bonnell, Date: May, 1998
> I am in doubt about which LX200 to choose.
> As you know the LX200 8" OTA weighs 43 lbs and the tripod 20 lbs, while
> 10" OTA weighs 51 lbs.
The weights you list are apparently total weight, including probably the tripod and accessories (shipping weight?). The real issue
is the tube and fork weight, which, for the 10" is about 70 # (with finders... attached) vs. perhaps 40 # for the 8". This weight
difference (and the physical size difference) is very significant logistically (moving around, setting up, storage...).
Although I have a 10" (LX-50), and really appreciate the extra aperture, I will have to admit that the setup effort probably keeps
me from trotting it out on marginal nights (esp. when the moon is up). As for taking it to dark sky sites, the difference there is
not a big one (I do have a small van). If you plan on other kinds of travel, the availability of commercial cases... is a real
advantage. One issue is the physical weight in picking up and mounting - I find I need to wear a back brace to avoid a sore back
in the morning - and heaving the assembly up onto the tripod is more than slightly an effort, especially compared to an 8".
If you want the most scope you can haul around and set up by yourself, the 10" is it in a Meade SCT - I know of people who can
assemble the 12" rig by themselves, but generally do not! The Celestron C14 on a German mount is also a one-person system, as
the German mount disassembles into more manageable chunks -- But, to take advantage of the large scope, you need to be
dedicated to observing, need the extra aperture for photography, or just be a big guy for which 70 # of dead weight (VERY
EXPENSIVE dead weight) is not an issue, for the 10" to be a choice. There is a very real possibility that the extra size/weight of
the 10" will actually keep you from observing, when the 8" would be "just right."
There has been a lot of other good advice provided to this thread - you need to weigh the pros and cons - the 10" is a great
scope, and I don't regret my choice. I probably would have always felt that I stopped short, somehow, particularly since the
(relatively small) price difference makes the 10" one of the real buys. You rarely get 50% (light or whatever) more for less than
10% more cost. But the 10" is physically a BIG rig, and 1/2 magnitude is not a lot of seeing. The 8", one the other hand, is pretty
easy to manage for almost anyone. Taking an 8" to a really dark site can more than make up for the aperture difference! And, as
the light pollution gets worse, the advantages of the 10" seem to melt away.
My advice -- unless you are planning a major commitment to this avocation and DSO's (deep space objects) are a passion, the 8"
is probably a better entry point scope. But, if aperture fever is an issue, and you really want to look at DSO's, the extra 1/2 mag
gain is noticeable (IMHO) - but I have looked through a number of scopes from 6"ers to 15"ers, and for those objects (like most
of the Messier list) that are moderately bright, the differences in what you see are relatively subtle, rather than "knock-yoursocks-off" different.
Don't get me wrong, the 10" is manageable, and a really sweet scope - just be aware that dead-lifting 70-odd #s on and off the
tripod is tougher than it sounds. You cannot "hug" this load very close to your body, so a lot more arm strength and control is
required than you would expect. If you decide on the 10", be sure to get one of the base to tripod head locator products (Scope
Saver) on the market or that are discussed on the Ed Stewart's home page, chose Stewart Sled: <http://www.MAPUG-Astronomy.
net/AstroDesigns/>
The good news -- you can't make a mistake -- both sizes are good tools, with lots to recommend them.
Subject: Sources of Information for Beginners
From: Jim Lowry <jim-lowry
att.net>
There have been many questions recently from novices, both to MAPUG and to astronomy in general. Having been there myself
just some two years ago, I would like to recommend some books and URL's that have been EXTREMELY helpful to me:
"The Backyard Astronomer's Guide" by Terence Dickinson and Alan Dyer
I believe that this book is an absolute must for the beginner. It starts off basic, but goes into wonderful detail. Types
of telescopes, both pros and cons....... types of eyepieces, all types....... filters ...... what to expect through the
scope...... eye relief, barlows, observing the planets, moon, and others.... you get the idea, it is thorough, detailed,
easy to read, with wonderful pictures.
"The 20-cm Schmidt-Cassegrain Telescope" by Peter L. Manly
Many have called this the bible for SCT's. Even though I have the 10", it really goes into detail on the optics,
mechanics, and maintenance of a SCT.
Get on the web and spend some time exploring. Here are sites that are a constant source of information for me. There are of
course others. Can't list them all:
Ed Stewart's page <http://www.MAPUG-Astronomy.net/AstroDesigns/>
Gems and pearls of wisdom from Ed and other MAPUGers. A must see!!
Doc G's website . Note: should open a new browser page over this one.
Technical data and information galore. Find out why we treasure our professor, and many thanks to others who have
contributed pages to Doc's site.
Bill Arnett's page <http://nineplanets.org/> Note: should open a new browser page.
An incredible wealth of information on general astronomy. Great links to SEDS and other places, I visit this site
often. Thanks to Bill!!
and last but not least.......... especially for beginners: SKY and TELESCOPE Astronomy Page
<http://skyandtelescope.com/> Note: should open a new browser page over this one.
This site also has a wealth of information, how to buy, what to buy, what to look for, what is seeing, secrets of deep sky
observing, etc. I hope that this list of informatio will prove useful to others. Enjoy our beloved hobby. I do!
Subject: LX200-7" Maksutov Vs. 8" SCT --part 1 of 2
From: Colin Haig <chaig
compuserve.com>
John Hilliard wrote:
>considering purchase of a LX200 7" Mak.
>I am aware of the claims for lunar, planetary, double
>stars etc. but from a dark sky
>site, how are they for deep sky. I am looking at the
>comparison to an 8" LX200.
>Disregarding the price difference, but performance wise on deep sky.
John, I have the 7" Mak, and in 3 words: "I love it". I have head-to-head compared it with several other scopes - 8" , 10", 12"
Meade and others, 7" astrophysics, and basically, it puts the 8" to shame.
Short answer:
If you must choose between 7" and 8", buy the Mak. You are only gaining V=0.5 Magnitude by moving to the 8", at a
considerable loss of optical quality, resolution, and really poor contrast (some people call it washed out images).
I went through the same question, and decided that the real question is Mak or 10". Ultimately, size, weight, and performance
made me decide on the Mak, which I have had for nearly 2 years and 100,000 light years now. The 10" will get you another full
magnitude, which was not enough for me to put up with 61 lbs versus 45 lbs.
Some Thoughts:
Meade's specs as published in the owners manual are "conservative" on the Mak, in my opinion. I had a "disagreement" with a
10" owner who insisted his scope had to be better, cuz Meade said so. Then he looked through it. Surprise! He spent the rest of
the night collimating. The 8" is the lightest at 37 lbs, and its tube will swing through the forks for slightly more compact storage.
The 7" Mak has a longer OTA, so this causes the weight/length trade-offs. Otherwise, mechanically they are identical.
The Mak has a fan to cool the interior of the OTA, and takes longer to dew up so you get more viewing time if you forgot your
Kendrick Money-Removers ;-> You also have to collimate the 8" well to get a great image, and there's no need to collimate the
7".
A few others on this list have tuned up their 8" scopes with flocking paper, and other mods to make them very good scopes. Rob
Roy taught me a fair bit about his, and also shared some of his "challenges" in getting a good set of optics out of Meade. He was
a great resource, and influenced some of my thinking. (Thanks Rob).
If dollars aren't the issue, consider the 10 or 12. If resolution and contrast, combined with portability are the issue, then buy the
Mak.
The 10 and 12 are heavier and bulkier. The 12" has significantly greater light grasp which puts it ahead a fair ways. These are
ideal scopes if you have a permanent observing facility. I would own a 12" (as well!) if I was in that situation.
Personal Experiences:
For dark skies under good seeing, you will really be glad if you purchase the Mak. Contrast is much better, and images are tacksharp without need to mess around with collimation and field flatteners. I have used my scope for deep sky under moderately
dark skies as well as up in darkest "cottage country" - northern Ontario, and am very satisfied with its performance. The best
conditions let you get down better than 13th magnitude.
With my particular scope, it is bested by the 7" astrophysics in resolution only slightly. I've had them both up over 650x on lunar
craters and double stars. For fun we tried a 2.5mm Lanthanum once at Starfest, but that was silly (over 1000x in my scope), but
it was workable as a "bet settler".
Resolution wise, a former university astronomy technician who owns a 12" decided to do some head-to-head comparisons with
my scope. We agreed that the difference was virtually imperceptible on a rare night of near-perfect seeing in the winter, splitting
Eta Orionis (1.5') easily, so we went on to tougher challenges, like 32 (?) Orionis (0.7'), which was still perceptibly split. And did I
mention nice diffraction rings?
From a light-gathering viewpoint, this is not a scope for deep sky photography. I have successfully used it for a fair bit of CCD
work, and video-astronomy. 9th magnitude is the limit on video cameras, and no limit on CCDs (Magnitude 15 or so is as far as I
have had patience for). I also purchased the Meade f/3.3 reducer which gives about f/5 on my scope, and this works well with the
video camera and CCD. (Paul Goetz came up with some mods to the PC-23C camera, and I have to check out how low I can go
now that I did it to my unit).
If you need a light bucket, buy the 10" or save up and buy the 12" and rent an assistant to heft it around. I often use the Meade
standard f/6.3 focal reducer to "shorten" my Mak to f/9.5, and then it is virtually identical to the 8", with less central obstruction,
better contrast, better resolution. I use this combination for galaxies (because the field of view is narrow on the Mak) and for
lunar photography.
If you are a "refractor guy" then you will love the Mak. If you want a light bucket this isn't it, but then neither is the 8".
------------------------------------------------------------------------------------------------Subject: LX200-7" Maksutov Vs. 8" SCT --part 2 of 2
From: John Hopper JohnLX200
aol.com Date: Oct., 1999
I think you've overstated the case for the 7" Mak, perhaps from not having looked through enough collimated SCTs. Comparing
to an uncollimated or poor sample of an SCT is like stepping on a frog, any scope can squish one.
First, the weight/aperture is downright bad. It actually is listed at 54 pounds (not 45) vs. 61 for the 10" and 38 for the 8" in my
manual. Meade threw in an iron disc to keep from having to lengthen the forks to reach balance, and some people (including me
initially) didn't realize most of the additional weight was not all glass and Meade blue, but just dead weight. It's also got to be one
of the main reasons for the fan, to get that iron disc to ambient temp along with the optics.
I've owned an excellent 7" Mak LX200, good 10" LX200, good 10" OTA, and excellent 8" OTA. I've also used some others,
including a superb 10" LX200, owned by Ken Milburn that we viewed Omega Centauri and other southern objects with before the
1998 eclipse in Aruba.
I loved my 7" and can still remember what the moon looked like at 1111x in it (see, your 1000x wasn't so outrageous!) In some
respects, but not all, it can hold its own against either of the 10" Meades I've owned, but it just doesn't compare at all to an
excellent or better 10", much less a superb one like Ken's was that night. It's quite comparable to my excellent 8" SCT, an f/6.3
no less.
Comparison to a 7" AP refractor is at least partially wishful thinking, probably caused by average seeing when the comparison
was done. Understandable, because by definition seeing often IS average. Under the same circumstances, you might find a 5" AP
performing about like the 7" AP also, with the 4" not far behind if at all, except for brightness at a given power of course.
Subject: Accessory Recommendations for New Owner
From: Danny Cobb <dndcobb
bellsouth.net>
I faced the same questions back in January when I purchased my first scope, a 10" f/10 LX200. I started out with the scope, the
supplied 26mm Plossl and the #140 2X Barlow. Then I caught a case of accessory fever. I did extensive reading on the web and
pondered and agonized over each purchase, so maybe my experience will be of value to you. Some of this stuff may be old news
to you, so apologies if any of it's too basic. Here's what I've purchased so far and my comments. Please remember that these are
my opinions and that I've been at this for less than a year.
1. Dew shield. In hindsight, I'd make one. It doesn't have to be pretty to work. Kept me dew-free during the winter.
2. ScopeSaver table. Makes it soooo much easier getting the scope mounted on the tripod. The eyepiece holders are a real
joy to have once you start accumulating more eyepieces. Once you have it, you'll wonder how you got along without it.
Mine stays attached to the tripod, but since it attaches with three screws, you can remove if necessary (e.g. car transport.)
Editor's note: there's a do-it-yourself design on the AstroDesigns home page.
3. 35mm Panoptic and 6mm Vixen Lanthanum. I highly recommend an eyepiece with a wide actual FOV. You might want to
consider the TeleVue 55mm Plossl and the new 31mm Type 5 Nagler in addition to the 35mm Panoptic. The 31mm Nagler
was just recently announced and may be hard to obtain for a while. Will also probably cost a zillion dollars. You'll need a 2"
diagonal as well. I only get to use the 6mm on rare nights of exceptional seeing; I'd advise against this much magnification
until you start running out of things to buy. However, I do use it when aligning the scope as the small FOV makes for more
accurate centering. (An illuminated reticle eyepiece would be even better though.)
4. Full aperture Type 2+ solar filter. Nice to have, but doesn't get much use.
5. 14mm Pentax and 22mm Panoptic. Both get a lot of use, especially the 22. The 22mm has an actual FOV that is wider than
that of the 26mm Plossl, so it's somewhat of a duplication in eyepieces. You may want to consider the 19mm Panoptic for
this reason (but the FOV of the 19 is still close to that of the 26.)
6. I bought a battery, converters, etc. and made a field power box that supplies 12vdc, 18vdc and 120vac. Based my design
on those in the archives. Can send you plans and photos if you want. Probably spent $250, but it's been well worth the
investment. Mine looks amazingly like the ($390) Kendrick power box, although I didn't see the Kendrick until after I made
mine. (But the Kendrick doesn't have 120vac.)
7. Kendrick dew heater (controller and 10" heater.) The dew shield alone wouldn't keep me dew-free during warm humid
nights in the South. Pricey, but well-made and effective.
8. Filters. (These are only my opinions!) The 82A is too light to notice much effect. Ditto for the 12 yellow. The 80A is better,
but I think the 56 light green enhances Jupiter better. The 56 also works good for the light colored features of Mars. The
21 orange is also good on Mars. Of course it will be a while before you need to worry about prime viewing of Mars. I
tended to stick with the lighter color (higher transmission) filters; I figured the least amount of coloration that would
enhance the contrast would be best. Some folks may say to use darker filters for maximum effect since you have 10" of
aperture. A neutral density filter works well on the moon; you'll need something to attenuate it with 10" of aperture. Of
course, the colored filters can do this as well. In hindsight, I should have bought a "4-pack" to save money instead of
buying them one at a time. An Orion UltraBlock and Lumicon O-III filters help with nebulas, but I would put them down on
the list due to the cost; I bought 2" filters so I could use them with both 2" and 1.25" eyepieces (use a 2"-1.25" adapter
with 2" filter threads when using 1.25" eyepieces.)
9. A "large" UV/dust seal. This screws onto the large (3.25"?) threads on the back of the scope. This item has given me great
peace of mind as it keeps the interior of the scope protected against contaminants. I would get this right away to protect
your investment. I went ahead and bought the large one instead of the SCT thread one in case I need the larger opening
for a NGSF focuser or other attachment in the future.
In summary, I would advise on getting the ScopeSaver and dust seal ASAP. Also plan for a dew shield, or you'll likely dew over
and get little observing done. You could use a hair dryer if you get dew despite the shield and have 120vac handy. The blast of
heat will degrade your seeing for a while, though. In the field, I use a "hot air brush" to clear dew from eyepieces, etc. Costs
about $11 at Wal-Mart. Runs off a 140 watt inverter. You could also use the Orion 12vdc blower.
I started out using the 140 watt inverter (about $40 at Wal-Mart) to field power the scope using the supplied 120vac-18vdc
power supply. Later, I mounted it in my power supply box along with the Meade 12vdc-18vdc converter. Have read of problems
with the 1812 converter, but mine has been fine.
Colored filters are helpful with Jupiter. I generally don't use them on Saturn. Mars won't be in opposition again until 2001, so no
rush there. If you don't have something to filter the moon, you'll need sunglasses!
I would suggest planning to go ahead and go for 2" capability. I got the Meade 2" diagonal. It is fine after you put an o-ring in the
SCT threaded end to keep it from locking down (use a 1-13/16" x 2" x 3/32" o-ring; industry standard #2-133); there's more on
this topic in the Topical Archives. I now have a TeleVue Everbrite 2" diagonal as well, but have not yet gotten the adapter to use
it on SCT threads. Most folks seem to think the TeleVue diagonals are better, but then again, they cost a lot more. If you don't go
to 2", the widest field of view will be with a 32mm or 40mm Plossl, which isn't all that wide, if your scope is f/10.
Happiness is a new eyepiece! I love having just the right magnification. I don't use the Barlow very much. I don't like having to
mess with it if I can avoid it, plus I don't like having a one pound eyepiece tilted over to the side on the end of a long Barlow looks too prone to falling over or hitting the forks. My eyepieces give me a 55-60% increase in magnification each time I change
to the next higher power: 35mm, 22mm, 14mm, 9mm, and 6mm. (I'm not including my 26mm and 20mm Plossls.) I recommend
similar planning for your ultimate set of eyepieces. If you were to get eyepieces of, say 32mm, 26mm, 20mm, 14mm and 8mm
(differences of 6mm), this will not work out to uniform relative changes in magnification. Also remember to try and avoid
eyepieces that give similar or overlapping actual FOVs, as this is really a duplication even though the magnifications are different.
Good luck with your LX200. I feel that the extra money for the GoTo capability was well worth it. Takes the frustration out of it
for a beginner. Now, I'm learning to star hop with a TV-85 refractor that I bought for those times when I can't take the LX200
along or don't have time to set it up. Also, I've never had the first problem with my LX200 (knock on wood) - it's always worked
perfectly. By the way, I'm still hauling it around in the original white cardboard box. I didn't like the idea of a soft case and,
although I drew up plans for making a trunk for it, I'm avoiding the extra weight that would add.
Subject: Re: LX200 Newbie - Top 10 books
From: Rashad Al-Mansour
The Night Sky Observer's Guide Vol. I & II
-------------------------------------------------------------------From: Edmond Pepper
Constellation Guidebook - Antonin Rukl, ISBN 0-8069-4299-1
The Messier Objects - Stephen James O'Meara, ISBN 0-521-55332-6
Philip's Color Star Atlas - John Cox & Richard Monkhouse, ISBN 0-913135-08-9 4) Sky Atlas 2000, Wil Triton &
Roger W. Siinnot, 0-933346-87-5
Choosing and Using a CCD camera - Richard Berry, ISBN 0-943396-39-5
Astronomical Image Processing - Richard Berry. ISBN 0-943396-32-8
------------------------------------------------------------------From: Dave Feldstein
The Backyard Astronomer by Terrence Dickerson
Starware second edition by Phil Harrington
A Practical Guide to CCd Astronomy by Patrick Martinez
Advanced Sky Watchers Guide by the Natures Company
-------------------------------------------------------------------From: Tom Wideman twideman
earthlink.net
Burnham's Celestial Handbook (3 vols) Night Sky Observer's Guide (2 vols)
Messier Objects (O'Meara)
Sky Atlas 2000
Backyard Astronomer's Guide
Skywatching and Advanced Skywatching
Star Names and their Meanings
Subscriptions to S&T and Astronomy
-------------------------------------------------------------------From: Ray Mote rmote
rain.org
Amateur Astronomer's Handbook, by J.B. Sidgwick, Dover Publications, 0-486-24034-7
Practical Astronomy With Your Calculator, 3rd edition, by Peter Duffett-Smith, 0-521-35699-7
-------------------------------------------------------------------From: Michael Cook <michaeljcook
rogers.com>
Observational Astronomy for Amateurs by J.B. Sidgwick Astronomical Algorithms by Meeus.
Software and Data for Astronomers by David Ratledge.
-------------------------------------------------------------------
From: Daniel Kell Date: Nov 1999
Guy Ottewell's Annual Calendar/Almanac.
365 Starry Nights
Uranometria 2000 (All three volumes)
The Photograhic Atlas of the Stars
Rukl's Atlas of the Moon
Subject: Aperature Fever, Need Advice...
From: Doc G, Date: Sept., 2000
Brent Boshart wrote:
> Okay, I have aperature fever and am considering letting go of my 8"
> LX200 and acquiring a 12" LX200. I would be interested in hearing
> comments from anyone else that ever made this move. Was it worth it? Any
> regrets? I'm kinda nervous about letting go of the 8" as it has been
> absolutely flawless in operation for me. I wouldn't have considered this
> before but now I'm putting up an observatory and don't have to worry
> about the weight.
I too had aperture fever. I had the 8" then got the 12". The 12" needs to be in a permanent building in my opinion. That is why I
donated it to the Madison Astronomical Society and built a building for it at their dark site.
I then got the 10" f/6.3 which I find easier to handle, but still a big pain to setup for imaging. I may well set it up in a permanent
building as well and soon.
The 12" f/10 and the 10" f/6.3 complement each other since they have different focal lengths by a factor of two. With focal
reducers and extenders this gives a large range of focal lengths and speeds. I believe that a medium focal length is most
appropriate for CCD imaging because of the small size of the chips.
I strongly suggest you evaluate your purchase on the basis of focal length and the objects you expect to image. I follow
SBIGUSER carefully, and see that most of the better imaging is done with modest focal length scopes. It is exceedingly hard for a
mount like the LX200 to control a scope of 3000 mm focal length.
Unfortunately, there is no single scope that will do everything. You need a medium focal length for most extended objects, but a
very long focal length for planets. However, any scope is easier to use with a permanent setup since a major issue for imaging is
precise equatorial alignment and excellent collimation. Both of these things are easily attainable with a permanent setup.
Subject: Pointing Accuracy--The Real Story
From: Bill Arnett <bill
nineplanets.org> Date: Sept., 2000
> Scott-- You will hear a lot about the pointing accuracy of LX200.
> everyone of us has its story to say...
And a lot of it is wrong. For instance, pointing accuracy is not strongly dependent on leveling or time of day or geographic
position. (Finding the Moon may be screwed up if you're off by an hour or more but you can find the Moon without the computer
can't you? :)
I have aligned my LX200 and gotten good pointing with the base off level by 20 degrees or more. Careful leveling just isn't worth
it.
Choosing a good pair of alignment stars (in altaz mode) is moderately important but you'll get good alignment even with a "bad"
pair if you do the rest carefully. Jim's "bestpair" program is neat but you'll get perfectly adequate results if you just pick any pair
of stars that aren't too close to the horizon or zenith (the good zone is from 30-60 degrees elevation but you can fudge that a
little if it's convenient).
What really does matter is centering the alignment star in the field. **Use an eyepiece with a reticle** or if you can't do that
then use a very high power eyepiece. This is by far the most important thing.
Aside from making sure you're scope is mechanically tuned up, that is. If you have too much backlash in your gears you've no
hope of good pointing accuracy. My Dec motor has several degrees of slop at one point. But it's not hard to take out most of the
slop. check the archives.
The bottom line: forget about your carpenter's level, your GPS and your WWV time source. But check your mechanical slop and
get a reticle eyepiece.
Subject: Eyepiece/Accessory Case Hints
From: <SkySgt
aol.com> Date: Nov., 2000
There has been some discussion about accessory cases here recently. Here are some of my ideas on eyepiece case layout. Hope
this info helps!
1. I have two of the WalMart aluminum cases. One is for all my optical equipment (i.e., items with lenses and/or mirrors). It
contains my eyepieces, Barlows, focal reducer, varimagnifinder, filters, camera, lenses, etc. The other contains all my non-optical
equipment. These items include power cords, hand-controller, cables, JMI focuser, tele-extenders, etc. After a long night of
observing, I’m usually too tired to unpack the van in the morning. This dual case situation allows me to quickly grab my optical
equipment (and my scope) for an initial unload of stuff that I don’t want sitting around in a hot vehicle.
2. You do not have to pluck out both layers of foam for items. Most eyepieces require only plucking out space in the top layer.
This keeps them near the top and within easy reach. If you pluck out both layers, you will most likely have to “dig down” to the
bottom to reach your smaller items.
3. You have to do some layout planning prior to plucking out the foam. Once plucked, it does not have the same rigidity or
handling/support characteristics as the non-plucked foam. Trying to put it back in place leaves a lot to be desired. The plucked
foam tends to fall, or gets pulled out, when removing items.É
4. Even the intact foam is rather limp and wimpy, and provides rather poor support. To help the foam hold items in place, I use
the original box that each item came in. I simply cut off or remove the top of the box and insert it into an area I have plucked
that is the same size as the box. This also prevents items from falling between the two layers of foam.
5. Wondering what to do with all those instruction manuals that come with your accessories? I place them in a large zip-lock
plastic bag and store it in the lid of the case. ÉJust pull out the “egg-carton” foam liner, insert the manuals, and replace the foam.
They are now safely and conveniently stored for future use.
6. Is your foam just too lightweight for your liking? Find a specialty foam distributor in your area (my area, San Antonio, has a
few listed in the Yellow Pages under “foam fabricators”). Take your prearranged, pre-plucked foam inserts to them and ask them
to die-cut some denser foam, using your foam inserts as templates. You can select as dense a foam as you like. Then, simply
place the new die-cut foam layers in your cases and your ready to go!
Subject: Light Pollution Filters Recommendations --part 1 of 2
From: Scott Oates <SOates4616
aol.com>
I live in Las Vegas and as you might guess, the LP here is BAD. I have used several filters and the IDAS is the best I've found.
Provides great views even here. Take a look at the following link for IDAS filters:
<http://www.sciencecenter.net/hutech/tokai/lps.htm> Note: should open a new browser window over this one.
------------------------------------------------------------------Subject: Light Pollution Filters Recommendations --part 2 of 2
From: Paul Markov <pmarkov
sympatico.ca> Date: Jan 2003
For advice on light pollution filters (and others), take a look at a straight-forward article I wrote some time ago about light
pollution filters at: <http://www.astrobuysell.com/paul/filters.htm> (All reference prices noted in the article are Canadian
dollars).
Subject: Nebular Filters URL
From: Robert Garrett <rgarrett
cais.net>
Here's an interesting link from a thoughtful observer who gives a pretty thorough run down of the various nebular filters including
the Lumicon O-III and UHC.
<http://www.blackskies.com/tips.html> Note: should open a new browser window over this one.
Subject: Telescope Dealers Rating Webpage
From: Paul Markov <pmarkov
ica.net>
This makes for very interesting reading. Here you can find out what customers think of many astronomy shops and you can even
cast your own vote.
<http://www.excelsis.com/> Note: should open a new browser window over this one.
This page echos what was said here over the past couple of weeks; OPT and Pocono rate quite well, among others.
Subject: Tips Web Page
From: Leroy Guatney <lwlguatney
usa.net>
I've been working on an LX200 tips web page. It is heavy on new user stuff. Have a look:
<http://home.earthlink.net/~ngc5139/SCI/LX200tips.html> Note: should open a new browser window over this one.
I still have a few more items on my list and am always getting ideas for more. Enough so, that I've had to start making a list.
Subject: Warning!! New LX200 Owners--Check Bolts
From: Edward Cafarella <edward.cafarella
dpw.com>
Just thought I'd put out this general warning to all of you who've purchased an LX 200 recently. A while back I posted a message
about my new 10" f/10 that arrived with an Allen head screw sheared off leaving just the shaft of the screw in the fork where it
mounts to the OTA. I told Meade and they offered to have it shipped back, at their expense, and send me a new one.
When the new scope arrived, the first thing I checked was that all of the Allen head screws were intact, they were. After two
weeks of horrible conditions I decided to take the scope out a few nights ago. Before moving it and after reading so many
messages about the fork/OTA mount Allen bolts being loose on new scopes people received, I decided to get out an Allen wrench
and see if the four bolts were tight. Three of them were tight but one was very loose. As I continued to tighten the screw, it never
got any tighter, When I pulled the hex key out, you guessed it, the head of the Allen screw came off with it. Yet another sheared
Allen head screw. I guess the head was hanging on by a thread.
I decided not to send this one back to Meade. It took me an hour, but I managed to scribe a line on the broken off shaft and back
it out with a screwdriver.
The only reason as to why this is happening is that possibly Meade must have read the threads here and on the Yahoo forum and
told the assemblers in the factory to make sure those bolts were tight, Unfortunately they've been tightening them too much.
MAPUG is hosted by
LX200GPS Specific Issues-Mount, Optics, Focuser, Misc.
GPS Firmware (v3.0i) Posted (also link for future updates as they are available from Meade)
DVD--"A Beginner's Guide to the Meade LX200GPS" --outside link
GPS Tips Source--outside link
14" Base Casting Beefed Up?
Peterson EZ Clutch kit on a 14" LX200GPS -- 4 parts
Scope Certification by Independent Company
Accurate Time Requirement?
GPS Alignment Stars Not in FOV
GPS Accessory Bolt Holes Specs & Tripod/Wedge Mounting Bolts (same as Classic?)
Schematic Diagrams for GPS --on 'Battery-p2' page
Reconnecting Connectors
GPS Owners Manual-- PDF Download --linked to Meade Contact page
Other On-Line GPS Owners Manuals-- pdf or web-version
Worth Upgrading from Classic?
Checklist for Inital Start-Up and After
Avoiding Hitting the Hard Stops
Link to Yahoo GPS Discussion Group
Control Panel Orientation
GPS Only Runs on 12v
Powering the GPS
Focuser Speed Selection Change
Focus Lock Adjustment
Microfocuser Step Size?
Centering the LX200GPS Microfocuser
Review: UHTC Enhanced Coating Group vs. Standard Coatings --linked to outside site
UHTC Coatings Equivalent to Classic Multi-Coatings? --3 parts
GPS: RS232 to USB Possible?
RS-232 Cable - GPS same as Classic?
GPS Interface Cable Diagram --outside link
External Antenna for GPS Scopes in a Dome?
GPS Loses Dates!
Does GPS Internal Battery Holds Ephemeris Data?
GPS RA Motor Stalled in East Direction --2 parts
GPS & GEG (Giant EasyGuider) --2 parts
Optical-Mechanical Alignment
Going to 2" Diagonal Worth It Visually Or Not?
Is SMT Worth It? --3 parts
Meade Dew Shield on GPS Models?
GPS Mirror Lock Like Classic?
Adjust Guide Rate Feature?
How to Calibrate Motor on GPS?
Parking the GPS Scope
Subject: LX200GPS Firmware Updates URL
From: Dick, Date: Dec 2004
For those folks with LX200GPS models, Meade posted updated firmware (v3.0i) on their site:
<http://www.meade.com/support/auto.html> Note: this is also the link for future updates.
3.0i seems to correct the major problems with 3.0d (Polar Park being the worst) while retaining its many improvements over the pre-3.0 series.
They also posted v33Ef for the 497 Autostars, too.
Subject:14" Base Casting Beefed Up?
From: Doc G, Date: Nov 2003
I have just had a long phone conversation with Pete Peterson about the 14" GPS scope. He is a fine gentleman and I trust his judgment.
He tells me that the base casting for the 14" scope has indeed been beefed up from that used in the smaller scopes. Additionally there are some differences in the drive mechanism
that he considers a definite improvement over the smaller versions of the GPS scope. Both he and Dr. Sherrod have the 14" scope and are very enthusiastic about it. It has
apparently had very few breakdowns and a better record of repair when necessary than the smaller scopes.
His statement is that the 14" GPS is improved enough over the smaller LX scopes both GPS and classic that it should really be called an LX300 because of the design changes. It is,
he says, the best scope that Meade has ever made in the LX line. I hope this information reflects reality about the 14" GPS scope. I trust it does. His is back to Meade at this time
for a repair of the electronics.
I would conclude, from this conversation, that the 14" GPS scope is the one to get if the size and price are suitable.
Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 1 of 4
From: Robert Darlington <bob@pihkal.com> Date: Jun 2004
I just finished installing a Peterson Engineering "EZ Clutch Kit" on my
14" scope. I took photos of just about every step along the way if
anybody cares to take a look. The kit was $29.99 and includes an hex
wrench (Allen key), pack of grease, cork ring, and instructions. It took
about 1 hour to degrease and install. The instructions were excellent.
Pics: <http://www.pihkal.com/gallery/view_album.php?set_albumName=EZ_CLUTCH>
------------------------------------------------------Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 2
From: Dale Chatham <dale@chatham.org>
I, too, just installed this kit on a new LX200 14" myself.. I was a bit skeptical about its utility, but since it was only $29.95, I figured "what the heck". All I can say after installing it
is "wow!". Although I didn't particularly think that the amount of torque to get the original clutch engaged was excessive, the amount with the new one is very small. I'm
impressed. I highly recommend it!
------------------------------------------------------Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 3
From: <Rick.Woods@AD.STATE.AZ.US>
The EZ clutch is not only cheap and easy to install, it's pretty much a must-have for the 14". Pete went into great detail somewhere about it, but the short version is the dec clutch
screw will end up stripping out, especially on the heavy 14", and there's no easy way to fix it when this happens like there is on the smaller scopes. I was pleased with mine. It does
exactly what it claims: cuts the amount of torque required to hold the dec adjustment just about in half.
VERY cheap insurance against what would be a lousy, inconvenient, and possibly very expensive failure.
------------------------------------------------------Subject: Peterson EZ Clutch kit on a 14" LX200GPS --part 4 of 4
From: Pearson <P26@cox.net>
Actually I'm flattered by Bob Darlington's being so impressed with the clutch upgrade that he went to the trouble of photographing it and posting it.
There is a fine line here regarding intellectual property as this upgrade solution isn't obvious. Where others focused on getting a bigger clutch knob I'd always been concerned
regarding the minimal thread tapped in the scope's aluminum trunnion. Development of the EZ Clutch took about 2 months of effort, and since the instructions are revised
whenever someone has to ask us a question, the instructions have been revised about 20 times.
Just about all of our upgrade instructions incorporate extra non-upgrade associated tune-ups and adjustments in the area being worked on. And many times the optimal techniques
that we have developed for the upgrade installation are not intuitive. This is why the installation instructions are considered to be a major part of the kit's value added, and why I've
asked folks not to publish the instructions.
In Bob's case, all he has is a series of un-annotated photos, and he hasn't documented any special procedures. So I'm not going to sweat it. Recently someone else got real excited
about another of our upgrade kits and posted a series of extremely detailed annotated step by step photos that did disseminate our intellectual property. He flattered us by putting
a huge amount of effort into his posting, and was shocked when I asked him to pull the posting.
We do have sample instructions posted for our most complex upgrade - the Buck's 14" Gears.
< http://www.petersonengineering.com/SkyDiv/14-inch_sample.htm> But because of the intellectual property situation we never transmit full instructions in digital form.
Upgrades for Meade's LX200GPS telescope is probably the smallest niche market in the world. I make my living from the engineering side of the business designing & fabricating
robotic machinery. The Sky Division is an offshoot of my personal need for things that weren't commercially available and were needed on my personal scope. I originally figured
that since we had some pretty sophisticated CNC mills, lathes and machine centers available, and since I'd gone to the trouble of designing & making an EyeOpener for myself, I
might as well make it available to fellow amateurs. Doc G was one of my mentors on development of the original EyeOpener.
I do thank you folks for being sensitive to the intellectual property thing. And for the kind words regarding our upgrade.
Subject: Scope Certification by Independent Company
From: Don Tabbutt <don
tabbutt.com> Date: May 2003
Arkansas Sky Observatory will certify the entire scope for a fairly hefty fee. Even so, some members of the LX200 GPS Yahoo group have their scopes shipped directly there when
they order them.
Check it out here: <http://www.arksky.org/> ...and click on "Services".
Subject: LX200GPS-- Accurate Time Requirement? --part 1 of 2
From: Kevin Wigell <kwemail
twcny.rr.com> Date: Jun 2003
Terry wrote:
> I am planning on letting the scope take a GPS fix at the beginning of every
> observing session primarily to have the time set accurately at the beginning
> of each night. I don't know how accurate the clock is on the scope, but if
> it is no better than clocks in computers, the time will need to be updated
> every night. I am thinking that this would be an easy, foolproof way to do it.
Terry, unlike the LX200 Classic, the LX200GPS doesn't keep time when it's turned off. So if you can't get a GPS fix, you will have to set the time manually each time you turn it on.
That is what we have to do with our club 16" GPS scope, which is inside a dome and can't get a GPS fix. On the other hand, accurate time is not important to either accurate
pointing or tracking. Anything within a few minutes of the correct time is fine.
------------------------------------------------------------------Terry wrote:
> Since "GoTo-ing," longitude, and time are all related, if the time is only
> good to a few minutes, the telescope can only point accurately if it thinks
> it is at a different longitude than the actual, correct? If that's the
> case, what happens the next night when the time is entered only to an
> accuracy of a few minutes? Is the scope forced to think it is at yet a
> different longitude? So, if your second night's time is right on, you still
> won't get good pointing, since the scope thinks it's at the wrong longitude,
> from LAST night's time inaccuracy. Is this not correct?
>
> It would seem to me to keep all three of these factors as consistently
> linked as possible, the time would have to be known by the scope as
> accurately as possible. An error of one minute of time can cause an error
> of up to 15 arc minutes in pointing.
Accurate pointing is not primarily a function of the correct time, date, or location. These factors are needed to calculate where your local horizon is, and how much atmospheric
refraction to correct for.
Accurate pointing (or GoTo-ing) is mainly a function of how good your 1- or 2-star alignment is. You can easily confirm this with a simple experiment. Deliberately set your time off
by 30 minutes. This is not enough to really affect your horizon calculation except for very low objects. Then do your star alignment as usual. You'll find your scope GOTO's just fine.
If the time were that important, you'd miss by a mile. The only problem with having the time, date, or location off is that some objects may be reported as being below the horizon
when they are not, and the correction for atmospheric refraction will be off. But if you are "close" on location and time (and date of course), your pointing accuracy will be very
good as long as you have done a quality star alignment. And the key to that is to use a reticule eyepiece.
Oh, and very inaccurate dates or times will cause the internal calculations of the positions of the planets, and especially the moon, to be incorrect.
---------------------------------------------------------------Subject: LX200GPS-- Accurate Time Requirement? --part 2 of 2
From: Bill Keicher <wekeicher
attbi.com>
If you want to open loop acquire and track satellites, you need fresh satellite ephemerides, good location information and precise time. Low earth orbiting satellites can move at a
few degrees/second.
Subject: GPS Alignment Stars Not in FOV
From: Richard Seymour <rseymour
wolfenet.com> Date: July 2005
>When I'm doing the automatic alignment process on my LX200 GPS 10" ,
> the alignment stars are nowhere near being in my finderscope field of view.
> I'm 5-10 degrees off. Smart Mount is turned off. Why is this happening?
First, do a Calibrate Sensors. That tells the Autostar your local magnetic deviation from true north.
Then, with recent firmwares, do *three* AutoAligns (this can take 3 nights, or be squeezed into one 15 minute session). The Autostar will learn, from your centering of alignment
stars, how to tweak the level sensor and magnetic readings and the initial slews will improve.
My own drops from a 5 degree error down to less than 1/4 degree, i.e. within the FOV of the 26mm eyepiece.
You could take either of two courses of action:
(a) simply -ignore- it, slew to center the stars, and continue with the evening... the actual GoTO's should be good. (and by the 3rd night, the problem will have gone away... unless
you do something that destroys the accumulated learning, such as a 2nd Cal Sensors)
(b) use Two Star alignment instead of Auto. When doing so, first -accurately- point the OTA due true north, and level the tripod head and OTA before powering up. You can achieve
initial slews that will only be limited by the accuracy of your north-pointing. (I use a landmark a few blocks away, and can achieve sub-1/4 degree slews).
Subject: LX200GPS Accessory Bolt Holes Specs & Tripod Mounting Holes
From: Jim Henson <jimh
bga.com> Date: April 2003
The accessory screws on the OTA are 8-32, just like the LX200 Classic. The tripod & wedge mounting bolts and spacing is also the same as the Classic.
Subject: LX200 GPS-- Reconnecting Connectors
From: Kevin Hobbs <ve3kh
cogeco.ca>
-----Original Message----From: M Whiteman
I got a new LX200 GPS 12" and have run into a little problem. When I was removing the long centre 1/2' dia. screw, it seemed that it was tight a couple of turns
before it released. No problem noted after that. I have not used it since.
I decided today to remove the bottom plate and see if I could see any problems. It turned out the inner nut with the two holes in it was loose. It had rotated and since
there was wiring that also fed through the nut to the other parts of the scope, it unplugged the connectors from the main circuit board on the front panel. I do not
know where each connector goes. The nut has been fixed.
There are one 9 pin, two 6 pin and one 2 pin. The nine pin was easy since there was an open 9 pin connector for it. I do not know where the two 6 pin go and there
are 2 available plugs. The 2 pin has 2 possible plugs to fit into.
-----End of Original Message-----The nine pin is obvious.
-The six pin with ferrite bead on the wire bundle goes to the mating connector nearest the power plug.
-Only one place left for the other 6 pin.
Editor's note: see photos above.
Subject: LX200: Worth upgrading to GPS? --part 1 of 2
From: Roger Hamlett <ttelmah
ntlworld.com> Date: Oct 2002
----- Original Message ----From: Alan Voetsch
> > I'm considering selling my 10" Classic LX200 and getting the 10" GPS version.
> > What are peoples thoughts on this?
>
> I won't comment on the GPS part of this equation.
> The other advantages that I see in the new over the
> classic are mainly of benefit to those doing
> astrophotography. The mirror lock and the microfocuser
> are features I would love to have. These are items you
> can live without for mostly visual use.
However the 'downside' for imaging, is that the existing focuser on the GPS, does not provide properly controllable positioning (even relative positioning). This means if you want to
autofocus, you'll end up buying either a third party focuser like the NGF-S, or an upgrade to the existing focuser, which puts you in a similar position to 'classic' owners. On both the
10", and 12" 'classic,' mirror lock is easy to provide, so the advantage here is very small...
The biggest question is how good one's existing optics are. If you are happy with them, it is the 'long term' support, 12v operation, and the UHTC coatings, that probably represent
the biggest advantages to the GPS.
------------------------------------------------------------------Subject: LX200: Worth upgrading to GPS? --part 2 of 2
Bill Arnet<bill
nineplanets.org> writes:
> Can anyone comment on the relative merits of the
> mechanical aspects of the GPS vs. Classic LX200s?
The fork and drive base, to me, appear just as good. As far as steadiness, I don't note any improvement, however--excellent on the 8, good on the 10, just OK on the 12 and ? on
the 14. The dec seems considerably smoother than most classics (those without ball-bearings in the dec). The gearing, the transfer gearing, in RA is worse according to what I'm
told (I haven't torn one down yet). Small nylon gears in a position where high torque is possible. I am told by Clay Sherrod that Meade is taking steps to improve this situation now,
however. Don't like the dec lock at all--it's a considerable step _back_ from that on the classic, appearing similar to that on the LX90. Works fine on an 8, but has problems locking
firmly with the larger scopes; that's why various entrepreneurs are selling "dec-fix" kits already.
If you have an LX200 that's working well, I'd hold off. Meade is still fixing problems with the GPS. There was a brand-new out of the box LX200 GPS 12 on the field at the recent
Peach State StarGaze. The new owner could not get it to align. Period. Operator error? Maybe. Software? Maybe. Hardware? Maybe.
Enjoy your "classic" 200 for a while longer...maybe 6 months or so...then come back. I would not upgrade even then unless you want to go to a larger (or smaller) aperture. The
GPS is nice, but it just doesn't offer enough advantages over the classic to be worth the trouble, in my opinion.
Subject: LX200GPS Checklist for First Set-Up & After
From: Rod Mollise <RMOLLISE
aol.com>
The good folks over on the Yahoo LX200GPS group have created a Checklist for first time set-up and quality check, and then steps for regular set-up. Goto: <http://groups.yahoo.
com/group/lx200gps/>. Go to the "Files" section (Note: you must first join the group before you can access the Files), and look for "LX200GPS Start-Up Checklist.pdf." There are
several other very useful files for the new GPS owner too, including tips, etc.
Subject: Avoiding Hitting the Hard Stops
From: Don Tabbutt <don@tabbutt.com> Date: Sep 2003
-------Original Message------From: Christian Molnar
The scope is, as others have stated, about inbetween hard stops, but it starts one way, goes about 150 degrees, then stops, but instead of changing direction, it
continues the same way. This puts it almost at its hard stop when it believes it is in home position. SO when it goes to Arcturus, it hits the hard stop.
So if anyone has any suggestions, please shoot. Right now I am thinking it may be a dirty sensor?
-----End of Original Message----It sounds like one of the Home sensors is inoperative for some reason. It could have a broken or loose wire, or more likely, has been fouled with grease or bent and simply needs
cleaning or straightening. Pictures are here:
<http://rseymour.home.wolfenet.com/LX200guts.html>
and here's what Pete Peterson found when he fixed his:
> I removed the base bottom plate, and eyeballed the position
> sensors. They consist of 2 pairs of photo emitter/detectors
> on a small 1" x 2" pc board. The clear LEDs are obviously the
> emitters, and they're oriented so that it's facing you if the base is
> inverted. About 1/4" away facing them is a black transistor shaped
> receiver. Each pair is at a different height and the light beams are broken by
> the respective split rings that control the 600å or so of rotation.
> In my case, the lower emitter was not standing erect off of the PC
> board, but was bent forward so that the light beam wasn't directed at
> the detector. The bottom part of the emitter was covered with black
> grease, and some of the grease was on the working side, blocking
> light. I cleaned it up, straightened it up, and wiped the excess
> grease off of the bottom of the split ring. And then I tested
> through full rotation stop to stop to insure that something wasn't
> going to clobber the LED again. It ran clear, so I closed `er up,
> fired her up, and got a good alignment. Problem fixed.
In any case, a first troubleshooting step is to turn off the Home Sensors: Select Item > Setup > Telescope > Home Sensors > Use Sensors > Off. With them off, the telescope will
not attempt to find Home (useless in Polar anyway).
With the telescope off, on a wedge, with Dec set at zero, and *the eyepiece end* centered over the power panel with *the eyepiece end* pointed north (corrector pointed south),
release the RA lock and rotate it west (counterclockwise) until it hits the hard stop. Now rotate it east until *the eyepiece end is* just pointed north again and centered over the
power panel (corrector pointed south), and lock the RA. Power up and align normally, and the scope should never hit a hard stop.
Also, be sure your friend is actually in Polar mode. Finding the Home sensors is not normally part of a routine polar alignment (One Star, Two Star, or Easy) unless he chooses Align
on Home. That last choice is really there for a "lost" remote telescope that got powered down (for whatever reason) in some position other than Park.
Subject: GPS Yahoo Group
From: Wade <sdwest
mchsi.com>
The LX200GPS group has over 1400 members already:<http://groups.yahoo.com/group/lx200gps//>
Try the LX200GPS group. Read the Archives, Files and Databases, you'll find a wealth of info already in there. I look forward to the almost 50 emails a day I get on that group.
I've already downloaded the new AS II v. 3.33 and build 1.1a firmware. There are still a lot of issues. After resetting and "taking out the trash" (one of the options on the v3.33)
and THEN loading 1.1a to my handbox, did I get it to do any GOTO.
Using my 26mm Meade "standard issue" eyepiece, I was able to find the two bright alignment stars (Sirius and Alioth) in this eyepiece through the hazy sky, and did a GOTO to
Jupiter and it was in the eyepiece. What a rush that was!!
I've since Calibrated Sensors and Trained Drives, and now it doesn't even come close!! I can only believe that the light overcast resulted in my seeing only the brightest stars,
which allowed me to pick the correct ones for the initial alignment.
I'm not too concerned about this scope, I think the mechanical and electronic problems will get ironed out. Meade has been pretty responsive so far. My biggest concern is the way
Meade seems to label each tube differently, I'm not sure what they are doing with the optics and then they come out with a new coating material for the mirror just a week after I
received mine! It was my own fault for jumping in right on the new release, I guess. I received mine on March 12, and it doesn't even say it has EMC coatings on the tube or on the
box. It's hard to know when this thing was really put together.
Subject: LX200GPS Control Panel Orientation
From: William Drelling <gatorchaser
earthlink.net>
The manual alignment is the same as the previous version of the LX200 except that the control panel of the GPS version must face south vice north, i.e., be on the south side of the
tripod.
Subject: GPS Only 12v Power Use? -- part 1 of 2
From: John Alfredo <john.alfredo
transcore.com>
I recently purchased a new 10" LX200GPS and have seen numerous postings about 18V and 12V-18V convertors and was confused, so I called Meade tech support and they told
me that, although older LX200's ran on 18V, I should _NOT_ run my new LX200GPS on anything other than 12V.
------------------------------------------------------------------Subject: GPS Only 12v Power Use? -- part 2 of 2
From: Roger Hamlett <ttelmah
ntlworld.com>
Dead right. This was one of the redesigns on the new scope, to get away from exactly the problem being discussed. Use of 18v, applies _only_ to the LX200 'classic'.
Subject: Powering the GPS
From: James Fisher <jfisher857
juno.com> Date: Jan 2003
Maybe I can help you with your power concerns and the 8" LX200GPS. On another users group dedicated to the GPS version of scope, virtually no one uses the internal batteries.
The scope responds best to a voltage of 13.6 to 15 when slewing and working with a load. The 8 C cell batteries at most will only put out 12 volts, add cold weather, and it will be
less. Don't get me wrong , the internal batteries will work, but the amount of time they will work makes them a very expensive way to operate the scope- in the field.
Most owners, including myself, use a 12v. 26 Amp Hr. Jumpstart Battery. They typically put out 13.5 volts fully charged and will run the LX200GPS 8" several nights before charging
is needed. I use this battery even though A/C power is available. I don't have to worry about the power company interrupting my viewing session or surges or power spikes or
electrocution. However, do not run any dew equipment from the same battery source.
Editors note: for additional battery power ideas see this topic.
I have two Jumpstart batteries, one for the scope and one for the accessories. Also do not try and use rechargeable C cell batteries, their power curve is horrible for use in this
scope especially in cold temps. Many have reported using these Jumpstart batteries for over three years on various scopes, and they still take a charge fine.
We use the battery compartments to hold counter weights to balance the scope in polar mounted (wedge) situations. Remember, if you feed your scope the proper diet ( 13.6v to
15v. ) to keep it happy.
Subject: LX200 GPS Focuser Speed Selection Change
From: Tom Mote <pytom
texas.net> Date: Apr 2003
After I sent the message about using the JMI hand paddle with my LX200GPS, I did some more testing and, to my dismay, found that I could not control the focus speed while
using the Meade paddle. The Meade microfocuser speed selection had worked perfectly just before I updated the firmware from version 1.2A to 1.6B but now, no matter what focus
speed I attempted to select, it always was "FAST," i.e., the speed which I reported took 11 seconds to move from either limit to the middle of the focus range. I phoned Meade and
the technician had not heard of any problems with the new version but suggested that, instead of using the numeric keys, as I had been doing, I try using the scroll up and scroll
down keys. IT WORKED LIKE A CHARM! the moral, if any, is that when Meade comes out with a firmware update, they make changes and it may be many months before there is
any documentation for the user.
Subject: GPS Focus Lock Adjustment
From: John Mahony
>
>
>
>
>
>
>
>
>
>
>
I just received my 8" LX200GPS, and I am concerned that there is a problem
with the focus lock, in that it does not seem to lock anything. With the
focus lock knob turned to the lock position (as tight as I feel
comfortable setting it, and tighter than I expected would be
necessary), I find very little difference in effort in turning the
focus knob. There is perhaps the slightest bit difference in turning
torque, although I had to go back and forth between the locked and
unlocked positions to be able to notice this at all. And the focus
changes either way, although there does appear to be a slight amount
of backlash in the "locked" position. I want to emphasize that I am
not forcing the focus knob at all - it turns very easily even when fully locked.
Buck Harley posted some info on a common problem with the lock in the files section of the Yahoo Meade_Uncensored group. Sounds like it may be what you're experiencing:
For those that can turn there mirror lock stop to stop, it is made the way I thought it was and is easy to adjust.
1. first turn the knob all the way to the unlock position
2. then remove the 3 cap screws remove the knob assy by tilting it slightly
3. after you have it out you will be able to see the 8" steel gear... that will have about 1" of it with no teeth this the stops.
4. you will have to take your finger and push down on the gear until the part with no teeth on the gear is pass the hole towards focus knob..
5. reinstall the knob and now your lock will lock and unlock do not worry if you cannot turn it 10 turns just turn until you feel resistance… you will be home Sweet ..
BTW Meade Sent the Allen wrenches for this job make sure they are pushed all the way in the alum cap screws as not to strip or mar them. He also posted a zip file there with
pictures of the insides of the scope, but it may be just the drives- don't know if it includes the lock.
Subject: GPS Microfocuser Step Size?
From: Dick <autostaretx
mindspring.com> Date: Apr 2005
> Does anyone know what the step size is for the Meade microfocuser?
The microfocuser on the LX200GPS is not a stepper motor. The Meade microfocuser uses a typical inexpensive DC "analog" motor. Such motors don't have a clearly defined "step
size" (they can stop anywhere, they call fall backwards a bit, etc.). They do, however, tend to stop with an armature pole aligned more or less (there's the "lack of STEP" again)
centered with relation to one of the field magnet poles.
The Meade driving circuit for the focuser is pulse width modulated (PWM) at nearly 12v (probably within a volt of full battery voltage). They're not trying for "stepping", merely
"delivered energy over time" (the area under the PWM's steps per second).
Subject: Centering the LX200GPS Microfocuser
From: Tom Mote <pytom
texas.net> Date: Apr 2003
To answer my own question: has anyone come up with a quick and/or reliable method for setting the Microfocuser to the center of its range? The answer: you simply run the
Microfocuser in and out until you have the "knobbed set screw" just even with the edge of the slot in the outer barrel of the device. This gives you approximately a quarter of an
inch (6mm) available travel either in or out from that point.
Subject: UHTC Coatings Equivalent to Classic Multi-Coatings? --part 1 of 3
From: Roger Hamlett <ttelmah
ntlworld.com> Date: Dec 2002
----- Original Message ----From: Kevin Wigell
> On another list in which I participate (APML), there is a thread
> floating around right now in which some are speculating that the
> new UHTC coatings are roughly equivalent to the classic multi> coatings, and that the new "standard" coatings are actually a
> downgrade from the classic coatings.
>
> Does anyone here have any evidence or comments on this one way
> or the other?
The point, is not that the standard coatings have been downgraded. The new coatings do what is claimed, relative to the older Meade coatings. What has become plain though, is
that compared to the Celestron coatings, the difference is not so large. It appears that the Celestron 'Starbright' coatings, have been significantly better than the older Meade
offerings for some time, but this was not being pushed in the same aggressive way. Meade have now overtaken Celestron, by a small amount (the new Meade coatings appear to
give a flatter response curve than the Celestron offering, with better response at the red end of the spectrum, but very fractionally less response in the green).
------------------------------------------------------------------Subject: UHTC Coatings Equivalent to Classic Multi-Coatings? --part 2
From: Radu Corlan <rcorlan
pcnet.ro>
Roger Hamlett wrote:
> > Oh, but the standard coatings have been downgraded; If you look into any
> > recent Meade advertisement, under 'specifications', it tells what the
> > 'Meade standard coatings' are: MgF on corrector, standard Al on mirrors > > that's obviously not what EMC was.
>>
> > And all the graphs and improvement claims use the 'standard' coatings as
> > baseline, not the EMC.
> The comparisons on the web, have all been against the EMC coatings, and give
> the claimed improvements...
I don't argue with that.
> > I have no way of telling how the UHTC are comparing to the old EMC, but
> > it's clear that Meade's advertisement doesn't compare UHTC with EMC.
> How is this 'clear'?.
Well, it's 'clear' because the baseline graph is labeled 'standard', not EMC, and because the specifications list 'standard' as MgF, which is not multi-coated.
The corrector plate coating doesn't contribute that much to throughput anyway (With MgF, the reflection coefficient is ~1.5%, so even going to a 'perfect' coating will only improve
throughput by 3% max; the difference from EMC, which is multi-coat should be even smaller);
However, reducing the reflections from the back of the corrector 2-3 times will significantly reduce multiple reflections and scattered light and improve contrast; this is the main
reason you want good coatings on the corrector, not throughput
Big improvements in thoughput are obtained by changing the mirror coatings; The 'standard' Al+SiO mirror coat is only 92% reflective at visible wavelengths, and can be improved
to >98%. My guess is that here is the principal difference between EMC coatings and UHTC.
To reconcile all information, this is what we have: 'classic (EMC)': multi-coated corrector, standard Al mirrors new non-UHTC : MgF corrector, standard Al mirrors UHTC : multicoated corrector, enhanced Al mirrors
This will explain the difference in thoughput between EMC and UHTC; but also mean that the 'standard' coatings have been downgraded - Not so much from the throughput point of
view, but from the contrast/multiple reflection point of view.
Anybody made a comparison between non-UHTC new scopes and 'classicals'? That would be the missing test to prove/disprove my theory.
----------------------------------------------------------------------Subject: UHTC Coatings Equivalent to Classic Multi-Coatings? --part 3 of 3
From: Don Tabbutt <don
tabbutt.com>
Read Dr. Clay Sherrod's review here: <http://arksky.org/uhtc_compare.htm>
In a nutshell, UHTC performs as Meade claims vs. EMC coatings.
Subject: GPS: RS232 to USB Possible? --part 1 of 2
From: Bob Benamati <bobbenamati
comcast.net> Date: Jan 2003
----- Original Message ----From: Susan-- Does the LX200GPS scope interface cable at the computer have to be RS232 to the Com port or is it possible to interface using USB? I suppose one
gets an RS232 to USB converter if it exists?
----- End of Original Message ----Meade makes a USB-RS232 interface now..... just saw it at OPT's website while shopping for something else. Works for "Classic LX200s, too!
------------------------------------------------------------------Subject: GPS: RS232 to USB Possible? --part 2 of 2
From: Don Tabbutt <don
tabbutt.com>
Autostar interfaces perfectly via USB using the Belkin USB to Serial adapter F5U109, $29.99 at Circuit City. It's marketed as a PDA adapter, but will work with any serial device.
Never misses a beat. I also use the Belkin 4-port USB Mini-Hub with the laptop, a tiny little thing half the size of a deck of cards.
I have five of them used as follows:
●
●
●
●
●
LX200 Classic to laptop.
ETX125EC Autostar to laptop.
RoboFocus to laptop.
208XT to laptop.
Uninterruptible Power Supply to desktop (for automatic shutdown in case of power failure).
Subject: RS-232 Cable - GPS same as Classic?
From: Bill Dougherty <bd5572
yahoo.com> Date: Dec 2003
Luigi Fontana wrote:
Does someone know if the RS-232 cable for the GPS and the Classic LX200 are exactly the same?
The Meade 9-pin RS-232 to LX200 cable that I bought for my Classic works fine with my GPS scope.
Subject: External Antenna for GPS Scopes in a Dome? --part 1 of 3
From: Mohammad Odeh <odeh
jas.org.jo> Date: Mar 2003
Kevin Wigell wrote:
> My club recently installed a 16" GPS LX200 in a dome. The dome completely blocks the GPS
satellite signals from getting to the antenna on the scope. Of course, the location never changes,
so that is not a big deal. But due to the lack of a clock chip in the GPS models, we have to reset the
time in the scope each time we turn it on. A minor inconvenience, to be sure.
>
> But, we were wondering if anyone knows of a way to connect an external antenna to the
scope-mounted antenna so that the GPS signals will get through? If there is no way to directly
connect an external antenna to the scope, what about some sort of "repeater" that would
re-broadcast the GPS signals inside the dome? <
This antenna should solve your problem:
<http://www.gpscentral.ca/accessories/mmwide.htm>
------------------------------------------------------------Subject: External Antenna for GPS Scopes in a Dome? --part 2
From: David Morris <dmorris
univ.llu.edu>
I haven't posted for so long I hope this works, but there is a place you can get a remote antenna that should work with your 16" scope in a dome. Look at:
<http://www.gpsoutfitters.com/> and check out the Vortech Antenna System. I think it is around $100 but might be worth it for some. One person reported he had one and it
worked very well.
-------------------------------------------------------------Subject: External Antenna for GPS Scopes in a Dome? --part 3 of 3
From: Radu Corlan <rcorlan
>
>
>
>
>
>
pcnet.ro>
However, on a good note, it looks as if I could open the casing and remove
the antenna. Perhaps, with a couple of lengths of wire, I could mount the
antenna outside and leave the rest of the unit inside, if I needed to. Don't
quite know how that will affect signal strength, though! Perhaps the same
can be done with the GPS scopes, with the addition of some type of signal
booster? At what cost, though?
You have to use special coax that has low losses at 2G; Most of the cost of remote gps antennas comes from the cable. Even with good cable, if you have to reach more than 1-2
meters, you will have to use an active antenna.
Subject: GPS Loses Dates!
From: Bill McCarthy <willymac1
btinternet.com> Date: Apr 2002
I would have thought with such sophistication that is built into the GPS scopes that there would have been a small clock panel incorporated somewhere that enabled you select local
time, hour angle, GMT, UT etc. There is certainly plenty of room on the forks.
Rod Mollise wrote:
>I find it reasonably annoying with the other Autostars...and yes, it would
>be laughably easy for Meade to "fix" this. I suppose it's not a huge thing
>if you're getting a GPS fix every time with the new scopes, though.
Subject: Does GPS Internal Battery Holds Ephemeris Data?
From: autostaretx <autostaretx
mindspring.com> Date: July 2005
R Hamlett wrote:
> The battery, allows the GPS, to hold it's ephemeris data, not just the location.
Yes, I should have mentioned that; however with the Sony chipset Meade uses (CDX2931R-9 in mine, I think they've upgraded to the 2932 in newer scopes) is able to achieve a full
fix in under two minutes, even from a cold, no-ephemeris, no-almanac condition. (the data sheet says 58 seconds)
I have seen that to be true, I've run multiple tests of unplugging my LX200GPS' battery to force the GPS receiver to its dead-cold state (random time/date, Tokyo's Lat/Long).
Subject: LX200GPS RA Motor Stalled in East Direction? --part 1 of 2
From: Roger Hamlett <ttelmah
ntlworld.com>
avecia.com> wrote:
McPherson Graham <graham.mcpherson
I have a 12" GPS system which has worked perfectly until last week when the dew heater control (BC&F) pulled from its fork arm velcro and landed on the wedge
(permanent metal pier into ground) and I guess there was an earth from the tape connector part as a nice tiny blue spark popped and the dew heater failed. At the
time both the LX and the dew controller were running off the same 12V battery supply.
From that point the LX complained that the RA motor had stalled whenever an "East" motion was required and although N,S and W work from the key pad I have no
joy with E (rightmost key) it just moaned that the motor had stalled.
I replaced the fuse on the dew controller (2Amp) and gave it its own battery (it works fine) and recharged the one for the LX - (in case it was the poorly charged
battery trick). To no avail.
Now I can turn on the scope go through the polar one star align and the motors slew to Polaris (so good so far) but after I adjust the mount and press enter - I get the
message "motor stalled" this is most frustrating as I have W but no East. I can only assume that this is 99.9 % going to be an electrical problem given the fuse
blowing coincidental timing. I don't have a problem having a poke in the guts of it but I have no idea where to start - does anybody have any ideas?
--------End of Quote-------Ouch...
We can rule quite a few things out. Power is getting to the motor controller (since otherwise it would not move W). The message, is saying that when it signals the motor to move
E, no pulses are being seen from the movement detector. Fortunately, we can rule out a failure in this detector, since it is the same system that detects motion in the opposite
direction (all that changes is the 'timing' of the two signals). Similarly, problems with the motor or gearbox, can largely be ruled out, since these work in the other direction. There
would seem to be two likely possible failures. The first is the motor driver chip itself. The second, is the op-amp circuitry feeding this chip (more fragile). Though both these parts
are partially 'common', to the other direction, they are being driven the other 'way', and different internal transistors are being used. The components are a L2724 driver, and parts
of two LM324 quad op-amps. These are U15, U16, and U17. Fortunately, none of these parts is expensive, and are readily available in the UK (in fact the L2724, is easier to get
over here, than in the States - I have a quantity, that I will sell to anyone who needs one.
It really is down to how good you are at electronics/soldering. The key with a repair of this sort, is to remember that the board is a lot more valuable than the parts. It is not worth
spending a lot of time trying to desolder the old parts, and risking damaging the board. Instead cut the old parts out (for the cost of a few pence for the op-amps, and a couple of
pounds for the driver), remove the legs individually, and solder in the new parts. It would be relatively easy with a scope, to identify which part has actually failed. Fortunately the
fact it works the other way, rules out a failure further 'inboard', to the main control logic. If you are not into soldering yourself, this board is not the place to experiment. Instead
see if there is a local TV repair shop, who will replace the parts for you (though see if you can have a look at the quality of their soldering first - a lot are remarkably bad...).
------------------------------------------------------Subject: LX200GPS RA Motor Stalled in East Direction? --part 2 of 2
From: Randy Marsden <jmarsden
san.rr.com>
Graham, based on the symptoms, it sounds like your motor driver has blown. These typically are a circuit usually called an H bridge with the motor as the cross bar and transistors
as the four vertical arms. Going one way, current through the H will flow Northwest to Southeast, while for reverse direction, current would flow from Northeast to Southwest,
reversing the direction of current through the motor. So what seems to have happened is that one of the four transistors was blown out - the motor would then move in one
direction and not the other. So, you need to determine which IC is the motor driver and repair it. Note: it may be a dual motor driver with two complete H-bridges. The part
probably costs less than $5.
Subject:10" LX200 GPS & GEG (Giant EasyGuider) --part 1 of 2
From: Roger Hamlett <ttelmah
ntlworld.com>
----- Original Message ----iwon.com>
From: <adicot
> I've got a 10" LX200 GPS and have a GEG (Giant EasyGuider by Lumicon) that I should
> receive in the mail any day now, but I have a concern which came to mind this morning.
> The GEG is designed to mount directly to the rear cell of the scope, but the GPS has
> the new design with the microfocuser. The microfocuser can be removed and
> it looks like the GEG can mount to the rear cell as always, but it doesn't
> appear that the GEG can mount to the scope with the microfocuser in place.
No the GEG will not mount with the microfocuser in place. One of the main 'points' of the GEG, is that it fits to the 3" visual back, to maximize the open aperture. The microfocusers
mounts to the same place, and does not offer 3" threads on it's tail.
>
>
>
>
>
>
>
>
This makes the microfocuser useless for GEG photography. Also, the
effectiveness of the mirror lock is reduced because there is image shift
when the lock is engaged and without the microfocuser there is no way
to refocus after engaging the lock.
Anyone out there already have the GEG with the GPS scope
who can elaborate on this?
Has anyone out there begun work on an adapter ring to allow the GEG to
mount to the working end of the microfocuser? I'd be interested.
This would 'throw away' a lot of the reason for the GEG. The actual 'clear' diameter of the microfocusers is less than that of the main scope, and also since you are shifting the
imaging plane further away from the scope, the vignetting caused by the baffle tube will get worse. I'm afraid that if you want the large clear aperture that the GEG gives, you will
need to ignore the microfocusers, and possibly consider an alternative solution to most of the mirror shift problems (such as attaching a RoboFocus to the main focussing knob, and
letting it compensate in software for the 'focus' shift - though not for the meridian shift).
----------------------------------------------------Subject:10" LX200 GPS & GEG --part 2 of 2
From: Doc G
It is not possible to mount the GEG on the new GPS focuser. The focuser takes 2" tubes while the GEG is designed to be threaded directly on the back of the scope with the 80 mm
thread. It is not possible to make and adapter which would do what you want to do. Sorry.
Subject: LX200GPS: Going to 2" Diagonal Worth Every Penny Visually Or Not?
From: Don Tabbutt <don
tabbutt.com> Date: Jan 2003
Why do you want a 2" diagonal? Do you have any 2" eyepieces? If not, then you don't need a 2" diagonal. Keep in mind Schmidt-Cassegrain telescopes, especially f/10 models like
your 8" (and mine), are not designed for wide-field vistas, such as those provided by 2" eyepieces. There's also the problem of the central obstruction caused by the secondary.
Unless you're at a pitch black observing site, with your pupils fully dilated, you'll never be able to satisfactorily use a wide-field, low-power eyepiece with your scope (neither can I).
Read Al Nagler's article, "Choosing Your Telescope's Magnification", from the May, 1991 issue of Sky & Telescope for a full explanation of this. It's available here:
<http://www.televue.com/engine/page.asp?ID=140>
Because of where I live, and the extremely rare opportunities for me to get to a really dark site, here's what I did, which I considered a better use of my money than investing it in
a top-of-the-line 2" diagonal and expensive 2" eyepiece set which would be used only occasionally:
1. Got a 1.25" Tele Vue Everbrite ($190) diagonal for use with all of my 1.25" eyepieces. It was like buying a new scope compared to the views I had through the Meade 1.25"
diagonal. This is the setup I use 90% of the time.
2. Got a William Optics Megrez 80mm f/6 refractor ($669) and piggybacked it on the LX200 with Losmandy rings and 3D counterweight set (about $400) for spectacular widefield views. With a 1.25" Tele Vue 32mm Plossl, I get a 3.3 degree field of view at 15 power that will blow your socks off. Also, it comes with a gorgeous 2" diagonal that
would fit into a Schmidt-Cassegrain 2" visual back if necessary. I don't use it in this manner, even when the occasional friend wants me to take a look with his new megadollar 2" eyepiece, because...
3. I got the Meade 2" flip mirror system ($250) for astro-imaging, but it also makes a fine 2" diagonal. The new ones have UHTC coatings, making them even better. Since the
mirror can be readily collimated (rare for a diagonal), you can get a nearly perfect setup.
I'm writing this not to discourage you from getting a 2" diagonal, but to give you some idea of the caveats and alternatives for your hard-earned dollar.
Subject: Is SMT Worth It? --part 1 of 3
From: Gene Horr <genehorr
texas.net> Date: Jan 2004
Rick Woods wrote:
> Thanks to everyone for the replies. As soon as I clicked "send" I
> realized "duh, use Google!
> But I'd still like to know: Is SMT worthwhile?
Assumint that it works as well as T-point, the answer is "maybe". Remember, it only can correct for repeatable errors. Mirror flop is still going to produce uncorrectable problems
assuming that the primary is not locked into place. And with these systems there really isn't an workable way to make all of the corrections perfect.
But it does improve things. If you are having problems now with getting an object on a CCD chip after a slew then it would be worthwhile. If after a slew the object is on the chip
just not centered then it is probably not worthwhile.
---------------------------------Subject: Is SMT Worth It? --part 2
From: Doc G
----- Original Message ----From: Richard Bennion
I have an LX200GPS and use T-Point to improve pointing accuracy.
I can get the pointing accuracy to less than 1.5 arcminutes everytime
with a short 10 point mapping run. This is down from about 8-10
arcminutes standard pointing.
----- End of Original Message ----I want to point out that my work was done some years ago. It was in the late 1990s as I recall. It is true that a very poor scope mount is hard to improve with T-point type
programs. But if the scope and mount are mechanically stable, that is, the scope always does the same thing without much hysteresis (backlash) the pointing can be substantially
improved.
I have the general feeling that in the past 5 years many scopes have either started life in better condition or they have be tweaked to the point where they are fairly good pointers.
I the latter case, the mount can definitely be improved and will give pointing to a (very) few arc minutes. I have had many reports of one or two arc minute pointing accuracy over
the whole sky.
It is very important to do the T-point model with the scope loaded exactly as it will be in use. Weight and balance can have a strong effect on the model since the weaker mounts
are more flexible. My general feelings about the usefulness of T-point like modeling is that these programs are definitely worth while if you have a reasonable mount in the first
place.
---------------------------------Subject: Is SMT Worth It? --part 3 of 3
From: Bob Denny <rdenny
dc3.com>
One other thing to look at, if you have a CCD camera, is ACP3. It has a "self-learning" pointing corrector, and it also re-centers as needed so that your images are centered starting
with the very first one. As you acquire more images, it learns from the centering errors and teaches the pointing corrector on the fly. <http://acp4.dc3.com/index2.html>
.
Subject: Optical-Mechanical Alignment for GPS Model
From: Bill Drelling <gatorchaser
earthlink.net> Date: Aug 2002
I actually started to use the Mark Simpson's OTA Alignment Method. It is great. But it is written for the LX200 Classic. I have the GPS version. The difference is that
with the GPS version, you cannot turn the optical tube over on itself the way the classic allows. The GPS tube rotates from just past the vertical in the up
direction to just past the vertical in the down direction ... maybe for a total angular motion of about 200 degrees at most. In other words, it rotates the direction
it points from straight down the fork arms pointing to the base, to straight up the fork arms pointing towards the sky with only slight motion past the vertical.
That is why I had to resorted to a fixed land object to start correcting the optical-mechanical misalignment. I had all day to tweak it with plenty of light to play in.
I later took it out at night and tried to get the fine alignment finished with Polaris, but it was too difficult due to the various factors that affect rotation of the
tube and adjustments:
1. declination error,
2. optical-mechanical tube misalignment error,
3. "slop" in the wedge, and
4. my own impatience
Declination error and optical-mechanical tube misalignment are closely tied together because it is hard to see which is which through the eyepiece. The best I
could do was get the stars to rotate in an oval pattern within the confines of the reticle--which means I am close. Problem was figuring out whether the optical-
mechanical tube misalignment was reflected in the length or width of the oval pattern of star rotation.
To complicate matters, there is always a little slop in the wedge. This is seen when you adjust the machine screws. Only a little pressure is required to turn the
screws and move the optical tube, but that is all it takes to make a slight motion of the wedge (I use the Super Wedge on my 8" LX200GPS). All these factors
combine to make the fine adjustment complicated.
What is need, ideally, is a way to make the adjustment with the scope in the Alt-Az mode. This is why your procedure works so well with the Classic LX200. Since
the GPS tube cannot rotate over on itself, however, your procedure doesn't work with it. Unfortunate.
Subject: Meade Dew Shield on GPS?
From: "messier27" <messier27earthlink.net> Date: Sep 2002
The current Meade Hard Dew Shield does not fit the LX200GPS units. The LX200 Classics had a groove running around the casting at the corrector end of the
scope; the set screws for the dew shield locked into that groove. The LX200GPS unit does not have this groove?
Subject: GPS Mirror Lock Like Classic? --part 1 of 2
From: Bill Dougherty <bd5572
yahoo.com> Date: Mar 2004
Walt Cooney wrote:
>Can anyone direct to some information on the GPS model mirror lock mechanism?
>Did they just install the equivalent of a shipping bolt that can be latched
>and unlatched or is it something more like the Bisque mirror lock collar?
No, the GPS mirror lock works very differently. It is a collet type mechanism that immobilizes the center mount of the primary mirror where it slides along the
central baffle tube. I have a 10" GPS and its mirror lock works extremely well --- very secure but producing no stress on the mirror itself. I consider it to be the
single most significant improvement of the GPS over the Classic.
I don't have a picture of the mechanism. It is hidden beneath the back end plate of the OTA. The locking knob has a gear on the inside end of its shaft. It engages
teeth on the outside edge of a large metal disk connected to the mechanism that locks the position of the mirror on the central baffle tube. Rotating the locking
knob one direction rotates the large disk to tighten the collet on the central baffle. Reversing direction loosens it.
The teeth do not extend all the way around the large disk. So sometimes the locking knob gear jams to a stop before the lock is fully engaged. Soon after the GPS
scopes first started shipping Buck Harley discovered that in such cases you can remove the locking knob with its shaft and gear, then reach in and rotate the
large disk with your finger. Replacing the locking knob will now allow sufficient rotation to fully engage the lock. If you happen to move the large disk in the
wrong direction, then just repeat the process and move the disk in the other direction.
You don't need to tighten the lock down hard. Just a little snug is enough. You should not attempt to use the coarse focus knob while the mirror is locked.
Damage to the focusing mechanism could result.
This design is intended to precisely hold the mirror position. So, yes, it is meant to allow effective use of a separate guide scope by eliminating mirror flop when
in the locked position.
Are you saying that the central baffle tube itself is moving inside the OTA as the scope slews across the sky? The mirror lock could not do anything about that,
since it secures the position of the mirror mount onto the baffle tube.
Of course, if the mirror lock is disengaged to allow use of the coarse focus knob, then the mirror is free to flop around as much as ever. Resetting the lock will
tend to move the mirror back to roughly the same angle has it had in the previous locked state, but this position can vary somewhat with each use of the lock. For
instance, if you want to test GOTO accuracy, then you need to set the lock before the first alignment star and not touch it again until after the last test star is
recorded.
Using the coarse focus knob while the mirror lock is engaged will result in severe image shift, and could damage the coarse focus mechanism. So changing the
focus with the mirror lock engaged requires use of a secondary focuser, such as the MicroFocuser included with the GPS scopes.
--------------------------------------------------Subject: GPS Mirror Lock Like Classic? --part 2 of 2
From: Roger Hamlett <ttelmah
ntlworld.com>
There is a measurable bend in the baffle tube. The 'key' problem to remember, is that any component before the secondary, has it's effect on the light path
amplified by a factor of about 5*. I calculated that for an LX200/12, the tube itself would bend by about 0.3 arc seconds through 180 degrees, with the weight of
the mirror, when at the normal focal point (I measured where my mirror was, for the scope focussed about 4.5" behind the rear of the focuser). This then gives
an 'unavoidable' error from this source alone, of about 1.5 arc seconds. The rear plate (I was guessing on the aluminium alloy used, but assumed 6061 - similarly
I was guessing on the plastic used for the baffle tube), gave a slightly lower distortion, but brought the total up to just over 2 arc seconds. There was also a
_tiny_ bend in the mirror itself. In a sense, there is a 'minimum' movement, that is as far as I can see, unavoidable for this design, no matter how well everything
else is locked. I'd put this at perhaps 2 to 3 arc seconds total for the worst case (180 degree) movement of the scope.
Moving the coarse focuser with the lock engaged, first 'rocks' the assembly hard to one side or the other, and then tries to 'scrape' the collet along the baffle
tube, putting much more force onto the focuser itself, and all the other components, than they are really designed to take. With the 'lock' done up, and moving
the scope round the sky, the total movement, in the axis parallel to the line through the coarse focus knob, and the centre of the tube, was down close to the
'bending' limits. However at 90 degrees to this, there was still a significant shift. It makes sense if you think of the system as being locked at the collet, and at
the focuser shaft, it can still rock at the front at 90 degrees to this line, till the end of the outer tube touches the inner tube.
The clamping force of the collet, reduces this motion, but does not completely remove it... I must admit I did find myself wondering about careful placement and
design of the guidescope mounts, to at least partially compensate for the motion, and wondered if this was how some systems appear to have very good
responses. When dealing with 'pure bending' (as opposed to nasty shifts/rocking motion), it would be possible to site the guidescope, so that it's bending is in
the same order as that of the main scope, and get a final result that is better than one scope on it's own. As has been mentioned by another poster, Al Testani,
was doing a lot of work in this area, trying to measure and model the errors between guidescope and main scope across the sky. It might well be worth talking
directly to him, to see how he was getting on.
Subject: LX200GPS Adjust Guide Rate Feature?
From: Dick autostaretx <autostaretx
mindspring.com> Date: Mar 2005
> Does the GPS have the 'adjust guide rate' feature?
Yes. On the keypad it's under: Setup > Telescope > Guide Rate
and has a range of zero to 100% of sidereal. The "factory default" is 66%
I provide free patch kits for the firmware (posted to the LX200GPS Yahoo Group's Files area), and one of their features is extending that range to 200% of
sidereal.
Subject: How to Calibrate Motor on LX200GPS ?
From: Rich Swanson, Date: Feb 2005
From the LX200GPS group files section: <http://groups.yahoo.com/group/lx200gps/>
I attempted to train my 10" as soon as I got it. Turns out that it worked great. And the best part is that I didn't even have to take it outside to do it.
1. Get a laser pointer.
2. Find a way to keep the laser pointer on by itself. I just wrapped a piece of tape around the trigger button.
3. Tape the laser to the OTA in some manner that the laser point projects onto a wall.
4. Tape a piece of paper, which you have drawn a target on, on the wall to act as your targeting object.
5. Complete the training process as described in the manual or on the AS II handbox screen. You don't even have to look in any eyepieces. Just guide the laser
point back to the target. VOILA!!! Laser Trained Telescope!
Editor's note: here's another method for training the GPS drives in polar mode. Outside link.
Subject: Parking the GPS Scope
From: Barry Gerdes <barrygastro
hotmail.com> Date: Apr 2005
The Park and sleep feature is not well explained in the manual and does cause some confusion. I have written a version that I worked out for my understanding
that may be of some help. You will find it on my web site (see below) under "Sleep and Park" on the LX200 files page:
<http://www.geocities.com/barrykgerdes> or direct download of .doc file: <http://www.geocities.com/barrykgerdes/Slp_park.doc>
MAPUG is hosted by
CCD Misc. Topics --Page 1
Review of "CCD Imaging Techniques" Video
What are the Definitive Books about CCD?
Pixels per Arc Second Calculation --2 parts
Calculating CCD Pixel Size
Calculating Pixel Size Needed
"Seeing" vs. Pixel Size
Image Size in Microns
Flat Field/Dark Frame
CCD Selection Questions
Equipment & Software Used for CCD Imaging
Useful Prime Focus Camera Adapter
LX200 Rear Cell Adapter
Camera Connections to Avoid Vignetting
Internal Mounting of a Barlow --linked to LX200 Miscellaneous Items
CCD Focusing Aid
An Improved CCD Focuser Mask
Color Filters, Filter Thicknesses, & 3-Color Imaging
Tricolor Filters for CCD --3 Parts
Filter Wheel Recommendation
CCD Miscellaneous Topics--
Subject: Review of "CCD Imaging Techniques" Video
From: Ed Stewart <stargazer
skymtn.com> Date: Dec 2001
Greg Pyros graciously sent me a copy of the new video tape his company produced for review. I'm very typical of a potential
purchaser of such a video on basic considerations for getting started in CCD imaging since I have never used this type of camera
or related equipment. My only knowledge of the subject comes from reading and editing the posts that come across this list and
become a part of the MAPUG-Astronomy Topical Archive.
After popping the tape into the VCR, the opening scene shows the high production values as parts of telescopes fly from behind
the viewer out into the foreground and assemble into three complete telescopes-- very cool! They are all Meades as they were
kind enough to loan the equipment primarily used in the presentation. The first information given is very basic stuff about the
designs of refractors, Newtonian reflectors, SCTs and Maks and mounts, but not much time is devoted to this so it passes quickly
(not assuming anything on the part of the viewer is the best approach). As other concepts are presented, such as periodic error
correction, battery power, dew prevention, off-axis guiders, polar alignment, etc., the broad picture of just how much effort and
resources are going to be required begins to pile up. And along the way good tips are dropped in, like running the cables of the
camera up to the Dec axis and then down to remove strain and possible weight shift. The tape ends with basic image processing
where the concepts are graphically illustrated, like showing ten short images as a stack of pages that collapse down to a single
image by the use of the stacking command go a long way to make a mental image of what is happening. Again, the production
values are high.
I believe this tape is best for those who haven't made their purchase decisions yet, but are in the process of exploring what all is
involved in getting into this part of the hobby. It reminds me a lot of a similar video presentation on building a log home that my
wife & I purchased several years ago-- after it ended 1.5 hours later, we knew that the project was beyond our abilities, time,
and resources. I think this video will do the same for prospective imagers-- it will either excite them into making the plunge or
will make them pause to think about the commitment before investing hundreds or thousands of dollars.
My only suggestion to Greg would be to include the word "basic" or similar phrase in the title, but otherwise I think it is a wellthought out production, informative, and enjoyable.
For more information and/or to order: <http://www.AstroVideos.com> The price is $39.95
Subject: What are the Definitive Book(s) about CCD?
From: Doug Carroll <voxr
attbi.com> Date: May 2002
There are really two good books about CCDs depending on what you want. One is "CCD New Astronomy" at: <http://www.
newastro.com/newastro/default.asp> and covers everything about imaging.
The other is "AIP4WIN" at: <http://www.willbell.com/> and is a very detailed book that goes into the depths of CCD and how it
works and to get the most out of the sensor. I have both and they are excellent books.
Subject: Pixels per Arc Second Calculation --part 1 of 2
From: Duane Baker <DBaker1047
aol.com>
In Winter, 1995, CCDAstronomy, the article Optimizing a CCD Imaging System, has a chart of pixel/arc seconds/focal length,
which is what I used to determine my scale.
The formula is: (M/FL)*206
Where M is the size in Microns of each pixel of the CCD Chip
Where FL is the focal length of the scope
Example: ST-7 CCD Camera with 9 micron pixel size + 8" SCT with 2000mm focal length =9/2000*206=0.92 pixels
Now if you were to use the f6.3 focal reducer you get: 9/1260*206=1.47 pixels
Now if you were to use Optek's f3.3 focal reducer (this reducer only works with f/10 scopes) you get: 9/660*206=2.80 pixels
This works for all focal lengths even when using a focal reducer.
As I understand the situation, the main reasons for larger pixels are:
●
●
●
Larger pixels are more sensitive -- shorter exposure times.
Larger pixels mean larger field of view -- more sky coverage.
Larger pixels mean less-stringent guiding requirements.
The problem with too-large pixels is undersampling. The main downsides of undersampling are square star images and poor data
sampling for analysis purposes. When an image is undersampled, star images can't be properly centroided, so the resolution of
astrometry is limited (I do mean resolution, not accuracy, don't I?). Photometry is more difficult -- imagine that a star image is
just under the size of a pixel. In this instance, some stars will be right in the center of a pixel and put all of their energy into it,
while others might be right over a border, and split their energy over two pixels. Some might even be at "the four corners", and
only put 1/4 of their energy into each pixel.
The best trade-off seems to be where the pixel size is about half the seeing. As I live at sea-level, I usually use a focal length that
gives me 2.4 arc-sec pixels -- any smaller and my images don't have any more resolution, they just take longer to integrate and
cover less sky. An approach that I have used with some success is to undersample an image -- say by using a telephoto lens -so that I get a nice big swath of the sky, and then resample and smooth the image to make the stars look less square.
BTW, it seems to me that the actual size of pixels is not an issue -- the question is the size of a pixel in terms of sky-coverage.
Since changing the focal length of the system changes the effective size of the pixels, so the question seems to really be "What
focal length do I want to use?" For a discussion of this, take a look at the Apogee site's CCD University: <http://www.ccd.com/>
Note: a new window should open over this one.
------------------------------------------------Subject: Pixels per ArcSec -part 2
From: Chris Fry <cfrye
ix.netcom.com>
2 arc-secs per pixel is about optimum for ccd imagong in average amature seeing conditions (below 5,000 feet elevation). Here is
the equation:
Arc-secs/pixel = 206,265 secs-per-radian x ccc-pixel-size (in mm)/focal-length.
Your scope has a focal length of 10" x f10 = 100" = 2540mm. So:
Arc-secs/pixel = 206,265 secs-per-radian x .009mm/2540mm = .7308602
This is to small for average seeing conditions at f10.
Using an f6.3 focal reducer will reduce your focal length to 2540 x .63 = 1600.2mm.
So: Arc-secs/pixel = 206,265 secs-per-radian x .009mm / 1600.2mm = 1.1600956.
Q.E.D. The focal reducer gets you closer to the ideal goal of 2 arc-secs/pixel.
Actually you would be better off with an "Optec f3.3" focal reducer; that will get you: Arc-secs/pixel = 206,265 secs-per-radian
x .009mm / 838.2mm = 2.2147279. This is almost ideal, as it is near the target 2 arc-secs/pixel!!! You can take ccd images at
f10 with 9 micron pixels, and they will probably look ok, but yu will be over-sampeling and therefore reducing your sensitivity and
introducing unnecessary noise into the image.
Subject: Calculating CCD Pixel Size
From: Doug Carroll <voxr
attbi.com>
Hi Rick, I think this is what your after, I want to know the same thing so I created a spreadsheet to figure it all out for me and
posted to my website. Take a look at it and see if it is what you need. You can download the spread from this site:
<http://www.ccdguy.com/other/ccdpss.htm>
Subject: Calculating Pixel Size Needed
From: Doug Carroll <voxr
attbi.com>
-----Original Message----From: Doug David:
I have a Meade 8" LX200 and am considering a Starlight Express MX7C for astrophotography. My question is, for an 8" LX200,
which focal reducer would perform better for deep space pictures, the f/3.3 or f/6.3? Pixel size of the MX7C is 8.6 x 8.3uM. If I
am correct in using the following to obtain 2 arc seconds per pixel (formulas from Starlight express)
F = Pixel size * 205920 / Resolution (in arc seconds)
In the case of the MX7C and a 2 arc seconds per pixel resolution:
F = 0.0082 * 205920 / 2 = 844mm
For a 203mm (8") SCT, this is an F ratio of 844 / 203 = F4.15, which falls right in the middle of the F/3.3 and F/6.3 reducers. So
which one would perform better?
-----Answer----I currently use a Genesis camera with 9uM pixels and image at f/10 and 2x2 binning and get great results you don't have to
image at 1x1 binning so you have the added flexibility of combining the two (binning and f ratio) to get the pixel size you want.
The 2 pixel is not a rule--it is a guideline based on the average seeing of sites. Ultimately I am going to be using a 6.3 and 3.3
reducer as well I have the 6.3 already.
If you want to check of combinations I have a spreadsheet that I did to do this with different optical configurations at:
<http://www.ccdguy.com/other/ccdpss.htm>
Subject: "Seeing" vs. Pixel Size
From: Doc G
I have followed this thread about seeing and pixel size with interest. Let me take a slightly different tack on telescope focal length
and CCD chip size. I have both a 12" f10 and a 10" f6.3 telescope (LX200s) I also have the 0.63 field reducer and the Optec 0.33
field reducer. Why?? I feel that the way to think about imaging is to make a list of the object sizes you are interested in. This will
vary from planets that are a few to a few dozen arc seconds to nebula and galaxies that are as large as a few degrees. It is clear
that no single telescope with a given CCD chip and vice-versa will be suitable for imaging all of these objects. We need a few
thousand millimeters focal length to fill a Kodak 400 chip with an image of say, M57. For a planet we need not only 3000 mm
focal length but a strong barlow to get a nice sized image on the same chip.
If we want an image of the larger nebula or M31 we don't need a telescope at all. We need a medium focal length camera lens.
This said, I have a philosophy for imaging which is simply this. Pick a focal length which gives an image size that uses up most of
the chip area. That's it! If you use most of the chip area, you get the most detailed image you can. This is what I learned from
photography. You choose the perspective first and then you choose the lens focal length to fill the frame. You need to use most of
the chip area for the image in order to get an image that is not "pixelated."
It is all very simple but you need a lot of different focal lengths to cover the objects from Jupiter or Mars to M27 or M31.
Subject: Image Size in Microns --part 1 of 2
From: John Mahony <jmmahony
hotmail.com>
Art Morton wrote:
>Thank you for your responses. I use a MX916 imager, which I believe has
>pixels that are 11.2 by 11.6 microns. I have not done the correct math to
>relate my most focused star images to (calculated theoretical) size, but it
>seems upon measuring star images with AIP4WIN (star image tool) that most
>of the time stars are not really pin point, but blobs. I am using a LX200 at
>f/6.3 that is collimated using CCD images.
>
>It does not matter if I use a computerized mechanical focuser with FocusMax
>or focus by hand, the smallest star image regardless of Max Pixel Value
>seems to be 3, 4 and 5 pixels across in the X/Y axis. Very, Very rough
>calculation would put the star images on the CCD at 35, 47 and 58 microns.
>
>I am just starting to investigate what the optics of a SCT can do, and after
>reading the advertisement of Meade, (Diffraction Limited Optics), just
>wondered what that meant in real world seeing. I have not taken in the other
>real world affects like the atmosphere, angle of where the star was when
>imaged or other factors. I was just wondering what is the starting point of
>potential star focus size.
I use CCD on a 12" LX200 for asteroid astrometry (discovery and follow-up tracking of asteroids). Star size is important there
because you're trying to measure the position of the asteroid to a few tenths of an arcsecond. But it's normal for the image to be
a few pixels wide (at 2" per pixel), primarily due to atmospheric turbulence. A more useful measurement is FWHM (full width half
maximum) which means the width at which the intensity (at the edge of this width) is one half the peak center intensity. This
number is usually much smaller, and is generally independent of a star's magnitude, as long as the star's image is not saturated.
More generally, a psf (point spread function, basically a bell-shaped intensity curve) is fitted to the star images, and this allows
sub-arcsecond accuracy in determining position, even though that's much smaller than 1 pixel.
-------------------------------------------------------------Subject: Image Size in Microns --part 2 of 2
From: Radu Corlan <rcorlan
pcnet.ro>
Dennis Persyk wrote:
> I have pondered your question a bit more and have come up with an
> alternative answer: Dispersion.
>
> Here's what I observe:
> Bright class O stars bloat the most.
> Problem worst with camera lenses piggyback; least at Cassegrain focus.
> Problem mitigated with IR blocking filter or stopping down lens 3 stops.
>
> So perhaps it is simple chromatic aberration. Perhaps the class O stars
> produce the greatest signal in the blue and this exacerbates the problem as
> the CCD is least sensitive in the blue and most sensitive in the near IR.
It's almost certainly chromatic aberration. The O stars put out a lot of UV and violet light; even if the CCD is less sensitive there,
there's still enough response to bloat the stars.
Once you get near 350nm, even a corrector plate or filters/windows can introduce chromatic aberration.
Seeing is also generally worse at shorter wavelengths.
It's apparently paradoxical that the IR filter improves bloat on blue stars. But i think this paradox can be solved: when you focus
the camera with the IR filter, you adjust optimum focus for a bluer region, so the bloat is less. Most lenses don't correct for
infrared, so when you focus on the full spectrum, you tend to shift the focus towards the infrared position.
Subject: Flat Field/Dark Frame
From: Gary Campbell
A member wrote:
>The Meade manual states:Take Dark Frame-Cover the Telescope. This seems
>simple enough. But what about "Take Flat Field". What exactly does it mean
>to "Prepare the Telescope"?
Blow off taking flat fields for awhile. They're hard to take effectively. And they aren't normally required to get some pretty good
pics. After your comfortable w/ everything else in your imaging, then try them. "Prepare the Telescope" undoubtable refers to
pointing the scope at a flat field (see below). Below are some of my experiences:
In a flat field exposure you want to image a very evenly illuminated field. The best way I know to describe this is liken it to a
'photographer's grey card'. Some people use a twilight sky as their grey card. While others actually some sort of card. By imaging
this very flat field, you'll record unevenness in your optical path and within the chip itself. You can then divide this pixel info into
your 'real' image. All chips and most, if not all, optical systems will have some unevenness. Maybe the biggest benefit is you can
'flat field out' little artifacts caused by dust on your imagers glass window. These artifacts will resemble little black donuts. Once
you see them, you will instantly recognize them. Proper flat fielding can also reduce the effects of vignetting.
Taking decent flat fields is harder than it seems. You want to expose your flat field image long enough to obtain pixel values
somewhere near 2/3s the saturation level. For an imager using the KAF400 chip, such as the Pictor416, this would be pixel values
around 45,000. If you're using a different chip, calculate the 2/3's amount. You don't have to be real close to this, but it's a good
rule of thumb. What you want to avoid is (1)your flat field image having saturated pixels, or (2) the pixel values being so low that
you don't get enough info. Hence the 2/3's generalization.
To be able to make a usable flat field image, your camera has to be in exactly the same position as it was during your 'real'
imaging. This means leaving the camera on your scope once you start imaging. Removing the camera, then putting it back on,
will make flat -fielding very difficult, if not impossible. So will changing the focus. So most people end up taking flat fields at the
end of an imaging run.
If you're taking flats of the sky, you need to wait until dawn. This way you can get the amount of illumination you need to reach
45,000 pixel counts. Timing is critical. If you shoot too early, your sensitive chip will record stars. If you wait too long, the
brightness of the morning Sun will saturate the pixel values. And in either case, your flat field images will be worthless.
Or if your taking flat fields of a 'grey card', if your timing is good, you can use the ambient light at dawn to illuminate the card.
Then adjust your exposure to reach ~45,000 counts. Timing is slightly less critical using this method. But only slightly. You'll
really notice how fast the Sun comes up after trying this.
If you can't wait till morning, it's possible to bounce a light off something onto your gray card. Much like bouncing a SLR camera's
flash unit off a ceiling. A flashlight beam bounced off a white shirt works well. Again, use your length of exposure to obtain the
~45,000 value. This method will *not* help your chances of winning a popularity contest if your observing w/ others <g>.
This previous method is fairly simple for people w/ observatories. Once you done it once or twice, and get everything set up, it's
repeatable. So subsequent nights are much quicker.
A third method involves making some sort of light box to put on the front end of your scope. This is harder than it sounds
because it's not easy to diffuse the light and get a perfectly illuminated field. Plus your light source can provide the wrong kind of
light. I wasted a lot of time trying this method and gave up unsuccessfully. Improperly flat fielded images will make your pics
look far worse than better. Averaged, or better yet -median combined, flat fields provide better results than single exposure ones.
Same holds true for dark frames.
Subject: CCD Selection Questions
From: Dick Green <dick.green
valley.net>
1. Why would one pay the same for an ST-6 with grainier images, and no self-guiding, as the ST-7? What is it's strength? Please
explain in layman's terms.
Hard to explain in layman's terms, but I'll try. Ask yourself this question: When I image a star, just how small a spot of light will
it cast on a CCD chip? In theory, the spot should be a point of light because at stellar distances, the light is coming from a point
source (i.e., a star is too far away for you to be able to see the actual disk) In practice, of course, many factors conspire to make
that spot bigger than a point. For example, I'm sure you've noticed that when the seeing is really good, and your telescope optics
are clean and well collimated, and your focusing has been really precise, stars appear as sharp "pinpoints" of light. Under such
conditions, you can see the airy disk of a star with a high magnification eyepiece. On other nights, when the seeing isn't so good,
or your telescope optics are dirty or a little out of collimation, or you just can't quite get things in focus (because it's 30 below),
the stars look a bit larger or smudgy and you can't see the airy disk at all. Sometimes just the seeing alone will be so bad that a
star looks blurred in a high mag eyepiece -- i.e., it makes a bigger spot.
Of course, I don't have to tell you that your LX200 doesn't have perfect optics, either. The primary mirror is relatively small,
there's a BIG central obstruction, and the figure of all of the optical components probably doesn't compare to, say, one of the
Keck scopes. That makes the spot bigger, too. To make matters worse, when you do a time exposure with a camera or CCD,
imperfect tracking and/or flexure in the mount is going to smear or wobble that image. So the spot gets bigger. One can
summarize the factors thusly: Focus, Optics, Seeing, Tracking, and Experience (of the operator). Hey... that almost spells
FOSTER, which is the title of Software Bisque's treatise on the subject (the R stands for Review -- wierd --) Guess it's obvious
where I learned about all this...
Anyway, the theory is that the best resolution is obtained when a star image takes one or two pixels to represent. Let's assume
that it's a great night and you've done everything you can to optimize Focus, Optics (clean and collimated), Seeing, Tracking, and
your own Experience. Then it boils down to how well the specific characteristics of your optical path match up with the size of the
pixels used in your CCD. If the best your optical path can do is make star images that are 50 microns in diameter, the 9 micron
pixels used in the 416 and ST-7 won't improve resolution over the roughly 27 micron pixels (they aren't square) used in the ST-6.
You might say, "So what -- the 9 micron pixels certainly don't degrade resolution." True, but they are a whole lot less sensitive to
light than the 27 micron pixels. You can easily see this if you use 2x2 binning for images from a 416 or ST-7. The resulting 18
micron pixels take about 1/4 the exposure time of the unbinned 9 micron pixels. Longer exposure time is a real liability because it
requires much more precise tracking (that's why the 416 and ST-7 come with autoguiders), steady seeing throughout, and no
mirror flop. The problem is exacerbated by the fact that the blue light sensitivity of the KAF-0400 chip is relatively poor. And tricolor images? Oh boy. Now you need precise tracking through three long exposures, you've introduced filters that reduce the
light reaching the chip, and the poor blue sensitivity just kills you.
Finally, the ST-6, big old rectangular pixels and all, actually has a much larger field of view than the ST-7, but with a lot fewer
bits to transfer to the computer. Typical exposure times are short enough that autoguiding is needed less often. As for graininess,
try comparing a well-exposed ST-6 image with an underexposed unbinned ST-7 image. The latter is much grainier. It takes a lot
of precision work (and some luck) to get that "photo-like" quality from an unbinned ST-7 image.
This is not an ad for the ST-6. In fact, I have an ST-7 because I don't like square stars, I couldn't bear the thought of waiting for
very slow serial port transfers, I wanted to do long autoguided exposures, and I didn't know all this when I bought the camera.
Maybe someday I'll get a better telescope to go along with my CCD camera. What with all the time it takes to optimize tracking
and take long exposures, it should come as no surprize that I built a permanent pier -- both for improved stability and minimum
setup time.
One last thought -- from what I've read, the ST-6 is a better choice for photometery due to the better blue light sensitivity and
short exposure times. Square pixels aren't a problem in this case.
> 2. You mentioned using a barlow .. does that mean the the CCD physically pops right into the star diagonal? the visual
back? Where exactly to you put the darn thing.
The 416 and ST-7 both have nosepieces that are just like the barrel on an eyepiece. You stick the nosepiece into the visual back
and use the thumbscrew. If you use a barlow, it goes in the visual back and the CCD nosepiece goes into the barlow. The single
thumbscrew mounting is a lousy way to mount a CCD camera (the camera can rotate on it's axis, requiring a new flat field image,
and do you want one little screw holding your $2,500 camera in place as the scope slews wildly around the universe at the end of
a long moment arm formed by the barlow?) The ST-7 has T-threads, so it can be mounted directly to the rear cell or focal
reducer. This makes for a much sturdier mount, but you can't use it with a barlow.
>
>
>
>
>
>
3. If one took a camera, and mounted it a prime focus, it would have a very
wide, rich field. Aside from the obvious inability to take in a lot of data,
why are CCD images so much smaller in area size, but so much larger in terms
of magnification? In other words, at f/6.3, on an 8" M51 looks like a huge
whirlpool, yet if you were to use a camera at prime focus, it would come out
as a tiny little thing. Is that a limitation of emulsion?
The size of the image projected in the chip and the film is the same, but the chip is a whole lot smaller than a piece of 35mm
film, so its field of view is much smaller. M51 fills up almost the whole chip, while it's just a tiny spot on the film. The chip image,
which is almost all M51, is blown up to nearly the full size of your computer screen (maybe about x 11 inches on my screen),
while the film, with a tiny image of M51 in the middle, is blown up to maybe 4 x 5 inches. If the grain of the emulsion if fine
enough, you should be able to blow the image up to the same size as the CCD image, with much better resolution.
>
>
>
>
4. With short shots, can one get away with alt-az. alignment on the LX200
rather than Polar.. it is much easier for me, I have seen this done
successfully in 2 minute shots, but would like more info ( I know we have gone
over this before, but we seem to be more experienced now as a group, and would like more opinions on it)
Sure, it works fine. But longer exposures will show field rotation, so it has limited utility. It would be nice if Meade came out with
a field derotator for the small scopes like the one on the 16". I, for one, would much prefer the stability of the ALTAZ mount
without the wedge. The drawback is that you can't use a tube-mounted guider
Subject: Equipment & Software Used for CCD Imaging
From: Mark de Regt <deregt
earthlink.net> Date: Aug 2002
Michael Wyatt asked:
> Could you provide more details as to your setup and how you
> were able to get such a great image. Did you have the LX200 PEC
> trained and what focal reducer did you use and how was it located.
From the ground up, here is my equipment list:
1.
2.
3.
4.
I set-up on grass, not preferred but my only available option at the moment.
Three one foot square ceramic tiles (the kind normally used for tiling floors).
Celestron "shock absorbers" for all three feet (I have removed the rubber pads from the feet of the tripod).
Meade Giant Field Tripod (the one for the 12"); I only just acquired this, and all pictures on my website other than the
NGC6946 were made with the Standard Field Tripod. I got the Giant Tripod with the plan to use it as a pier, just leaving it
in place, with the wedge attached).
5. Milburn Wedge--a real quality product, both in form and function.
6. 10" LX200 (four years old); non-stock equipment on the scope: a two pound weight taped to the East fork arm; an NGF-S
focuser; a RoboFocus stepper motor for the NGF-S focuser (the RoboFocus has only been attached for the last four images
7.
8.
9.
10.
11.
I have made--M63, M82, M51 and NGC6946); rails top and bottom from Bonnie Lake Astro Works (Ken Milburn's shop),
with various weights for balancing at different points in the sky; a mirror stabilizer lock,
from ScopeStuff <http://www.scopestuff.com/>;
an EZ Focuser from Peterson Engineering <http://www.petersonengineering.com/SkyDiv/sky_division.htm>,
which is a must for good control of the difficult SCT focuser.
Meade .33 reducer, without spacers, yields an effective focal ratio of a bit over f/4.6.
I should use the Hutech light pollution filter, which I have, but I have not used it yet.
SBIG CFW8 color filter wheel.
SBIG ST-7E CCD camera--aside from the high quality of the camera, the built-in guide chip is a lifesaver.
Software used in image acquisition--CCDSoft v5 from Software Bisque <http://www.bisque.com/>. This is a very nice
piece of software, particularly in that it allows one to orient the camera at any angle and still guide as well as the mount
can. It also includes
Focus, a very good automatic focusing routine. Finally, working with TheSky, also from Bisque, one
can figure out precisely where a guide star is, which saves a lot of blind searching.
12. Software used in image processing--AIP4WIN, which I typically use for calibration (darks and flats), alignment, RichardsonLucy deconvolution, and Digital Development Processing (another sharpening routine); CCDSoft can be useful for
alignment (but I don't have a lot of luck with it), and it is good for image combining (combining the subimages into one
image, after calibration and alignment). Final image combine, tweaking levels and curves, and some useful filters are to be
found in Photoshop. AIP4WIN is, IMO, a must have for all imagers, and is a bargain at well under $100. Although it's not
software, another must is Ron Wodaski's book "THE NEW CCD ASTRONOMY" <http://www.newastro.com/newastro/default.
asp>.
As to how the images turn out well, it is a combination of a lot of things. First, PRACTICE. While one is typically able to get
recognizable images the first night, it takes a lot of work to achieve good focus, combine images effectively, and process them
optimally. I still have much to learn, but I have benefited from the second imperative--doggedness. Your images will only be as
good as the effort you are willing to put into them. I started imaging in the Spring of 2001; it took a couple of months before I
felt good enough about my nascent skills to attempt a color image, and it took several more months until I started getting pretty
consistent results. The other thing which cannot be overstressed is the help one can get on the internet groups, in my case the
SBIG group on yahoogroups. The world's best imagers are regular contributors on the group, and are happy to answer questions.
Particular kudos must go to Ron Wodaski, who is tireless in helping out, but many, many others post frequent responses to us
newbies as we claw our way up the learning curve.
You asked particularly about PEC training. In doing so, you hit on the biggest sore spot I have in trying to image with the LX200.
I believe that the RA mechanism is not machined to particularly high tolerances, and PEC is not particularly effective in getting rid
of the odd bumps in the mechanism which appear at various times. My next significant purchase will be an AO-7 from SBIG,
which seems to be quite effective at neutralizing much of the annoyance of the less-than-perfect LX200 mount/drive system
(don't get me wrong, I think that the LX200 is a marvelous value, but it does have its shortcomings).
Even if you acquire quality data, you cannot get a good final result without careful image processing. All of my images have
pretty detailed descriptions of the image processing I have performed on them, but it is a long, hard road learning processing,
and I still am feeling my way on that.
Astro Images: <http://home.earthlink.net/~akilla/MAD/>
Subject: Useful Prime Focus Camera Adapter
From: Bill Nicoll <bill
billnicoll.com> Date: Sep 2003
I recently purchased a 2" Prime Focus Camera Adapter, made by Orion, which I find to be very useful. One end has a standard T
thread which screws directly to the front of the CFW8 filter wheel on the front of my SBIG ST-7 camera. The other end has a 2"
metal barrel. A unique feature is that the barrel unscrews from the body of the adapter and the two sections have mating
Schmidt threads. This allows me to sandwich a Meade Focal Reducer and/or a deep sky filter between the two halves of the
adapter. In addition, the front of the adapter barrel is internally threaded for standard 2" filters.
The complete stack on the back of my 12" LX200 for imaging is as follows: Eyeopener Visual Back, JMI NGFS Focuser, Orion
Prime Focus Camera Adapter with sandwiched reducer & filter, and the CFW-8 coupled the to ST-7 camera. I have no problem
achieving focus and have the largest possible diameter light path back to the camera.
I purchased the adapter from Oceanside Photo & Telescope.
Subject: LX200 Rear Cell Adapter
From: Dave Schanz <dave23sch
valleytranscription.com> Date: Mar 2004
----- Original Message ----From: Clifford PETERSON
Does anyone know who makes a 3-3.25" to 2" rear cell adapter for a classic LX200 10"?
Cliff, I bought this adapter. It's very well made, and I like the compression ring with the three thumbscrew set up. It's very solid:
<http://www.buytelescopes.com/product.asp?pid=5669>
Subject: Camera Connections to Avoid Vignetting
From: Roger Hamlett <ttelmah
ntlworld.com> Date: Apr 2003
----- Original Message ----- From: Lawrence Harris:
> After spending quite some time I am still not managing to fit my MX916
> CCD to the LX200 without getting considerable vignetting. I have used the train:
> LX200 - NGF focuser - f/6.3 converter - T-adapter - CCD camera
> But the result gives excessive vignetting. What I really want is the
> camera right next to the converter, but the adapter is several cm long
> and I think this increases the vignetting.
> I then tried to use the camera with a filter but found it impossible to
> find a combination of fittings to allow this. Someone must have an answer here?
Start at the beginning. If you put the camera 'right next to the compressor', then you might as well not have the compressor at
all!... The compression ratio, is dependant on the spacing. The formula, is: rf=(f-s)/f
Where 'f' is the focal length of the compressor, and 's' is the separation. The f*.63 compressor has a focal length of about
240mm, and is designed for a spacing of about 90 to 100mm. The spacing here is the distance to the optical centre of the
compressor lens, but the distance to the corner where the threads end on the compressor is close to the right distance. So if you
put the camera tight to the compressor (reducing this distance to only perhaps 40mm to the CCD), you would get a compression
ratio of only (240-40)/240 = 0.84*
The next question, is how bad the vignetting is. It is worth understanding, that even without a compressor, the scope itself will
not produce a completely 'flat' illuminated field. Many scopes have a 'fully illuminated' field, that is only a very few mm across,
and will display some vignetting beyond this diameter. However the amount is normally small. If (for instance), the illumination
varies by a few hundred counts, out of several thousand, this is both normal, and acceptable (and easily corrected by using a flat
field). When looking at the causes of vignetting, you need to work out which part of the light path is the likely culprit. So if you
imagine a situation, where you have the optical train as you describe, with the separation from the CCD to the compressor at
(perhaps) 90mm, and the final optical ratio (measured using the drift method, or by scaling off a star image), at f/7 (the scope
itself will be generating a slightly longer than quoted focal ratio, because of the increased back focus distance), then if you work
'forwards' from the CCD, things progress as follows: At the CCD, the field required is 10.9mm diagonally. The cone of light
needed to illuminate this, tapers at f/7 (from the imaginary measurement taken), forward from here to the compressor. So over
90mm, will taper outwards by 12.9mm, bringing the clear field needed to avoid vignetting, to 23.8mm at the compressor.
This is still comfortably smaller than the clear diameter of the compressor module. From this point forward, the cone now tapers
at perhaps f/11, so by the time you reach the front of the NGF-S (perhaps 100mm forwards of the compressor?), the field
diameter has risen to 32.8mm. From here, the light cone carries on tapering out at the same rate, down the entire length of the
telescope, to the secondary (you do not say whether this is a 8", 10", or 12" scope, which changes the length, and the diameter
of the baffle tube). If at any point, the outside edge of this imaginary cone, is larger than the available diameter, then vignetting
will result. In the case of an 8" scope, the diameter needed will rise to perhaps 75mm at the secondary, and will be slightly
vignetted, not by the compressor, but by the front edge of the baffle tube, and the secondary. However the amount involved, will
be less than 10% (in intensity measurement), and it is better to have this, than to be increasing the secondary obstruction...
There is a balancing act, between the size of field that can be used, the blocking of 'stray' light, and the size of the central
obstruction. Most image programs, make vignetting look far worse than it actually is (by applying automatic 'stretches' to the
dark parts of the image), and a bit of careful processing, can comfortably deal with normal vignetting levels.
Subject: CCD Focusing Aid
From: Bruce Johnston
My method of focussing either my Cookbook camera or ST-7 is to get close with an eyepiece as you now do, then I flop a
cardboard mask over the end of my 10" LX200, the mask having two round holes in it, each about 1" or so in diameter.
Making the mask is easy and takes about 10 minutes. I just lopped off the end of a cardboard box that was more than 10" to a
side... leaving about 2" of the each side of the box intact. I then cut off two of these sides. So what I then had was a flat box end
with two edges, of the original box. I flopped the box end, over the end of my scope so that the two "sides" were resting against
the tube. A quick session of measuring showed me where to cut the two 1" holes so that they'd be on opposite sides of the
central obstruction, and equal distances from it.
From then on, to make a very fast focus, I aim at a bright star, begin downloading and displaying the star, and I see two
representations of the star. The further from focus, the further the stars are separated. Just tweak the focus a bit at a time ... I
use a JIM Zero-image-shift focusser to keep the star from shifting during focus -- and presto, when only one clean star is
visible... perfect focus! Takes maybe one or two minutes, max, to get focus bang-on. Quick and cheap!
Subject: An Improved CCD Focuser Mask
From: Paul Gitto <PaulGitto
aol.com>
I've recently developed an improved focusing mask for CCD imaging. After working with diffraction focuses and Hartman masks,
they were still time consuming.
Basically a focusing mask is an opaque material, placed in front of the telescope's objective lens. Usually 2 holes are placed on
opposite sides of the mask to let light through. When the 2 images merge as one, as seen in an eyepiece or CCD camera's image,
the telescope is focused. I have determined that placing a triangular hole on an standard 2 hole mask, simplifies the process. The
third hole is used as a guide to inform the user if the focus has gone beyond the desired focus. If the focus has gone beyond the
focus point, the triangle will move to the opposite side of the focus point.
First, the triangular hole is placed at the North (top) of the telescope's objective lens. The 2 round holes represent East & West.
The telescope should be pointed at a fairly bright star. The first images are at a low resolution to speed download time. Even with
the telescope way out of focus, the mask will automatically guide you as which direction you need to turn the focuser. The
triangle will move either north or south, depending which direction the focuser is turned.
Images and further explanations can be found at my webpage:
<http://www.cometman.com/> Should open a new window over this page.
Subject: Color Filters Used for Three Color Imaging
By: Doc G
For 50 years I have used Wratten color filters for photography and have done everything from minor color correction to color
separation photography. This includes minor color correction to correct for tungsten to 3200 K or from daylight to 3200 K. I have
also spent several years in the 1940s and 50s doing three color separation photography. I believe that I understand color
correction and three color photography quite well. With that long introduction, I will make a few comments about the use of
filters for astronomical imaging using both film and CCD imagers.
The topic of color filters has become of interest to several CCD imagers on the MAPUG site recently as a result of questions about
the thickness of filters and the exposure times required in order to obtain correct color balance. A list of the thickness of some
filters is appended at the end of this note. I became interested when I purchased a set of color filters from Optec and found a
rather large ratio of red to green to blue exposures for this filter set. As an aside, which I will not discuss, I note that the color
filters provided by Meade with their color filter wheel are not all of the same thickness and thus all but impossible to use. This
problem was addressed by J Hoot in a recent post. However, in the same note he recommended a set of Wratten color filters
which included the choice of an 80A. I was quite astonished by this recommendation and will discuss this choice in the following
comments.
It must be noted that the choice of filters depends upon the application including elements about the spectral sensitivity of the
film in the case of photography and of the CCD chip in the case of electronic imaging. There is probably no best set of color filters
to use in general but there may be a best set to use when all factors are known. In a recent experience, I heard a talk at the
Florida Keys Winter Star Party in which images very much more blue that I have ever seen were presented with the comment
that these images were more accurate than most of those seen in the past. They were beautiful.
We do not know, in terms of what the eye might see exactly what color the many objects in the sky really are. Most dim
extended objects appear gray to out eyes. I recently saw M57 through a 40" scope and for the first time I saw slight color. For
bright objects, like stars and planets, we do of course see color. Obviously the lack of color is a defect of the eye. The objects of
course have color which may be captured with film and CCD.
Color filters may be of two types. Multi-layer dichroic filters can have very sharp and well defined pass bands. Wratten filters are
dye controlled filters and have pass bands which are in general much less sharp. As a starting point, and to limit this discussion,
we will assume that a three color system of imaging will be used. This will require a set of three filters that are broadly Red,
Green, and Blue. There are numerous sets of RGB filters that are traditionally used for three color imaging. We must also note
that the reconstitution of the image might be on a computer screen with RGB colors of their own hue and saturation or by
printing processes which all for their own color representation and balance.
Common sets of RGB filters for photographic purposes are Wratten filters: Some possible sets are: (in order RGB)
●
●
Separation filters 29, 61, 47
Tricolor filters 25, 58, 47
Interjection: Because the filters will be represented by numbers, a brief note is interjected at this point to describe the filter
colors as they are described in the Kodak manual:
Red filters:
●
●
●
23A, Light red.
25, Medium red. Red tricolor. For color separation work.
29, Deep red for use with No. 58
Green filters:
●
●
●
●
56, Light green.
57A, Medium green. (but lighter than the 58)
58, Medium green. Green tricolor. For color separation and tricolor printing.
61, Deep green tricolor. for use with Nos. 29 and 47
Blue filters:
●
●
●
80A, Light blue. Color correction to convert from 3200 K to 5500 K light (tungsten to daylight)
38A, Medium blue. Absorbs red and some green.
47, Deep blue. Blue tricolor. For color separation work with Nos. 29 and 61.
Because of the way these filters, all of which are pass band filters, (Except the 80A which isa correction filter used with color
film.) behave in the pass and stop bands and particularlyhow rapidly the cut off, they will produce distinctly different color
balance in the finalimage. Astronomical, printed color images rarely give all of the information necessary to beable to judge the
accuracy of the color displayed. Often though the type of film, if color film,and the exposure times are given as well as the
technique used to generate the image. Malingives great detail about these matters in his book. But even then the variety of
photographictechniques used is largely directed to make nice looking images. That is, nice detail, nicecolor and the like.
Photometric color accuracy is not usually the goal.
An example of deviation from the normal (traditional) filter set is suggested by Wallis andProvin, whose color images are quite
wonderful. They suggest using the Wratten filter set forphotography of 23A, 57A and 47. This set has a slightly lighter red filter
and a slightlylighter green filter. Their filter suggestions gives a smoother coverage of the spectrum whenused with monochrome
film and fills in the spectral gaps where there is appreciable astronomicalinformation. They also recommend an exposure ratio of
1:1.5:2. This seems to me to be a wisechoice of filters and exposures.
We must realize that the spectral response of the CCD chip is very different from that ofphotographic film. CCD chips of the types
used in popular amateur imagers are highly sensitiveto red and infra red and very insensitive to blue light. This means that
images taken with thetraditional filter sets used for photography will require very long exposures for the blue filtercompared to
the red filter in order to obtain good color balance. Additionally, the infra redportion of the spectrum must be suppressed or it will
alter the color balance of the compositeimage. Note that newer blue sensitive chips are being worked on but are currently
expensive andnot generally available in amateur imagers.
Exposure ratios for the RGB of 1:2:4 or even 1:3:6 are not uncommon. It is generally required for accurate color rendition to use
an infra-red reject filter since leakage of infra-red through the color filters will spoil the color balance of the image. Infra-red
rejection filters are of two types. The "hot mirror" or multi-layer type has very sharp rejection characteristics and is generally
considered the best. Another type is simply heat absorbing glass which works fairly well but has a very slow cut-off and not
complete absorption of the infra-red wavelengths.
There is still considerable difference among professionals about the exact filter sets to use. Clearly it depends on the exact
spectral sensitivity of the CCD chip and the spectral accuracy required by the particular application. All manufacturers on filters
sets have shown images which are very beautiful. The color balance is controlled by exposure times and the color balancing
attained in the reproduction of the images as much as in the original choice of filter set.
This bring me to a few final comments. I have a set of filters from Optec, a company well known for its excellence in photometry,
which has a light red filter, a normal green filter and a very dark blue filter when compared visually to the normal tricolor or
separation filter sets. It appears that this filter set requires a very long blue exposure both because of the density of the blue
filter and the lack of sensitivity of the typical CCD cell. I have seen a filter set consisting of 25, 58 and 38A recommended. This
seems to me to be a very good filter set for CCD imaging since it has a slightly lighter blue filter than the 47 recommended for
photographic film. Because the CCD chip is so insensitive to blue, the exposure for the blue image should not have to be
unreasonably out of proportion to the red and green exposures.
On the other hand Mr. Hoot has recommended a filter set consisting of a 23A, 56 and 80A. The 23A is a light red filter, the 56 is a
light green filter and the 80A is a very light blue filter. In fact the 80A is not really a band pass filter at all but a color correction
filter used to change 3200 K tungsten light to daylight balance of 5500 K. It passes 80% blue and 20% red and is used to correct
daylight color film for use with 3200 K (tungsten) illumination.
This does not mean that this filter set is necessarily bad. This set has an exposure ratio of 1:1:1. Such a ratio is useful since it is
conserves some time to take a blue exposure which is shorter than that usually recommended for blue filters. The total time
required for the blue image so often nearly half of the total time. It was also stated that this filter set gives nice looking images
rather than color accurate images. Since the red and green filters are also lighter than usually recommended light, The whole set
gives overall shorter exposure times. Since the blue filter is very light it gives an image which is heavy in blue but with
considerable green and red. The very lightness of the blue filter makes up for the lack of sensitivity of the CCD chip in the blue
region of the spectrum. If this set of filters gives nice looking color images, that is fine. But, we should have no illusions that it is
accurate color. For astronomical color imaging a great latitude is allowable since no side by side comparison can be made as it
can with photographic imaging of earthly objects. We are happy to see images that are not just gray. A photometrically accurate
and set of color filters combined with the lack of blue sensitivity of the CCD chip requires an almost excessively long blue
exposure. We may have to wait for the general availability of blue sensitive CCD chips to solve this problem.
Then again what is accurate color? Is it the image in one book or another, the color slides I saw a year ago, the color I see on the
computer screen, the color I saw at the Winter Star Party or some other color balance? It's hard to tell. One might now say, what
about the color that color film shows? Is that accurate? Not so simple to say. Color balance is a strong function of exposure time
and reciprocity failure often dominates. Color film can give quite unbalanced color images as well. Professional films are made for
short exposures of under 1/10 second and for exposures of several seconds to insure controlled color balance.
It is probably best to judge a color image on the basis of its detail its range of colors and its general beauty. These are subjective
judgments indeed. Filter thickness is an important issue when taking three color images. The filters must be exactly the same
thickness or there will be an image focus shift at the imager. Filters vary in thickness considerably. I have always made a practice
of keeping a record of filter thickness for my photographic work.
For a reference, here are some values for a few 2" filters I use.
●
●
●
●
●
●
Lumicon Deep Sky Filter 2.55 mm
Lumicon UHC Filter 3.30 mm
Lumicon H alpha pass 2.18 mm
Lumicon Minus Violet 1.90 mm
Clear Filter 2.60
Clear filter 3.30
I keep these to match the Lumicon filters above when used in the Optec 2" filter slider.
●
●
●
Optec Hot Mirror (minus IR) 4.25 mm
This filter is used with all color filters to get rid of IR
Optec separation filters Red, Green and Blue 2.00 mm
This set of color filters are each exactly the same thickness which is essential for color imaging.
●
Hoya ND Filter 2.5 mm
●
●
●
Hoya Orange Filter 1.94 mm
Hoya Red Filter 1.98 mm
Hoya Blue Filter 2.18 mm
I hope that this information will be of some value to those considering color imaging.
Subject: Tricolor Filters for CCD--Part 1 of 3
From: Michael Hart
John Hopper wrote:
>
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I have added to my web site a long description, with pictures, of the
Optec filter slider. It is under Attachments/Filters/Optec. I have also
added some photos to the article on focal reducers that show the
Lumicon, Meade and Optec reducers in some detail.
Finally, I have just read a fine book, called Pluto and Charon. It is
reviewed briefly in my bibliography section under Bibliography/History
Doc G
> Doc, Thanks for posting this practical guide to filters and tricolor! I was
looking for information just like this. I have a question and comments:
Has anyone else on the list used different filter combinations with good results?
I believe over time, I have posted considerable information about this based on manufacturer's data, transmission curves and
actual use. Some of that information is on Doc G's web site under Tricolor Imaging. I have probably tried every conceivable
combination you can imagine to test the viability of various combinations that remap wavelengths to compensate for non-linear
CCD chip response. I have also tried various dicroic filter sets made for CCD imagers as well. Some use creative ways to improve
response at problematic wavelengths. I believe nothing in the following comments contradict Doc G's filter information. I have
tried subtractive dicroic sets (CMY) which are quite useful for camcorders at high light levels with custom automatic color
compensation circuitry built in, but somewhat marginal with software based traditional CMY color models. The reason is likely the
nature of the subtractive color filter to pass all light minus one of the additive colors. Thus, C (cyan) is green and blue minus red,
M (magenta) is red and blue minus green, and Y (yellow) is red and green minus blue. As expected, a filter combining two colors
would have excellent throughput- arguably excellent for the ST-7/8 with built in autoguider chip. Unfortunately the nonlinear
response of the popular Kodak chips in these cameras considerably complicates the process of reproducing the original image.
Thus far, I have not seen a software based modified CMY color model that addresses the fundamental problems of accurately
restoring the original wavelengths that accounts for the frequency response differences among CCD chips operating at low light
levels. I have used photometric filters (BVR) as well. After careful study of transmission curves, I believe there are no significant
shortcuts to good tricolor results in substituting wavelengths for those more readily available and/or more efficiently recorded for
the desirable true visible wavelengths. The bottom line-- after a considerable amount of tricolor imaging over the last several
years, I have found no filter set I prefer better than using straight RGB filters because the results are predictable and precisely
match RGB color models.
This is not to say RGB color filters do not require balancing, but I believe remapping or shifting visible wavelengths is best left for
scientific endeavors such as displaying far infra-red, visible and ultraviolet wavelengths simultaneously. One can deviate a bit
from true RGB filters, but the closer, the better. > Are the "filter thickness" values you give the actual thickness of the glass?
Knowing the thickness of the filter is important to maintaining focus between filters. Mixing a 2 and 3 mm filter means the
telescope must be refocused between shots, though, using micrometer/DRO readouts will minimize this inconvenience.
>
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I think your discussion of the 80A as giving good aesthetic results with short
exposure times was extremely interesting. I'd done a little thinking about
this myself, and came to the conclusion that a good "tricolor" setup, now that
most astrophotographers have Photoshop or other good software for combining
the multiple images any way they'd like, would be to use something like
80A/(either "no exposure", "no filter" or some type of light or medium
green)/85B and then experiment as to exposure ratios and how to combine the
two or three images using various fudge factors summing them. The exposure
ratios should be closer to 1:1:1 (or maybe 1:0:1) than with cutoff filters.
I do not generally prefer the results of using a pale blue (80 A) filter, though John Hoot has suggested it's possible use. The
leakage from other wavelengths gives somewhat unpredictable, though "colorful" results. Attaching a camera lens adapter to a
CCD camera and shooting terrestrial scenes may be a good way to illustrate why. I do not generally recommend such techniques
as you describe above for a number of reasons as related to color balance, S/N ratios, kernel filters and more. For example, nonlinear CCD chip response in the visible wavelengths often requires long blue exposures to produce an adequate S/N ratio. Using
an 80A passes so much non-blue light that the results are unpredictable. Of course all that non-blue leakage is misrepresented as
blue in the RGB color model. We can approach a 1-1-1 ratio for the popular 0400 chip using 770 nm, 650 nm and 550 nm that
may produce visibly balanced star colors.
When mapped to a RGB color model, the result is wonderfully blue images, because all that is really green is remapped to blue.
Imagine the above terrestrial experiment and the resulting blue grass. We can also synthesize a third color from two others with
mixed results. It is difficult to use programs such as Photoshop to compensate for the lack of adequate color information with
predictable results. If we don't care about color accuracy, we can use an image processing program to do just about anything
with mixed results. However, armed with accurate color information, predictable results are not difficult and arguably worth the
effort needed for longer exposures. In the case of RGB, we want signals as close as possible to accurately representative RGB
wavelengths.
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The 80 series moves the color temp upward with shallow bandpass
characteristics, the 85 series moves it downward an equivalent amount with
shallow bandpass, "no filter" leaves it alone, and hopefully there's a green
which when added in some proportion will smooth out the frequency response of
the sum. To move the color temp, these filters have nice, bell-shaped
response curves centered on different wavelengths, somewhat like bandpass
filters but not nearly so steep at the sides and a bit less flat on top.
While it's not as rigorous-sounding an approach as using steep, perfectly
matched bandpass filters to do a true separation, it throws away fewer
photons, and would very likely give more accurate color rendition to the eye
if my photographic instincts are correct. The reason for this is that a
response curve shaped like a bell or sine wave is more forgiving than square
waves which don't have their cuts at the exact same frequency or aren't
perfectly square (none do and none are!!) It's much like the speaker cross-over design problem before and after arbitrarily steep electronic crossovers
became available.
Reproducing true color from individual additive colors is best done using sinusoidal bandpass with overlapping curves. The
weighted center of the curve should be quite close to the actual wavelength represented. Dicroic filters are quite efficient but
have transmission curves with rather steep cutoffs and flat tops. Camcorders use dedicated circuitry not found in CCD cameras to
compensate. However, camcorders typically see adequate S/N ratios, low dynamic ranges and low resolution. Your audio analogy
is good, though the dicroic filter can in fact have a greater photon throughput at a particular wavelength than absorption type
filters. Overlapping transmission curves are important because the overlap (mixing of colors) is what produces even color
representation in the RGB color model.
We cannot forget that most CCD cameras are sensitive to the infrared leakage of most color filters. An infrared (hot mirror) filter
should be used to stop undesirable infrared leakage.
>
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At least with electronics, you can twiddle with the
parameters more easily than you can by looking for exactly the right color
glass. Murphy's law tells us that the downward spikes due to mismatch on
steep bandpass filters will fall at some important emission line of our
subject, and the upward spikes at the emission line of our town's streetlights
If we remove any narrow wavelength in the visible spectrum, it effects the image.
That effect may be undesirable enhanced with image processing techniques such as background and range adjustments (levels),
saturation enhancement, etc., limiting the ultimate potential of our results.
>
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>
The frequency response curve of this approach might not be as flat at most
frequencies as using bandpass filters, but its lack of horrible atrocities at
crossover frequencies is a major advantage. It also makes the ratios of the
three exposure times less critical to maintaining a good overall response curve.
I presume you are stating an advantage of traditional colored filters whose transmission curves produce smooth tops, gradual
slopes and good crossovers as compared to dicroic filters which function much as an interference filter, reflecting undesirable
wavelengths and passing the desirable ones. Fundamentally, I believe traditional colored filters have an edge at producing good
results without the aid of dedicated circuitry, though in practice, a CCD image without adequate S/N ratio in one color arguably
produces poorer overall results. The exposure ratios used are not really that critical by themselves. We are looking for good initial
S/N ratio, then initial color balance which may be adjusted as needed.
------------------------------------------------------Subject: Tricolor Filters for CCD--Part 2 of 3
From: Michael Hart
Jon A. wrote:
>
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>
I have tried subtractive dicroic sets (CMY) which are quite useful
with built in autoguider chip. Unfortunately the nonlinear response
of the popular Kodak chips in these cameras considerably complicates the
process of reproducing the original image.
Thus far, I have not seen a software based modified CMY color model
that addresses the fundamental problems of accurately restoring the
Michael and John,>
Great stuff. Have you monitored Al Kelly's work on the CCD list with CMY?
How would you judge this effort?
I have not monitored Al Kelly's work directly, though I have had inquiries such as yours. I have examined images sent me using
current CMY color models and have tested CMY filters independently. CMY filters are not new which begs the question- why
haven't they been used before? The answer is, they have. Emulsion base print films use the CMY process. Camcorders use CMY
(often with a variation of the yellow filter) and of course printers use CMYK (K is for black). Mixing all colors using print inks does
not produce a very dark black, so printers use a black ink. Using CMY, the combing of wavelengths makes accurate color
reproduction of the original scene quite difficult in low light with a non linear CCD chip, though achieving color balance is not very
difficult. While CMY filters DO pass more photons, all the light in the blue wavelengths are in the cyan and magenta filters. If we
balance CMY colors against a gray card at the effective temperature of the sun (5770 degrees K., spectral type G2), the cyan and
magenta filters pass all the blue wavelength to accurately represent the desired blue emission present in the original scene.
However, the CCD detector often needs a disproportionate amount of blue to compensate for it's poor response in the shorter
wavelengths. This is where CMY color models fall short, because the total exposure time of actual blue wavelengths contained in
the COMBINED exposures of cyan and magenta to achieve a color balanced exposure is less than that used to produce a single
color balanced blue exposure in the RGB color model. The result is the remapping of other wavelengths to blue which do not
accurately represent the original scene. I believe the possible solution for CMY color accuracy is to have a CMY color model
written for specific CCD chips. Even CCD chips that have a better linear response such as the TC series are not likely to produce
more accurate color than straight RGB filters whose transmission curves produce smooth tops, gradual slopes and good
crossovers. Using a light blue 80A filter for the blue channel is also is very efficient because it passes non-blue wavelengths that
the CCD chip can readily record- all the blue light and a lot of red and green light. I have described a process of using IR, Red
and Cyan filters with a resulting throughput exceeding CMY, however, this also does not produce accurate visible color, though
the colors (channels) are well balanced.
>
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>
I'll be attempting color work for the
first time this summer and have heard the siren call of more photons,
but my current plan is use my 616 and its stock filters. Al and others
have also been promoting an NRGB method. I think I follow it as generally
a long mono exposure which gets colored by shorter ones. Are you
thumbs ups or down?
Many times, simplest is best, like plain old RGB? LRGB and various synonyms to this acronym are not particularly new, though
the process may be new to some in CCD imaging. Jerry Lodriguss proposed using the Photoshop CMYK color model 2-3 years ago
for tricolor film imaging. There has been a lot of new terms tossed about recently such as WRGB (White RGB) MRGB
(Monochrome RGB), LRGB (Luminance RGB) quadcolor (doesn't really use 4 colors) and more. I have no idea what "NRGB"
stands for. All (and likely NRGB) are essentially based on a 50 year old television process which recognizes the eye's inability to
discern detail in color. As details becomes very small, all the eye can discern are changes in brightness. Beyond a certain level of
detail, color cannot be distinguished, and the human eye, in effect, becomes color blind.
The color television signal is composed of the luminance (higher resolution black and white) and chrominance (low resolution
color). Doc G and myself describe details of this process on Doc G's Info Page under Tricolor Imaging. Essentially, substituting a
higher resolution luminance image for the one contained in a lower resolution color image produces what appears as a higher
resolution color image. As a result, the color accuracy is maintained while displaying details of the luminance signal. If we
increase the luminance signal enough, we can mask over irregularities in color balance, color filter choices, and the color model
used.
In conclusion, I believe the RGB color model along with color filters that reject (either through absorption or reflection)
undesirable frequencies produce the best, most predictable, and most accurate CCD color results readily adjusted to a variety of
CCD chips with non-linear color response. The use of the color television process designed to conserve bandwidth, regardless of
what it is called, can play a useful role in RGB tricolor imaging with minimal effect on color accuracy. I believe we should strive
for color accuracy if we are representing images as true color, then if a colorful result is desired, the use of filters that leak other
wavelengths into the represented color channel may be considered as can a tint to a converted monochrome image.
However, we must keep in mind the results misrepresent the original emissions and may mask important details.
---------------------------------------------
Subject: Color Filters for CCD Imaging--Part 3 of 3
From: Ric Ecker <rlecker
juno.com>
This is some information that I got from John Hoot for filters used for CCD imaging. He suggests a basic set called the Easiest Set
and the Fidelity Set. The easiest set to image with is: #23A red; #56 green and the #80 blue. This set is used by John on the
Pictor 216 XT because of its exposure times. This set gives reasonable images at almost a 1:1:1 exposure times.
The Fidelity Set consist of: #23A red; #58 green; #38 blue. This set give the best results but takes considerable exposure time
with the green and blue filters. This filter set will give reasonable color balance and good signal to noise (S/N) ratios.
The best way to achieve color balance is to defocus a 2nd or 3rd magnitude G2 star and make a 1 minute exposures through
each filter and record the brightness reading. Than take the inverse of the average brightness to figure out the proper exposure
ratio for each image. You want to use the proper exposure times so that faint background objects are recorded in all three colors.
Just changing the gain and contrast on equally exposed image will not record faint objects in the weak exposures. If you don't,
faint objects will all shift towards the red.
Deep sky objects can be taken without a filter wheel although they are a nice piece of equipment to have. Using a device like the
Optec Maxfield reducer which can use 48mm filters and has a registered fit helps in taking color imaging. Making sure all filters
are the same thickness helps in keeping each color in focus. Making sure each filter fit the holder and hold the filter in the same
fashion as the other filters also helps with each image having the same focus.
Ric has investigated John Hoot's work and posted the results here. I am pleased that John uses the terms "Easiest Set" and
"Fidelity Set" to distinguish color filter sets that remap colors from those that only allow colors representative of the actual
wavelengths. Since color balance
is related to color temperature, I would suggest the use of a spectral class G2 star as the calibration source as well. I use the
light of the full moon well above the horizon and image a neutral gray test card (from a camera store) noting the light intensities
recorded to determine exposure ratios. -- Michael Hart
Subject: Filter Wheel Recommendation --part 1 of 3
From: Gregg Ruppel <ruppelgl
slu.edu> Date: Jan 2003
From: Michael Blaber
> I am considering the purchase of a filter wheel and am trying to decide between:
> 1. Optec Intelligent Filter Wheel
> 2. Adirondack Custom Filter Wheel
> 3. SBIG CFW-8 Filter Wheel
> If anyone has any experience with these,
> and can provide any helpful comments, I would appreciate it.
Mike: I have the True Technology Custom Filter wheel which I believe is what you referred to as the 'Adirondack' wheel (sold by
Adirondack Video Astronomy in the US). I have been using the True Tech wheel for about 9 months and it has worked very well.
It can be operated manually with the included handbox and is also supported by several different software packages. It has 2"
attachment ports and can use wheels with different size filters (1.25 or 2") so you can adapt to various different cameras. True
Technology also has a variety of adapters so that you can hang it onto almost anything. The wheel does hang up on rare
occasions, but there is a reset button on the hand control that quickly fixes the problem; this can also be done by re-initializing
the device remotely. I use the TT wheel with my MX916 camera on an LX200. You can see a picture of the device on my web site
at:
<http://www.biz1.net/~ruppelgl/tech.htm>
-------------------------------------------------------------Subject: Filter Wheel Recommendation --part 2 of 3
From: Doc G
I have used the Optec products for some years now. They are excellent and operate exactly as advertised. That includes the TCFS, the IFW and the older filter slider.
-----------------------------------------------------------Subject: Filter Wheel Recommendation --part 3 of 3
From: Gene Horr <genehorr
texas.net>
If you have an SBIG camera then you don't need to add an extra data line with the CFW-8. Disadvantage is that you get
occasional filter errors at certain orientations (generally not an issue with SCTs). But it is allegedly fixed by a 3rd party cover
plate.
MAPUG is hosted by
Check List for the LX200 Classic
Not for GPS models with AutoStar
Created By: Rich Eppler
<REppler102
aol.com>
Doc Downloads
----------------------------Page 1----------------------------A. ALTAZ SETUP
1. Place telescope with power panel on the NORTH side of tripod, you are facing south when looking at it.
Exact alignment is not critical.
2. Level telescope using built-in bubble level. See MAPUG-Astronomy Topical Archive-->Leveling for other
more accurate methods; however, leveling is not critical.
B.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
ALIGNMENT IN ALTAZ CONFIGURATION
Confirm N / S switch in correct position for location.
Telescope power switch -- ON.
Confirm location data -- SITE (refer to page 4).
Confirm Time data (refer to page 4).
Loosen DEC lock knob.
Position OTA until DEC circle reads "0."
Tighten DEC lock knob.
Loosen R.A. lock knob.
Point OTA due south (at best estimate).
Tighten R.A. lock knob.
Press STAR, ENTER, ENTER. This puts you in the mode to select a star by name.
Use NEXT/PREV to select the first alignment star (See Alignment Star Library below).
Press ENTER, GOTO. This will point the telescope in the general neighborhood of the first alignment star.
Press MODE. Display reads TELESCOPE and OBJECT LIBRARY.
Press ENTER key with arrow next to TELESCOPE.
Display reads SITE and ALIGN
Use NEXT key to position arrow next to ALIGN.
Press ENTER key.
Press ENTER key with arrow next to ALTAZ.
Select 2 star alignment mode -- Press NUMBER key 2.
Press ENTER if base is level.
Press ENTER to select align star (See Alignment Star Library below).
Select the first alignment star again using NEXT/PREV, then press ENTER.
Center star in high power eyepiece (reticle eyepiece is more accurate) using the "E, W, N, S" keys and
SLEW, FIND, center -- Press ENTER
25. Repeat steps 19 -- 21 except that after second star is selected, select GOTO & the OTA will move close to
the second alignment star automatically.
Note: see owner's manual for alternate AltAz set-up procedures.
----------------------------Page 2----------------------------C. POLAR ALIGNMENT
1. Level the telescope using bubble level on base/wedge. See MAPUG-Astronomy Topical Archive-Leveling for
other more accurate methods; however, leveling is not critical--this adjustment will be altered in
perforning Step 21.
2. Set compass to magnetic declination -- (your magnetic declination).
3. Loosen compass/knob -- slightly
4. Rotate compass/knob until magnetic arrow lines up over declination setting arrow.
5. Rotate wedge in azimuth until centerline of wedge lines up with "N" on compass.
6. Tighten compass/knob.
7. Set the wedge loosely to your latitude--this adjustment will be altered in Step 21.
8. Loosen RA lock knob.
9. Point OTA due south (at best estimate).
10. Tighten RA lock knob.
11. Loosen DEC lock knob.
12. Rotate OTA until DEC setting circle reads 90.
13. Tighten DEC lock knob.
14. Confirm N / S switch is in correct position.
15. Telescope power switch -- ON.
16. Confirm location data -- SITE (refer to page 4).
17. Confirm Time data (refer to page 4).
18. Select ALIGN in menu.
19. Select POLAR.
20. Press ENTER key and telescope should slew to precise offset position of pole star in DEC and RA.
21. Adjust altitude and azimuth of wedge until pole star is centered in field of view.
22. Press ENTER.
23. Telescope should slew to bright star overhead visible in viewfinder.
24. Center star using DEC and RA controls on keypad.
25. Press ENTER.
26. Telescope should be polar aligned with all GoTo functions available.
----------------------------Page 3----------------------------LX200 ALIGNMENT STAR LIBRARY
STAR
Constellation
Star #
MAG.
R/A
DEC.
ACHERNAR
ERIDANUS
13
0.5
01 37.7
-57 14
ACRUX A
CRUX
121
1.3
12 26.6
-63 06
ALBIREO
CYGNUS
223
3.1
19 30.8
+27 58
ALKAID
URSA MAJOR
140
1.9
13 47.6
+49 19
ALDEBARAN
TAURUS
33
0.9
04 35.9
+16 31
ALNILAM
ORION
50
1.7
05 36.2
-01 12
ALPHARD
HYDRA
95
2
09 27.6
-08 39
ALPHEKKA
CORONABOR.
165
2.2
15 35.5
+26 43
ALTAIR
AQUILA
226
0.8
19 50.8
+08 52
ANTARES
SCORPIUS
177
0.9
16 29.5
-26 26
ARCTURUS
BOOTES
147
0
14 15.7
+19 11
BETELGUESE
ORION
56
0.4
05 55.2
+07 25
BOGARDUS
AURIGA
58
2.6
05 59.8
+37 13
CANOPUS
CARINA
63
-0.7
06 24.0
-52 42
CAPELLA
AURIGA
42
0.1
05 16.6
+46 00
CASTOR A
GEMINI
78
1.9
07 34.6
+31 53
DENEB
CYGNUS
232
1.3
20 41.5
+45 17
DENEBOLA
LEO
114
2.1
11 49.1
+14 34
DIPHDA
CETUS
8
2
00 43.6
-17 59
ENIF
PEGASUS
238
2.4
21 44.2
+09 53
FOMALHAUT
PISCES AUST.
247
1.2
22 55.7
-29 38
HADAR
CENTAURUS
144
0.6
14 03.9
-60 24
HAMAL
ARIES
17
2
02 07.2
+23 28
MARKAB
PEGASUS
249
2.5
23 04.8
+15 12
MIRA
CETUS
20
2.1
02 19.4
-02 58
POLARIS
URSA MINOR
19
2
02 14.7
+89 17
POLLUX
GEMINI
81
1.1
07 45.4
+28 02
PROCYON
CANIS MINOR
80
0.4
07 39.3
+05 14
REGULUS
LEO
100
1.4
10 08.5
+11 58
RIGEL
ORION
41
0.1
05 14.6
-08 12
SIRIUS
CANIS MAJOR
67
-1.5
06 45.2
-16 43
SPICA
VIRGO
138
1
13 25.2
-11 10
VEGA
LYRA
214
0
18 37.0
+38 47
Note: See page 63 in LX200 Classic instruction manual for more detail.
----------------------------Page 4----------------------------LOCATION DATA ACCESS
1.
2.
3.
4.
5.
6.
7.
Select TELESCOPE -- press ENTER key
Select SITE -- press ENTER key
Press and hold enter key until key pad beeps and display shows "AAA" with first "A" flashing.
Press ENTER -- Displays LAT/LONG information.
Press NUMBER keys to enter LAT/LONG (use "E/W" keys for corrections).
Press ENTER to complete process.
Press MODE key twice to exit.
TIME/DATE DATA ACCESS
TIME:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Press MODE key until LOCAL and SIDE times are displayed.
Select LOCAL time by pressing ENTER key until keypad beeps.
Enter LOCAL time (USNO time) using NUMBER keys.
Press - ENTER after time confirmed.
GMT time zone shift will be displayed.
Enter GMT time zone shift using NUMBER keys.
To enter a negative sign position cursor under symbol using "E/W" keys.
Press NEXT key to enter symbol.
Press ENTER key and date information is displayed.
U.S.A. TIME ZONE CONVERSIONS
DATE:
PACIFIC
MOUNTAIN
CENTRAL
EASTERN
STANDARD
+8 hrs.
+7 hrs.
+6 hrs.
+5 hrs.
DAYLIGHT
+7 hrs.
+6 hrs.
+5 hrs.
+4 hrs.
1.
2.
3.
4.
Press and hold ENTER key until keypad beeps.
Enter date MM/DD/YY using NUMBER keys.
Press - ENTER to lock in date.
Display should then show "Updating Planetary Data."
Downloads of text file versions:
PC Word 6 Doc file PC Word 6 Doc (Zipped) MS-RTF text
Mac Word 6.0 .hqx
Acrobat.pdf
MAPUG is hosted by
AltAz Aligning Concerns --Page 1
Polar & AltAz Aligning Concerns, Page 1
Also see the Checklist for quick set-up and alignment
LX200 Classic Longitude Calculator
Procedures for Obtaining Best Alignment
Initial Alignment Procedures
Backlash-Aware 2-Star Alignment
Selecting Slew Speeds for Alignment
Choosing Alignment Stars for 2-Star Alignment in Alt/Az
AltAz Re-Alignment by Sync Operation
Keypad Enter Key Problem During Alignment Routine Solution
How close is "close enough" OTA alignment?
Leveling & Entering Lat/Long under v3.34 Pointless?
Solar Tracking URL
Lunar Tracking Software URL
LX200 Daytime Observing/Alignment --separate page
GoTo: Polar Aligning
Subject: LX200 Classic Longitude Calculator
From: Clark Williams <S.I.G.H
ix.netcom.com>
Someone had a question about the Classic longitude values a few days back. Several years ago I wrote a WinTel based
LX200LatLon calculator (enter your latitude and longitude and it displays what you should enter for the LX200 Classic). It is
available at: <http://www.s-i-g-h.com/lx200lon.zip>
Known Issues:
None that I know of. I put together a Java applet to do the same at: <http://www.niteis.com/NILX200LatLon.html>
Known issues:
I put this into an applet from an application. The application used a call to the system exit() function to terminate. This will of
course throw a java exception in the applet world. So when you click on the Quit button you'll see an exception on your java
console. Just close the browser window and the world will exit gracefully.
I'm sure you can 'fool' the thing, especially at the 180/360 degree boundaries. So if you are on GMT you enter 000 00 00 Lastly--if you can't figure out how to use it---don't. As always with RAD code, no flames, no law suits USE AT YOUR OWN RISK!!!
Subject: Procedures for Obtaining Best Alignment--Classic
From: James Burrows <burrjaw
earthlink.net> Date: June, 2000
Don Tabbutt wrote:
>Didn't we conclude years ago (a lot of it through your work) that the net
>effect of tilt (lack of level) was that errors could be introduced in the
>refraction correction algorithms for objects near the horizon, and that the
>actual horizon itself could be offset?
Meade's AltAz alignment, as I mentioned, has second order errors in the modelling of tilt, trying to correct tilt about the level NS
axis by altering sidereal time. I'm not quite sure what the result of that error would be; probably not much effect on the
refraction correction, and the tilt would have to be pretty ferocious to get a star out of the field of view.
Review of ancient (3 years ago!) notes on AltAz alignment (polar mode guys can delete the rest of this message):
1) Get the best out of Meade's algorithm, beyond leveling and a reticle EP. I get about 3' whole-sky (scope dependent).
a) Run my program BestPair II:
<http://home.earthlink.net/~burrjaw/lx200/odyframe.htm> to choose the best pair of alignment stars visible from
your location. Rules of thumb don't seem to work too well. Also see Software & Computer Issues topic for more on
BestPair II.
b) Be backlash-aware centering the stars. This means the last motions centering a star must use the same drives as
used during tracking. To see which way that is, point near the star, push W in GUIDE mode - that's the tracking
direction.
2) Ralph Pass and I developed a Kalman filter n-star alignment - choose more than 2 stars around the sky. I found that it doesn't
help much, maybe down to 2' whole-sky for my scope (still scope dependent).
3) The most important errors not covered in the above algorithms are gear errors: runout and scale factor. I wrote a program to
estimate those errors and alter the RA/DEC pointing commands. I understand the POINT program has this capability. The trouble
is that this desynchronizes the laptop and keypad, so you can't use Meade's object databases, but I did get down to the 1' wholesky goal.
Subject: LX200 Initial Alignment --part 1 of 2
From: Ralph Pass <rppass
rppass.com> Date: Jan., 2001
juno.com wrote:
astroviking
> If your using zero Dec and zero hour angle are you referring to the
> computer readout on the hand controller? Or the mechanical scale on the
> scope, i.e. RA ring and Dec scale? If your referring to the mechanical
> scale for Dec the LX200 tells you to move it to 90 deg. after bootup
> and doesn't make much difference if you move it to 90 deg. before boot or
> after boot. Give it a try and you will see that it makes no difference
> which method you choose. Setting the RA hour wheel makes no difference
> where it is set because it not connected to anything that can change,
> just about totally useless on the LX200. Maybe I'm missing something in
> your reason for setting to 0 Dec and 0 HA.
I use the mechanical scale. After aligning once I slew the telescope to 0 deg. and 0 azimuth (yes that is azimuth since that will
give me 0 hour angle). I then note the offset on the mechanical scales. I set the scope to this when I start and given accurate
time and location, the scope is darn close to aligned, see below for the caveat.
If you loosen the Dec axis and manual move the scope to 90, then it makes no difference where the Dec axis started. However,
setting a 0 hour angle and slewing to Polaris (select star 19 and press GoTo). will get you closer on your initial align (you can also
GoTo a star, sync on it and then slew to 19).
Now for the caveats:
1. Before I got my permanent pier I would take my scope to one of several locations I used. I had marked each after a trip
there so I could put the scope back in the same location. If I went to the same location for consecutive evenings, I could
use the method described above to be able to start the scope during daylight and have Venus comfortably in the field of
view of the finder, and many times in the field of view of the 26 mm eyepiece. Final alignment was always quick. NOTE
THAT I WAS USING A MEADE SUPERWEDGE and had little problem with it once I learned not to overshoot on corrections
(backlash it its major problem in my opinion).
2. Once I got my permanent pier, I found that the SuperWedge was stable enough that using the method above would put a
star in the field of view of my 416 on my 10" F/6.3. I stopped trying to tweak the alignment more than a year ago. Now I
simply tell the software to center the star and sync on it and I am set for the evening.
-------------------------------------Subject: LX200 Initial Alignment --part 2 of 2
From: Bob Denny <rdenny
dc3.com> Date: Jan., 2001
Due to ACP's (Astronomer's Control Panel software) being attributed as starting alignment at 90 deg. DEC. I feel the need to
comment. The correct starting point is 0 deg. Dec and 0 hour angle. If you start the LX200 (in polar alignment mode) in this
position, it knows where it is pointing immediately. If you park it in this position, you can turn it on and it will be ready to use
without even syncing. There is no other start position for which this is true. This proves that the firmware designers meant it to
be started in this position.
Note that the firmware designers went further... if you put the scope into LAND mode and slew to the Alt/Az location
corresponding to 0 Dec and 0 hour angle then shut off the scope... then later you turn on the scope (still in LAND mode) allowing
it to slew off from the perfect parking location as it does when it starts, then put it back into Polar mode... it will be lined up
perfectly! Even if you wait for an hour before switching to polar mode!!! The firmware designers had it together when they did the
LX firmware.
ACP slews the LX200 to 90 Dec as part of the Alignmemt Wizard process. It's part of the process of removing Dec calibration
errors. For the Alignment Wizard to work, you must start the scope at 0 Dec and 0 HA.
By the way, ACP is controlling the scope that has discovered 5 supernovae in the last 3 months, the 24" Ritchie at Puckett
Observatory. In addition, ACP was just brought online at the Tenagra Observatory, on the Tenagra 3 20" scope, again for
Supernova searching. There are not LX200's (!!) -- ACP is being used with ASCOM telescope drivers, and is serving as a scripting
object host and script controller.
Subject: LX200: Backlash-Aware 2-Star Alignment
From: James W. Burrows <burrjaw
earthlink.net>
Altaz users: There has been a lot of discussion lately about DEC backlash, which I have been ignoring as a polar problem, but it's
at our (altaz users) peril. The first step was to measure the RA and DEC backlash on my 8" (during the day in LAND mode - no
use wasting good night time on such as this). Results: RA, .21 mrad (44"); DEC, .32 mrad (67"); width of reticle guidance
box, .16 mrad (34"). I have devised a "backlash-aware" 2-star altaz alignment which prevents backlash from messing up the
alignment. I assume a reticle EP.
1. Center the alignment star in the Telrad (or finder).
2. In the EP & center speed, get the star approximately on a line from the EP center toward the NCP. Using the star diagonal,
this would be in the upper right quadrant of the FOV for stars E of the meridian, upper left for stars W of the meridian
(hope I've got that right).
3. lip the W button (still on center speed).
4. Switch to GUIDE speed, and without touching the S button (i.e., hold down N button and use E or W buttons as
necessary), run the star toward the guidance box.
5. Release buttons right when the star first enters the guidance box and hit ENTER (no hurry) to say the star is centered.
If the star can't be gotten into the guidance box in step 4, go back to center speed and step 2. The critical part of the procedure
is step 5; stars W of the meridian will drift out of the box after the button(s) are released, drift which would be cured by hitting
the S button - DON'T DO IT! - this is where backlash would introduce alignment error.
The interesting part of this alignment mod is that it is faster - you don't waste time chasing stars W of the meridian. As I said,
backlash isn't fixed, a slew to an object should do an intermediate GOTO a position N of the object, then GOTO the object;
objects W of the meridian will drift to the "other side" of the DEC backlash.
Results (errors evaluated by centering as above, not including backlash):
A1: Meade(Altair, Alkaid); errors.
AZM ALT: ERR, mrad
E: 79 62: 0.75 @ Deneb
E: 189 55: 0.82 @ Rasalhague
E: 297 49: 0.27 @ Alkaid
A2: SYNC; errors.
AZM ALT: ERR, mrad
Y: 192 54: 0.85 before SYNC @ Rasalhague
E: 297 48: 0.90 @ Alkaid
E: 194 54: 0.11 @ Rasalhague
E: 81 64: 0.81 @ Deneb
SAO 44752 13:47:32 49d18'48" 1.86: 85 eta UMa, Alkaid
SAO 49941 20:41:26 45d16'49" 1.25: 50 alf Cyg, Deneb,
SAO 102932 17:34:56 12d33'36" 2.08: 55 alf Oph, Rasalhague
This particular trial shows approximately 2' whole-sky pointing accuracy, which could probably be improved by a better choice of
alignment stars; Alkaid and Altair are 84d apart, best I could do from my site last night. Note that, as usual, SYNC improves
accuracy near the SYNC star at the cost of reduced whole-sky accuracy.
Subject: Selecting Slew Speeds for Alignment
From: James Burrows <burrjaw
earthlink.net> Date: Aug 2001
FLag wrote:
>I had no idea that the 7,4,1 and 0 key
>effected more than the rate of speed that you slew
>(sensitivity). I usually set the 4 key for hand slewing and then sometimes
>switch to the 1 key for final centering (which it says the 1 key is for
>centering). I didn't know that the 0 key turned off tracking though.
We're talking altaz here. The 7 (SLEW), 4 (FIND), 1 (CNTR) keys just set the rate of speed as you say. Moreover, for these three
speeds, the N,S buttons cause rotation about a horizontal axis (up and down); E,W buttons rotate the telescope about a vertical
axis (the buttons should say L(eft), R(ight), rather than E, W (I always hesitate - which way is the E button going to move the
telescope?)). The 0 (GUIDE) speed rotates slower and the axes are different - E,W now rotates about a parallel to the Earth's
polar axis, N,S changes the declination the telescope is pointing toward. If you're at GUIDE speed, the tracking motors are turned
off only when you push the E button, and the stationary telescope rotates E relative to the stars.
>Anyway, you are basically telling me that once I get my second alignment
>star centered and it goes drifting off before I can sync on it is due to
>backlash, right? Why do I not have this problem with the first alignment star?
Oops, I forgot one very important point relative to tracking the first alignment star. When you turn on the telescope, Meade starts
immediately tracking, but this only tracks the real stars if you put the telescope in the position Meade assumes before you turn it
on: OTA level and pointed south. We've called this the 0-star alignment. It works fairly well for daytime viewing if your time and
position settings are good.
>Any further information on this would be appreciated......
OK, here's almost the full dope on backlash-aware centering. As I said, the main thing is that the star has to sit still and centered
after you push the last button(s). If you grab it on the run, Meade won't have the right readings from the encoders for the
alignment algorithm.
Star
Azimuth
center
GUIDE
0-90
NW
(NW W SW)
E
90-180
NW
(N NW W)
E
180-270
SW
(NW W SW S)
E
270-360
SW
(N NW W)
E
The first line says if you're trying to center a star to the NE, the last buttons pushed at center speed have to be N, W, or N and W
simultaneously. If you push E or S last, the star will drift for a while. For the final centering at GUIDE speed, push W or N&W or
S&W last (and you can always push E last).
To end this long dissertation, the way I work it is to have the reticle crosshairs vertical and horizontal as I look in the eyepiece. If
I'm centering a star to the east, I hit SE simultaneously at center speed to push the star almost to the edge of the field of view,
then get it close to the center using only N and W buttons. Switch to GUIDE speed and put the star in the reticle box using only
the allowed buttons. The star had better stay there while you pause a moment before the push-and-hold ENTER.
Subject: Choosing Stars for 2-Star AltAz Alignment
From: James Burrows <burrjaw
earthlink.net> Date: Aug, 2001
In the following table, the column labeled "Star 1" has the 20 alignment stars visible at latitude 45 deg last night, "Az" and "Alt"
their azimuths (0=N) and altitudes. The column labeled "Star 2" is the best star to use with "Star 1" in a 2-Star alignment, best
in the sense of whole-sky pointing accuracy, expressed by the number "RMS", described later.
The first fact that can observed in the table is "don't use low altitude stars." None of the freely chosen stars in column "Star 2"
are below 35 deg. All the alignments which are forced to contain low-altitude stars in column "Star 1" (e.g., the last 5) have the
poorest pointing performance. It is interesting to note that the method of evaluating pointing performance used here is purely
geometric, i.e., it doesn't contain refraction. Maybe Meade came out smelling like a rose in forgetting to put refraction into the
alignment algorithm because one doesn't want to use low-altitude stars anyway...
RMS
Star 1
0.759 HAMAL
Az
Alt
145 63
Star 2
POLARIS
Az
0
Alt
48
0.759 POLARIS
0
48
HAMAL
145 63
0.768 CAPELLA
67
47
MARKAB
226 50
0.768 MARKAB
226 50
CAPELLA
67
47
0.775 ENIF
244 34
CAPELLA
67
47
0.776 MIRA
155 37
POLARIS
0
48
DENEB
292 47
0.778 ALDEBARAN 106 36
0.778 DENEB
292 47
ALDEBARAN 106 36
0.791 DIPHDA
184 24
POLARIS
0
0.801 BOGARDUS
72
MARKAB
226 50
0.812 VEGA
302 24
HAMAL
145 63
36
48
0.837 CASTOR A
62
18
MARKAB
226 50
0.85
267 15
CAPELLA
67
47
285 25
CAPELLA
67
47
ALTAIR
0.855 ALBIREO
0.859 BETELGEUSE 97
16
DENEB
292 47
0.865 POLLUX
63
13
MARKAB
226 50
0.874 ALNILAM
107 13
DENEB
292 47
0.894 RIGEL
115 11
DENEB
292 47
0.899 FOMALHAUT 207 8
POLARIS
0
1.018 ALCAID
MIRA
155 37
352 7
48
A rule-of-thumb for the azimuth choice is more difficult. In general, one wants to choose a 2nd star as far away, in azimuth, as
possible from star 1. However, the available altitude choices interfere with this choice. For example, (Polaris, Hamal), with 145
deg azimuth separation, is a better choice than (Polaris, Diphda), 176 deg apart, apparently because Diphda is a lower altitude
star. Other examples of this phenomenon can be dug out of the table.
"RMS" is the whole-sky average pointing accuracy as a factor times the centering accuracy, for example, 1 arc minute centering
accuracy during a 2-star AltAz alignment using Polaris and Hamal results in .759 arc minute pointing accuracy. Please note that
this calculation is only geometric and doesn't include esoteric errors such as tilt error misrepresentation, altitude axis
nonorthogonality, worm wheel runout, etc.
Just for fun, here's the:
5 _Worst_ Choices:
92.157
ALCAID
POLARIS
154.903
CAPELLA
CASTOR A
290.545
CAPELLA
POLLUX
1233.78
CASTOR A
POLLUX
3813.965 ALDEBARAN
ALNILAM
See "Software & Computer Issues, page 1" for the BestPair II freeware that will calculate the best alignment pair for you (Mac,
PC, & Dos).
Subject: AltAz Re-Alignment by Sync Operation
From: Rob Preston <rbrtprstn
earthlink.net>, Date: Oct., 1998
The method under discussion here has two related but quite different features. First, it's an alignment trick (for both polar and
AltAz modes, although it has, by far, its greatest usefulness with the known-site, non-leveled AltAz mode). Second (and perhaps
less obvious at first sight), it makes it feasible to get into and out of the aligned mode in the blink of an eye. Thus, it is now a
simple matter to **unlock the axes** of an LX200 and manually slew 180 degrees in less than one second, relock the axes,
SYNC on any convenient star in that area of sky (e.g., one of the 250 brightest stars in the sky, listed in the database as star #1
to star #249, although any of the SAOs would work too), and be perfectly 2-star-aligned again. This could eliminate 90% of the
slewing noise and motor wear associated with long-distance slews, for example.
One of the supposed advantages of the Celestron Ultima system (with encoders on the axes instead of the motors) is that the
scope always "knows" where it's aimed, even if the clutches are released, so unlocked manual slewing is possible. The ease of the
one-star realignment that Bill Arnett pointed out (which preserves the off-level tripod corrections that were achieved in the initial
2-star alignment) means that, essentially, the LX200 system also can be unlocked routinely. Since it's easy to remember the
locations of the 250 brightest stars in the sky, a quick SYNC on any one of them can easily reestablish the accurate initial
alignment, even if the tripod were grossly unlevel. It works! I tried it with a grossly unlevel tripod and got the alignment back
near-perfectly. I assume it would have been perfect if I had used a reticle for the SYNC.
This method is mentioned in the LX200 user manual under the heading, "The permanently-mounted, polar-aligned LX200". For
those of us who have no permanent polar alignment, it's easy to miss the significance of the method and suppose that it applies
ONLY to the polar mode and a precise, permanent alignment. This is especially true since the manual doesn't even define the
"sync" operation except by that casual mention in the polar alignment section (they forgot to put it in the manual!) As Bill Arnett
discovered: in the AltAz mode, the bias corrections (made via a two-star alignment) for a non-level tripod are independent of the
wormwheel position, and a SYNC (*without* GoTo) is possible and it restores the full 2-star accuracy after any unlocked axis
motion.
Check it out, you AltAz people. Polar people, too, feel free to unlock those locks for super-speed slewing. A simple SYNC-withoutGoTo on any object in the database restores the alignment.
P.S: SYNC means that, after selecting a star or M- or NGC- object from the database, so it's name is displayed on the controller
paddle window, the object is then centered in the eyepiece, as during the initial alignment, and then the ENTER button is pushed
and held down until the paddle beeps and displays "coordinates matched". (Most Mapuggers know that, but it isn't in the manual,
at least, it's not in the manual that came with my own scope).
Subject: Keypad (classic) Enter Key Problem During Alignment Routine Solution
From: Ed Stewart <stargazer
skymtn.com>
> I think I'm having a problem with my keypad. Each time I go through my 2-star
> alignment routine I find that when I'm done centering the star (whether
>
>
>
>
it's the first or second star), I have to press several time the ENTER key
for it to finally register or beep. Is this normal? What I don't understand
it that I only get this problem during the alignment routine. Otherwise the
ENTER key works great !
This is a know "feature" of the alignment routine. The answer--> a quick press or almost a tap of the Enter key. Why Meade
decided to make it this way is unknown.
Subject: How close is "close enough" OTA alignment?
From: Joe Diregolo <JOE.DiREGOLO
kla-tencor.com> Date: Aug 2000
-----Original Message----From: Gregory Pyros <gpyros
home.com>
Thanks to the MAPUG Topical Archives, after I first brought the scope home and had alignment problems with it, I returned it to
Meade for an adjustment. What happened was that when I polar aligned the scope on the SuperWedge with everything turned
off, and did a 360 in RA, I would get a nice tight little circle of Polaris, but it was nowhere near the center of the 26mm eyepiece.
Imagine drawing a 3" diameter circle on a piece of paper, then drawing a 1" circle just about touching the outer edge of the first
circle. Meade agreed that it was an OTA alignment problem, and adjusted it.
Now I have it back, and trying the same test, the two circles are perfectly concentric, but if the full 26mm eyepiece is a 3" circle,
Polaris will, at best adjustment, form a 2" circle within it. So there is no setting where I am perfectly aligned that I can have
Polaris in the center of my eyepiece, and not even in the field of view of the 9mm illuminated reticle.
For visual observing it would probably be fine, but my goal is to do CCD photography, and I'm sure I will have enough problems
there without worrying about mechanical scope alignment causing tracking problems!
Answer to question:
I noticed the same problem with my scope. But to check it requires that you point the scope to a fixed object. You are correct in
using Polaris since it is close enough to the celestial pole that it move so slow that it would not effect your test. What you are
seeing is the mismatch of the Optical axis and the RA axis. Meade seems to do a good job getting RA and DEC axis orthogonal.
But they fail to get the all three axis's to intersect each other at the same point in space.
If the error is large enough one would see dec drifting even after perfect drift polar alignment.
There is another test that you can perform that will show what direction the error is. Rotating about any fixed object at least 100
feet away and adjust the dec to 90 deg or to the exact location that you achieved the smallest orbit of the object.
Without moving the dec axis point the scope at a diffuse light source. (A florescent fixture should work fine). Remove the cover at
the bottom of the fork arm. This will expose the upper RA bearing. Using a 12.5mm or smaller eye piece project the light on to
the screw and washer holding the RA bearing. Adjust the focus so that the light circle is slightly larger that the screw. If the light
is centered then its as good as it going to get. If not then one of two thing are still out of alignment. If its off in the Fork direction
it indicates that the OTA is not centered between the forks.
If its off in the other direction this indicates that the forks are tilted and that the dec axis does not intersect the RA axis.
Now how to fix this error...
If the error is in the fork arm direction one could theoretically add different size trust washers to the dec assembly to offset the
OTA until it is concentric with the RA axis.
I would be very interested in knowing if anyone has done this adjustment. I would like to know about it because this is exact
error I have with my scope. I'm off center about 1/4" in the fork direction. Still I get good tracking of unguided CCD images for
about 5 min.
If the error is in other direction this would indicate that both forks arms are tilted and would need to be adjusted. This adjustment
can be found at OTA Alignment here in the MAPUG-Astronomy Topical Archives.
Subject: Leveling LX200 and Entering Lat/Lon under Classic v3.34 Pointless?
From: Paul Rodman <paul
ilanga.com> Date: Dec 2002
>From: Hari Seldon
>I came across this interesting point made by Meade in its official
>product guide for 1996, which put me into some thinking.
>Quote from page 20, titled "Version 3.34 software": "The very latest
>in telescope operating systems, Meade Version 3.34 software,
>included with all 8" and 10" LX200's, enables quick (less than 10
>seconds!) 2-star alignment of the telescope in the altazimuth mode,
>without requiring input of the observer's latitude or longitude,
>without even leveling the tripod. Just use 2 easy-to-find reference
>stars and the LX200 tracks and actuates GOTO with extreme precision."
>
>Now, the above statement clearly says that a) leveling the base, and
>b) entering the site geographic coordinates, is pointless with v3.34
>software for Alt-Az use. I have long believed (and empirical
>evidence supports this) that leveling the base as best as possible
>along with the input of site lat/long data improves pointing
>accuracy. [Still, the scope performs nicely even without being level
>or entering the site coordinates.]
>And if indeed leveling the tripod and entering lat/long is pointless
>under v3.34, why didn't Meade remove that little bubble level from
>the LX200's base after they started rolling out the 3.34 scopes?
>Could it be that a level base (along with the coordinates) is still
>needed for 1-star alignments in altaz?
If the computer knows how to point the telescope to two fixed (RA/Dec) positions in the sky (2-star alignment), then with a
couple of 3D matrix transformations it can figure out the actual direction its physical axes are pointing with respect to the diurnal
rotation axis (the invisible shaft through both celestial poles) and RA=0. From this it knows how to rotate its axes to point at
various parts of the sky.
This doesn't require time, date, lat or long. However, not knowing the correct time, longitude, etc. means that it can't compute
the current position of planets and other non-stationary solar system objects.
With a one-star alignment it can't do this bunch of 3D transforms. In order for the one-star alignment to work it has to make
additional assumptions:
a. For AltAz: the scope base is exactly horizontal (i.e. RA axis pointing straight up) and the OTA is pointing exactly south and
level (i.e. alt=0, az=0) when the computer is fired up, and the date/time/long are correct. This effectively means the computer
can perform some math and figure out the RA/Dec of where the scope is initially pointing - giving it one "star". The one-star
alignment gives it the other. In fact, you don't even have to do any alignment at all if the above initial conditions are exact...
b. For polar: the RA axis is assumed to be pointing exactly at the pole and the OTA is pointing at Dec=+/-90, RA=0 (?). The onestar alignment (or even just a GOTO+Sync) just calibrates the RA and Dec axes to a known RA/Dec. Since the RA axis is
physically coincident with the diurnal rotation axis, two-star alignment is not necessary.
The GPS models allow a 2-star alignment in polar I believe - presumably to adjust for a bad physical polar alignment.
Subject: Solar Tracking URL
From: Doug LePage
Check out this web page called LX200 tips and tricks by Anthony W. Haukap, He has some real useful information about solar
tracking and alignment procedures down near the bottom of the long page.
<http://myweb.accessus.net/~090/lx200.html>
Note: should open a new browser window over this one.
Subject: Lunar Tracking Software URL
From: James Burrows
Scott Rosenberg wrote:
>57.9 Hz Lunar rate; Best for tracking the Moon.
That's the average lunar rate in RA. The current rate depends quite a bit on the azimuth of the Moon because the observer is
whizzing (almost supersonically, right?) around the Earth's spin axis. I reved up my "moon3" program and it said the current rate
was 57.3 (with the Moon below the horizon) and declination rate -1.2% of sidereal. Changing the PC clock time to 23:00 with the
Moon near upper transit, the lunar RA rate increased to 58.5. If anyone's interested in this niche of LX200 lore, the lunar pointing
and tracking program is at:
<http://home.earthlink.net/~burrjaw/lx200/odyframe.htm>
Note: should open a new browser window over this one.
GoTo: Polar Aligning
MAPUG is hosted by
Aligning-- Polar Concerns--Page 1
Accurate Polar Alignment Procedures--Drift & Iterative
LX200 Polar Alignment Routine
Southern Polar Alignment Suggestions
Explanation for the Polar Alignment Problem
Polar Alignment -- Iteration Method
Polar Alignment-Drift Method
Drift Alignment Procedure
John Mahony's Polar Alignment Method --outside link
Leveling Accuracy and Polar Alignment?
Polar Alignment with CCD? --3 parts
Polar Aligned Start-Up Position
Polar Alignment Questions Answered -- 2 parts
Maintaining Polar Alignment on a Tripod --on Wedge/Tripod Page
Polar Drift Alignment Described
Meade Polar Alignment Method -- Avoid Second Star with the Same RA as Polaris
Keypad (Classic) Enter Key Problem During Alignment Routine Solution
Better Alignment Accuracy for the LX200
Polar Axis Balance with Equatorial Mounts
Fork Weights & Tracking
One-Star Alignment for Wedge-Mounted LX200s
Aligning -- Polaris is Visible -- 2nd Alignment Star Isn't
Polar alignment When Polaris is not Visible --3 parts
How close is "close enough" OTA alignment?
Polar 'GoTo' Adjustment Web Page
LX200 Daytime Observing/Alignment --separate page
Polar Alignment w/ROM3.30 --separate page
GoTo Page 1 of AltAz Aligning Concerns:
Subject: Accurate Polar Alignment--Drift & Iterative
From: Philip Perkins <philip
astrocruise.com>
Here's a reminder about two articles that deal specifically with polar alignment of the LX200:
<www.astrocruise.com/polarnew.htm> Detailed description of the DRIFT method of polar alignment, complete with Field
Document.
<www.astrocruise.com/polarold.htm> Detailed description of the ITERATIVE method of polar alignment
(clarifies and expands upon the method described in the Meade manual)
Subject: LX200 Polar Alignment Routine --part 1 of 2
From: Chris Vedeler <cvedeler
ix.netcom.com>
This may be nothing new, but it occurred to me tonight that I could polar align my LX200 Classic within it's pointing accuracy
(about 2 - 5 arc minutes) simply going back and forth from Polaris to other known stars using the LX200's internal map of the
night sky. There is no need to let any time elapse between iterations as the scopes pointing accuracy will tell you immediately
how far off you are. This is what I did:
I centered the scope on Regulus and synched on it. Then I hit GoTo star 19 (Polaris) and the LX200 moved the scope to where it
though Polaris was located. Using the Superwedge adjustments I then centered Polaris. (Note -- if you remove only half the error
at the Polaris step, it will converge faster--Bob Denny, see part 2 following.) Then slewed back to Star 100 (Regulus). Then using
the hand controller I centered Regulus and synched on it again. By repeating this process about 5 times I was able to get the
scope to slew from Polaris to Regulus with less than 30 arc seconds of error. I then checked the pointing accuracy to other stars
all across the sky, and they were all within 2 to 3 arc minutes (within the field of view of my 9mm reticle eyepiece). Spica was
the only star which did not end up well within the field of view of my 9mm reticle (250x) eyepiece, but it was close enough to the
edge that I could easily tell which way to move the scope to center it.
To test the new polar alignment I let the scope track on Spica for 30 minutes. When I returned to the scope to see how much Dec
movement there was at 250x, I was surprised to find none what so ever! In less than 10 minutes of polar aligning, I aligned my
scope to show zero Dec movement in 30 minutes!
Synching on Regulus sets the LX200's computer to think that it is pointing at Regulus (as it is in reality). Slewing to Polaris, the
LX200 moves to where Polaris would be if the scope was perfectly polar aligned (assuming perfect pointing accuracy and perfect
time and date settings). By manually moving the wedge to center Polaris, one is in effect reducing the polar alignment error. By
slewing back to Regulus it permits a test of the new alignment. Doing this a number of times will widdle away at the polar
alignment error until the only error remaining is no more the error in pointing, or no greater than about 5 arc minutes on a
typical LX200. This accurate of polar alignment is probably about as good as could be realistically obtained with the LX200
regardless of the method used.
Using this method is quicker and easier than using the drift method, and from my experience tonight, it is more accurate as well
(assuming your scope is pointing well, and your clock is set accurately).
-----------------------------------------------------------------------Subject: LX200 Polar Alignment Routine --part 2 of 2
From: Bob Denny <rdenny
dc3.com>
Right. This is what Astronomer's Control Panel's Alignment Wizard does, with a couple of refinements. It knows about Sigma
Octans for the Southern hemisphere. It picks the "other" alignment star for you, and gives you a selection of alternates in a
droplist if you find the primary is obscured. It also does a 2-phase Dec-axis bias calibration as a first step.
One thing to note -- if you remove only half the error at the pole star step, it will converge faster.
Assuming your scope is sited and timed "right", the results are comparable to drift alignment and it takes much less time.
Subject: Southern Polar Alignment Suggestions
From: Doug McEachern <applejuice
ozemail.com.au> Date: Nov 2003
----- Original Message ----mira.net>
From: Peter Narkauskas<wunili
> I don't know why, but polar alignment has me stumped! I'll try and explain
> what happens on my 12" LX200 on Meade (unmodified) Superwedge.
> I am in the Southern Hemisphere (Birregurra, Australia)
> Okay, scope placed in 'Pole Home' position and tripod level. Checked and
> found stars rotating around centre of EP. Autostar in Polar mode and then
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tried easy and 1 star alignment, both times went to Sigma Octantis - was a
bit difficult 'cause of the Moon brightness, adjusted wedge to align that
star. Then Autostar chose Canopus, I aligned with keypad arrows.
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Nevertheless, I still tried a drift alignment. Chose a star (with the help
of Astroplanner) to the North, near the Meridian etc. The star drifted down
in the EP, so I adjusted the horizontal axis of the wedge. But no matter
which way I went (and I mean I went to the extremes both ways), I could not
make any difference at all to the star drift. It did not improve or change at all.
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I have read as much as I can find on the web. But find that confusing. For
example the Meade manual says leave the motors running when polar, aligning,
but I read elsewhere to leave motors off. I have often found conflicting
advice. (I kept the motors running last night).
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I know this is not really that hard, but like I said, I am extremely
frustrated and lost as to what I am doing wrong. In normal Alt/Az my
GoTo's are pretty okay and have always been. I have the 1.7k version of
Autostar. What I find particularly weird is my GoTo's in polar mode are way
off. Perhaps I am not picking Sigma Octantis properly...it is a hard star
to pick...we are not so lucky to have a Polaris down south here! But I have
studied star charts to get an idea of the area and I have slewed in Alt/Az
mode a few times to Sig Oct to get to know it. Even if I picked a wrong
star close by, surely my GoTo's wouldn't be that far out?? Or would they??
Once again, I am sure my initial setup in Polar home is correct. And yes, I
allow for pointing true south etc.
I went on to try drift alignment for the first time, but, and this has
happened a couple of times previously to me at this point, when I did a
GoTo, the object was well and truly off the mark. Anywhere from about 1-5
degrees out and to the left of the object (when looking straight up at the
sky). Even a GoTo canopus was out like this. So something is obviously
wrong with my setup at this point. I tried this Polar alignment about three
times last night and each time my GoTo's were way out.
Just a couple of suggestions for you-Firstly just to be absolutely certain that you are picking true south, you might want to do a quick Alt setup which you say is ok.
Then when you are happy with that, GoTo sigma Oct. It is star #351. When you have it you now know exactly where true south
is both in elevation and Azimuth. As for Azimuth, mark a point (maybe on your fences, buildings) so that you have a permanent
line running N/S. Refit your wedge, make sure you have the polar angle set to your latitude. Note that you already have a good
idea from your altaz setup what the angle should be. No insult intended but it might be possible to have set your wedge to the
compliment of your latitude angle. What I mean is as latitudes approach 45 deg the difference between 40 and 50 is not as
obvious as say between 30 and 60 (just a thought). I'm not sure what your latitude is down there in Vic, up here around Sydney
it is 34 deg, that is why I guess you are getting up around Lat 40. In my set up I can't even see Sigma Oct. thanks to a
wonderful. neighbor that thinks everyone should live in pine forest. I just press enter as soon as my 12" LX200 thinks it has
found Sigma; why disillusion it? And then centre the next star it selects. I have found though that if I want really good GoTo I
have to turn on the High precision feature. Not bragging but in case you are wondering, I can track unguided for several hours in
Polar so don't confuse accurate GoTo with accurate polar alignment.
The other thing to make sure of is that you set the N/S switch to the south position. I think you say that you do, but I'm not sure.
That switch has no effect in Alt/Az mode that I could ever find, but it a must for polar, but I guess you would know if that was the
problem.
Subject: Explanation for the Polar Alignment Problem --Classic
From: Ralph Pass <rppass
rppass.com>
The problem is easily understood (see below for explanation). The bottom line is that you should avoid using stars with RA close
to that of Polaris (2h 15m) or close to 12h away (14h 15m). The closer the 'sync' star is to 2h 30m the more likely you will
converge to a bad alignment (mathematically there is a singularity at RA 2h 15m with this procedure, also known as bad
geometry). The closer the 'sync' star is to 14h 15m the more likelihood of the near perpetual oscillation. This is also because of
bad geometry. See below for more details.
The polar alignment procedure provided by Meade is for convenience. If you manually do the procedure (where you pick the
second star), then you can control the geometry and can avoid frustration and waste of time. The closer the second or 'sync' star
to RA 8h 15m or 20h 15m the better and faster the alignment.
In the northern hemisphere, Deneb (Alpha Cyg, star 232) is close to optimal for the 20h 15m area. Pollux (Beta Gem, star 81) or
Regulus (Alpha Leo, star 100) are about as well as you can do for bright stars around 8h 15m.
In the southern hemisphere, Avior (Epsilon Car, star 86) is close to optimal for 8h 15m and Alpha Ind (star 231) is close to
optimal for 20h 15m.
1. Stop reading now if you are not interested my attempt to explain the bad geometry problem.
Suppose the local sidereal time is that of the RA of Polaris, 2h 15m. Suppose that by chance your mount is perfect in
azimuth and off by 10 degrees in altitude. You go to a star with RA 2h 15m besides Polaris, center it and sync on it. The
LX200 has now adjusted for a presumed bias in the dec axis readout of 10 degrees. If you now slew to Polaris, the LX200
will move in Dec by the distance between the two stars and amazingly Polaris is centered and you think the alignment is
perfect. The 10 degree error in elevation was corrected by the 10 degree bias introduced in the dec readout. This happens
because the RA does not change. With a little thought you can see that if the Polar axis is misaligned but points to a point
on the RA 2h 15m semi great circle then the problem is there, although with a combination of AZ & ALT errors and Dec &
RA readout 'corrections' applied by the LX200. You cannot beat this system with the second or 'sync' star being at RA 2h
15m.
2. Suppose the local sidereal time is that of the RA of Polaris plus 12 hours, 14h 15m. Suppose that by chance your mount is
perfect in azimuth and off by 10 degrees in altitude. You go to a star with RA 14h 15m, center it and sync on it. In doing so
you will introduce a bias in dec readout of 10 degrees, just as
in the first case. You now slew to Polaris. In doing so, the RA axis rotates by 180 degrees (12h). and is now pointing 20
degrees from Polaris (10 degrees for the altitude error and 10 degrees for the bias in dec readout introduced when you
synced on the star). You correct by 20 degrees. Now suppose we slew back to the first star. We will find an error of 20
degrees. If we center and sync and repeat, then we are in an infinite loop. It is this observation that has led people to
suggest making mechanical adjustments of half the observed error at Polaris. If you do this when the LX200 picks a star
close to 14h 15m, then you will see a rapid convergence to polar alignment. If you do this with a 'good' star like Deneb,
then you are making the process take longer.
Subject: Polar Alignment -- Iteration Method
From: Chris Heapy <Chrish
easynet.co.uk>
Consider:
If you set the scope to Ohr RA and 90°DEC, as described for Polar Aligning, then the LX200 will slew around to the offset required
to center Polaris (about 89.2°). You will then centre Polaris using the wedge adjustments. However, this step is not quite as
simple as it seems. All the following assumes that you have correctly set the time, the time zone and the observing site.
There are three sources of error in the Polar-Align routine which will prevent the LX200's 'Polaris-finding' function from working
with anything like the precision required:
1. The OTA may not be *exactly* orthogonal to the mount's axes (this is a factory setting - see Michael Hart's DEC bearing
mod for details of resetting this). This error cannot be corrected by polar alignment.
2. The setting circles may not be correctly registered with the mount's Polar and DEC axes (example., the circle reads 89 deg,
but the scope is pointing at 90 deg).
3. You would not have set the mount to *exactly* 0hr RA and 90° DEC, you just made the best judgment you could by lining
up the marks on the circles, something of a crude estimate at best.
Normally, the second stage of the Polar-Align routine then slews the scope to an alignment star (e.g., Altair), you move the scope
to center it in the FOV using the handset controls, and finally press 'Enter' synchs on it. This gives the computer the two datum
points it requires from which it can then calculate the position of all other objects in the sky.
However, after this last step, if you do a 'GoTo' to Polaris you will most likely find it's not in the center of the FOV (maybe not
even *in* the FOV). Why?? Well, the amount by which Polaris is misplaced is the summation of the errors listed above.
What can you do about it? - Perhaps the easiest is the 'interation' routine. I use it myself and it works well. Fine tuning can
subsequently be done using the 'drift method' which will get your alignment very close indeed. The latter is only really necessary
for astrophotography and not visual use.
For the Iteration Method:
1. After the last step mentioned in the example above (synching on Altair), do the GoTo back to Polaris. This position is where
the LX200's computer 'thinks' Polaris is.
2. Use the wedge's adjusters to move Polaris back into the center of the FOV (using a 9mm reticle eyepiece is better than
guessing the center of the 26mm's field).
3. After that, press STAR, and select Altair again, and press GoTo. The telescope will slew back to where it thinks Altair is. Of
course this will now be misplaced too (because you moved the wedge).
4. The next step is to move Altair's position in the FOV (using the hand controller only) until it is *half-way* from where it is
now, to where it should be meaning the center of the FOV.
5. After moving it hold ENTER down for a couple of seconds to synch on it.
Next step is to select STAR again, choose Polaris and do a GoTo. Polaris should not have moved much from the center of
FOV - if it has, bring it back to the center. Do NOT hold ENTER down at this stage - you don't want to re-synch Polaris'
position.
6. The next step is a repeat - press STAR, select Altair, do a GoTo. Now, this time you will see that the positional error is less
(about half actually), and once again you want to move Altair half the distance toward the center of the FOV and synch on
it.
7. The rest of the process is to repeat the cycle, Altair to Polaris and back again, each time shuffling Altair closer to the center
of FOV. After a half-dozen cycles (iterations) the error will be very small.
Notice that at no time in this process have you re-synched the position of Polaris, only Altair. This is important. At the end of this
process any further GoTo's should be correct.
It's worthwhile at this stage refining the alignment using the drift technique, and then checking the exact positioning of your DEC
circle (the manual mentions this step). Use the handcontoller to point to 90 deg and ensure the scale also reads 90. If it doesn't,
you will need to loosen the center knob and turn the circle until 90 lines up with the mark. Correcting any error in the DEC will
help speed up polar alignment next time out.
Subject: Polar Alignment--Drift Method
The polar alignment description in the LX200 manual is pretty good, but try this description from Chuck's Astrophotography Page
and Scott Tucker's Guide to Astrophotography site:
<www.aa6g.org/Astronomy/Articles/drift_align.html>
Note: should open a new browser page.
Chuck's Home Page has links to other interesting articles:
<www.aa6g.org/astro.html> Note: should open a new browser page.
Also a good polar (drift) alignment description is available on Scott Tucker's site:
<www.darkskyimages.com/guide.htm>
Subject: Drift Alignment Procedure
From: Bruce Johnson, Date: Jan 2001
I did a writeup on 'drift alignment' for SCTs. It just might help some of the people having trouble with it.
<www.mapug-astronomy.net/ccdastro/drift-align.htm> Note: should open a new browser window.
Subject: Polar Alignment with CCD? --part 1 of 3
From: John Teel <mapuglist2
yahoo.com> Date: Jan 2002
Basically just you the autoguide feature to track declination drift. Of course, you need to turn off guiding corrections in declination
but leave RA corrections on. I use CCDOPS on my SBIG camera and autoguide with only RA corrections. It shows what the
current declination drift is but also allows you to log the error into a text file that allows easy importation into Excel so I can
create drift graphs. This is much more accurate than just eyeballing the drift in an eyepiece. See next...
-------------------------------After spending a couple nights trying to absolutely perfect my polar alignment I'm beginning to think that using a CCD to track
for drift alignment is NOT the best way. I've read others making this same statement. I think the biggest problem is that it
requires absolutely perfect seeing because the CCD isn't smart enough to tell the difference in seeing and drift because of poor
alignment. Maybe I'm not either but I think the human eye can differentiate between seeing and drift better than a CCD. I've
found it very very difficult to get absolutely zero drift according to the CCD. About the best I can get it 1-1.5 arc-sec every 10
min. If I make the smallest azimuth/altitude change I can (I watch star movement to monitor how much I changed it) it seems to
overshoot the ideal alignment and I get drift in the other direction. The seeing lately hasn't been very good so I think this may be
a factor. All I know is that I've got it good enough that my GoTo accuracy is nearly dead-on everytime (i.e. object within 20% of
CCD center) and my periodic error dominates for unguided exposures under 30 minutes or so. I tried desperately to achieve
perfect polar alignment but I'm getting tired of making adjustments. I may try one more iteration using my old reticle eyepiece. I
think they same problems apply when using a CCD to guide while training PEC and I think the human eye may be a better choice
for this.
---------------------------Subject: Polar Alignment with CCD? --part 2
From: Jim Seargeant <JimSarge
attbi.com>
I use a CCD to polar align because I don't want to de- and re-mount the CCD every time. My CCD scope is pretty well fixed in
place, but the mount isn't very stable - got'a get a pier installed.
I use dial indicators to measure wedge movement in R.A. and Dec. A .001" measured movement equals to about 34 arc sec and I
can interpolate to about half or a quarter of that. (I just got a dial test indicator that will measure to .00005", but don't know if I
can move the wedge in such small increments - haven't tried it yet.) By measuring actual movement of the wedge, it's possible to
adjust based on drift/time and really home in on 0 drift. Unless you measure wedge movement, it seems to me very difficult to
avoid overshooting.
I've got it down to 0 pixel drift over 20 min, but it takes me the better part of an hour to get there in both axes.
Did a previous reply on this topic suggest using CCD images compared to a high definition star field - such as USNO A2.0 and the
DSS- to point the mount at true North? Sounds worth a try - I'll do that when it clears off.
Editor's note: see part 3 below.
---------------------------Subject: Polar Alignment with CCD? --part 3 of 3
From: Berto Monard <LAGMonar
csir.co.za> Pretoria, South Africa
Hi Mapug readers, as promised, herewith my approach to polar alignment using a CCD camera which, in my case is a dedicated
one, permanently attached to the scope, an LX200 12" f/10. As a matter of interest I have mounted the ST-7E CCD camera via a
Meade focal reducer f/3.3 and the (with it) delivered short spacer piece with T-ring fitting. This combination gives a very sturdy
connection which allows the CCD camera to even travel through the fork (if necessary). The result of this set-up is an image size
of 19.2 x 12.8 arcminutes. The telescope is then effectively a LX200 12" f/4.2 instrument. I have also made the flat top part (with
the attachment platform for power supply and PC connectors) of the CCD camera parallel to the declination axis. The flat top is
also on the side where the finder scope is. This positioning produces images with North up, and East to the left, the way that DSS
images show it. I think it must be different in the Northern hemisphere.
I hereby wish to thank all those that contributed towards my earlier queries on focal reducers and adapters.
I am a mechanical engineer since 1974 but never really practised engineering as a profession. Sometimes I feel sorry about that.
However I have always used my acquired engineering problem solving approaches based on my training to reach high standards
in whatever I did (at least I like to think so...). One such approach is the 'back to basics' approach.
What is the aim of a polar alignment?
Answer: we want the RA rotation axis to point exactly to the North (or South) pole. The only way we can check that is if we are
able to point the OTA in the same direction as the RA axis and check it then via the eyepiece or a CCD image.
The procedure to align the OTA accurately to the RA axis can be done in the day by viewing a distant reference point. But you
have to wait until night to do polar alignment.
I will here describe the procedure to do both at night. This is the way most applicable for those with permanently housed
telescopes. It only requires a coarse polar alignment (within a degree), or an established method to do so. Obviously you need an
open/clear sky towards the pole...
The first task: align the OTA roughly in the direction of the RA axis, i.e. set the declination to 90 degrees. It would be nice if we
could do that by relying on the DEC setting circle, but for that it needs calibration first. In my case it is a full degree off!
Actually we do not need exact alignment in DEC, just to within some 10 arcminutes depending on the actual FOV depicted on the
CCD chip. The alignment must be preferably better than half the FOV. But then even that is not required initially.
We can use the CCD images (from 'dim' exposures of 3 seconds in focus mode (CCDOPS)) to tell us where we stand. All we must
do is to rotate in RA manually (with the LX200 switched off!!) or, if we are reasonably aligned to the pole, by pressing E or W in
slew mode during the exposure time. The image will show concentric arcs around a centre position. That centre position is the
apex of the RA axis and will not be at the centre of the CCD image. What we want to achieve is to align the centre of the arcs to
the centre of the CCD image, not? The only ready way to do that is to fine tune the Declination. The continuously updating
exposures will show an eventual improvement by having the two centres coming closer. However, what you will notice is that the
two centres will never match. They'll come closer up to a point and then start moving away from each other again. Possibly (in a
bad case, or with a narrow FOV) the rotation centre (RA apex) might not even enter the image...
In my case it stays at best some 7 arcmin away from the image centre. I can't get it closer. What this means is that my DEC
setting is now optimized (90 degrees) but there is a misalignment from the Dec. axis itself. It is not 90 deg. to the RA axis, but
some 7 arcmin off that. Note: Try to get this information (RA apex position and the approx. size of the misalignment) with a
reticle eyepiece!!??
What can we do about it?
I don't know the specifications claimed by Meade on the OTA alignment accuracy. The only possible adjustment is to slide the
OTA where it is mounted onto the fork. There are Allen screws holding the OTA connected to the fork mount. Since there is no
system for fine adjustments (at least I didn't see them), it is very likely, unless one has an optical workshop, that after loosening
those screws it will be difficult to even get back to the previous accuracy. But then I claim significant practical ignorance on this
matter. I just have a bad feel about doing this at home... (Editor's note: see OTA Alignment Procedures topic in the Topical
Archive.)
Next point: to align your RA apex to the pole by using the wedge adjustments..
Keep the CCD focus mode going, consult the 30'x30' or 15'x15' DSS image of the polar region, centered on the actual (2000
pole) and try to match the RA apex from the CCD image with the centre of the DSS image (2000) using the alt and az
movements of the wedge. You can possibly derive the pole position for 2002, but I don't think it will make much difference. The
wedge movements are far too coarse to worry about that. But then others have taught you how to improve the Superwedge...
(Editor's note: see Wedge/Tripod Modifications topic in the Topical Archive.)
Once I had aligned to the South pole to the best of my ability and I pressed E or W in slew mode during a 3 second exposure, I
saw concentric star trails around a point which was within 2 or 3 arcmin of the South pole which is shown at the centre of the
DSS pole image. As mentioned above, this centre is some 7 arcminutes from my CCD image centre. I can't do much better
without taking a risk..
In conclusion I would like to put things in perspective. The well known tracking problems in RA, the backlash, the sagging of the
OTA and mount (in RA and DEC) and other trade-offs in the construction of LX200 telescopes will always limit expectations for
precise pointing and tracking. I suggest one should polar align just good enough so that its influence is only a minor factor in the
error budget.
Subject: Polar Aligned Start-Up Position
From: Vince Gardiner
Regarding a way to avoid the polar alignment 2-star routine, we know that in Alt/Az mode the 'scope needs to be in a certain
position at boot up so it knows its orientation. I thought it may also have a position in polar mode. It appears so. You do need to
have your declination setting circle accurate. (Pointing straight up it should read your latitude). Align the two RA pointers
together, point the scope to zero declination (the equator), and power on. If necessary, GoTo an object and 'synch' on it and
bingo! Simple. Of course the scope must be in polar mode first and accurately polar aligned.
Subject: Polar Alignment Questions Answered --- Part 1 of 2
From: Philip Perkins <philip
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astrocruise.com>
I have a few questions about polar aligning my 8" f10 LX200 v3.34 Classic
on a standard wedge. Until now I have only used it in alt-az.
1. Can anyone explain why the polar alignment routine requires the finder
(and eyepiece unless you rotate the diagonal) to be UNDERNEATH? It's
driven me to distraction tonight, the first clear night in weeks, trying to
use the iterative method (a la Philip Perkins) as I keep on having to get
on my knees and look upwards through the darn things. I have a 9x60 RA
finder, BTW which is usually very convenient in use; as far as I can see
this technique would be impossible with a straight through finder as you
could not get to the finder eyepiece to look through it. Related to this
question, the scope will point to, e.g. M81 & M82 with the eyepiece and
finder the right way up, but then a slew to anywhere near the pole puts the
scope upside down again. Why???
This is because Polaris is not at exact celestial north, it is about 0.8 degrees away. This means that Polaris rotates around the
celestial pole just as other stars do. In order for the LX200 to land on Polaris it therefore has to match the rotation of Polaris by
an equivalent rotation of the RA axis. It just so happens that in winter the amount of RA rotation required positions the LX200
'upside down'. This means that the finderscope is upside down which I agree, can be a pain in the neck. It's somewhat easier if
you use a Telrad or suchlike.
There is another reason why the Iterative method can be a problem in winter months, and that is because you're likely to be
Synching on a star in the same sky quadrant as the zero hour angle and the closer you are to 0 RA the bigger the error that will
creep into the Sync.
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2. I found that successive iterations between Polaris (centered using wedge)
and Aldebaran (centered using keypad, and synched) gave me a similar error
each time, with adjustments in altitude always being in the same direction,
which implies that I am driving the alignment further out each time. When
I finally got reasonable alignment so that it would go from one to the
other repeatably, pointing accuracy on other stars was off by about half a
degree. Synching on a new star would then give reasonable pointing in that
part of the sky. I guess this means my polar alignment was not accurate.
Pointing in alt-az has always been good.
I have experienced similar problems. I believe this is due to either pointing inaccuracy or Synching on a star near to 0 RA (as
described above) or both.
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3. I used to use my 9x60 finder on an LX50 for polar alignment, as it has
a polar alignment reticle, but never checked by drift and didn't use it for
prime focus photography, so don't know if it was really accurate. I tried
this method instead of the above, and then tried a GoTo Polaris, which was
off by over half a degree. Any suggestions?
Nigel, the Iterative method can work very well, however it is *totally* dependent on pointing accuracy. Therefore it can only work
as well as the pointing accuracy of your scope. It worked very well for me when I first got my LX200 because I was lucky enough
to have one with good drives (initially); however as the gear trains started to wear I got more and more errors creeping into the
Iterative method. I soon got into a never ending 'to and fro' mode - no matter how many times I slewed between Polaris and the
Second Star, Polaris would never converge. Recently there has been evidence of quality problems in Meade drives, and even new
scopes can have problems with pointing accuracy.
There is a solution to all of this -- the Drift Method. The Drift Method is much easier than you might imagine and can also be quite
quick once you get the feel of it. You may want to access:
<www.astrocruise.com/polarnew.htm> Note: this should open a new window over this page.
There you will find a complete description of the Drift Method as it applies to the LX200. The Drift Method has the following
advantages:
1. It will yield very accurate polar alignment - the degree of accuracy depending upon how long you are prepared to drift for.
No drift for 5 minutes per axis is enough to achieve sufficient accuracy for almost all astrophotography applications.
2. It is simpler to understand and implement.
3. Has no dependency on pointing accuracy at all. It will work equally well on a scope that does not even have pointing
4.
5.
6.
7.
ability.
No continual slewing between Polaris and the Second Star, and this saves the drives from wearing out prematurely.
Has no dependency on atmospheric refraction for stars that are close to the horizon.
Has no dependency on pointing errors induced by Synching on a star that is close to 0 hour angle.
The drift process is an ideal time to become familiar with sky conditions, degree of turbulence / transparency, behavior of
the drives (periodic error, declination backlash, etc.) -- I find this information an essential precursor to an
astrophotography session.
There is just one disadvantage -- initially it is likely to take you longer than the Iterative method, however after a little
experience you will find that it takes no longer, and may even take less time. This is especially true if, like me, you were at it with
the Iterative method for half an hour or more and still did not have polar alignment at the end of it.
-----------------------------------------------------------------------------Subject: Polar Alignment Questions Answered -- Part 2 of 2
From: Michael Richmann
This problem's easier to solve than you might think. I typically use my 8" LX200 for astrophotography and have to transport it to
a dark site. So quick setup is crucial to maximize the amount of time spent getting photos and a big part of that is getting a
precise polar alignment in a minimal amount of time. My general procedure is as follows: Setup your scope normally (wedge
facing due south, etc.). Align the scope on a reasonably bright star and use it to align your finderscope with respect to the main
scope as accurately as possible. Next, start the polar alignment procedure as you normally would. When the scope slews to the
position where you would align the equatorial wedge on Polaris, use the finderscope to align the wedge, not the 90 deg.
diagonal/9-12 mm eyepiece combo on the main scope. It's much easier this way and hair splitting alignment on Polaris is not
necessary at this point.
Next, continue on with the alignment and allow the scope to do its slew to the bright overhead (celestial equator) star. Use a high
power eyepiece at this point *without* a diagonal. Otherwise, there's a very good chance you'll introduce an offset unless the
diagonal is very precisely constructed.
Now, instead of following Meade's instructions to use the keypad to center the star, use the wedge adjustments. The first
adjustment on Polaris was just a crude one to make sure your bright overhead star would definitely be in the field of view. At this
point, you're ready to go ahead and follow the standard Meade instructions for drift aligning the scope.
So far, this technique has worked like an absolute charm and virtually never requires that I move the drift testing stars more
than about a full viewing field's worth in azimuth w/a 9.7 mm eyepiece and no more than about a half field in latitude. Drift align
till you see no apparent motion in either the azimuth or latitude cases for at least 5 minutes (I prefer 10) and you should be good
to go. Also, since you'll end up tweaking the various adjustments, it's not a bad idea to slew to a known star and SYNC the
computer's position to that star.
As for your specific questions, in order:
1) Polaris is about 0.8 degrees away from the true north pole at about RA 2:28. Depending on the local time and the particular
time of year, your scope may slew to an inconvenient position. Not pleasant but you'll learn to live with it. The trick of using the
finderscope alone was partially an attempt to make things easier as well as remove the error introduced by using a diagonal in
the alignment process. When the finder scope is impossible to use in this case, I skip the initial alignment on Polaris step and
continue on to the bright overhead star and use the finderscope and then high power eyepiece combined with the wedge
adjustments to achieve the "normal" or non-precision polar alignment, then I drift align.
2) The misalignment might be due to the use of a diagonal or another good possibility is the fact that the mount is not perfectly
rigid. For this reason, I use the high precision option when doing the critical alignment of the camera/scope before taking a photo.
3) Without knowing whether the polar alignment finder scope is carefully aligned during installation on the LX200, it's difficult to
say what the problem most likely is.
Subject: Polar Drift Alignment Described
From: Michael Hart
Typically, we use Dec drift methods to tweak polar alignment in part because this eliminates RA drive clock and worm/worm
wheel errors. Three things happen when we are NOT polar aligned:
1. The stars appear to drift in RA.
2. The stars appear to drift in declination.
3. The field rotates.
The term "declination drift" itself implies a polar aligned scope will drift in declination only. In fact, a scope that is not polar
aligned drifts in RA as well, however, we ignore any RA drift during the process as Ric states and watch "declination drift". As we
approach polar alignment, RA drift slows as well. The reason for RA drift is easy to visualize. If our mount is not quite aligned
with the celestial poles, the amount of misalignment formed causes the RA to appear to drift. The greater the misalignment, the
faster the RA drift. The idea is to line up our scopes to turn parallel with the earth's rotation. Anything less than parallel produces
RA drift. The result is a drive tracking at perfect sidereal time will appear to drift in RA.
Those experiencing unusual RA drift should assure polar alignment is quite accurate and then erase and reprogram their smart
drive which adds or subtracts pulses to correct clock crystal drift and worm errors in the RA drive. Erasing the smart drive also
removes any "extra" pulses programmed in to correct RA drift.
Why accurate polar alignment BEFORE smart drive programming? Because poor polar alignment produces changes in the RA drift
as well. With smart drive programming, in addition to clock frequency errors and worm errors (which are repeatable), we
introduce another error (RA drift) which is corrected by the smart drive as well. The next day, we set up and roughly align again
and find our RA drive doesn't track as well. This is likely because we programmed in the RA drift produced by a the previous
night's poor polar alignment. The previous night's rough polar alignment is usually more difficult to replicate than accurate polar
alignment.
How do I tell which way is drifting north in the eyepiece? Align the reticle eyepiece crosshairs with the RA axis by moving the
telescope in RA. If the star drifts ABOVE the RA axis, the star is drifting is north. When in doubt, move the telescope in RA to
determine which reticle lines to use. What if I prefer NOT using a diagonal (SCT) or live in the southern hemisphere? Reverse the
action performed as a result of drift.
Perhaps polar alignment is more difficult to visualize than it would seem. Wallis has abandoned the "mean photographic
declination" suggested in his book to that of using the celestial equator which I have found improves the speed of drift alignment.
Subject: Leveling Accuracy and Polar Alignment? -- Part 1 of 3
From: John Mahony, Date: Dec 2005
> > I can understand that in most cases leveling isn't
> > needed for AltAz, (although I can think of situations
> > where it's useful) but I don't understand for polar?
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Technically, all that matters for a polar align, is that the RA axis, is
pointing exactly at the celestial pole. It doesn't care what is happening
below this bearing, to actually 'achieve' this. So it would (for instance),
be possible to mount a scope on a plate at an angle of 30 degrees from the
horizontal, north-south, and then just adjust the latitude setting to still
get the RA axis at the right line!. That having been said, the sky 'model'
in some scopes, can get slightly confused as to where the meridian line
actually 'is', if the scope is sitting on a base that is well out of level
east-west (it appears that they may actually shift the internal
relationship to sidereal time, to compensate for this, and result in errors
here). Hence it is usually safer, and easier, to start from reasonably
close to 'level', but it is not usually anything like as necessary as some
people would have you believe....
On the classic, if you're using the standard polar alignment method in the manual, the method starts on the meridian (0 hour
angle). But 0 hour is determined by matching two marks on the moving and fixed parts of the scope. If the tripod is unlevel in
the E/W direction, then the mark on the fixed base will be off.
If you use advanced methods such as the iterative or drift method, it will correct this error, although if you use the standard
method to start, and then refine with the iterative or drift method, it will take more iterations or more drift checks, since your
starting alignment is less accurate. But the error from E/W level is slight to begin with. Roughly speaking, each degree of E/W
level error will cause only 1/2 arcminute of polar alignment error when using Meade's standard polar alignment method.
Your theory is correct, but in the real world, check the numbers to see what is practical. As I stated earlier, each degree of E/W
level error causes about 1/2' error when using the basic polar alignment method. Given the effects of atmospheric refraction,
there is no "perfect" polar alignment that will give perfect tracking for all parts of the sky. Fork flex is another unavoidable error
(and in most parts of the sky, this error is in the same direction as the atmospheric refraction error, so these errors add rather
than cancel).
Given these errors, I consider 1' to be the practical useful limit for desired accuracy in polar alignment, so levelling to better than
2 degrees accuracy doesn't really help. That works out to roughly a 1 inch adjustment of the length of a tripod leg, if the legs are
not extended too far. If the tripod is taller, then the adjustment is even less sensitive.
So you only need to adjust the legs to 1" accuracy, which you should be able to do with the usual leg adjustment.
Keithnk wrote:
> Thanks guys that makes sense. So here's what I'm thinking
> now. Reasonably good leveling is not necessary but
> facilitates the drift method of AltAz wedge
> adjustments. (I do have to set up from scratch most
> sessions, so reducing set up time without sacrificing
> tracking accuracy is always a goal) If level is way off it
> may take several sets of drift alignments to get dialed in,
> but you can. However, I'm thinking at least a good E/W level
> would be useful because if for example it's dead on, then
> the azm adjustment would leave you pointed true north and
> now you're done with that adjustment. Any out of level N/S
> can be taken care of in the alt adjustment.
> If I'm understanding correctly, 5 or even 10 min. spent
> getting a good level could reduce the drift check/adjust
> sets to as little as one. A common recommendation for drift
> check/adjustments is about 10-15 min per axis, (10 min. is
> usually my longest exposure).Each drift check/adjust saved
> is therefore worth at least 20-30 min time. So, I can still
> see where a device to quicken and get good level would be a
> time saver.
-----------------------------------------------------Subject: Leveling Accuracy and Polar Alignment? -- Part 2 of 3
From: Randy Marsden <jmarsden_at_san.rr.com>
John and Keith, and Roger,
You are all correct. There is another factor to consider when doing polar alignment - the coupling between altitude and azimuth
adjustments if the platform is not level. If the platform is not level, then when an altitude adjustment is made, it also changes the
azimuth angle and vice versa.
It is this coupling that causes many people to have to iterate back and forth between the altitude and azimuth adjustments when
doing polar alignment. But if the platform is level to start with, then as long as the altitude and azimuth axes are truly
orthogonal, then making an adjustment in one axis will not change the setting of the other.
So, while starting out with an out-of-level base does not prevent obtaining good polar alignment, it can make the alignment
process more difficult. It is much faster to get the tripod or pier level than it is to iterate an extra three or four times to get good
alignment.
-----------------------------------------------------Subject: Leveling Accuracy and Polar Alignment? -- Part 3 of 3
From: John Mahony
Keith, and Dan Simpson, both raised the issue of AltAz interaction with an E/W tilted wedge. Again my answer is, do the math, to
see if it's really a practical concern. I've said many times that the big obvious weak point in Meade's basic method is that it starts
by relying on the dec setting circle to set the tube parallel to the RA axis (90 dec), but the circle is crude and prone to slipping,
and any error here will translate to similar sized pointing/alignment error. A quick way to cure this is to rotate the scope in RA
while at 90 dec, to see if the image rotates around the center of the FOV. If you _don't_ use that, error in the circle (or in reading
it) may be a significant fraction of a degree.
So let's look at a hypothetical case where the tripod E/W levelling error is substantial, say 10 degrees, and the initial alignment is
off by 20', mostly due to dec circle error. You start a drift alignment by aiming at a star near the meridian/equator intersection, to
adjust the wedge az. Making a 20' az correction with an E/W tilted wedge has about a 3.5' effect on alt, but at this point we
haven't even adjusted the alt yet, which we expect to be off by a significant fraction of a degree, so the 3.5' alt change isn't
significant. But then we aim at a star near the E or W horizon to do a drift check, to adjust the wedge alt. Now if we need a ~20'
adjustment in alt, on a 10 degree E/W tilted wedge, this will have about a 5' affect on az, which is not within the 1' limit I
mentioned earlier as the practical limit for polar alignment accuracy, so we have to do a second iteration.
The second time around, making a 5' correction in wedge az has somewhat less than a 1' affect on alt, so we are done. An extra
half-cycle of drift alignment was needed, not three or four. If you use the "rotate in RA while at 90° dec" method to confirm the
initial alignment, then if done carefully enough, the initial alignment may be so accurate that you won't need the drift method at
all. Done a little less precisely, the initial error may be on the order of a few arcminutes. Then the effects of the AltAz interaction
will be less than 1'.
Subject: Meade Polar Alignment Method -- Avoid Second Star with the Same RA as Polaris
From: Ralph Pass
When you are using the Meade polar alignment procedure picking the second star with the same RA as Polaris will result in
convergence with an arbitrary offset. This is due to the mathematics of the alignment. To see this assume you have a second star
with the same RA as Polaris. Suppose your mount is now 5 degrees (or any value) from the pole on either Polaris' RA or 12 hours
from that. Suppose you loosen the dec axis lock, mechanically move the OTA so it points to Polaris and relock (so you have
moved through the NCP (North Celestial Pole) to get to Polaris). Tell the LX200 you centered on Polaris, and then when it slews to
the second star, it does not need to move the RA axis!. The bias that was introduced at Polaris will be applied to the next star and
the LX200 will travel exactly the proper distance to get the second star and it will be centered. You press enter and you think you
are polar aligned but you really are not! The star to really avoid here is Diphda, star 8.
If, on the other hand, you have Polaris below the NCP (so the telescope has to rotate through 180 degrees to get the second star,
then any bias in Dec at Polaris will be reflected as twice than error at the second star. You correct twice the error and go back to
Polaris and you have twice the error. Which you correct and then go to the second star and you have twice the error. Repeat until
you get tired and you have not improved your accuracy. Again this is a limit in the mathematics of the algorithm. It is this
scenario that prompts some people to suggest correcting half of the error. Slower convergence but it does converge.
Subject: Keypad (classic) Enter Key Problem During Alignment Routine Solution
From: Ed Stewart
>I think I'm having a problem with my keypad. Each time I go through my 2
>star alignment routine I find that when I'm done centering the star (whether
>it's the first or second star), I have to press several time the ENTER key
>for it to finally register or beep. Is this normal? What I don't understand
>it that I only get this problem during the alignment routine. Otherwise the
>ENTER key works great !
This is a know "feature" of the alignment routine. The answer--> a quick press or almost a tap of the Enter key. Why Meade
decided to make it this way is unknown.
Subject: Better Alignment Accuracy for the LX200
From: Ralph
The retical is definitely not necessary for accurate 2-star alignment. I center my alignment by eyeballing my alignment stars with
a 20mm Nagler and objects are "ALWAYS" in the field of view in the 20mm Nagler afterwards even without using HPP. Remember
the 20mm Nagler is a fairly wide angle eyepiece. This is an advantage.
I have found 5 areas that are critical to perfect centering:
1. Don't refocus on the second alignment star once you have picked the first one. The image shift of the primary will be enough
to throw off your centering. Even if the second star is blurry and not focused, don't refocus until the alignment process is
completed.
2. The exact time entered into the hand controller is very important. I tried my telescope with the time off by over 20 minutes
and accuracy definitely degraded. I recommend setting the clock on the hand controller to the exact WWV time before every
outing.
***Counterpoint: WWV is overkill. Setting your wristwatch to the time from the Net or the phone company or the TV news and
setting your LX200 from that is sufficient. There's no need to get paranoid about milliseconds here.
3. Perfect leveling of the scope has much more effect on centering than some people realize or are willing to admit even though
the manual says its not that critical. Spend the extra time to level the scope perfectly and make sure the scope is on a hard
surface and wont sink into the ground over time.
***Counterpoint: My experience is different. One day I deliberately set up with my tripod very badly out of level. After 2-star
alignment everything worked perfectly. If I recall the discussions here correctly, the 2-star alignment algorithm corrects for
leveling errors as well as encoder biases. The *amount* of level correction shouldn't matter much.
4. Exact latitude and Longitude. Also contrary to what is believed, your exact latitude and longitude is very important to
centering. This is especially important when viewing objects close to the horizon where there is a parallax effect of the
atmosphere as you view lower in the horizon. Take the time for either borrow or buy a GPS unit. They cost as much as a good
eyepiece and are well worth the expense for the advantage you will get from its precision. With out precise lat and long, your
scope will be off at the horizons, as noted in the manual.
***Counterpoint: A cheap GPS is also a good time source. But again, GPS accuracy is way overkill. You can enter the lat/long
only to 1 minute accuracy anyway.
5. Finally, pick your pointer stars carefully. Learn the sky enough to always pick stars low on either side of the horizon, east and
west, north and south or at least opposite areas in the sky. Keep your stars low on both ends of the horizon. The farther apart
your alignment stars will be, the more accurate your scope will be.
***Counterpoint: Wrong. The alignment stars should be between 30 and 60 degrees elevation. Refraction correction is NOT
applied during the alignment process. If you use stars too close to the horizon refraction will foul it up. See freeware BestPair II in
Software & Computer Issues, page 1 topic.
Don't expect bullseye accuracy every time if you are not using HPP, but you should always be able to keep any star or object in
the field of view of a good wide angle low power eyepiece, even without the HPP active. You will definitely not get the centering
accuracy if you go to a higher power eyepiece, for example, something over 200x, even using the Naglers tremendous field of
view. Keep your searching to lower powers and wider field of views and when the object is there, then up your power if you like.
Sometimes if you use a high power eyepiece with HPP, the alignment star may not be in the field of view of your eyepiece. Just
check your finder for the brightest star. That will be the one you are trying to center on. Use the slowest slew speed to recenter
the star, then when you press GoTo, the object you were searching for will be right there. This is usually never necessary unless
you leave a higher power eyepiece in you scope when moving to the next object.
My opinion based on my experience is that if you follow these guidelines, you will be amazed at the accuracy of your scope.
Subject: Polar Axis Balance with Equatorial Mounts
From: Richard Davis
What follows is some discussion on the subject of balance of the LX200 around the POLAR AXIS, under the condition that the
scope is mounted on a wedge that places the base of the scope in plane which is parallel to the earth equatorial plane. I believed
there is a strong case for working with a balanced fork assembly on the LX200 under these conditions.
==============================
Recently, <wjm
authority:
sarnoff.com>, William Murray, has submitted the following comments, together with a quote from another
"I'm not sure what the internal workings of the RA motor assembly on LX200 scopes are but the idea of letting the motor "guide
the fall" is old astrophotography wisdom. In his book "Astrophotography", page 74-5 Barry Gordon states:" (quoting Mr. Murray.)
"Note that, for the polar axis, perfect balance is NOT what we want. If we achieved such balance, then any play in our right
ascension tracking mechanism would allow the instrument to wander back and forth between the limits of that play. We are
generally better off with slightly imperfect balance, so that the instrument has slight tendency to fall behind or, even better, to
fall forward in its tracking."
==============================================================
I do wonder what is really meant by "...slightly imperfect balance..."?
While the sentiment is respected coming from this astronomy authority, such terms are next to useless in evaluating a given
situation. Given any echanical configuration could be very different from all the rest of our LX200's. But, for any given LX200,
what is the degree of imperfect balance recommended by Mr. Gordon, or any other person on this list who has recommended
some degree of imbalance?
Well, how could the degree of imbalance be stated in quantitative terms that each of us could reproduce with our own systems? I
suppose that Mr. Gordon could have stated the degree of imperfect balance in terms of torque, say 345 gram meters, or 14 inch
pounds. But then we'd need to have some consistent way of measuring this torque.
But why even bother? What is this "west" torque designed to do? The idea that this torque will place a "load" on the RA drive
train so that the gearing is under a "constant" load--a load which keeps the drive gears under some constant force. This will
promote a consistent advance of the RA drive. If this is done, then the guiding process only needs to remove the constant error
rate in the RA drive which is either leading or lagging the local sidereal rate.
Now suppose that you decide to place your LX200 pointing due south so that the forks are aligned in the east-west direction.
Now, suppose that you add some weight to the west fork arm that makes it heavier than the east arm. Well, why do that? You
have already had that done for you! Meade has placed a quite heavy weight on the west fork arm--the declination motor
assembly.
Notice that this weight is exerting the MAXIMUM westerly torque when the fork is aligned along the east--west line. As the fork
turns in RA, either to the west or the east, the declination motor weight moves toward the north-south line, and the moment arm
about which the weight is applying torque to the scope is getting shorter. This means that the force, which was loading up the RA
drive train at the maximum level when the fork was aligned east-west, will decrease steadily as the fork is rotated toward the
north-south line. When the fork becomes aligned with the north-south axis, this force will be reduced to ZERO. At that point, the
benefit of an "imperfectly balanced" mount will VANISH!
Moreover, when ever the scope axis passes through the east-west line, the DIRECTION OF THE IMPERFECT BALANCE TORQUE
WILL NOT JUST CHANGE IN AMOUNT, IT ALSO CHANGES IN DIRECTION! If you work at higher declinations and follow objects
year round, then this happens to you frequently.
It seems to me, that when deviations in RA tracking are critical, it is best to have the RA drive mechanism under consistent,
constant load. This condition can only be realized when the scope is balanced about the polar axis, so that at every RA setting,
there is not any net torque on the scope due to weight distribution.
There may be other variations in actual RA movement, which need to be addressed. These variations may be so large that they
require special attention. But, at least, once the weight of the scope has been balanced around the polar axis, then this source of
RA deviation can be eliminated.
Remember that Mr. Gordon suggested a " ...slightly imperfect balance..." to guarantee that the RA drive train was under load,
and thus would be constrained to work in the 'loaded condition.' This would reduce the effects of loose play in the RA drive train
from Mr. Gordon's view. Perhaps the loaded condition suggested by Mr. Gordon can be found even when the fork is balanced
around the polar axis.
Well, in your LX200, when you are using the GUIDE rates of RA adjustment, and if you ask for an easterly move to correct the RA
track, the scope DOES NOT MOVE EAST IN RA. Instead, the LX200 drive system is slowed down to 1/2 the sidereal rate. This lets
the 'sky' move on to the west, thus the stars run away from the optical axis of the scope. The net result is an 'eastward' apparent
movement.
Because this is the way guiding works on the LX200, the RA drive train is ALWAYS LOADED UP IN THE DIRECTION REQUIRED TO
MOVE THE SCOPE TO THE WEST. It is NOT necessary to unbalance the scope around the polar axis to obtain a continuously
loaded RA drive train.
I do not believe that the RA drive train of the LX200 is completely free of friction. Having inspected the gearing and RA
suspension of this scope, I believe that there is substantial friction in the mechanism when the scope is mounted on a wedge and
polar aligned. This friction is quite sufficient to provide the load that is needed to keep the RA drive up against its mechanical
limits.
What remains to produce deviations in RA tracking is probably mostly related to the main, large, 8 minute gear in the LX200 RA
drive, and the 'worm' gear which drives the 8 minute gear with their individual imperfections.
When the scope is balanced around the polar axis, and my drive hits that really big imperfection on the 8 minute gear (which it
does every 8 minutes), at least the mechanical load due to torque around the polar (RA, that is) axis is consistent--not varying
due to RA position. Well, that's just my opinion, and I could be wrong! If you want to do the right thing.....don't believe me, or
Mr. Gordon, or any of the rest who are readily giving you free advice. Do the following study, and you'll know for sure:
Use a wedge mounted, polar aligned LX200. Use precisely the same scope and mount configuration throughout the study. Do a
careful drift alignment. Get both declination and RA drift down to the smallest possible levels.
1. Take a pleasant drive to your local hobby store that supports the model airplane hobby. There you can buy strips of lead, 6
inches long, with an adhesive backing. The strips are scored very 1/4 inch so you can vary the weight in small amounts.
You'll need just under two pounds.
2. Apply these strips to the arm of your LX200 that is opposite the declination motor. Apply just two or three strips to the arm
itself, and then stack strips thereafter. This will minimize the number of strips you apply to the scope itself. Add enough
weight to allow the scope fork to remain on east-west line without moving. Use weight on the OTA, aligned with the optical
axis, to balance when the scope is pointed due east and west. Check that the scope doesn't rotate in RA when placed in
any arbitrary RA position.
3. Take one night to work on training the LX200 Periodic Error correction system. Do this slowly and carefully. Repeat the
training process at least 8 times. Use your highest magnification possible with an illuminated and graduated reticule
eyepiece. I use a 2x or 3x barlow with the Meade 9mm illuminated eyepiece. Remember to work with stars that are near
the celestial equator, and about one hour before crossing your local meridian (due south).
4. Establish some method of observing a star and noting the RA deviations at periodic intervals, say every 5 minutes for an
extended period, say all night. Just let the scope "free-run". You'll nee a good drift alignment and PEC training session to
make this possible. Plot these deviations for the initial "balanced telescope" night. Make sure you work from far easterly RA
over far into the westerly RA. A set of CCD images works best for this purpose to get accurate and consistent
measurements of RA deviation.
5. Add one pound of lead weight to the 'east' arm of your scope and repeat step 3.
6. Shift the added one pound of lead weight used in step 4 to the 'west' arm of your scope and repeat step 3.
An eye-ball inspection of the results plotted together on the same graph should answer the question for you, for once and for all.
If you really want a surprise....repeat this study at a declination of around 60 degrees. Use stars that are about 7 hours east of
your local sidereal time, or 5 hours west. This will show you the effect of the CHANGE IN DIRECTION of the load torque as the
fork moves thru the north- south line.
So, you can see that this is a lot of work... Ask who has done this study, if its not worth it to do it for yourself. I have not done
precisely this study myself. But I've done portions of the procedure, and the results have convinced me to work with a balanced
fork on my LX200 when mounted in the polar aligned mode.
Subject: Fork Weights & Tracking --part 1 of 2
From: William Murray
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From: <jon
hpcvlx.cv.hp.com>
I've noticed that my wedge mounted 12" LX200 lists to west. This happens
even when the tube is balanced in declination, and is in fact independent
of declination setting. By "west list" I mean that when the RA axis is
un-clutched the scope tries to rotate such that the heavy fork arm (the one
with the dec motors) ends up on the bottom.
I'm considering gluing/nailing/bolting a weight into the light fork arm.
Anybody have a design that they like? (Or do you all think I should worry
about real issues?) I would like things to stay put when un-clutched.
Jon -I use a set of exercise wrist weights I got at a sporting goods store on my 10" LX200. These things come with a set of 1/2
pound ingots so that you can vary the weight from 1/2 to 5 pounds total. They come with a covering that is meant to wrap
around your wrist (or ankle) and secure with velcro. I just vary the weight as needed and wrap them around the fork arm near
the handle, they are very secure and do not slip.
Since I do a lot of astrophotography I try to adjust the total weight so that the scope falls slowly to the west through the
meridian. This allows the motor to control the fall of the scope instead of having to push it around. I find that this is a better
solution than having the scope perfectly balanced.
---------------------------------------------------------------------------------------------------------------Subject: Fork Weights & Tracking --part 2 of 2
From: William Murray
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Bill and Ric,
Both of you are advocating letting the motor "guide the fall" rather than
push. Sorry about further MAPUG time on this but am very curious why
you've chosen to go this way. Aren't there thrust bearings and the like
in the RA motor assembly that would be happier pushing? This would
speak to over weighting in the other direction wouldn't it?
Jon -I'm not sure what the internal workings of the RA motor assembly on LX200 scopes are but the idea of letting the motor
"guide the fall" is old astrophotography wisdom. In his book "Astrophotography", page 74-5 Barry Gordon states:
"Balance is a problem when heavy telescopes sit atop tilted- over-to-one-side mountings. Hanging a significant weight in
eccentric fashion results in that weight trying to occupy the lowest position available. It is our wish, however, that it will tend to
remain exactly where we place it. This requires careful balancing of the equipment about each active axis - that is the polar axis
and the declination axis - ignoring any now-locked axes used only for initial polar alignment. While balancing is often provided for
in the telescope's design, it may also require attaching additional weight. Whatever the method, balancing must be done,
particularly if the equipment is to be driven mechanically. To make matters worse, the job cannot be done once and for all; it
must be redone when a camera is added or removed or even shifted from one location to another. Fortunately, this is a simple
chore. Note that, for the polar axis, perfect balance is NOT what we want. If we achieved such balance, then any play in our right
ascension tracking mechanism would allow the instrument to wander back and forth between the limits of that play. We are
generally better off with slightly imperfect balance, so that the instrument has slight tendency to fall behind or, even better, to
fall forward in its tracking."
I have a tendency to hang a lot of equipment on my 10", ( I mount a 5.5" Celestron Schmidt camera on top for wide field
astrophotography. ) this increases the scope's tendency to fall forward rapidly. I use about 2 to 3 pounds of counterweights on
the eastern fork arm to reduce the rate of fall. To make the scope fall behind would require more weight than I care to hang on it.
I have gotten very good results with my setup.
Subject: One-Star Alignment for Wedge-Mounted LX200 Classics
By: Robin Casady
To do a one-star alignment:
If your wedge is polar aligned, you can do a one star alignment on any object in the LX200 catalog. The accuracy of subsequent
GoTos will depend on the accuracy of your polar alignment of the wedge. For visual observing, a precise alignment is not
necessary.
1.
2.
3.
4.
Make sure the keypad is set to Polar.
Do a keypad GoTo of an object in the sky.
Align the telescope on that object with the NEWS keys or by loosening the clutches and hand slewing.
When the object is aligned, press and hold the ENTER key until it beeps and says coordinates matched.
Subject: Aligning the Classic -- Polaris is Visible -- 2nd Alignment Star Isn't
From: Ralph Pass <rppass
mediaone.net> Date: July, 2000
Just press Enter, select a visible star, press GoTo, use the keypad buttons to center, and then press and hold enter until it beeps.
I am of the opinion that using Polaris and the same star does not converge as fast as it could. I use this technique to alternate
the 'second' star to get better convergence.
You should be aware that there are two conditions where the alignment technique has a problem. The first is when the selected
second star is around RA 2h 30m (the technique can converge to an arbitrary solution). The second is when the selected second
star is around 14h 30m (where the technique can oscillate and never converge). Each of this is due to the geometry of the stars
and not the alignment technique. The solution is very simple. Do as suggested above. Simply press enter and then go to a star
away from these bad RAs, center, and sync.
Subject: Polar alignment When Polaris is not Visible --part 1 of 3
From: John Mahony <jmmahony
hotmail.com> Date: Mar 2003
Syncing the second star only synchronizes for that area of the sky and doesn't improve the overall alignment. For visual work,
AltAz is better. Besides saving a little set-up time and effort, when using the polar method, the computer assumes the mount is
accurately polar aligned and doesn't try to compensate for errors.
For long exposure imaging (polar required) when you can't see the north star, there's a (probably very old) method that will get
you very close quickly. Since you already have the latitude pretty close, you can simplify this even more:
1. Aim at a star near the intersection of the meridian and the celestial equator. Sync on this star.
2. Now go to a star that's either far to the east or far to the west, and still roughly near the equator. Use the keypad to
"GoTo" this star. Check the error. If the star is in the western sky and the scope aimed too far north, that means your
wedge azimuth is too far east. Similarly if the scope missed to the south, the wedge azimuth is off to the west. Reverse all
this if the star is in the east.
The amount of wedge azimuth error is roughly the same as the north/south pointing error for this star. This all assumes the
latitude is accurate.
------------------------------------------------------------------------------Subject: Polar Alignment -- Polaris Is Not Visible --part 2 of 3
From: Keith <keithnk
prodigy.net>
-------- Original Message ---------Within the next few weeks, my school's robotic observatory will be installed (LX200 10" classic in a Robodome) at its
rooftop location. Due to the nature of the location, the view to the north is blocked. This probably means that I
won't be able to align the 'scope on its meridian using the Pole Star.
---------------------------------If you're just trying to get a better idea of where north is compared to what a compass will give you, here's a method I'll use to
get me quite close.
If you have an astronomy program like TheSky, or something similar, then - assuming you have it set up for your longitude and
latitude and the program clock is correct - check out the minute or even the second when the sun will be due south. Then look at
the shadow of a vertical pole up in your observatory at that minute or second. The shadow will point due north. If you set it up
right, you can get the shadow to fall across the center of your telescope and onto the opposite wall. You can mark the opposite
wall (or note a landmark) where the due north spot is. You can surprisingly close just standing in front of your telescope and at
the appointed time when your shadow is pointing straight at the center of your wedge or scope, taking note of a landmark or spot
that is straight away to the north. This is not nearly as accurate as a tall vertical pole's shadow, but may be close enough to give
you an idea. If you miss that time, you can also check when it's due east or west to find that line, and then can work off it. This
should get you close enough so that the methods also located here on this Archive page should enable you to be able to easily
dial it in the rest of the way.
------------------------------------------------------------Subject: Polar Alignment -- Polaris Not Visible --part 3 of 3
From: Michael Gerszewski <mgerszew
antaressol.com>
I am assuming that you have a wedge, and that you are attempting to do polar alignment. There are several good resources and
methods that have already been mentioned. I am also assuming that with a RoboDome, you will be using a CCD. Here is a link
for a nice CCD method that I found a couple of years back: <www.ucihs.uci.edu/pandb/hall/polar.htm>
I used this method with a 16" LX200, and it worked quite well. I think it will be useful to you, especially with a RoboDome. You'll
probably want to use a drift method of some sort, especially with a permanently mounted scope, and are probably forced to
because of your inability to use Polaris as a first-order starting point.
For a first-order starting point, you'll probably have to use magnetic north, corrected to offset, for your azimuth, and your
latitude for altitude. Remember to iterate between meridian and horizon when doing your drift align to increase your accuracy.
Just a warning with a RoboDome and a 10" scope w/CCD. Watch the CCD with your system set up in equatorial. If you add any
extra accessories (focal reducer, adaptive optics, filter wheel, motorized crayford focuser, etc.) the CCD may get dangerously
close to brushing the wall of the dome, possibly binding the scope. I know they say it will fit, but it can be a pretty tight fit (at
least with a RoboDome I had some experience with a couple years ago)
Subject: How Close is "Close Enough" OTA Alignment?
From: Joe Diregolo <JOE.DiREGOLO
kla-tencor.com> Date: Aug 2000
-----Original Message----From: Gregory Pyros <gpyros
home.com>
Thanks to the MAPUG Topical Archives, after I first brought the scope (classic) home and had alignment problems
with it, I returned it to Meade for an adjustment. What happened was that when I polar aligned the scope on the
SuperWedge with everything turned off, and did a 360 in RA, I would get a nice tight little circle of Polaris, but it was
nowhere near the center of the 26mm eyepiece. Imagine drawing a 3" diameter circle on a piece of paper, then
drawing a 1" circle just about touching the outer edge of the first circle. Meade agreed that it was an OTA alignment
problem, and adjusted it.
Now I have it back, and trying the same test, the two circles are perfectly concentric, but if the full 26mm eyepiece
is a 3" circle, Polaris will, at best adjustment, form a 2" circle within it. So there is no setting where I am perfectly
aligned that I can have Polaris in the center of my eyepiece, and not even in the field of view of the 9mm illuminated
reticle.
For visual observing it would probably be fine, but my goal is to do CCD photography, and I'm sure I will have
enough problems there without worrying about mechanical scope alignment causing tracking problems!
-----End Original Message----Answer to question:
I noticed the same problem with my scope. But to check it requires that you point the scope to a fixed object. You are correct in
using Polaris since it is close enough to the celestial pole that it move so slow that it would not effect your test. What you are
seeing is the mismatch of the Optical axis and the RA axis. Meade seems to do a good job getting RA and DEC axis orthogonal.
But they fail to get the all three axis's to intersect each other at the same point in space.
If the error is large enough one would see dec drifting even after perfect drift polar alignment.
There is another test that you can perform that will show what direction the error is. Rotating about any fixed object at least 100
feet away and adjust the dec to 90 deg or to the exact location that you achieved the smallest orbit of the object.
Without moving the dec axis point the scope at a diffuse light source. (A florescent fixture should work fine). Remove the cover at
the bottom of the fork arm. This will expose the upper RA bearing. Using a 12.5mm or smaller eye piece project the light on to
the screw and washer holding the RA bearing. Adjust the focus so that the light circle is slightly larger that the screw. If the light
is centered then its as good as it going to get. If not then one of two thing are still out of alignment. If its off in the Fork direction
it indicates that the OTA is not centered between the forks.
If its off in the other direction this indicates that the forks are tilted and that the dec axis does not intersect the RA axis.
Now how to fix this error...
If the error is in the fork arm direction one could theoretically add different size trust washers to the dec assembly to offset the
OTA until it is concentric with the RA axis.
I would be very interested in knowing if anyone has done this adjustment. I would like to know about it because this is exact
error I have with my scope. I'm off center about 1/4" in the fork direction. Still I get good tracking of unguided CCD images for
about 5 min.
If the error is in other direction this would indicate that both forks arms are tilted and would need to be adjusted. This adjustment
can be found at OTA Alignment here in the Mapug Topical Archives.
Subject: Polar 'GoTo' Adjustment Web Page
From: Bruce Johnston Date: May 2002
I've completed a write-up on analyzing problems with Polar 'GoTo' operations. Hopefully, it will help people to find more of what's
wrong when their 'GoTo' is off, and some ways of adjusting things accordingly. It's written with the LX200 in mind, but it actually
applies to pretty much any 'GoTo' scope.
Also, inside the info, is a new method of Polar aligning that I've found to be very accurate, and much, much faster than drift
aligning. Just go to: <www.mapug-astronomy.net/ccdastro/goto-tests.htm> Note: should open a new browser window.
MAPUG is hosted by
PEC--Periodic Error Correction
"Smart Drive"
How PEC Works
PEC "Smart Drive"-- Training --7 parts
PEC Questions for the Beginner
More PEC Questions & Answers
PEC Training -- Stored? Update Often?
Keypad and PEC Training Trick
RA Tracking by the LX200 (Analysis)
PEC Training Experiences
PEC and Long-Term RA Drift Solution
Polar Alignment and PEC Accuracy?
First Pass PEC Graphs After Cleaning
PEC Training w/CCD Camera
PEC Training w/CCD URL
PEC Training Best with an Autoguider or Manually?
Refining PEC Finally Pays Off
PEC Training on Different Teeth?
PEC Training & Elongated Images
PEC--New Use
PEC Problem Caused by RA Worm Damage
PEC Programming as Related to Drift Alignment
Difference Between Periodic & Pointing Errors
PEC Training -- Constructing a Guiding Keypad
Dec Blocking Autoguiding Device
Effective Use of PEC with an Autoguider
Smart Drive (PEC) Quantitative Info
Guide Correction Speeds? --3 parts
CCDWare Releases PEMPro, learns mount's PE to create perfectly tracked exposures w/o an autoguider
Subject: How PEC Works
From: Bruce Johnson Date: Sep 2001
<dateach
va.prestige.net> writes:
<< My question is this: How does the scope know where in the 8 minute cycle to
start the script? I mean suppose it starts the script when turned on, with
the first correction, say, at the 2 minute point. But suppose the first
error doesn't occur until 3 minutes? How do it know? >>
Tom, It's quite easy to understand..... once you know the secret! There is a small magnet mounted on the RA worm shaft, and a
sensor right next to it, mounted permanently. When you turn the scope on, one of the things it does.. in Polar mode.. is to go
forward to detect the magnet, then back up a bit, then approach it again slowly. When it detects it that second time, it is in sync
with the stored buttons and when they were pushed.
Likewise, when you train the scope, the actual training session begins just as the magnet is sensed, and continues for the eight
minutes you already know about.
The idea is pretty good, but at this moment, I am not completely sure just how well the magnet sensing is, timewise. I mean, it
seems possible that the sensor might detect the magnet, say, 100 ms later, the next time you turn the scope on. If that
happened to be the case, then your PEC training would be out by 100 ms for the night. Overall, that wouldn't make much
difference for the grand sine wave of the periodic error of the worm, but it could definitely throw your 'quickie tweats" out of step,
and you could end up with a significantly different PEC on one neight to the next with nothing else having changed.
This is something I haven't confirmed that happens as yet, but I have reason to be suspicious along these lines. Anyway, that's
how PEC timing is detected.
Subject: PEC (Smart Drive) Training --part 1 of 7
From: Fred Park
Observations:
1. Daytime work. With the clutch off, turn on your LX200 and go to the PEC (Smart Drive). Do an erase. Go to the RA and DEC
readout. Check the time on your watch and record time and the RA. Let the system run for about three hours and each hour
record the RA. Note that the is little or no change in RA. I got four second drift in three hours.
2. Nighttime work. Do a Periodic Error Correction (in Smart Drive) using Learn only. Now repeat #1. I got a drift East of one
minute in three hours.
3. Conclusion: When doing a PEC, if you don't correct the same for West errors as for East errors you will introduce a long term
drift which is undesirable for astrophotography.
Method of observation: Setting up as in #1, I logged the time every time the RA would change. The cycle of correction could be
observed and the repeatability of the gear could be observed. I was bothered when I saw a gradual drift in the RA, and I'm still
not sure what to do about it. Question: Am I nit-picking or is this a problem? More work: See how update effects the RA.
---------------------------------------------------------Subject: PEC (Smart Drive) Training (a method) --part 2
From: Doc G
Richard G. Davis posted on MAPUG a note on PEC training giving his error curve. On 7 July Fred Park discussed the fact that PEC
training can introduce long term errors in the RA rate.
In this note I discuss a training method which should allow for training of the worm which avoids the introduction of long term RA
error. Note that this technique does not account for the possibility or even probability that the RA gear has periodic irregularities
in addition to those introduced by the worm defects.
The technique is as follows and is based on the need to establish the correct baseline against which to make worm error
corrections.
First take data similar to that shown by Davis over one whole period of the worm (8 minutes). It might be wise to take several
cycles to get an nice average curve. Then plot the curve and integrate over the entire curve for one period.
That is add up all of the positive errors and add up all the negative errors and subtract the two numbers. Then divide the
difference by the total number of data points. This number is the current bias setting of your crosshair. Now correct the position
of the crosshair by the amount of this bias (positive or negative as the case may be) and call that the correct (zero) position.
Now train the worm using the PEC technique by making the telescope point as accurately as possible to the zero reference. This
training method should reduce the wobble without introducing a long term bias in the RA rate.
PS: Note that this technique is similar to that used to balance an operational amplifier using integrating feedback. This last
comment is for all those Electrical Engineers out there.
----------------------------------------------------------------------
Subject: PEC (Smart Drive) Training: Some Conjectures --part 3
From: Richard Davis <richdave
ma.ultranet.com>
Some comments on this subject:
WHAT YOU GET WITH PEC (Smart Drive) TRAINING
Fred Parks has confirmed my findings reported earlier. The RA tracking curve data which I reported in a graphical plot of
telescope position against a constant object position, a star, did not show any appreciable long term RA drift. Those data were
obtained with UNTRAINED RA tracking, that is, the PEC (Smart Drive) was NOT operational.
In that report, after training the telescope carefully, a constant RA drift of about .6 arcsec/minute was observed with the PEC
(Smart Drive) TURNED ON. That residual drift is surely the result of "DC" bias introduced by the RA training work that I did.
Conclusion: If you work real hard on PEC (Smart Drive) training, you can greatly reduce the VARIANCE in RA tracking due to the
WORM gear to less than 3 arcsec. However, a constant small RA drift rate is likely.
You can "guide" out the small, CONSTANT RA drift error, easily enough, if you have some way of guiding during exposure.
However, the persistent variance of RA tracking of some 2 to 3 arcsec has a cycle time of around 20 seconds. Autoguiders must
have a correction cycle time of at MOST 5 seconds to have any chance of reducing that inherent, TRAINED PEC (Smart Drive)
variability. You need bright stars, short CCD guider exposures, fast image analysis times and short correction times to make that
work for CCD guiders. ...or, you must use visual guiding that is continuous! Or, use a scope configuration which gives 3 to 6
arcsec per CCD pixel image scale so that the RA variability is smaller than the pixels in the camera.
===========================================
"AVERAGING" OVER MULTIPLE TRAINING SESSIONS OF THE PEC (Smart Drive): "NOT"
My suspicion is that there is NOT any arithmetic averaging of successive sessions of the PEC (Smart Drive) training! Of course,
MEADE appears to be silent on this issue. (And, why should they speak up? We'd just use the information to beat them up for not
giving us a professional grade machine for junkyard prices! Of course, has QUALITY at the MEADE LX200 price point been
maximized? Hmmmm... Read on.)
My speculation of how this works is as follows:
The data retained in the PEC (Smart Drive) memory is probably as simple and compact as it can possibly be. If so, then all that is
recorded during a PEC (Smart Drive) training session are the RELATIVE TIMES, measured from the beginning of the training
session, when one of just three possible events has occurred. These events are: (1) go EAST at GUIDE speed (EAST button
press), (2) go WEST at GUIDE speed (WEST button press), (3) STOP moving at GUIDE speed (release of either EAST or WEST
button).
After one training session, there is just such a list of commands in memory which is an exact record of your EAST and WEST
button presses.
Now, when you return to UPDATE the PEC (Smart Drive), the button presses you now make on the second pass are merely
inserted into the list of previously recorded presses. The only "averaging" that occurs is what you do visually by noting the
performance of the PEC (Smart Drive) on the second training session, and superimposing on that performance additional EAST/
WEST corrections.
Have you ever noticed that while training the PEC (Smart Drive) in an UPDATE session that there are times when you need an
EAST correction, you press the EAST button and there isn't any response? ...for a while. ...and as you continue to hold down the
EAST button, at some point, a correction eventually begins to occur?
What happened, I suspect, is that the PEC (Smart Drive) was already in an EAST correction command from the previous session
when you started pressing the EAST button. Therefore, no response is possible. The EAST moving rate is already at its maximum.
Eventually, the current EAST command terminated, the computer checked the EAST and WEST buttons, found that the EAST
button was pressed, and initiated an new EAST move. Then, you would see the newly commanded EAST move. You can
determine when this occurs because, if the PEC (Smart Drive) is in an EAST command state, the RA drive has been STOPPED. It
will be silent! And, as you command the EAST move, the scope can't go east any faster than it already is--that rate is determined
by the rotation of the EARTH!!
Likewise, any WEST commands issued by you while in an update session may appear within the intervals of previous WEST
commands. And, likewise, the effects of these new WEST commands can't be processed until the pending WEST command
terminates. Even if the command in progress were terminated, the rate of WEST correction wouldn't be increased above the
GUIDE rate!
(I will not continue here to consider the cases where the current PEC (Smart Drive) command is in one direction, and you press
the opposite direction button. This message is already long enough. Try it for yourself.)
Now, for the inevitable steady RA drift AFTER lots of PEC (Smart Drive) training:
Notice that the mechanical problem for going EAST and for going WEST at guide speed ARE NOT SYMMETRICAL in a mechanical
sense. The EAST corrections involve stopping the RA drive motor and gear train. The WEST corrections involve speeding up the
RA drive motor and gear train. Due to the inherent "coast" of the drive mechanism, I suspect that the EAST correction cycles are
not going to have exactly the same amount of "zero-length" cycle effects as the "zero-length" corrections in the WEST direction
will have.
I believe that the well trained LX200 PEC (Smart Drive) will always have some small, relatively constant RA drift attributable to
the mechanical asymmetry of the RA drive resulting from stopping it in the EAST direction and speeding it up in the WEST
direction. The residual RA drift should be in the same direction for all LX200's, I suspect, and generally all scopes should have
about the same amount of residual RA drift. My best estimate of that is about 0.6 arcsec per minute.
Remember, the net RA drift over three hours is near zero. Fred Parks reported this observation, and my data also showed this to
be true. Then, after RA training, careful RA training, repeated RA training, the drift emerges. Some part of that is probably due to
the correction process itself.
Well, this little analysis is all speculation based on my experience and studies of my LX200. I may be wrong.
-----------------------------------------------------------------------------Subject: PEC (Smart Drive) and Training --part 4
From: Ralph Pass <rppass
rppass.com>
I am not associated with Meade (other than being a satisfied user of their telescopes and a frustrated user of their CCDs). The
information I am providing is my best understanding of what is happening with PEC and training. It does reflect several
conversations with Meade over the years.
First, the RA motor is being driven by 45 pulses per second. Pulses are counted to provide the pointing location (this is why it is
more precise than typical amateur encoders).
Second, the period of the worm gear is eight minutes plus or minus a bit.
Third, Meade has divided this eight minute period into 100 subdivision. Each subdivision in 2.4 seconds long.
Fourth, PEC correction is accomplished by changing the number of pulses per second and is constant during each 2.4 time period
(although it may be different for each subdivision).
Fifth, during training PEC is off.
Sixth, the one hundred adjustments to the pulse rate are store in the LX200.
Seventh, as training progresses the net adjustment to the average pulse rate in each 2.4 second period is stored (learn mode)
or averaged with the existing value (update mode).
Eight, in the x.34 version of the ROM (and perhaps in the x.30 version as well my aging memory is failing me), there is a five
digit number my the SMART entry on the keypad. This number is normally about 21600 ( = 8 minutes * 60 seconds * 45 pulses
per second).
Ninth, deviations from 21600 counts may or may not reflect 'RA' creep in time. This reflects creep and the difference between
crystal frequency and true sidereal time.
Tenth, training at one temperature (e.g., winter) and using at another temperature (e.g., summer) will change the crystal
frequency and hence the apparent creep of the telescope.
Eleventh, any variation induced by the large gear may degrade the accuracy of the tracking (including PEC).
This summarized some of what I know about PEC and training.
Other comments:
What is clear is that if there are significant drive deviations over time periods less than 2.4 seconds, the current implementation
of PEC will not correct for this. I try to return my scope to a 0 HA at the end of the evening to use the same area of the drive
gear each evening. I have provided this information to help people understand the operation of their scopes. I think that
clarification of this information is appropriate follow-up. I do not think that criticism of Meade design choices is appropriate followup. The magic number '21600' is the nominal value. The actual value shown is the number of pulses sent to the RA drive motor
with the current PEC correct applied. Deviations from 21600 reflect RA creep or variations from the nominal crystal frequency.
For the training I have, it is 21575. Mine ranges from 21550 to 21597. I have never seen either of my scopes exceed 21600. I
have not regularly gotten the number above 21590.
------------------------------------------------------------------Subject: More PEC (Smart Drive) Speculation --part 5
From: Doc G
Additional thoughts on RA motions.
I have read very carefully the many posts on the topic of RA motion and correction of the rate in Meade telescopes. First let me
say that my experience with guiding has been very good. I am pleased with the training of the worm drive and the good short
term corrections that can be obtained.
The many posts have been very informative and well thought out I think. I hope to make a few points about all these matters
that may have been lost in the large traffic in the last few days. I am starting with the assumption that the need for accurate
motion of the telescope is driven mainly by the needs of imaging. This implies that accurate motion over periods of an hour would
be generally adequate. To get accurate guiding, one must guide manually or with an appropriate CCD guider. A guider will
certainly make enough corrections to take care of motions over the longer periods of several minutes. The really important
question, it seems to me, is "can the CCD guider work fast enough to smooth out the short term wobbles." These short term
wobbles are in the range as short as a second or a few seconds and of amplitude in the range of a few arc seconds.
If the above situation is correct, then we need to be concerned with two sorts of imprecision in the guide rate. One is due to the
imperfections in the worm and the second is due to imperfections in the main RA gear. Since the worm turns once per 8 minutes,
it rotates 180 times in 24 hours and thus the main RA gear has 180 teeth. We must face the fact that this is one-half the number
of teeth in a precision drive such as those from Byer or Losmandy. (at half the cost of course) Nevertheless, a four minute worm
with 360 teeth is inherently more precise. This is not a criticism of the LX200 design but a statement of fact. The LX200 is
amazingly accurate in its pointing capability and RA drive stability for a modestly priced mechanism.
A major question, which we are near answering, is the relative importance of the worm and the gear defects. I have observed
many cycles of the worm in my LX200 12" and feel there is a very strong repetition of the shape of the periodicity at 8 minute
intervals. This means that the principle defects are in the worm and not the RA gear. (Though there are certainly some defects in
the RA gear as well.) This situation is very encouraging since it means that the 8 minute training of the worm will eliminate most
of the rate variations. I and others have found this to be the case.
Thus I feel that users should concentrate on doing a good job of training the worm using the recommended techniques and not
worry about long term drift that this method might introduce. Such long term drift is very small and has essentially no effect
during practical exposure lengths. (Anyway it is easily correct by the guider.)
The question still to be answered is how quickly a CCD guider can correct even a well trained worm.
I think that a bright star cycles the imager more quickly and results in more frequent corrections to the drive. Continued study of
the quickness of the corrections and the effect these corrections actually have on the drive motor rate and in what length
intervals is still needed.
At the present time, corrections seem to take place at intervals of 5 to 10 seconds. Possibly under computer control of the imager
and the telescope together, software could be devised to decrease the interval between these corrections.
-----------------------------------------------------------------------
Subject: Summary of PEC (Smart Drive) Operation --part 6
From: Doc G
Summary of some issues regarding the Meade drive systems.
>From the many posts on LX200 drives, I have gleaned some design information which seems to me to fit together and make
good engineering sense. I have designed similar system over the past many years and feel it is time to try to come to closure on
some of the issues that have run on over the past month. I believe the following descriptions are reasonably accurate.
First, the drives are closed loop control systems from the control electronics through to the motors. The motors are connected to
the actual main drive axes through a set of gears and a worm. The main shafts are not inside the control loop but are extensions,
through the gears, of the positions of the drive motors.
One source of slack or looseness in the drive systems is then any lash in the gear trains between the motors and the main shafts.
Any defects in the gear train or looseness cannot be fixed simply through control of the motors since it is out of the loop.
However backlash in the gear train can be compensated for to some extent with the backlash setting provided by the design.
Additionally some of the most dominant errors in the worm drive can be fixed by the PEC (Smart Drive) training technique.
To keep absolute track of the position of the telescope, the number of turns of the motor shaft must be known and kept track of
by a counting mechanism. I believe this is accomplished as follows: The motor has an optical transducer on the shaft which sends
to the control electronics a series of pulses which the electronics counts and compares to a computer generated number. The
number of counts tells the computer where the telescope is and the computer drives the motor to force the number of counts
sent by the motor to the number it knows is correct.
Counts are generated by a disk with 90 slots and two photoelectric pickups. The reason there are two pickups is so that there is
no ambiguity about the number or direction of the count generated by the motor. With only one pickup it is possible to have false
pulses generated and the direction of the encoder disk cannot be determined. With two transducers very slightly offset, the
transitions from the transducers will generate a two or four pulse code that gives both the number of counts and weather the
count is going up or down. This a simple type of Gray code. (I will not go into coding for unique output here. Too complicated for
this discussion.) Thus the 11.25 slots per second that the motor shaft moves at the normal RA drive rate yields 4 time as many
pulses to the control circuit or 45 pulses per second. (Both of these numbers have been reported in posts.)
Now the computer generates 45 pulses per second and the computer pulses and motor pulses are counted in an up/down
counter. When the motor gets behind the computer applies, through pulse width modulation, more current to the motor and
speeds it up. The computer demands that the motor follow. Sort of like the computer puts 'em in and the motor must take 'em
out. (Or vice-versa for the other direction) When the number is 0 the motor stops.
Then once the telescope is synchronized with a known position, it moves the telescope to a new position by simply demanding a
calculated number of counts from the RA And Dec. motors. This is a very simple, inexpensive and accurate method of positioning
a mechanism.
It has been reported that one slot movement corresponds to 1.3333 arc seconds of motion and that there are 11.25 slot moves
per second for the normal RA drive rate. Meade states that the position is accurate to 0.333 arc seconds. This is a factor of four
and corresponds to the supposition above that one slot motion generates 4 pulses just as expected from the transducer scheme
described above.
It is certainly not difficult for the computer to generate the required differential position distances in the form of RA And Dec
motions or for that matter Alt. and Az motions in the form of a pulse count.
Now consider the more subtle issue of correcting the backlash in the drives. The correction number is entered by the user by
selecting it manually. The computer simply remembers to add or subtract this number to the appropriate move command. Thus
the seemingly difficult backlash correction is taken care of easily by the computer through the same drive counting mechanism.
How about the correction for the irregularities in the worm gear. This correction is entered by the user in the form of E and W
pushes of the direction keys on the keypad. The computer knows exactly the position of the worm gear. For an 8 minute period,
one turn of the gear, a total of 200 corrections are entered. This is one correction for each 2.4 seconds. At the nominal R. A. rate
for example the computer demands 45 pulses per second or 108 pulses in a period of 2.4 seconds. Pushing the E key stops the
motor for the pushed period. This action must subtract pulses from the number demanded by the computer for that period. Also,
pushing the W key doubles the speed of the drive. So this action must add to the number of pulses demanded by the computer in
the period in question.
I cannot address the precise algorithm used to add or subtract pulses in the computer for the 200 periods. It could be on/off or a
proportional number depending upon the length of the key press or the key actions might be tallied and averaged in some way.
The details of the algorithm would be interesting to know, but it is not an issue of principle concern here. It is sufficient to know
that Meade has provided a very nice scheme for correcting the worm drive rate in 200 increments per revolution and that the
user can train the worm through setting up the PEC (Smart Drive) mechanism with great accuracy.
Many experiments can be done to ferret out the exact counting algorithm but I think it will be a difficult task. If someone has
figured it out with certainly, I would certainly like to know. I am satisfied at this point to feel I understand the basic system and
to simply train the worm as well as I can.
A way to determine the exact pulse train structure would be to use a logic analyzer and print out the entire pulse train. This
would be 45 pulses per second for a total of 8 minutes. (21,600 pulses) Clumsy but not impossible to do.
It has been reported that the total number of pulses deviates from the number 21,600 for one turn of the worm. I do not
understand how this can be the case since the number is determined by a gear train which can be calculated exactly. I suspect
that the worm rotation is not being measured accurately or some other systematic error is creeping in. This must be checked.
Sixty pulses represents 1 degree of worm notion. Alternately, the training routine might be introducing a systematic drift. This
phenomenon has also been reported.
Update:
Subject: PEC/Smart Drive --part 7 of 7
From: Doc G
But here is my impression of how it works. There is a sensor on the worm which is the start of the PEC process. I believe this is
the correct way to do the PEC thing. (Meade never tells how to do it, unfortunately)
Turn on the scope and Erase the PEC. Then go into learn mode and watch the display until it gets near 0. This may take up to 8
minutes. When it gets near zero it will beep. Then start guiding as fast as possible, about every 2 seconds for as long as the thing
beeps. It will beep 200 times or 8 minutes which is one turn of the worm. That should do it.
Then if you want to refine the PEC you go into update mode and do the same thing all over again. After three times, you have a
well trained worm. (Or you fall in the floor with serious eyestrain) I got my wobble from about 50 arc seconds down to 3 arc
seconds with three cycles.
Subject: PEC Questions from a Beginner
From: Ralph Pass <rppass
rppass.com> Date: May 2002
Dave Schanz wrote:
> I am just starting to work with PEC training as I get closer to doing some
> film work. I need help for the beginner.
>
> I started out with a very good polar and drift alignment. I was
> using a 12mm illuminated reticle on my 10" LX200 f/10 classic. I realize I
> might want to jack up the magnification, but for my first attempt at PEC
> training I wanted to keep things as simple as possible. The star I used was
> almost directly overhead and about 5 degrees west of the meridian.
>
> My questions are:
> What is the significance of the "pulse count" figure that shows on the
> display after training is complete? My first training ended with a pulse
> count of 21611 and I read in the archives that number is low (but no
> explanation is offered). After an update, the pulse count was 21597.
> However, I don't know what a good pulse count range should be and I don't
> know why mine were that low.
>
> During training my RA drift was very minimal and I was very careful to keep
> the star centered on one of the crosshair intersections. During the first 8
> minute cycle, there were several times when no corrections were required for
> periods of 10-15 seconds. Most corrections that had to be made were minor
> and to the west. DEC drift was also minimal, requiring perhaps 2-3 quick
> corrections to the north in total. Several articles in the archives mention
> making 2-3 corrections per second - which is way more than was necessary
> during my training. Is my initial experience of not having to make a lot of
> corrections indicative of anything in particular?
>
>
>
>
>
>
>
>
It did occur to me after I was done that perhaps the reason I didn't need a
lot of corrections was because of the relatively low magnification I used during training.
Was my choice of a star near the zenith a contributing factor to the
relatively infrequent RA corrections?
My last question (for now) is perhaps a really stupid one -- once I have done
PEC training, will the scope always use that training from now on -- until I erase it?
1. Stars closer to the equator are better. The error effect is reduced by the cosine of the declination of the star (so at 40N it is
reduced to about three quarters of what it is at the celestial equator). This is great for tracking but makes you need to be
that much more sensitive and careful in your training.
2. NEVER adjust in DEC while training RA. There can be a wobble in RA due to Dec motion. This would cause a correction for
a phantom RA error.
3. The motor is driven by 45 pulse per second. The cycle on the drive worm is 8 minutes. This leads to an expected total
number of pulses of 45 * 60 * 8 or 21600. Variations from this are due primarily to small frequency differences from the
nominal value. These vary with temperature. However, the PEC training is tied to the position of the drive worm and, once
done, is not affected by temperature (so you can train the summer and use in the winter.
4. RA training is remembered from power off to power on, DEC training is not.
5. More power helps
Subject: More PEC Questions & Answers
From: John Mahony. Date: July 2005
>
>
>
>
>
From: Keith
I'd like to ask further about.
1. John M wrote "In the end, the PEC count should be around
21600 when you finish." What does this mean, how is it
useful, and where do you get or find this count?
The encoder wheel has 360 slots, and rotates once every 8 seconds, so there are 45 tics/sec. A PEC training session runs for one
cycle of the worm, =8 minutes=480 seconds. So the total number of tics in the training cycle is nominally 480X45=21600. This
number is displayed on the keypad somewhere in the PEC training process. When you train, if there is something causing longterm drift (gear eccentricity, etc), you'll press one of the E/W bottons more than the other, so after being trained, the scope will
expect to see a total number of tics/8minute cycle that's more or less than 21600.
It's been awhile since I looked at this on our scope, but I think a good accuracy is if you're within a couple dozen tics of 21600. If
you're off by a few hundred, you'll want to do something about it. Long-term drift from fork flex or atmospheric refraction can be
minimized by training on a star near the meridian.
Main-gear eccentricity causes one part of the gear to be too close to the axis, and the opposite part to be too far, so the scope
will appear to run fast when using the first part, and slow at the opposite point, with good speed at the points half way between.
A way to find the good part of the gear is to aim at a star on the meridian with a crosshair EP, let the scope run for 8 minutes,
then check to see if the scope has run fast or slow. Then move the scope 2 hours west (30 degrees along the celestial equator)
with the keypad, then loosen the clutch, and manually move the scope back to the meridian. Now the worm will be meshing with
a different part of the main gear, so test again. Keep this up until you've tested half the gear, and find the best part of the gear.
If you have a permanently mounted scope, once you've found the good part of the gear, avoid ever loosening the RA clutch
again. This way you'll be using the good part of the gear when you're aimed near the meridian, where you do the most imaging.
>2. and "The PEC records in 2.4 second time increments, ..."
> Does this mean the scope records the average of all
> corrections made during an increment and when running
> normally corrects once (the avg obtained during training)
> every 2.4 sec?
Right.
>3. I was wondering how much do the stars themselves tend to
> wobble and jiggle?
> The steadiness of the seeing seems to affect the performance
> I get. On what I'd call a bad night I'll get an average
> (some peaks higher, some less) of 4-5 arc sec peak to peak,
> a good night about 2-3.(all testing with the same scope
> setup across the same arc of sky)
Sounds about normal.
> 5. I have a 1997 10" classic that I use for photos, and
> have used the newer (last 2 years) gps versions but only for
> live observation. The newer ones seem to be a lot tighter.
The two obvious mechanical weak points in the classic were the sloppy gearbox, and the nylon dec bearings. Meade switched to
metal ball bearings for the dec in about the last year of the classics, and kept this in the GPS. The gearbox is also much better in
the GPS scopes (but if your's has plastic transfer gears, you might benefit from an upgrade to Buck's gears. Meade eventually
switched to metal gears).
> I was wondering if that "tighter" sense in fact translates
> into better astrophoto tracking.
It should.
>6. The new RCX400s seem to have had the astrophotographer
> in mind during it's design and developement. I'm wondering
> if anyone has an experienced opinion on it's tracking
> stability or accuracy compared to the recent and older LX200s
The RCX mount is basically the same as the 14" LX200GPS mount, which is the same as the smaller GPS mount, except for a
beefed up base casting.
Subject: PEC Training -- Stored? Update Often?
From: John Mahony <jmmahony@yahoo.com> Date: Dec 2004
A. Levine wrote:
>I have done the PEC for my 10" Classic about two or three times on
>consecutive nights. Are these corrections stored in the telescope or
>do I need to do it each time I power up?
It's stored.
> If it is stored, will using the erase function erase all
> of the stored PEC data or just the last entry?
Check the manual. I think there's a way to delete just the last entry if you decide it's no good. You can also completely delete all
PEC training.
> Also, even it is stored, should I from time to time continue to do the
> training. I understand that the more times you do the training the
> more accurate it becomes.
Not necessarily. The way Meade does this is not very good. If you re-do the training without erasing the old (use the "update"
command), it will average the new with the old. But it gives even weight to both. So after you've done it a few times, the old
training gets less weight. For example, if you do it twice, each gets 50% weight. But if you then do it a third time, then weighting
the new evenly with the old averaged training means you get 25%,25%,50% weighting for the three trainings. So the result is
that one bad training can screw up the previous training pretty bad.
If they had stored just one more number (the number of previous trainings), then they could give even weighting to all.
Subject: Keypad and PEC Training Trick
From: Doc G, Date: Nov 2002
----- Original Message ----> In trying to do PEC training, the keypad seems to be very "jumpy" when
> pressed to make a small correction, and the star overshoots center on the
> reticle. When "learn" is complete, the corrections are worse than baseline.
> Is there a trick to using the keypad to get more precise star centering
> during PEC training? ------end of quote------The trick, if it is a trick, is to watch your guide star with the PEC zeroed out for several cycles. This way you can count steps
(beeps) and memorize what is coming. Then when you do the PEC training for "real," you anticipate the swings and jumps. This
gives you a bit of lead time to do the button pressing. It takes some practice.
I have found that with one initial training and one update you can get the RA guiding to 1/5 to 1/10 of the original.
Subject: RA Tracking by the LX200 (Analysis)
From: Richard G. Davis
Recent messages here have discussed the motion of the LX200 in Right Ascension (RA), and the performance of the Periodic Error
Correction capability in the LX200. What follows is a presentation of a quantitative method used to characterize the tracking of
my LX200. This is just one machine in the LX200 class of telescopes. I DO NOT SUGGEST THAT THIS IS TYPICAL OF THE LX200.
However, it is reasonable to assume that these results are typical until evidence to the contrary is presented.
The LX200 was mounted of the standard Meade tripod. A SuperWedge was used to mount the telescope onto the tripod. The
scope was polar aligned by the drift method. The declination drift was reduced to about 6 arc seconds per hour, which could be
safely ignored.
The scope was configured with a CCD camera. The scope was an 8-inch, f10 with a reducer operating at f6.3. The CCD camera
was a 9 micron pixel KAF400 chip device. Under these conditions, it was determined that one pixel on the CCD was equivalent to
1.35 arc seconds of angular measure. The results are presented below in terms of arc seconds.
A series of CCD images were obtained. The camera was set up to take images as fast as they could be exposed and saved to the
disk of the computer used to control the camera. Thus, exposures were obtained at 2.67 second intervals. Exposure time was 0.2
seconds, which should make OTA motion insignificant.
Images were collected for about 20 minutes, which covers more that two revolutions of the worm gear. No telescope motion
commands were sent during the time images were being taken.
The data presented in the following graphic were obtained WHILE THE LX200 SMART DRIVE (PEC) WAS NOT RUNNING. Thus, the
following graph shows the worst performance of the LX200. The graph shows an idealized version of the results for a single 8
minute cycle of the worm gear.
+----Seconds of Elapsed time
| ____________________________________
| |
Relative Tracking Deviation
V |
units= arc seconds
|-15 -10 -5
0
+5
+10 +15
sec. |
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sec. +----+----+----+----+----+----+
|-15 -10 -5
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+5
+10 +15
^ |
Relative Tracking Deviation
| |
units= arc seconds
| ____________________________________
|
+----Seconds of Elapsed time
These results show several significant features. First, there is a distinct higher frequency cycle motion superimposed on the 8
minute worm gear cycle. This regular motion feature is about 55 seconds cycle time and has an amplitude of about 7 arc seconds.
Thus, in the relatively stable part of the 8 minute cycle, there is a regular deviation for this configuration of about 5 pixels. Even
this small periodic variation is large enough to be noticed.
At about 240 seconds into the cycle, rapid and extreme deviations occurs which go through two large alternating deviations
before resuming the more stable 7 arc second cycles. These large excursions cover a range of about 30 arc seconds. During these
large deviations, the rate of change in RA reaches a high value of about 0.45 arc seconds per second. These large, rapid
deviations are where the SMART DRIVE (PEC) in the LX200 is presented with its greatest challenge. Thus, the ability of the
SMART DRIVE (PEC) to correct this telescope is going to be limited by the maximum rate at which the drive can adjust RA
tracking.
To correct a RA deviation to the EAST, the LX200 drive must be slowed down. If the maximum possible rate of EAST moving
corrections is going to be made WITHOUT REVERSING THE DIRECTION OF MOTION of the worm gear, one would just STOP THE
DRIVE MOTOR. Thus, the highest EAST correction rate would be the sidereal rate, which is 15 arc seconds per second. The worst
RA deviation rate observed in my telescope is about 0.45 arc seconds per second, which is very small in relation to the best
correction rate for the LX200.
The same data gathering procedures were repeated with the SMART DRIVE (PEC) well trained and turned on. Under these
conditions, the RA deviation rate was reduced to a steady rate of 0.57 arc seconds per MINUTE on the average. The deviations
around this average deviation rate had a maximum peak-to-peak amplitude of about 2 arc seconds. Thus, if the telescope
configuration is adjusted to give 2-3 arc seconds per pixel, this SMART DRIVE deviation would be less than the size of a pixel.
Tracking adjustments of 0.5 arc seconds per minute would keep the image on the same set of pixels. If the tracking correction
rate is 15 arc seconds per second, then a 0.5 arc second deviation could be corrected by stopping the worm drive for 1/30th of a
second, a correction that is well within the capabilities of the LX200 SMART DRIVE (PEC).
OK. SO MUCH FOR THE GOOD NEWS! The bad news is that there are other large RA deviations, which occur at frequencies below
one cycle per 8 minutes. They can be as much as 4 to 8 arc seconds deviations which occur in 1 to 2 seconds. These sudden,
large jumps are at rates from 2 to 8 arc seconds per second. These transients are so large that they approach the maximum
possible rate the SMART DRIVE (PEC) could demand, and possibly even exceed the basic capability of the SMART DRIVE (PEC).
Likewise, these rates are a challenge for autoguiders to correct at the GUIDE rate capability of the LX200.
These low frequency events appear to be related to irregularities in the large, main gear which the work gear drives, and in
spurious electronic variations in the LX200 drive electronics.
Subject: SMART DRIVE: Back to PEC
From: Jerry Gunn <jgunn
mtco.com>
Thanks to all of you who spent so much time learning how the LX200 drive and electronics operate. You have all done a lot of
great detective work.
Doc. G. seemed to have it all the correct numbers which made sense. So it would seem from all this information that a sort of
averaging of PEC multiple training runs is what the LX 200 does.
1. The 8 minute worm period is time sliced into 200 pieces of 2.4 sec each. 200*2.4=480 sec = 8 minutes
2. The on board computer wants to see 45 pulses/sec to operate at the sidereal rate.
3. If we want to correct the RA drive rate, we need to store 200 pieces of information about how many encoder counts to add or
subtract to each 2.4 sec time slice to correct for worm inaccuracies.
4. During training, the numbers of pulses received during each 2.4 second time slice is recorded and difference value from 45 is
stored. This is done 200 times, once for each time slice.
5. When PEC is in playback mode, these difference values are added or subtracted (east/west) to the normal 45 pulses per time
slice and the servo motor is either speeded up or slowed to get the proper drive rate.
6. Subsequent training runs would just add or subtract from the values stored in memory if and when the east or west buttons
were pushed during the time slice. Although this is not an averaging of values, (its really better than averaging) it accomplishes
increased precision with each training up to some mechanical limit.
Also, if all this is true, some constant long term RA drift will occur if the number pulses received by the computer from the
encoder is not equal to 9000 (200*45) over the 8 minute worm period. Theoretically, if the worm turns once and you have
accurately trained on a star the pulses must equal 9000, but this obviously cannot happen exactly. So long term drift is to be
expected.
Subject: PEC Training Experiences --part 1 of 2
From: Michael Clary Date: June, 2000
Based on inputs from LOTS of people, I did the following:
1. Drift aligned for 15 minutes, east and south. No drift...status quo.
2. Visual PEC training (has been done with CCD in past). Erased, Learn(ed) once, and update(d) once. My understanding is
that this results in an average for the LX200 mount rather than an improvement on the initial Learn corrections for PEC.
3. Checked collimation with 9mm illuminated reticle (278X). Very slightly off, realigned.
4. Bundled CCD power and SCSI cables and tied off to east fork and tripod leg to avoid cable drag. With cables on the east
fork, balance (with slight bias to the west) achieved by removal of 1/2lb ankle weight attached to east fork (1 pound left
attached to east fork). Good dec balance in all positions, mount has slight tendency to move west in all positions (very
slight).
5. Did +/- X and Y tests with CCD. Guide speed (2X sidereal for LX200 mount) for 10 seconds each direction. MaxImDL/CCD
used for all camera control. Started with 00 dec backlash set by Meade paddle. On all tests, results showed orthogonality (i.
e., move in +/- X direction did not show change in Y pixel location and vice versa). Tests were done sequentially (i.e., 7
tests in +X and -X directions followed by 7 tests in +Y and -Y directions). Results: had to set paddle dec backlash to 75 to
get +Y and -Y distances almost equal (left a slight undercorrection)...this does cause some jerkiness in the movement!
6. Located star field in vicinity of celestial equator at the southern meridian. Located and exposed guide star for 5 seconds.
Did guide star calibration resulting in settings of -10.34 in X axis, -4.87 in Y axis. Started tracking...relatively steady X,
oscillation in Y.
7. Took sequence of 9 X 5min exposures. Results: football stars!
8. During PEC training, I noticed that the object star did not move in either the + or - dec direction. Decided to try guiding
with only X corrections (assumption being that radical and jerky dec corrections might be effecting RA).
9. Took sequence of 9 X 5min exposures. Results: still football stars, but not quite as pronounced.
10. Took sequence of 9 X 2min exposures with both X and Y corrections turned off (i.e. unguided). Results: slight figure 8 stars
(i.e., slight tracking error in both X and Y without correction). Conclusion: the mount DOES need guiding inputs, but not as
aggressive (BTW aggression was set at 1 for all above and following tests).
11. Now the weirdness: Although calibration numbers were -10.34X and -4.87Y, I manually input -8X and -3Y. Took another
sequence of exposures. Results: almost ROUND stars! Further reduced numbers to -7X and -2Y, resulting in rounder stars,
but with a slight bulge in the y direction (i.e., dec still not perfect).
12. Slewed to north meridian near zenith. Recalibrated and got similar numbers (-10.3X and -4.4Y). Manually input corrections
of -7X and -2Y. Sequence of 9 X 5min exposures still showed "almost" round stars (still slight bulge in +/- Y direction).
Long night but maybe some progress. The input of manual correction numbers works, but why?? As I understand it, calibration
said that a 1 second move in X equals a move of 10.3 pixels, so a move of 1/10 second moves just slightly more than 1 pixel.
Instead, I insisted that a 1 second move in X equals a move of only 7 pixels, so a move of 1/10 second moves 7/10 of a pixel. I
would think that my manually input numbers would cause MORE movement instead of decreasing the moves. What's up??
Anyway, muchas "THANKS" to all who offered advice. I'm obviously still not satisfied (won't be until they're all perfectly round)
and I'll keep klutzing around. Still need to try slightly "misaligning" from pole and various other tweaks of parameters.
--------------------------------Subject: PEC Training Experiences --part 2 of 2
From: Ralph Pass <rppass
rppass.com>
Michael: It is suggest that you only touch the RA button during PEC training. As you noted, DEC corrections sometimes confuse
the issue.
Subject: PEC and Long-Term RA Drift - Solution
From: Craig Tupper <ctupper
erols.com> Date: July, 2000
This problem is well described in the Topical Archive, but there is no real solution to it offered other than to live with it, i.e., guide
out the long term drift that occurs after PEC training.
I came up with a simple little solution, maybe so simple that it was obvious to everyone but me. Simply change to a higher
tracking rate.
After PEC training 3 times (2 runs each time) I found that I consistently got pulse counts of around 21535, pretty low, and had
very noticeable drift. Autoguiding with an ST7 at 63" focal length gave oblong stars on anything longer than about 15 sec guiding
exposures, and sometimes you just can't go shorter than that, especially if you are using Track and Accumulate.
I did the math and found that my pulse count rate was about 0.3% low ( 1 - 21535/21600 ) . Multiplying 0.3% times the
standard 60.1 Hz tracking rate, I decided to try a manual tracking rate (adjustable with the hand paddle) of 60.3 Hz. To make a
long story medium, I find that in practice a rate of 60.4 Hz gives me practically zero drift. I have taken several unguided 8 minute
test exposures at this rate and was shocked to see round stars. Needless to say, my autoguiding performance is now much
improved.
Subject: Polar Alignment and PEC Accuracy?
From: John Mahony Date: June 2005
Alan Sickling wrote:
> I am intending to try some imaging soon, so I have attempted to
> perform an accurate polar align on my pier-mounted 12" Classic.
> 2 nights ago I got some targets to set up on.
> I drift aligned for about 3-4 hours, and I am now wondering
>
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how good my finished alignment is for imaging work. I have
a Meade Superwedge, to which I have fitted a long T-dog on the Az
thread, and bushes/bearings in all the critical pivot positions. The
adjustments worked smoothly with minimal backlash. I tried to measure
the final tweaks I had to apply to get each axis spot on the final
position, and as near as I could estimate they were in the region of
30-45". I presume from this that I can expect the RA axis to be at
the NCP within about 60" overall. After locking down all the
fastenings, I checked both axes and could discern no drift off-line
after 15 mins. The engineering in the pier and mount is such that I
do not expect much (if any) creep from the set position.
Any comments from you experienced imagers? Are my assumptions OK?
And how does this figure of 60" max error stack up with the
practical requirement for good imaging? I have seen no actual
quantified figures anywhere.
I use that as the "practical limit" for fine-tuning a good alignment. Due to atmospheric refraction, there's no such thing as a
_perfect_ alignment that will give no dec drift anywhere in the sky. Atmospheric refraction makes objects appear higher above
the horizon than they really are. For objects with alt higher than about 20°, the effect, in arcminutes, is about 1/tan(alt). From
that it's not hard to calculate that a drift test done on an object 30° above the E or W horizon will leave the mount's RA axis
adjusted a few arcminutes above the pole. It is generally considered beneficial to have the axis slightly high, since the tracking
will more closely match the refracted path of an object this way for most objects, but the drift test leaves the alt of the polar axis
"corrected" for objects low on the E or W horizon (since that's where you tested), so you might want to drop the alt of the polar
axis a bit, since most imaging is done close to the meridian.
I use a direct method of polar alignment, at <http://geocities.com/jmmahony/LX10/polaralign.html>. The idea is simple: set the
tube to 90° dec (where here "90 dec" means relative to the mount, so that the tube is parallel to the mount's polar axis), and
then use the scope as a giant polar alignment scope. To do this, the tube must be precisely parallel to the mount's polar axis, but
this is easy to check: with the tube at 90°, rotate the diagonal up between the forks so you can view from the south side of the
mount, then loosen the RA clutch, and view through the scope while rotating the scope slowly by hand in RA. The image should
rotate around the center of the FOV. If not, tweak the dec until it does.
To use the scope as a precision polar alignment scope requires a knowledge of the stars near the pole. Charts are available on my
webpage. Keep in mind that your view of these stars will be refracted by about 1', if viewed from mid-northern latitudes.
When rotating in RA, you'll notice that even with the dec tweaked precisely, the image never rotates in a perfect circle, since the
aim of the scope drops by a few arcminutes when the RA is near 6 or 18 hour angle compared to when the RA is at the 0 or 12
hour angle position. This is due to fork flex- the long axis of the fork cross section is parallel to the ground when in this position,
so they don't resist bending as well. This is another reason why I use 1' as a practical limit for polar alignment.
Of course, orthogonality issues can also show up when rotating while at 90°.
>
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While I was watching the drift sequences, I also observed the
lateral wanderings of the RA drive, which has had no training yet.
(The PEC file has been cleared.) The maximum lateral excursions I
measured were in the region of 90-100" overall (i.e.+/-45-50"). I am
quite surprised that it was this bad. Does anyone know what the
normal range of PE error is for an LX200? Does mine seem
particularly bad? I have set up the RA worm/pinion engagement to be
as good as it can be got.
That does sound somewhat on the bad side, but not terribly. One problem with checking other sources is that many do not say if
their number is overall total, or +/-. IIRC, before I trained the PEC, ours was around 40"-60" total, and I've heard similar
numbers for other LX200s. Of course, a big question is whether the error is smooth, where PEC will help, or erratic, where PEC
may not be able to keep up.
Subject: First Pass PEC Graphs After Cleaning
From: Gene Chimahusky <lynol1000
yahoo.com> Date: Oct 2005
Here is the final installment of the gear cleaning and PEC measurement saga: I did a second full learn cycle followed by an update
on the PEC after the gear cleaning. Seems to have taken out the RA creep I added the first time around.
Graphs and the image of M57 of the PE from a stack of 29 images each 60 sec long:
<http://www.geocities.com/lynol1000/lx200_internals/pec_100105.html> (about 38k total)
Subject: PEC Training with CCD Camera
From: Bruce Johnston Date: Sept., 2000
I managed to get my ST-7E to PEC train my LX200, and do it pretty successfully!! When done, I watched a star for perhaps 15
minutes to see the results. The star stayed right on the crosshair at 500x, with a couple of exceptions. Those exceptions are the
same ones I've always fought, I believe. Those being, when there is a rather radical 'hop' or speed-up/slow-down that would
appear to me to be slight irregularities in the worm tooth. I've always been chasing those buggers and really would like to find a
good way to minimize them. (Perhaps the lapping of the gears??)
To train the scope, I set the speed at 63 Hz and trained, using corrections of .2 seconds. Then I set the speed for 57 Hz and did
an update. Presto!
I must admit that I've been spending a pretty fair amount of time with my CCDOPS for DOS program, trying my best to learn
how to minimize overcorrections, and although I still have a lot to learn about the finer points of the program, I think I now know
enough to give it a fair try.
The seeing wasn't very steady at all tonight, so I really didn't expect much in the way of results, but I was quite pleased in the
results. Hopefully, when I get a really steady night of seeing, I might be able to get the thing to get better. And if I can ever get
those pesky quick speed-ups and slow-downs mastered, I would have even higher hopes for the method. All I can really say at
this time, is that the results were about the same as what I've gotten when training manually. (I really don't know the thickness
of my 12 mm Meade illuminated eyepiece crosshairs nor their spacing, so I can't give a decent arc second estimate.)
I just thought some of you might be interested, because, like me, you've probably thought it just couldn't be done!
Subject: CCD PEC Training URL
From: Frank Roddy Date: Nov., 2000
You might check the site for info on PEC techniques with a CCD.
<http://telescope.8k.com/Operating.htm>
Note: should open a new browser window over this one.
Subject: PEC Training with an Autoguider or Manually?
From: John Mahony <jmmahony
hotmail.com> Date: Feb 2003
>Doc G wrote:
>Tim Long is quite right about the autoguider technique being used by many over the
>years. The Pictors do send a signal directly to the CCD port. But the problem with
>using this technique is that there is a delay in correction depending on the
>camera and the brightness of the star and the update chosen as so forth.
>
>I still believe that the general conclusion was that a good manual training
>was still the best. The good trainer can watch the behavior of the mount
>for a few cycles and then anticipate its erratic motion. Thus the good manual
>trainer has an advantage over the CCD camera which always lags. The
>manual trainer has a big advantage in fixing sudden erratic motion of the drive.
>
>One good manual training and one additional training should reduce the
>errors in the drive by a factor of five to ten times.
Since you have a wide range of guide stars to choose from, you can choose a bright one and use .1 or .2 second exposures for
the pictor. The pictor takes less than a half second to check the image and do the correction calculation. Since the corrections are
usually small, that gives you corrections at nearly 2 per second.
If you practice doing it manually, you could eventually do better, especially with the human ability to anticipate, once you've
learned your drive's error. In fact it occurs to me that some software will give you the ability to record the error- in fact you can
just take an 8 minute exposure with the polar axis slightly off- for deliberate drift- to record the error directly on an image, as a
graph of time vs. RA error. This record could be useful for training yourself to anticipate upcoming error.
But the drawback to all this is that the PEC code on the classic divides the 8 minute cycle into rather coarse chunks- 2.4 seconds,
I believe- (i.e., in each 2.4 sec increment, any corrections during that interval are added together to give a single correction for
that interval during playback), so in practice it would be difficult to do significantly better manually than with the pictor. And the
pictor will do it easily.
Anyone know what time increments are used for PEC on the GPS?
Subject: Refining PEC Finally Pays Off
From: Randy Marsden <jmarsden
san.rr.com> Date: Feb 2003
At various times I have mentioned the work I have been doing on my LX200 to reduce the periodic error and improve my polar
alignment and PEC training. It finally all came together last weekend. My first target was M82. The only convenient guide star
required 6 second exposures for guiding with a clear filter and 30 seconds to maintain guiding for the blue filter. The seeing was
very steady, which combined with very small guide corrections every six seconds, yielded 3.0 arc-second FWHM stars on a ten
minute exposure. The resulting color image is posted at:
<http://members.aol.com/rmarsden/Astrophotos/M82_color_2-8-03.jpg>
Then I moved on to M51 for which I wanted to do a longer series of luminosity exposures to get more of the detail. I found a
brighter guide star and was able to use 0.3 second exposures for guiding. This yielded 2.0 arc-second FWHM stars that are very
round. I was able to shoot ten 10 minute exposures before dawn began to break. The result of that series is at:
<http://members.aol.com/rmarsden/Astrophotos/M51_monochrome_2-8-03.jpg>
An example of the residual periodic error after one round of PEC training is posted at:
<http://members.aol.com/rmarsden/Astrophotos/PPEC_residual_error.jpg>
All of the results are from my 10 inch LX-200 that is about 5 years old. I am not positive of the exact age since I acquired the
scope from the estate of an astronomer who had died.
I was seriously considering buying an expensive equatorial mount for the optical tube. But persistence has finally paid off. Now I
will build an equatorial mount in my leisure to carry the OTA from my old LX-6 for which the mount is beyond hope for
astrophotography. I am using an SBIG ST-7E anti-blooming version.
After tweaking and tuning the mount for months, I concluded that most of the problematic error is actually inside the RA drive
gearbox. Only after going inside and carefully cleaning the gears did I get acceptable performance. The camera can correct for
slow periodic error but it cannot compensate for high frequency error which can come from irregularities, dirt and imperfections in
the gears inside the gearbox. Careful cleaning, tooth by tooth, of those gears yielded the biggest change in performance. Careful
polar alignment also greatly reduces the amount of guide corrections sent by the camera.
Of course, having an evening of exceptional seeing helped as well. The high declination objects like M51 and M82 also minimize
the effects of periodic error. The real test of the performance will come when I go back and try to image lower declination objects
like M16.
Subject: PEC Training on Different Teeth? --part 1 of 2
From: Doc G, Date: Aug 2001
Wayne Watson wrote:
>
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In an exchange about worm gears and PEC sometime ago by Bruce Johnston
and Doc G, I found the following:
=============
Question (from Bruce Johnston?):
> I'm disappointed in the inconsistency I get after a training session.
> Next night, it's right back to the erratic movements.
>
>
>
>
>
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>
Answer (from Doc G?):
That happens because the PEC trains on only one tooth of the wormier.
The LX system does not allow for more sophisticated training. Though
it should be realized that if you do successive training on the same
star, you are training on several different teeth. The hope is that the PEC
makes the scope smooth enough so that the CCD guider takes care of the rest.
=============
Holy Moly what indeed is a "wormier."
Doc G: What I meant to say is this: The PEC trains on one section of the worm and on one tooth of the large gear. Note: I do not
call this the worm wheel since it is a simple spirally cut gear and not a true throated worm wheel. But that is a different issue.
The PEC trains for one turn of the worm and thus it trains on one tooth of the large gear and on the surface of the worm, over
one turn, that happens to be in contact with the large gear. If you train further, the worm trains on another tooth of the large
gear, but one the same surface of the worm. It is clear that the worm surface used is the same, over and over, since the worm
remains in place tangential to the large gear and in one place. This goes on for each training session.
The theory PEC of training assumes that the main deviations are in the worm and not the large gear. Technically perfect training
of the worm/large gear would require training for one full rotation of the large gear and keeping the data for the entire 180 turns
of the worm required to make the large gear turn one full rotation. This record would then have to be kept synchronized with the
data record.
Note that professional telescopes can and do use such precision training for the entire sky.
As a practical matter, the PEC trains for mechanical deviations in the worm and keeps a record for one turn of the worm only.
This record is used to correct the motion of the worm for each turn of the worm and for successive teeth of the large gear.
Thus it is not only possible, but likely that as the worm contacts different parts of the large gear, the mechanical deviations will
differ. Typically PEC training will reduce tracking errors by a factor of 5 to 10 times. This usually means from untrained values of
30 to 50 arc seconds to 5 arc seconds. This is an excellent improvement, but not perfect and not good enough for precision
imaging. Thus the guider is required to give arc second or sub arc second guiding as required for long focal length imaging. As a
consequence of the PEC training method used, One might find good PEC on one part of the large gear and less satisfactory results
on another part of the large gear.
---------------------------------------------------------Subject: PEC Training on Different Teeth? --part 2 of 2
From: Doc G
Gregg Ruppel wrote:
> Hi Doc-- Thanks for the detailed explanation (again) of PEC training. Let me restate
> a couple of practical points based on your description and get your feedback:
>
> 1. I have a permanently mounted LX200; always park it at 00 RA and 00 Dec.
> If I PEC train on a star near the celestial equator and local meridian, the
> PEC should be most accurate at that location in the sky because of the "one
> tooth" phenomenon.
Correct. But PEC will help everywhere.
>
>
>
>
>
>
2. If I slew to a region of the sky to the east or west, my PEC training
may be less accurate because now I'm tracking on a different "tooth" (i.e.
section) of the large gear. I may see periodic errors that didn't show up
in the area of the sky where I originally trained PEC. Guiding is still
better than with no PEC training, but may not be as good due to differences
in the large gear.
Possibly and to be expected. But PEC will help everywhere since the major errors are in the worm.
> 3. As the scope tracks an object over several hours (as in long exposure
> photography), PEC performance may change considerably as the worm encounters
> different sections of the worm wheel.
Yes, that is why a good guider CCD is still required. A residual of 5 arc seconds will give oval stars. CCD guiding is essential sine it
can give you sub arc second lock on the star field. Atmospheric effects will then give you fatter stars, but you will be guiding well
anyway.
> 4. To maximize PEC (say for CCD imaging), training should be done with the
> scope pointed to the area of the sky to be imaged (I think this has been
> discussed before but I was never quite certain of the rationale).
It is not too practical to do the PEC at many locations because of the time factor. The same portions of the gear will be used only
if you never unlock the fork from the drive using the clutch.
I recommend this in any case for a permanently mounted scope. You can find a sweet spot on the gears and use that section
over and over.
Subject: PEC Training - Elongated Images
From: John Murphy Date: Jan 2002
------Original Message----From: Maarten Vanleenhove <maarten.vanleenhove
pandora.be>
I have bouncing around getting elongated stars (at f/6.3). It is a real pain. It is a very fast error, which is not
periodic. I've tried just about everything to get it right, with no results. Some say it is caused by little chips of metal
between the gears, others say it is the RA drive assembly...
If anyone has a good solution for this problem please let me know.
PS: check my elongated ccd images at: <http://www.supernovae.be/>
I have a 12" LX200 and an ST8 and have experienced the same problems when attempting to image at f/6.3 to f/10. I have
talked to both Meade and SBIG to no avail. I have looked for metal chips and found none, and have tried almost every
combination of numbers possible in CCDsoft.
I finally backed all the way up to square one and did the following:
●
●
●
●
●
●
- deleted the PEC
- turned guider corrections off, acquired a star on the guide chip, dumped the errors to the log, imported into excel and
graphed the error ( about 30 arc mins).
- trained PEC with camera
- turned guider corrections off, acquired a star on the guide chip, dumped the errors to the log, imported into excel and
graphed the error ( about 10 arc mins).
- erased PEC, trained PEC manually (1 plus update)
- turned guider corrections off, acquired a star on the guide chip, dumped the errors to the log, imported into excel and
graphed the error ( about 5 arc mins).
(for clearing PEC, Meade recommends running learn mode of the PEC without pushing any buttons for one worm period, then
train over again." This is supposed to do a "better" job of cleaning out an erratic PEC. Sounded like bull pucky to me, but I'll try
anything once.)
I was also able to see that when I turned autoguiding back on, that the lower PEC led to better guiding. I was still seeing random
large errors, but the magnitudes of the errors were better. It is worthwhile to note that by reducing the focal length to f/4 (f/3.3
reducer with no spacer) guiding works great, no jumps at all.
I now believe that my camera will guide at longer focal lengths without the random RA errors if I can get the PEC down low
enough. This probably entails adjustments to the worm, finding the sweet spot, and some other adjustments, that I haven't had
time to make yet. For me, having the camera train the drive resulted in worse correction than doing it manually. I have also
heard others report that training the PEC in the area of the sky in which you plan to image helps.
I guess, the moral of my story is don't guess about your PEC. Measure it, graph it, change it, compare it. Just altering the values
in CCDsoft had me chasing my tail for many, many nights. I figured something had to be broken. By taking a step back and
empirically looking at what was going on, I think I have proven that the equipment is doing what is expected. Such are the
travails of owning a mass produced (relatively) low cost instrument.
Subject: PEC - New Use!
From: Emery Hildebrand <emeryh
earthlink.net>, Date: Jan., 1998
I do a lot of hour-long manually guided exposures and accidentally discovered something interesting in this respect.
If you erase PEC and retrain at the beginning of each exposure, you barely need to make any adjustments even for prime focus
shots. Because of the weight of all the accessories and differential flexure, it appears that best PEC values are different in
differing parts of the sky. This is true for both my 8" and 12" Classic LX200s, but it may not be true for all LX200s. It would be
interesting to see how many others can benefit.
Specifically, retraining does not seem necessary unless pointing more than 20 degrees from the last position it was trained in. As
soon as the scope is pointed to some other quadrant, required guiding corrections increase dramatically. Point back to the original
location and very few corrections are needed.
If you don't erase the existing PEC values this system will not work as well since it will merely average with the previous training
and, while improving things, will not make such a dramatic improvement. The improvement is so dramatic that a typical hourlong exposure at prime focus of the 8" scope may need only 3 minor guiding corrections.
These are not artifacts of polar misalignment either since there is no evidence of field rotation on any of the resulting photos.
If this result is repeatable, it can obviate the need for any CCD to be used as a guider.
Subject: PEC Problem Caused by RA Worm Damage
From: Doc G, May 2004
I am now advocating another fix for the RA drive. If the scope has ever been punished to the point where the main gear has
jumped the worm, you very likely have a damaged worm. The very parts of the worm that get damaged are the parts that
contact the main gear. If you have a PEC which has a sudden correction required, you likely have a damaged worm.
This can be fixed, or at least helped very much by polishing the worm. I suggest removing the RA drive and connecting the motor
to a single or possibly two battery cells so it rotates at about 2 or 3 rpm. Then take a very fine and tiny file, a triangular or
square file is good, and chase the worm from one end to the other about 50 times. Then take a piece of 600 emery and fold it
and chase the worm another 50 times. This will remove or reduce the damage from the worm bearing surface.
I have one LX200 12" that will track for 3 minutes without guiding.
Subject: PEC Programming as Related to Drift Alignment
From: Michael Hart, Date: May, 1998
BACKGROUND
Programming the Smart Drive (PEC) should be done on a night of good seeing, no wind, at high power, and on an excellent polar
aligned scope because improper polar alignment introduces RA drift that effects the PEC programming used in other parts of the
sky. One possible variation might be to program the PEC near the object of interest to compensate a bit for polar alignment
errors which could including Dec drive training. I use 800-1200X on my 12" LX200 on a star quite near meridian close to the
celestial equator. I make 2-3 small corrections per second to avoid overcorrecting at each 2.4 second recording cycle. This is
done in RA only. No Dec corrections are ever made. The measured results are consistently around 4-5 arc seconds periodic error
peak to peak over the 8 minute worm cycle. Once done, the PEC corrects for small drive frequency variations and virtually stops
RA drift for at least 2 minutes. With a well programmed PEC and accurately polar aligned scope, one does not need to make
frequent guiding corrections at all. In fact, a human is often better at guiding than an autoguider during poor seeing, because the
human can easily determine seeing errors from alignment/drive errors. Attempting to autoguide out seeing anomalies is a
daunting task, especially with a computer controlled autoguider approaching a limited maximum update rate of 1.45 seconds or
greater.
DRIFT ALIGNING BEFORE PEC PROGRAMMING
If your scope drifts consistently in RA, you may need to tweak polar alignment before PEC programming. Three things happen
when we are NOT polar aligned: The stars appear to drift in RA. The stars appear to drift in declination. The field rotates. Using
the drift method to polar align is recommended highly for high power visual work and precision imaging. As we approach 3000+
mm focal lengths, alignment that was satisfactory for a camera lens or small refractor is wholly inadequate. The term "declination
drift" itself implies a polar aligned scope will drift in declination only. In fact, a scope that is not polar aligned drifts in RA as well,
however, we ignore any RA drift during the process and watch "declination drift". As we
approach polar alignment, RA drift slows as well. The reason for RA drift is easy to visualize. If our mount is not quite aligned
with the celestial poles, the amount of misalignment formed causes the RA to appear to drift. The greater the misalignment, the
faster the RA drift.
Note: Start by erasing the PEC to remove any programmed RA drift.
The idea is to line up our scopes to turn parallel with the earth's rotation. Those experiencing unusual RA drift should assure polar
alignment is quite accurate.
LEVELING THE POLAR MOUNT- IS THIS REALLY NECESSARY?
There is a good reason to level the mount along the altitude and azimuth axis. When drift aligning, a mount out of level will cause
adjustments in one axis to effect the other, increasing the number of iterations that are required arrive at a polar alignment
solution. For example, a correction that might require an azimuth move will also move a bit in altitude when the mount is not
level in azimuth, the amount depending on the degree of error from level. Once quite level, we are then ready to start the
declination drift alignment process. The method outlined in the Meade manual is based on using a diagonal. Straight through
users and south celestial pole users, should reverse the correction directions. It may be a good idea to label the direction moved
on the mount azimuth and altitude knobs to prevent mistakes that would unnecessarily prolong the process.
DECLINATION DRIFT ALIGNMENT OF A POLAR MOUNT
Now that we know which star to select and have done so, we're not quite ready to drift align. First, we must align our reticle
eyepiece with the RA axis. We can consider this the E-W axis. Everything above the E-W (RA) axis is NORTH, everything below is
SOUTH. If you are uncertain, merely moving the scope with the E-W keys will identify the E-W (RA) axis in the eyepiece. It is
vitally important that we understand that the use of the term north or south as described in drift alignment procedures is not
related to your position at the telescope, rather, the direction the star drifts with respect to the RA axis. Now, we select a star
within 5 degrees or so of the celestial equator and within 30 minutes of the meridian. This provides maximum declination drift
which readily speeds the alignment process. A moderately bright star often provides better results than a very bright star. Using
a 2-3X Barlow with extension or star diagonal will produce powers that are quite high, amplifying small drift movements. If the
seeing is so poor that your moderately bright star is too dim and/or moves about, postpone the PEC programming for a day of
better seeing. If the star drifts NORTH, use the azimuth control to move the scope EAST. Keep adjusting and re-centering the star
until the movement virtually stops over a 3-5 minute period. Now, locate a star at about 6 hours RA not much less than 15
degrees of the horizon (this avoids refractive errors) If the star drifts NORTH, use the altitude control to move the scope DOWN.
Keep adjusting re-centering until the star does not drift 7-10 minutes. Now return to the paragraph immediately above and
repeat, but strive to improve star drifting from 3-5 minutes to 7-10 minutes.
RETURNING THE TELESCOPE TO A POLAR ALIGNED WEDGE
This leads to the subject of reproducing polar alignment when removing the scope from an adjustable wedge or other device
which maintains the scope parallel to the earth's rotation (aligned to either celestial pole). Once the
wedge is aligned, we can move the scope base up, down, right or left as long as the scope base is not TILTED by a non-flat
surface. I use indexing pins to position the scope base at the exact point it was aligned. However, are they really needed if you
have a flat mounting surface (no bumps or warpage)? An even better question is, (thanks to Paul Goetz), how non-flat (irregular)
must the surface be to cause a significant polar alignment error? If moving the scope base laterally across the wedge surface
(parallel to the earth's rotation) introduces a 12 minute error west (due to a .020" bump or warp in the surface), a 60 minute
exposure could drift around 3 minutes in declination. A .020" deviation in a short span of less than .25" (maximum anticipated
variance) is clearly visible on the wedge surface and quite easy to see in the eyepiece during drift alignment. However, the
maximum amount of field rotation seen in a typical 60 minute exposure near the guiding point would be fairly small- around 30
seconds. If the amount of field rotation produced is so small, should most bother with indexing pins? Probably not. Why then,
bother at all?
Three reasons come to mind.- First, manual guided exposures are much easier with an alignment precision that requires almost
no Dec corrections or RA corrections in two minutes or longer. One can relax a bit. Thus, more precise polar alignment is
desirable. Second, two minute unguided CCD images will move less than 1 pixel, enabling electronic stacking with minimal loss of
field of view and object centering. Third, guiding errors while using an autoguider are narrowed to flexure, vibrations, wind, drivetrain, and seeing. We could use precision milling of the wedge surface to 0.002", but simple eyeballing the bolt hole centers or
simple indexing pins as a means to assure returning to precise polar alignment is quite adequate.
CONCLUSION
I believe the value of accurate polar alignment is often underestimated. For casual observing, casual polar alignment is quite
adequate. However, for improved PEC programming and good photography results at focal lengths of 3000+ mm, a well aligned
mount is essential to excellent results.
Subject: Difference Between Periodic & Pointing Errors
From: Bill Ezell Date: May, 1998
> They are talking about periodic tracking errors, and they give an number (15
> arcseconds in that case). My question is : is it 15 arcsec each second,
> minute. What is the period of time?
There's a lot of confusion between periodic error and drift, and people seem to sometimes use the terms interchangeably.
'Periodic error' should be used to describe tracking errors that repeat in a cycle over some period of time, hence periodic. 'Drift'
should be used to describe tracking errors that persist and accumulate in one direction.
Periodic error in the referenced article should refer to the total amount that the image moves back and forth in the field over one
period. This shouldn't be a time-referenced quantity. So, what this means in practical terms is that you should see the target
move back and forth over a period of time over a total distance of 15 arcsec, and this would repeat indefinitely. Note that at one
point in the cycle, the image should (theoretically) return exactly to the location it had at the same point in the previous cycle.
Drift is caused by misalignment of the mount or an incorrect tracking error. The appearance of this is that the image slowly
moves in one direction, never reversing its movement. In practice, both drift and periodic error are usually present
simultaneously, although drift can be essentially eliminated by careful alignment, assuming an accurate drive clock.
For the LX200, the significant time interval for periodic error is 8 minutes. This is the time the worm gear in the RA drive takes to
complete one revolution. There are additional second-order error sources, such as differences between tooth spacing on the main
RA gear.
And then there's pointing error, caused by mount flexure, alignment errors, drive encoder resolution, etc. which causes the scope
to point to a different area of the sky than it should when slewing to a particular location.
Subject: PEC Training -- Constructing a Guiding Keypad
From: Michael Hart, Date: May, 1998
A CCD guider port keypad is quite easily built using Radio Shack parts. The CCD guider port keypad is much simpler to construct
than a LX200 hand control keypad I use that relies on digital signals.
Making your own keypad control box is really quite simple and easy to do and is excellent for manual guiding and PEC
programming. I prefer snap action type switches for this application as the button travel is shorter than standard push buttons.
Unfortunately, these are not available from Radio Shack. It is quite likely this will work on scopes other than the LX200, such as
the Celestron Ultima 8 & 11, hand controller which I have verified as roughly pin compatible for this application.
RADIO SHACK PARTS NEEDED:
(1) 279-422 six conductor telephone modular to modular 25' extension
(1) 275-1547 normally open push button switches (4 in package)
(1) RSU 11907680 molded enclosure
Solder
Soldering iron or gun
Hot-melt glue gun (optional)
$ 1.99
$2.99
$7.99
CONSTRUCTION STEPS
1. With a sharp Xacto knife, cut the six conductor modular cable at a length of around 3-1/2 feet. Cut another piece of around
4 inches and remove the wires. You will use these to wire up the switches.
2. With the Xacto knife, cut a slot in the molded enclosure base for
3. the six wire flat telephone cable to allow the lid to close. You may need to remove a bit of plastic in the lid to allow the lid
to seat
4. Mark 4 positions in the lid for the bush buttons and drill with a 7/32" bit and install the 4 switches.
5. Wire one contact on each of the 4 switches to each other. This is used as a common ground.
6. Look at the telephone plus so that the wire is away from your eyes with the plug retaining clip on the bottom. The pin-out
is counted from the left to right to- 6, 5,4,3,2 & 1. Now tip up the plug so that you are looking at the retaining clip. Write
down the colors of the wires you see from left to right. They will be: blue, yellow, green, red, black, white --OR-white,
black, red, green, yellow, blue. Match up a color with the pin-out above. You will use this information to wire the switches
so that the telescope moves in a expected direction.
7. Pin 6 goes to the right button (blue or white).
Pin 5 goes to the up button (yellow or black)
Pin 4 goes to the down button (green or red)
Pin 3 goes to the left button (red or green)
Pin 2 goes to the ground in step 4. (black or yellow)
Pin 1 goes to NOTHING (+ 5v) (white or blue)
8. Final assembly involves optional hot gluing the telephone cable to the top to provide strain relief, if needed and attacking
the base.
Subject: Dec Blocking Autoguiding Device
From: Wesley Erickson <twesley
twesley.com> Date: Oct. 2002
I have posted a PDF document on my website that contains instructions for building the "Dec Blocking Autoguiding Device". Credit
goes to Adam Block, lead observer for the Advanced Observing Program at Kitt Peak, who suggested the concept to me in a
phone conversation. I built a prototype the next day, and, after testing it with my LX200 and Pictor 201XT and Pictor
216XT, I sent it to Adam, who has extolled its virtues on the SBIG group.
The device installs inline between the autoguider and the LX200 control panel, and prevents Dec reversals by allowing the user to
turn off guide corrections in either the north or south direction.
Both switches should be on during calibration, then the desired switch can be turned off before starting the autoguiding process.
The link appears as Block Autoguider Device on the Technical Reference page at:
<http://ourworld.compuserve.com/homepages/twesley/blockdev.htm>
Note: should open a new browser window over this one.
The Adobe Acrobat PDF file may be downloaded directly at:
<http://ourworld.compuserve.com/homepages/twesley/blockdev.pdf>
or here.
Subject: Effective Use of PEC with an Autoguider
From: Michael Hart, Date: Aug., 1998
BACKGROUND
Since the introduction of affordable and reliable autoguiders, autoguider use has increased considerably. And why not? Guiding
can be a tedious and a monotonous task. With an autoguider, one can set an alarm and wake up hours later refreshed when the
exposure is complete. Still, it is not unusual (though perhaps less so in recent years) to see an amateur using rather inexpensive
equipment, minimal accessories and no autoguider. That amateur may walk away for a minute or so, return, converse, and
casually make a small correction. Contrast this to the amateur with many accessories, a much better drive, more expensive
scope, and an autoguider. Of course, the former amateur will get worse results as compared to the later amateur. Perhaps not-
here's why:
Conventional wisdom used for film imaging with high quality mounts under excellent seeing is not simply transferred to
inexpensive amateur mounts used under typical seeing by many amateurs. I have used inexpensive mounts simultaneously along
side high-end amateur mounts and produced similar results, but not using the same techniques. Clearly, it is more of a challenge
to obtain similar results with an inexpensive mount. However, if we modify our techniques a bit to compensate for known
anomalies, good results are possible on inexpensive mounts with a reasonable level of effort. This is important for those that
have limited resources to invest in astrophotography.
WHY USE PEC
PEC is, of course, needed less with high quality worm and worm-wheels at shorter focal lengths. It is easy to dismiss mass
produced mounts as unusable if we are fortunate enough to own or have access to a better mount. However, as we start moving
up in focal length to over 3000 mm coupled with long exposures, PEC again starts to become useful, even for the high-end
amateur mount. Fortunately, PEC is available on many of these mounts. If used properly, PEC and an autoguider can have a
synergistic effect. This is especially noticeable with long exposure tricolor CCD imaging at 3000+ mm using a CCD chip where the
CCD chip records small errors much more efficiently than film. Many PECs are capable of averaging corrections over periods of
0.50 Hz (2 seconds) or less (LX200) while a typical autoguider is operating at 3-5 second correction rates or greater. If we
increase the autoguider correction rate too much (faster), we may start chasing the seeing resulting in oscillation of the mount,
especially under average to marginal seeing.
THE ROLE OF AUTOGUIDER CORRECTION RATES
We should not confuse the exposure time setting of the autoguider with the correction rate which is the sum of exposure time,
integration time, any software/hardware overhead, and drive hysteresis. Thus, the correction rate is always longer than the
autoguider exposure time. This is an important consideration is we try to use an autoguider to program the PEC. A short exposure
setting might not be adequate to assure correction rates are less than the desirable sampling rate of 1/2 the record period or
about 1Hz (1 second) for the LX200 Then, of course, the autoguider is fully capable of programming non-periodic seeing related
corrections (undesirable) easily ignored by the human when the seeing isn't superb.
CORRECTION RATE LIMITATIONS IN MOUNTS
We should not assume that because our mount appears to oscillate in response to guiding corrections as a result of seeing, worm
errors, vibrations, alignment errors, and/or PEC programming errors that a given mount is not capable of fast guiding rates. For
example, a slightly modified LX200 is capable of responding to simultaneous X-Y guiding corrections at 2 Hz (0.5 seconds). For
the RA axis, this consists of typical slowing and speeding of the RA drive. In the Dec axis, full worm reversal slows drift or
changes the direction of star movement. Of course, obtaining smooth correction rates at 2 Hz requires a thorough understanding
of the relationships of various adjustments in the drive and mount. For most, such fast correction rates are not needed, however,
the reduction in hysteresis required to achieve these rates is desirable.
THE PEC ADVANTAGE
For a LX200, if the PEC was calibrated and updated under excellent seeing and polar alignment, not only are the worm errors
smoothed, but residual RA drift is virtually stopped as clock crystal drift and minute alignment errors are corrected. Then,
subsequent updates are used to add or subtract pulses (0.3333 arc second movements) to memory segments which tweak the
drive further allowing the drive correction to track the worm quite close to real time- much closer than is practical for an
autoguider, especially under marginal seeing.
It is important that permanent PEC programming is preceded with good polar alignment and initial PEC erasure. Why good polar
alignment BEFORE PEC programming? Because poor polar alignment produces changes in the RA drift as well. With PEC
programming, in addition to clock frequency errors and worm errors (which are repeatable), we introduce another error (RA drift)
which is corrected by the PEC as well. The next day, we set up and roughly align again and find our RA drive doesn't track as
well. This is likely because we programmed in the RA drift produced by the previous night's poor polar alignment. The previous
night's rough polar alignment is usually more difficult to replicate than accurate polar alignment.
Once the PEC is carefully programmed, we can use the autoguider independently of PEC at whatever correction rate that
produces the best results- perhaps several seconds to even minutes (if desired) for a well aligned mount. Now, autoguiding is
truly optional because manual guiding corrections may result in one correction every few minutes or longer as the PEC has
corrected residual RA drift and the excellent polar alignment checks the Dec drift. Those on a budget can save considerable
expense without sacrificing results using their PEC wisely on a well aligned mount while manually guiding.
CONCLUSION
This is not to say an inexpensive mount will outperform a high end mount, however, clever implementation of PEC such as by the
LX200 can minimize the differences in results- which is what is important. Moreover, high-end mount users can use well
implemented PEC to improve results at longer focal lengths as well as improve manual guiding results.
Subject: Smart Drive (PEC) Quantitative Info
From: Frank Roddy Date: March 2002
You might want to look at the operating section of the Oak Mountain Observatory web site:
<http://telescope.8k.com/Operating.htm#Tracking>
to get some quantitative information on the improvement that can be obtained with Smart Drive.
Subject: Guide Correction Speeds? ---part 1 of 3
From: Blair MacDonald <b.macdonald
ns.sympatico.ca> Date: Jan 2003
----- Original Message ----From: Don Tabbutt<don
tabbutt.com>
For years, members have said that when East (West down under) is pushed during guiding in Polar mode, the RA
motor simply stops. It also says this in several articles in the Topical Archives. But the manual says this:
"The 2X sidereal speed in GUIDE has one difference in that it will not interrupt the Right Ascension tracking direction
to make Easterly (for Northern hemisphere) or Westerly (for Southern hemisphere) adjustments; it will merely slow
down the tracking drive to one half its normal speed."
The reason I'm bringing this up is that I just bought Ron Wodaski's book "The New CCD Astronomy", which has an
excellent section on calibrating an autoguider.
If the manual is true, the guide star will move at three different speeds on the autoguider's chip (reverse East and
West for down under):
●
●
●
2X sidereal in declination.
Sidereal when correcting West.
.5 sidereal when correcting East.
Has anyone specifically measured these speeds? They are critical when setting the calibrate time with any
autoguider. I could certainly measure it myself, but it will be at least a week before we get clear skies around here.
----------------End Original Message------------------Don: I have measured the speeds while I was writing APT. They are 2 times sidereal when the west button is pressed and zero
when the east button is pressed.
--------------------------------------------------Subject: Guide Correction Speeds? ---part 2
From: Bruce Johnston
I've measured these speeds. Going West, you go at 2x Sidereal speed for corrections. That is, the motor does indeed run twice as
fast in guide-correction speed as does the scope when it's just cranking along, following a star on its own. Then, for a correction
to the East, the motor does indeed stop. This makes the sky itself do the 'moving' while the scope sits still, giving it the 'effect' of
running to the East at Sidereal speed.
One easy way to prove that the scope stops when going East is to just set up in the daylight. Aim the scope at something on the
ground. (Be quick! It'll be 'moving'! <G>) Then press the East key and you'll see that the scope just stops. I've done this many
times for various experiments.
--------------------------------------------------Subject: Guide Correction Speeds? ---part 3 of 3
From: Eugene Lanning
I did am empirical test to verify that the motion is zero when the East button in Guide is pressed. I aligned the scope using a
imaginary two star alignment ( done during the day). I the slewed the telescope to a terrestrial object ( a lattice work some
distance away). Over a 15 minute period, while pressing the East button, the telescope location on the lattice did not move.
When the button was released, the telescope position on the lattice started moving. It convinced me that the motion was
stopped.
MAPUG is hosted by
Polar Alignment & Database Errors
in ROM 3.30 (Classic)
Subject: Database Errors in ROM 3.30 for LX200 Classic
From: Ralph Pass
There are 250 in the main Meade star database. The table below is a list of the stars in the database, the errors in RA and Dec (in
minutes for RA, in arc minutes for DEC), and the total error (in arc minutes). These numbers are for ROM 3.3 or earlier (and are
true also for ROM 4.2) The star names are omitted (they were included in the tables for parts 1 and 2) simply to reduce the
number of characters in the message.
See the description afterwards for detailed column description and explanation of how the numbers were created. Please note
that N/A means that this star does not have a location in the star database used.
Meade RA Dec Error
1 0.24 0.84 3.29
2 0.03 0.40 0.46
3 0.19 0.43 2.80
4 0.16 1.16 1.28
5 0.05 1.06 1.21
6 0.07 1.10 1.46
7 0.14 0.68 1.32
8 0.15 1.25 2.51
9 0.12 0.46 0.99
10 0.07 0.36 0.83
11 0.07 0.72 1.09
12 0.21 -0.36 1.58
13 0.14 0.35 1.19
14 0.08 0.09 1.09
15 0.12 0.43 0.99
16 0.01 0.42 0.43
17 0.21 0.40 2.86
18 0.16 0.90 2.17
19 15.35 -0.42 3.06
20 0.01 0.04 0.09
21 0.08 1.59 1.84
22 0.03 1.27 1.35
23 0.25 0.29 2.2
24 0.16 0.26 1.82
25 -0.02 0.68 0.70
26 -0.01 0.36 0.39
27 0.10 -179.56 179
28 0.21 0.80 1.17
29 0.03 0.19 0.46
30 0.13 0.80 1.74
31 0.11 0.68 1.72
32 0.09 -0.28 0.86
33 0.15 -0.01 2.13
34 0.18 1.20 3.00
35 0.18 -0.47 2.36
36 0.03 1.00 1.04
37 0.06 0.37 0.91
38 0.08 0.70 1.16
Meade RA Dec Error
126 0.09 0.44 0.67
127 0.05 -0.02 0.51
128 0.15 -0.02 1.50
129 0.12 0.60 1.84
130 0.19 0.06 1.04
131 0.04 0.23 0.39
132 0.12 0.13 1.04
133 0.10 0.64 1.39
134 0.14 0.08 2.05
135 0.06 1.20 1.48
136 0.13 0.75 1.70
137 0.04 1.00 1.05
138 0.04 0.80 1.02
139 0.18 0.46 1.71
140 0.05 0.21 0.56
141 0.13 -0.02 1.43
142 0.06 0.25 0.87
143 0.04 0.09 0.43
144 0.09 1.98 2.08
145 0.10 0.41 1.41
146 0.10 0.15 1.20
147 0.14 0.26 1.98
148 0.09 -0.26 1.05
149 0.20 0.77 2.40
150 0.04 1.09 1.13
151 N/A
152 0.11 0.92 1.46
153 0.12 0.69 1.01
154 -1.52 0.64 20.31
155 -8.99 219.92 236.87
156 0.12 0.49 0.68
157 0.12 0.09 1.31
158 0.15 -0.13 1.69
159 -0.01 1.18 1.19
160 0.15 0.06 2.23
161 0.06 0.26 0.42
162 0.06 0.15 0.69
163 0.13 0.06 0.62
39 0.02 0.46 0.51
40 0.12 0.34 1.73
41 0.11 -0.41 1.68
42 0.24 -0.42 2.52
43 0.04 0.93 1.10
44 0.08 0.74 1.35
45 0.19 0.21 2.53
46 0.14 0.21 2.00
47 0.16 1.86 3.08
48 0.12 0.47 1.79
49 -11.00 0.24 164
50 0.17 0.72 2.69
51 0.16 0.40 2.29
52 0.08 0.41 1.04
53 0.02 0.31 0.42
54 0.13 0.73 2.08
55 0.09 0.84 1.41
56 0.12 0.39 1.76
57 0.18 -0.16 1.92
58 0.20 -0.26 2.38
59 0.09 -0.49 1.35
60 0.13 0.34 1.73
61 0.17 0.97 2.59
62 0.09 0.80 1.52
63 0.05 0.42 0.61
64 0.14 0.22 2.00
65 0.12 0.50 1.36
66 0.04 0.17 0.57
67 -0.06 0.34 0.97
68 0.04 0.85 0.90
69 0.12 0.46 1.22
70 0.04 0.08 0.52
71 0.03 0.43 0.56
72 0.20 -0.13 2.67
73 0.10 0.12 1.02
74 0.08 -0.33 0.96
75 0.11 -178.62 178
76 0.09 0.95 1.68
77 0.08 -0.49 1.00
78 0.10 -0.06 1.23
79 0.10 -0.06 1.23
80 0.05 0.16 0.77
81 0.12 0.27 1.64
82 0.09 0.14 1.30
83 0.02 -599.38 599
84 0.14 0.58 2.02
85 0.09 0.65 1.10
86 0.22 0.35 1.69
87 0.17 0.55 1.60
88 0.04 0.83 1.04
89 0.08 -0.39 0.90
90 0.02 -0.79 0.83
91 0.05 1.15 1.18
92 0.16 0.68 1.42
93 0.07 0.77 1.12
94 0.07 0.58 0.82
95 0.15 -0.27 2.31
96 0.08 -0.81 1.02
97 0.03 -0.09 0.33
98 0.08 0.77 1.37
99 0.08 1.01 1.14
100 -0.08 0.43 1.27
101 0.12 0.14 0.65
102 0.11 -0.07 1.60
103 0.15 0.41 1.70
104 0.15 0.35 1.15
105 -0.01 0.83 0.84
106 0.17 1.30 2.07
107 -0.01 -0.11 0.17
108 0.16 0.48 1.40
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
0.02 -0.05 0.18
-0.71 -0.18 9.54
-13.74 32.15 159.06
-9.97 0.42 148.53
0.12 -0.01 0.80
0.16 0.96 2.41
N/A
0.25 0.49 3.53
-0.04 0.44 0.71
0.10 1.05 1.78
0.07 -4.87 4.98
0.00 1.09 1.09
0.13 0.50 1.03
0.02 -0.31 0.37
0.12 -0.02 1.61
0.19 0.61 2.54
0.10 0.54 1.54
0.11 0.71 1.52
0.16 -0.17 0.88
0.05 -0.12 0.65
0.15 0.62 1.86
0.04 0.93 1.12
0.13 1.01 1.47
0.17 0.23 1.09
0.11 0.85 1.75
0.01 -0.02 0.15
0.23 1.73 3.78
0.04 1.66 1.74
0.08 1.86 2.10
0.02 0.29 0.38
0.01 0.45 0.45
0.09 0.58 0.97
0.24 0.45 2.91
0.13 -0.71 1.35
0.08 0.62 0.95
0.09 0.96 1.41
10.11 0.78 148.10
0.18 0.29 1.98
0.06 0.32 0.76
0.04 1.15 1.28
0.05 0.47 0.77
0.14 -0.52 1.71
0.10 1.36 1.63
0.07 0.59 1.13
0.10 0.52 1.43
0.11 1.18 1.73
0.09 0.17 1.20
0.06 -0.07 0.92
0.06 0.75 1.04
0.08 0.51 1.17
0.08 0.77 1.21
0.16 0.24 2.16
0.07 0.82 1.26
0.17 0.97 2.31
0.11 0.76 1.62
0.19 -0.64 2.87
0.04 -0.68 0.90
0.08 1.11 1.60
-0.04 1.20 1.23
0.13 -0.03 1.73
0.03 0.14 0.33
0.03 0.09 0.52
0.15 1.37 2.67
0.16 1.85 3.04
0.05 0.20 0.69
0.06 0.48 0.82
1.58 -6827.04 6827.07
0.04 0.51 0.62
0.07 0.80 1.09
0.02 1.16 1.20
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
0.04 0.59 0.65
0.10 0.46 1.14
0.06 -0.03 0.80
0.09 0.33 1.36
0.06 0.39 0.56
0.12 -0.09 1.68
0.08 0.27 0.79
0.01 0.24 0.26
0.18 -0.60 2.56
0.09 -0.35 0.78
-0.01 0.54 0.54
0.16 0.06 2.30
0.13 -0.37 0.97
0.03 0.63 0.67
0.02 -0.35 0.43
0.21 1.71 2.44
0.04 -0.24 0.57
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
0.13 0.44 1.79
0.07 -0.07 0.48
0.10 1.39 1.48
0.11 1.47 2.20
0.15 0.19 2.27
0.08 0.04 1.17
0.14 0.76 1.87
0.14 0.42 2.15
0.14 0.94 1.69
0.08 0.99 1.16
-0.01 -0.58 0.59
0.08 -0.22 1.05
1.10 1.23 15.90
0.19 1.14 2.75
0.14 0.43 1.97
0.12 0.78 1.96
0.15 1.36 1.45
The table was created by using the SAC star database (which is a corrected SAO database). Star locations were converted to
apparent positions by accounting for precession, nutation, and aberration using formulae from Meeus' book. The date for the
comparison was 1 April 1995.
I take full responsibility for properly dumping the numbers in the LX200 database, for the programming of the routines to use the
star database, and for computing the errors.
There is, however, a workaround the errors for polar alignment if you have the 64K object library (e.g., ROM 3.3, ROM 4.2, or the
library option for earlier versions). The key is to use the SAO star locations and to manually do the alignment.
Try the following steps:
1. Do two iterations of the normal polar alignment procedures. This means to select polar alignment, press GoTo instead of
Enter on the first option. Note the Meade number of the star selected as the second star.
2. Tell the LX200 to use the SAO database (STAR, ENTER, UP/DOWN arrow to get to SAO, ENTER, MODE).
3. From the list of Meade numbers versus SAO numbers, find the SAO number for the Meade number found in step 1.
4. Repeat the following until you are close enough
5. GoTo Polaris (STAR, 308, GoTo ). After the beep, press GoTo again.
6. After this beep, proceed.
7. Use the manual adjustments on the wedge to place Polaris at the center (I assume you are using an eyepiece with
crosshairs, so Polaris should be under the crosshairs).
8. GoTo the other star (STAR, <SAO NUMBER FROM STEP 3>, GoTo ). After the beep, press GoTo again. After this beep,
proceed.
9. Use the keypad controls to place the star under the crosshairs and when done, press and hold ENTER until a beep. The
message on the display should say matched coordinates.
10. Repeat back to Step 5 until you are satisfied with the alignment.
Note: I am usually satisfied after four iterations starting at step 5.
Table of Meade Number versus SAO Number:
1
73765
2
21133
3
91781
4
255670
5
215093
6
54058
7
21609
51
52
53
54
55
56
57
77336
196059
132444
132542
196240
113271
40750
101
102
103
104
105
106
107
250885
81298
43310
251006
251083
222321
156256
151
152
153
154
155
156
157
N/A
225128
252853
83500
225128
8102
225335
201 228201
202 209163
203 122671
204 228420
205 209318
206 30653
207 142004
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
147420
11482
215365
54471
22268
232481
75012
248474
37734
75151
55306
308
129825
216113
110920
23789
38592
38787
39053
76199
256029
56799
56840
149283
233564
94027
112106
57522
39955
170051
40026
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
58636
78135
196698
78297
151428
234480
95912
218071
78682
151881
249647
234735
172676
172839
173047
218549
197795
173651
115456
218755
60198
N/A
115756
79666
174601
198752
175217
219501
235932
236232
117264
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
27876
15384
43629
81727
99512
251472
99809
28179
239689
180531
239791
28315
157176
251904
N/A
157323
240022
180915
251974
223603
223603
138917
252019
240259
28553
63256
100384
181543
204371
28737
157923
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
225344
183139
140430
253097
225691
8220
29520
83893
225691
121157
253346
183987
N/A
184014
159682
141052
141086
184336
17074
184415
84411
184481
160006
65485
253700
208078
208102
121962
244315
17365
160332
208 209696
209 209957
210 186681
211 142241
212 210091
213 186841
214 67174
215 187239
216 187448
217 67663
218 187600
219 104461
220 187683
221 187756
222 18222
223 87301
224 48796
225 105223
226 125122
227 144150
228 163481
229 49528
230 246574
231 230300
232 49941
233 70474
234 71070
235 19302
236 10057
237 145457
238 127029
39 131794
89 42630
139 241047
189 227707
239 164644
40 150237
90 220878
140 44752
190 102680
240 213374
41 131907
91 250495
141 224471
191 84951
241 145862
42 40186
92 236808
142 100766
192 65890
242 230992
43 132071
93 61414
143 224538
193 185320
243 255193
44 112740
94 236891
144 252582
194 244725
244 231258
45 77168
95 136871
145 182244
195 244726
245 90734
46 170457
96 237067
146 205188
196 208896
246 165375
47 132220
97 27289
147 100944
197 30429
247 191524
48 150547
98 81004
148 64203
198 228069
248 90981
49 132323
99 250695
149 225044
199 208954
249 108378
150 252838
200 102932
250 10818
50 132346
100 98967
MAPUG is hosted by
Better Mount for LX200 OTA
Best Mount for LX200 OTA --5 parts
Switching from the LX200 Fork Mount to an Equatorial? --3 parts
Other Mounts for Large OTAs --2 parts
Subject: Best Mount for LX200 --part 1 of 5
From: Alan Voetsch <avoetsch
mail.com> Date: Mar 2001
I'd like to get some feedback on the subject of mounts. I use a 12" LX200 Classic. Add to that a NGF-S, Taurus Tracker, OM1,
Meade counterweights, a Losmandy dovetail plate that will soon be holding a TV-85 and you can see there's a potential for
trouble.
So, I'm starting to look into replacing the mounting. Another of many subjects I know little of. I know of the G-11, MI 250,
AP900, 1200... I'm sure there are others.
What I'd like to find out is: what are you using, how well does it work, how happy are you with it...
-----------------------------------------------------------------------Subject: Best Mount for LX200 --part 2
From: Doc G
This is a very good question. I have studied mounts for about 6 years now. There are several things about them that I feel are
mechanical basics. I will try to explain briefly.
Let me first confess that I have used fork mounts (the LX scopes) almost exclusively. I also confess that I generally do not like
GEM mounts for the reason that they swing the eyepiece to all sorts of unpleasant viewing positions and they have some
problems in passing through the meridian when imaging. Though some of the newest GEMs are quite good in this respect.
Now I will get into trouble. Fork mounts of the size and construction that we (Meade users) have in hand are not as solid and
stable as the better GEM mounts you are considering. Of course the GEM mounts alone that you list cost more than the entire LX
in most cases. So this is not a completely fair comment.
Still from a purely mechanical design aspect, the GEM mount can be made very strong and stiff because it is very compact. The
RA and Dec axes are generally one solid block of metal with both relatively large bearings and large worm wheels. The required
equatorial angle can be built into the mount with great mechanical strength since it can be applied very near to the point where
the RA and Dec axes cross.
In summary, the mount is compact and mechanically strong. The center of gravity of the OTA is as well near the confluence of
the axes. It can easily be balanced with counter weights.
The Fork mount in contrast has a much more spread out structure. In the case of the LX scopes, The entire weight of the forks
and the OTA are suspended some 19 inches out from the RA bearing. (in the equatorial mode)
This puts great stress on the bearing structure and requires the bearings to be extremely stiff. Any flexing of the bearings is
multiplied by the long lever arm. From basic mechanical considerations, the fork mount is a large mass at the end of a spring.
Getting the springiness, which is mainly in the bearings, to be small enough takes large, high precision and thus expensive
bearings. Supplying bearings of the required size would make the costs of the fork mount much higher. I actually half completed
a fork mount which was strong and solid. But I terminated the project which was getting so costly that I would have just as soon
purchased a Paramount or equivalent.
Thus, a very much better fork mount, than that of the LX, could be (and are) built, but again at a cost of more that the whole LX
scope costs. Note that mechanically, the fork mount is similar to the English mount used on the Hooker telescope, but in that
case the fork is held on both ends. There are many variations of mounts of course. Unfortunately the fork, held at one end, is
probably the least stable of them all.
But I have gone on long enough. What this has to do with your question in summary is this.
You have purchased an affordable scope with a mount that is adequate for viewing and somewhat problematic for imaging
because of its strength and stability. You are considering mounts that are certainly better, but at a cost that is probably several
times the cost of your entire scope.
Thus as with so many things, you need to balance your use and needs against the investment you want to make. This is a
personal decision. I would choose if I had unlimited resources, an RC optical tube and put it on a AP1200 mount. That would
certainly be better than any LX scope. Of course it would cost a bit more.
-----------------------------------------------------------------------Subject: Best Mount for LX200 --part 3
From: Michael Gregory
I switched my 10 inch LX200 to an Mountain Instruments MI-250. I normally have two scopes, a camera (sometimes two at the
same time), ST 4, upper and lower Losmandy dovetails, and 45 pounds of counterweights. The measured PEC with this setup is
about 7 arcseconds (without training the mount's PEC correction).
I think all of the mounts that you mentioned are good with the AP 1200 probably being in the spectacular category.
I have been very pleased with the MI-250, although at times I miss the GoTo capability. DSCs work great with the MI-250 (high
resolution encoders are built-in), but it's just an extra step in the process. Mountain Instruments has just released a GoTo mount.
Another nice thing about using the MI-250 with the Meade 10 inch is the ease of setup. The mount Dec assembly is easily
removed so none of the individual pieces are very heavy. I still use the Meade tripod. The mount will run for two nights of
imaging using one small nine-volt battery (one of the advantages of not having GoTo capability).
-----------------------------------------------------------------------Subject: Best Mount for LX200 --part 4
From: Bert Katzung <katzung1
home.com>
My little bit of feedback (but without any experience mounting an LX OTA on a GEM). I have an LX200 8 inch and pretty much
abandoned it for photography because of shaky forks and inability to get it to track with an ST-4. (The LX is still my favorite for
star-parties.) I switched to a Losmandy G-11 and 5 inch refractor and can highly recommend the mount with this kind of load
(including an 80 mm f/11 guidescope on a side-by-side plate). The G-11 is truly rock solid; damps vibrations in less than a
second and tracks beautifully with the ST-4, even in moderate winds. I have just taken delivery on a 1200GTO and will be putting
a 12.5 inch RC on it. It is another order of magnitude up in solidity (if that's possible) from the G-11 and also tracks perfectly
with the ST-4. Depending on your load, you can't go wrong with either of these mounts.
-----------------------------------------------------------------------Subject: Best Mount for LX200 --part 5 of 5
From: David Bahr
I have a Parallax Instruments HD150C mount and it is wonderful. Great features, great stability, etc. I waffled between the
Mountain Instruments and the Parallax and finally selected Parallax because of the AP GoTo features and their excellent
machining (they custom built a pier adapter that would fit my observatory). I elected to fix the latitude on my mount which also
increased the stabililty.
Subject: Switching from the LX200 Fork Mount to an Equatorial? --part 1 of 3
From: Emilio Robau <ejr
consult-rwa.com> Date: Nov 2003
-----Original Message----aol.com
Herb HReiher
> I'm still curious as to what people think about switching
> from a fork to EQ mount, say if I take my 10" LX200 OTA and put it on a
> new or used Celestron CGE 1400 or Losmandy G-11 mount. Would such an EQ
> mount solve the problems we've discussed, and could they handle a
> piggybacked 4" refractor?
A couple of months ago I purchased a Losmandy G-11 with the Gemini GoTo and took the 10" Mead OTA off of my LX50. The
difference is like night and day. I am only talking stability not the GoTo function which are excellent on the G11 with the Gemini
GoTo. I had a choice to purchase an entire Meade 12" GPS unit and opted out for the Losmandy without the OTA.
When I first got back into observing I remember all of the experienced salts saying spend your money on a mount. A good mount
can make a marginal OTA perform. This is not a two way street. A good OTA can not make a marginal mount perform. This is
absolutely the best advice I ignored. Of course I went for the most that my money could purchase and in that vein Mead is one of
the best. I regret not purchasing the excellent mount first.
I have absolutely no regrets about the switch over to the Losmandy. I am actually thrilled with the performance of the mount
from every aspect. The bottom line is you get what you pay for. In my opinion the selling price of a G11 at approximately $3,200
new with the Gemini GoTo without the OTA is a better long term value if you want to do CCD imaging and was worth passing up
all that was offered with the comparable 12" Meade GPS with the OTA at about $3,600. I think that GEMs (German equatorial
mounts) are inherently more stable than fork mounts.
I think that anecdotal evidence suggesting that the Losmandy is somewhat more steady is kind of an understatement. I think the
10" LX50 has the same basic construction as the 10" LX200 with respect to fork structure. If this is the truth, then I can tell you
from experience (anecdotal evidence have not done the study that Doc G would do) that the G11 is far superior with respect to
stability. Rock solid mount when matched with a 10" SCT OTA which weighs approximately 28lbs. Matched with the 10" Meade or
the 11" Celestron OTA, I think the combinations are the best long term value in the industry today. I think this comes from the
fact that the GEM has the load directly above mount, Losmandy sells a great mount and Mead and Celestron have become
masters at mass producing good OTAs.
My fork mounted scope hung quite a ways away from the main structural loading point. The forks as a result were more prone to
vibration when knocked or worse yet in a small breeze. I looked at the new Celestrone CGE units and after lurking on the user's
group, hearing of the problems and realizing that this is a first production run I paid the extra money and went with the tried and
true Losmandy.
------------------------------------------------Subject: Switching from the LX200 Fork Mount to an Equatorial? --part 2
From: Emilio Robau<ejr
consult-rwa.com>
-----Original Message----From: Mark de Regt
I do have a couple of questions:
Can you take pinpoint images at 2500mm focal length, including the ability
to take long-exposure individual images (20 to 30 minutes, which is
necessary at that slow focal ratio when imaging very dim objects like
Stephan's Quintet, or when imaging with a hydrogen alpha filter)? I would
be curious to see such images with that load on a G-11.
Do you have to flip the OTA at or near the meridian? I hear that is
often necessary with GEMs, and that would be a drag in the middle of the
night, in the middle of an imaging session.
I trust that you are not suggesting that a $3200 mount is necessary for
purely visual work, but, rather, for quality imaging.
There is another, much less expensive, alternative for many, which I lucked
into because my first CCD camera was a used SBIG camera. The SBIG AO-7,
which I bought used for $1000 (it's $1200-$1300 new), when used with an SBIG
dual chip camera, solves all of the shortcomings of the LX200 mount. If one
is just making the decision to get into CCD imaging, for not much more than
the price of the G-11 with GOTO, one can buy a sensitive, large-chip CCD
camera with built-in internal guider and small pixels (the ST-2000XM) and
the AO-7. This certainly is a less expensive alternative than buying a
mount, and then still having to buy a camera, and gets you a great camera in
the bargain. In fact, right now, one can buy an ST-7ME for $1295, and color
filter wheel for $1000, and an AO-7 for $1300, and have a wonderful
combination for just about the same price as the G-11 with GOTO. I find the
convenience of the fork mount very nice, and the combination of the SBIG
camera/AO-7 to be a superb match for the LX200. I have had a great deal of
fun, and success, imaging with that combination.
-----End of Original Message----The responses to your questions are as follows.
I can not take pinpoint images at that long of a focal length. I am not sure anyone can. That is a tall order at that focal length.
Maybe someone else can but I can't. Some of this is due to my lack of experience and need to tweak the set up further. I am a
not a beginner but certainly not ready to publish anything. More importantly I think that the limitation of the equipment, even
with the good performance of a G11, will ultimately govern the ability to take the type of images you are talking about at 2500
mm. When you ask that question my initial reaction is no way. I think flexure and other issues will play havoc with the pinpoint
goal. Judging from what I have seen others do, it may be possible but very difficult to achieve. I have gained great respect for
those who have mastered imaging. Take a look at Philip Perkins and his migration to better equipment which included a switch to
a GEM. He and many others end up with GEMs as they progress in the hobby There is an abundance of examples of work done
with the G11. I think you can judge for yourself. At the end of the day I think your probabilities of achieving what you are
referring to are enhanced with the G11 or better stated a quality GEM.
I am not sure that I would replace good structural design provided with the gem with electronics such as the adaptive optics you
are referring to. I think again that it is better to start with a good foundation and build from that. I will never purchase a fork
mounted scope again. I don't have any problem with flipping at the meridian. I just plan for the flip. In my short time with this
scope It has not been an issue. When I looked at the 12 " Meade one drawback was the inability to have the scope swing fully
through the mount.
In the could have, should have, would have, done category here is how I feel. I should have not purchased the LX50 when I could
have purchased the G11 and an OTA without the Gemini GoTo for a few dollars more.
The only reason I chimed in was that I made mistakes and the gentleman that is asking should consider my opinions. I will go out
on a limb and state my opinion absolute terms and get back to work. The LX 200 is the best most versatile innovative (at the
time it first came out on the market) and has probably had the biggest impact on amateur astronomy since the invention of the
GEM. With all that said if you want to get deeper into imaging............Herb, go out and buy yourself a quality GEM. You won't be
disappointed. It will outperform a fork mounted scope hands down. Spend the extra money on the mount platform. You will never
regret it. All of the pros advise accordingly. You can even add all of the adaptive optics and such and get even better results at
the end of the night.
------------------------------------------------Subject: Switching from the LX200 Fork Mount to an Equatorial? --part 3 of 3
From: Glen Sharp <dernedid
insightbb.com>
I went to a G 11 with my 7" Mak with a 4" Vixen f/9 piggybacked and I find it way more stable than the LX200 fork. BUT as I
have learned, there are just as many tracking issues present with the G11 as there were with the LX mount. And the added
inconvenience of no GoTo, and the ever present meridian flip needed with the G11. Also with the 7" OTA, 4" OTA, finder, camera,
ST6 for CCD or autoguiding, and the needed counterweighting on the OTAs I have the G11 Close to 46 lbs of it's 60 lb max rated
capacity. As such the balance issue seems to be even more critical with the G11 than it was with the LX fork. Would I make the
change again...no. IMHO I didn't gain enough for the extra investment I made.
Subject: Other Mounts for Large OTAs --part 1 of 2
From: Scott Oates <SOates4616
aol.com> Date: Jan 2003
...Gary, since you've decided on to find an AP1200, might I suggest you also take a look at the new Losmandy Titan mount.
Initial reports show a PE of 4 arc sec and the mount is rated for a 100 lb. load. It also comes with Gemini LVL 3 Goto. The link is:
<http://losmandy.com/hgm-titan.html>
---------------------------------Subject: Other Mounts for Large OTAs --part 2 of 2
From: Alan Chen
I posted a PE plot of the Titan on my website in the equipment section (maybe this is what Scott is referring to). Without any
major adjustments, I'm getting approximately +1.8/-1.5 arc-seconds of PE out of the box. I haven't yet attempted any PEC, but
just allow my guider to correct the PE! There isn't much in the way of "high frequency" error (large transient spikes), so my
guiding is no longer a limiting factor.
<http://www.heavenlyview.com/>
MAPUG is hosted by
RCX400 Ritchey-Chrétien Telescope
Initial Product Announcement on January 3, 2005 of the
RCX 400 Ritchey-Chrétien telescope.
See Meade webpage: <http://www.meade.com/rcx400/>
Reactions to announcement
Yahoo RCX400 Groups
Factory Tour with Detail Photos --outside link
More Detailed Specs at CloudyNights --outside link
RCX400 Review --outside link
Photos— 20" on Maxmount
Subject: Reactions to Announcement of the RCX-400
From: Doc G, Date: Jan 4, 2005
I am of course concerned about the mechanical design of the fork mount. Meade has been improving the strength and quality of
their fork mounts and I suspect that they will put their best effort into the new scope. I personally prefer using a fork mounted
scope. After some experience now with the Paramount, I still have a general dislike for GEM mounts. The Paramount may be
among the very few GEM mounts that is both mechanically excellent and actually graceful in its operation through the meridian. It
is still an annoyance to do the GEM flip at the meridian. GEMs also take a much larger observatory space.
I believe Meade is putting considerable effort into eliminating the problems with the early "classic" fork mounts. The GPS line
certainly has better motors and better electronics. With a more expensive RC line, it is my hope that they will do even better with
the details of the mount. Let us hope so. My general feeling for the new line is very friendly and optimistic. If Meade can bring the
full advantage of their mass production capability onto this line, it will be a wonderful thing to see happen.
An RC with a corrector plate will certainly push current RC designs. This is a startling and excellent optical design. If Meade can
make these complex optics in large and consistent numbers, it will be a significant step forward in optical quality for the amateur
at much more reasonable prices. If anyone can do it Meade can. Remember that all has not been well with the RC scopes on the
market. They have been very expensive and the optics have been marginally made in many cases.
From: Randy Marsden <jmarsden
san.rr.com>
The new RC scopes certainly look appealing. However, given Meade's track record with new products, the DSI travails being the
latest example, I will wait a year or two to buy one so that the early adopters (unknowing beta testers) can find the majority of
the problems.
Many questions remain:
•
•
•
•
•
•
•
Did Meade use a true worm wheel this time?
What is the typical tracking error after PPEC training?
Are the optics as good as they claim?
Are the optics that much better than an LX200?
How big an imaging area do I need to be using before the advantages of the RC design will benefit me?
I already have a pier, eyepieces, etc., so can I buy the system without these accessories?
What is the power consumption relative to an LX200?
Note the spot diagram that they show is for a classical f8 Cassegrain, not for a Schmidt Cassegrain which is very deceptive as far
as I am concerned. They also show only the green spot diagram - over what range of wavelengths is this spot diagram valid?
So, around 2007, if it is demonstrably better for imaging than is the LX200, then I will buy one used, that has been debugged maybe sooner if the list of bugs does not live up to Meade's previous history.
From: Doc G
I have to say Mark that I really find this move on Mead's part to be exciting. I do hope fervently that they will have a great
success with them.
I see that James Marsden has a lot of questions. These are valid questions, But with his attitude about getting one, there would
never be any new equipment. There do after all have to be new users right away. I also think it is a total myth that the first units
are not up to standard. This is an old fashioned view. In fact the new units are often absolutely up to standards since they are the
representatives of the new line. I would not hesitate to get one right away. I have always gotten the Canon digital cameras right
away and never been disappointed. The Meade GPS line has been very good from the start as well.
I might also point out that the use of a corrector plate can actually improve the optical performance over the standard RC.
I note that many of the RCs used by SBIG members have been really poor quality. They have had many primaries which show
thousands of optical spikes due to bad edges or turned down edges. Many have been Russian made. I rather think that Meade will
not let that happen to their excellent optical reputation. Their optics have always been very good.
All in all, I am very happy about their move to a higher end scope for those more advanced amateurs. Now RC scopes are within
reach of those who have less that $50,000 to spend. Hurray and happy new year. Things are getting better and better.
From: Dave Schanz <dave23sch
valleytranscription.com>
The mount base sure does look tiny in comparison to the size of the fork arms and OTA. Perhaps it's just a problem with the
perspective shown in the picture. I wonder if the design still uses the cone/bearing set up the classics use. (I'm not sure what the
GPS models use). If it does use the cone/bearing design, that could possibly be another problem area if the OTA has some weight
to it.
I cringe to see that beautiful piece of hardware mounted on the same old. same old superwedge - on a tripod no less. I have not
heard of any changes to the Meade wedge but that's the last thing I would mount it on.
I also wonder about the three motor focusing set up that moves the corrector/secondary assembly. I'm guessing that will be an
area that is problematic - at least at the start of the production models. I am sure a computer can keep the motors synchronized,
but wouldn't it be a shame to have one of the three motors go into runaway mode? I'd like to see how that mechanism is
designed and executed.
I assume that most of these scopes would be inside domes or other types of observatories. The built-in dew heater is a nice
touch, but in my neck of the woods I need a dew shield to keep out the stray light and increase contrast. The shape of the new
OTA doesn't appear to lend itself well to using a dew shield.
So are the pictures in the advert real? Are they pictures of a real live prototype or are they a very well done computer generated
images?
All in all, if Meade can pull this off it will sure raise the bar...
Subject: Yahoo RCX400 Groups
From: Andy Blanchard
I have set-up a chat group on yahoo for this conversation to continue for those who will be buying a RCX400 or want to follow the
conversations. <http://ca.groups.yahoo.com/group/rcx400chat/>
Editor's Note: you are welcome to continue the discussions of the new RCX400 scope here on Mapug.
Another Yahoo Group: <http://groups.yahoo.com/group/rcx400/>
MAPUG is hosted by
Photos—RCX400 20"
on the Maxmount
Subject: RCX400 20" Photos on the Maxmount
From: Benito Loyola <Benito
Loyola.com>
Following are photos provided by Scott Roberts, Meade's Vice President - Brand Community & Consumer Solutions,
meade.com>
<scottroberts
Meade Maxmount webpage click here.
MAPUG is hosted by
LX50, StarFinder Dob, & Magellan Topics
Magellan II Accuracy & Alignment Issues
Magellan: Building an RS232 Cable
LX50 Dec Fix Kit
LX50 Connector Pin-Out
Connecting to Computer for Software Control
Dec Test Results -Chips, Motors, & Gears!
Fixing LX50 Dec Axis Stiffness
LX50 Dec Wobble Fix
Dedicated LX50 Web Sites
Reinstalling LX50 RA Fine Adjustment Knob
Fix for LX50 RA Adj. Knob Looseness
Magellan II Digital Setting Circles for LX50
LX50 RA Drive Solution
LX50 Drive Upgrade
LX50: Power Cord/Supply
StarFinder & Magellan Topics
Subject: Magellan II Accuracy & Alignment Issues
From: Nigel Burge <nigel.burge
pobox.com>
I own an LX50 8" with Magellan II and I have seen a number of posts which seem to fall into two distinct camps. Firstly, those for
whom it works well and secondly, those who simply cannot seem to get it to work accurately. Since
I have now moved from the 2nd category into the 1st, I thought I would share my thoughts and experiences and hopefully this
will assist others who are currently struggling with the Magellan.
1. It seems to be important to accurately level the scope. I do not understand why since the scope is polar aligned but it does
make a difference. (Any ideas why?)
2. Reasonably accurate polar alignment is important. I set the setting circles to the coordinates of Polaris and then center Polaris
in the FOV.
3. The most important consideration with Magellan is choosing the two alignment stars. The following does not apply if only one
alignment star is used. When I first started using Magellan, the accuracy was very variable indeed. Sometimes it would be very
good and sometimes quite appalling. I have found that the two alignment stars should be between 25 degrees and 75 degrees
apart. I usually try for 45 degrees apart which is usually achievable. The stars should be as close to the celestial equator as
possible. The first alignment star should be where you intend to first observe since accuracy will be best around the first
alignment star.
At first, I was trying for as large a separation of alignment stars as I could get, but have found that if the separation approaches
80 degrees, accuracy suffers enormously. For example, Hamal and Castor are 82 degrees apart and if these are used as
alignment stars, the accuracy decreases as you approach the zenith and can easily be 30 degrees out. On the other hand, if
Hamal and Aldebaran are chosen which are 37 degrees apart, accuracy is very good throughout the sky. Common sense would
indicate that a wide separation would be better so I wondered why this was not the case. On the assumption that the algorithm
that Magellan uses is a cosine function, it would be inaccurate at a separation less than 25 degrees which is what the handbook
says and would also be inaccurate approaching 90 degrees. This would appear to be the case here. If anyone knows how
Magellan works out its alignment, I would be very interested to know.
One point to watch is that as long as you accurately center on ANY alignment stars, Magellan will give you an accuracy reading of
about 100. This is purely the accuracy of your centering the stars and initial polar alignment: it is NOT a reflection of the accuracy
of how Magellan will perform. I have had Magellan giving me 100% accuracy on centering stars with terrible actual accuracy
when the alignment stars have been close to 90 degrees apart.
4. Once you have performed the two star alignment, accuracy will be very good in the region of the first alignment star chosen,
to within ten degrees. Anywhere outside that region and the accuracy will fall off. However it is easy to synch on any bright star
in the region in which you wish to observe to bring the accuracy back. The Magellan manual only gives a few stars and implies
that this is all that there are. This is not the case. Magellan has the same star catalogue as the LX200 comprising 251 alignment
stars and 100 double stars. Somebody kindly sent me a copy of the pages from the LX200 manual detailing these stars and I
transcribed them into an Excel spreadsheet to show star number, position, Bayer letter and proper name. These can then be
sorted by any of these, but sorting by Bayer letter is very useful.
Before a nights observation, I make a list of the objects I want to find, look up each one's brightest star neighbor and then look
up the Meade star number. It is then a simple matter to synch on the bright star and then go to the object I want to find. This
invariably puts the object very near the center of the FOV of a 32mm eyepiece.
I hope this helps others with Magellan so that they do not have to go through such a long learning curve as I did. At the
beginning, I thought I had made a mistake buying the Magellan but I am very pleased with it now and get excellent accuracy
every time. What I cannot understand is why all this is not in the manual!!
If anybody would like a copy of the Excel spreadsheet comprising the alignment stars, let me know by private Mail, and I will
send it.
Subject: Magellan: Building an RS232 Cable
From: Alistair Symon <asymon
gushie.demon.co.uk>
I put a question to the group a few weeks ago on how to wire up an RS232 cable that will connect a Magellan I to a PC. Thanks to
the many replies (especially from Pat Hensley) I now have this working. The reason I had to ask the question in the first place
was because the pin numbering diagrams in the Meade manual were confusing. To help others who may want to build such a
cable in the future I have put a page together on my website that describes (hopefully more clearly than Meade) how to build
such a cable. I believe the same instructions will also work for a Magellan II. The page can be found at:
<http://www.gushie.demon.co.uk/construc.htm>
Should open a new browser window over this page.
Subject: LX50 Dec Fix Kit-Now Available
From: <jblessin
worldnet.att.net> Date: Jan., 1998
While this is also a commercial advertisement I hope it will be excused this once to make an announcement of an available fix for
the many LX50's out there with Dec motion problems. An archive search will show that myself and others have been searching
for an answer to this for some time. I promised in an earlier post that I would make it known if I could source the proper parts
and put something together for all of us. It's not quite like I'm hawking red LED flashlights...
--------------If you own an LX50 and are experiencing either of these problems:
1. Slow/Fast/Slow/Fast "straining" motion in declination.
AND/OR
2. Grossly mismatched DEC vs. RA speeds. (Dec runs much faster than RA making small corrections difficult, especially when
combined with #1!).
Then your fix is finally here! The LX50 Declination Modification kit. This kit works by "Correcting" the declination gear ratio from
Meade's poorly selected 1.8:1 to a much more suitable 6.75:1. It appears Meade made a "compromise" in gear ratio selection
due to physical constraints on the fork arm. This modification bypasses those physical constraints through the use of a third
(idler) gear which allows greater selection of proper gear sizes. Once installed the dec motion much more closely matches the
speed of the RA drive AND available torque is more than TRIPLED!
This allows more accurate guiding (manual or autoguider), easier centering, and more torque available for heavy accessories
mounted to the OTA. The kit installs easily in about 5 minutes.
Includes:
1.
2.
3.
4.
Idler gear assembly (gear, bracket, shaft, preassembled)
Resized Pinion gear
Cable corrector (installs on dec cable to correct reversed rotation due to idler gear).
Illustrated installation instructions and 1 Year warranty
The gears are high quality, constructed of nylon and black acetal, manufactured by the same OEM as factory Meade gears. This is
a nice easy clean installation, no hack! NO HOLES TO BE DRILLED, fits under existing screws. Can be restored to original in
minutes.
Introductory Price $29.95 (US) + $5.00 shipping/handling.
To order or for more information contact <jblessin
worldnet.att.net>
Subject: LX50 Connector Pin-Out
From: Joe Torelli
Here are some posts that helped me to get it to work:
Post 1:
I used the settings as listed in the Magellan II manual, -300 baud, etc. My initial setup didn't work either, until I realized that the
phone jack connector pin-out was backwards from what I interpreted. The proper perspective for the cable jack pinout drawing is
viewing it from the rear (cable side). Maybe that's the problem you have also. Viewing the cable from the rear the connections to
a 9-pin RS232 connector are, looking at rear of cable connector (cable side), 1st is far left, 6th is far right.(Sequence: 1, 2, 3, 4,
5, 6) 1st - no connect
2nd - DB-9 pin 5
3rd - no connect
4th - DB-9 pin 2
5th - DB-9 pin 3
6th - No connect
If your using a standard phone cable the 1st and 6th (outside) are usually not terminated. Only the center 4 are (2-5)
Post 2:
I used ECU ("Earth Centered Universe") when I had it working. I used COM1. I'm sure I used COM port settings; 300 baud, 8
data bits, Odd Parity, & 1 stop bit.
You might have a COM port conflict. You don't want to use COM 1 & COM 3 or COM 2 & COM 4 at the same time, i.e., if your
mouse is on COM1, don't use COM3 for the Magellan. It would be safe to use COM2 if COM4 was configured for your modem since
you probably wouldn't be using your modem and Magellan at the same time. You might want to try playing with HyperTerminal or
the windows terminal program (Win3.1). The various commands are listed in the Magellan II manual.
Subject: Connecting LX50 to Computer for Software Control
From: Joe Torelli
I use Sky Map Pro on my LX50-10. I must plug it into the Mag-II hand controller. Without the hand controller there is no serial
port. There is a solution.
Try: <http://www.nova-astro.com/mg5.html>
This will go from the encoders to the serial port.
Subject: LX50 Dec Test Results -Chips, Motors, & Gears!
From: Jordan Blessing
After receiving quite a few emails about the new Dec motor & Rev. 6.0 chip, and about the Dec fix kit I decided to do some
comprehensive testing. I tested all the various parts in all possible combinations to see what works best, and what doesn't.
Below is a table showing the most interesting (bleh!) or promising combinations. I know tables often get skewed in postings, I am
adding carriage returns so make your window wide and hopefully it will be straight. There are two numbers listed for each speed,
the # to the left of the "/" is in Degrees Per Minute. The number to the right of the "/" is a smoothness rating. This rating is from
0-5. 0=Unusable! 1=Speed is very inconsistent to 5=Speed is very even and motion is very smooth. Here are the results:
Combination
2X
8X
16X
32X
--------------------------------------------------------------------RA Speed as
a reference
.82
2.3
4.1
5.4
5.X Chip
Old Motor
3.6/1
7.2/1
8.7/4
14.8/5
5.X Chip
Old Motor
Dec Fix Kit
1.8/4
2.5/4
3.2/5
5.0/5
6.0 Chip
New Motor
.72/1
3.2/1
5.4/2
7.6/4
6.0 Chip
Old Motor
.36/0
3.2/0
9.0/5
13.3/5
6.0 Chip
Old Motor
Dec Fix Kit
1.0/5
2.2/5
3.8/5
5.3/5
My personal favorite is the last one. Notice how closely the speeds match the RA speeds, also notice the excellent smoothness
rating across the board. I don't think it gets any better than this. Compared to the same setup with the 5.X chip you are slowing
the 2X speed even more (the slower the better for guiding) and still getting a wee bit more speed at 32X (a nice acceptable slew
rate for the Mag II 2 degree slews).
Notice the scores for the new motor with 6.0 chip. While the speeds are very good the smoothness ratings are pretty poor. I even
reran this test to make sure it wasn't a typo when I started typing it in! It is usable but lacks the smoothness I expect of a
precision instrument. The lack of smoothness is what can really frustrate guiding, one tap..no movement... another tap...out of
the reticle (or off the CCD chip).
Note that the testing was done on an 8" LX50, moderately loaded, reasonably balanced, tangent arm centered, 6 new alkaline
cells (all ratings would probably be somewhat improved by running from a solid 12V
source, the scope comes with AA's so I feel it SHOULD be able to operate properly with them). Degree Per Minute readings were
calculated from Mag II encoder counts. You can also see that the terms 2X, 8X, 16X, 32X have little relevance to real
comparisons of sidereal rate in either Dec or RA.
Subject: Fixing LX50 Dec Axis Stiffness
From: Gary McKenzie
Part 1-The Problem:
In common with most, if not all LX50s (apparently), my scope had very stiff motion around the Dec axis. It made it impossible to
use a finder scope or Telrad to align the scope with an object by hand - getting to within 2 degrees was a trial, and the scope had
to be slewed using the drives to center an object. One handed motion was not possible, I had to grab the scope with both hands
to move it even close to where I wanted to go. This became a real problem recently when I fitted an NGCMAX DSC. I could move
the scope beautifully in RA guide mode till the display read 0#0, but in Dec I still had to electrically slew the last couple of
degrees in dec. The problem was a great deal of "stiction" i.e. it took a lot more force to start the scope moving than to keep it
moving. This resulted in jerky movement and overshoot. Also correction in Dec at 2x speed seemed jerky - like the scope was
straining to move, then broke "stiction and moved.
The Result:
The Dec axis is "silky smooth", has no "stiction", and with the clutch off will drop to heaviest point down from any position with
no push to start it. I now, no longer have to slew electrically to position objects according to the DSCs. In addition, I
"orthogonalized" the mount and accurately set the Dec circles, while it was apart. This has resulted in the following:
- after rough polar aligning and
- two star aligning on Vega and Achernar using a reticle eyepiece I receive a warp value of 0, and can GoTo an object
ANYWHERE in the sky and find it in the central quarter of a 32mm Plossl eyepiece field of view.
Subjectively, it just feels "nice".
What You Will Need:
1. Download from Ed Stewart's MAPUG Topical Archive, the procedure for orthogonalizing the Dec axis.
2. hex keys for:
❍
the fork bolts
❍
Dec motor mounting bolts
❍
Dec gear
❍
tangent arm adjuster (at top of fork)
❍
screws that hold tube adapters that permit mounting of scope to fork 3. LARGE flat bladed screwdriver
3. wheel bearing grease or similar thick grease.
4. couple of pillows to support and protect the scope as it is lying down.
5. tissues or clean rag.
6. pair of long nose pliers (not everybody will need these)
7. GOOD, i.e. accurate, spirit level (for setting the Dec axis circle to "0") 9. screws to fit the adjusting points for tube
adapters on side of scope (see article on orthogonalizing mount)
Part 2-Step 1.
Remove the setting circles from both sides. Note that on the side with the encoder socket, that there is an easily lost small
black washer that fits between the setting circle and the Dec shaft. On this same side there is a space roughly an inch in
diameter and an inch long that looks like it is the Dec shaft, give this a tap and it will fall off- it adheres only by some dried
grease if at all. This will expose the actual Dec shaft.
Step 2.
Lay the scope on its side on the pillows - I worked on a carpeted floor on the principle that if anything fell over, it would
have less distance to fall. The side with the Dec motor should be facing upwards. Loosen the set screw on the small Dec
gear (the one attached to the motor). Remove the 2 hex screws that hold the Dec motor to the fork - note that the one
closest to you may not be fully removable yet as it may hit the gear. Now, holding the motor in one hand, take your large
flat bladed screwdriver and insert the blade between the motor and the fork. Twist the blade such that the motor is forced
away from the fork perpendicularly, this will have the effect of bringing the small plastic gear hard up against the other
side of the fork. With gentle pressure keep twisting the screwdriver and the plastic gear will pop of the motor shaft. This
may require quite some force as the gear appears to have a spot of glue added to it as well as having the previously
loosened set screw. You can now remove the hex screw that the gear interfered with. Put the motor aside.
Step 3
Loosen and withdraw the 4 screws that hold the fork to the central axis. These tend to make an alarming "CRACK" noise
when first loosened as they are VERY tight.
Step 4
Place one hand under the top of the fork arm such that you are supporting the fork and the tangent arm and one hand
under the bottom of the fork and lift away - this was sticky on my mount as the nylon bearing at the top of the fork
gripped quite tightly. If this nylon bearing is stuck in the fork arm push it out. The Dec bearing assembly consists of the
following from the fork towards the tube:
❍
-hole in fork for nylon bearing
❍
-nylon bearing
❍
around Dec shaft on tube:
❍
-washer
❍
-flat roller bearing
❍
-washer
examine the fork, mine had several bits of casting that rubbed against my tangent arm stopping it from seating correctly,
if yours is the same, snap them off with the long nose pliers (these casting leftovers are unmistakable so don't worry. My
bearings had little to NO lubrication, the nylon had a smear, the rollers had none!!!
Coat every part of the bearing assembly with copious amounts of grease, don't be worried about any excess. Coat both
sides of the washers, put a thick coating on the roller bearings, coat both sides of the nylon insert, coat the hole in the
fork, COAT EVERYTHING. When you put it back together grease should ooze out of the parts. Clean any excess with
tissues/rag. Now loosen the adjusting screw on the tangent arm - a hex screw at the top of the assembly.
To reassemble, insert the nylon bearing into the fork arm, - watch the oozing grease. Then maneuver the fork arm over
the Dec shaft and firstly, let the tangent arm seat itself, then slide the fork over the Dec shaft more oozing. Seat
everything properly. Now insert the four bolts into the fork arm and base and screw them up loosely (you will have to
adjust them later).
Step 5.
Do the other fork arm in the same way - you don't have to worry about the tangent arm though. The bearing is exactly the
same construction here.
Step 6.
Follow the procedure for orthogonalizing your Dec axis. Then adjust the tangent arm to suit. Refit the Dec motor.
Step 7.
Set the Dec setting circle as follows:
❍
- Sit the scope on its drive base with the control panel facing you.
❍
- Using a GOOD spirit level, level the base in a left / right direction i.e., place the spirit level across the top of the
control pane (may have to rotate the scope about the RA axis to do so)
❍
- rotate the scope such that the tube assembly is also in a left to right direction ( a fork is directly in front of you in
the center of the control panel)
❍
- make the tube horizontal using the spirit level, set Dec circle to zero, spin around DEC axis 180 and is level, check
circle still reads zero, adjust as necessary.
❍
-tighten up the setting circle with the scale reading 0 .
Your Dec axis should now be as smooth as silk, and it should point very well as it is now assembled better than it left the factory.
If anything is not clear let me know, and hope it improves your viewing pleasure as much as it has mine. (Mr. No responsibility
taken should you screw-up your scope!!!!)
Subject: LX50 Dec Wobble Fix
From: Nigel Burge <nigel.burge
pobox.com> Date: Feb., 1999
The original poster found that the wobble in the Dec train which shows up clearly in a side to side motion of the large Dec gear
and in a fast/slow speed on 2X (even with the excellent Jordan Blessing Dec Fix Kit) was not due to a bent threaded rod etc. but
was solely due to the fact that the carrier for the large Dec gear is fixed to the end of the threaded rod with the usual hex screw
and that this causes the carrier to be fixed eccentricity on the rod.
Since the gear carrier is not a particularly snug fit on the threaded rod, the original poster suggested shimming between the rod
and the inside of the gear carrier with tin foil to remove the play and cure the wobble.
I got round to trying this out on Friday and ....... it worked brilliantly. It was a long job to get the tinfoil shim in exactly the right
place since everything moved as soon as I tightened down the gear carrier hex screw, but after a considerable amount of trial
and error, I finally got everything in a position where the wobble of the large Dec gear against the smaller pinion gear was
virtually eliminated.
This in turn has resulted in the 2X Dec speed being completely smooth with no variations in speed at all.
I would like to thank the original poster (I wish I knew his name) for this excellent idea which removes a most annoying problem
which seems to affect a considerable number of LX50s. What is even better is that it is so simple to cure.
Subject: LX50 Dedicated Web Sites
From: Bryan Tobias <btobias
sbcglobal.net>
I have a number of upgrades and fixes for the LX50. They are listed on my website at:
<http://www.solar-system.com/>.
Note: should open a new browser window over this one.
Also see Bill VanOrden's LX50 site <bill
beevo.com> <http://www.beevo.com/Telescopes.htm>
Subject: Reinstalling LX50 RA Fine Adjustment Knob
From: Joshua Kent
>>I thought my RA fine adjustment knob felt loose so I unscrewed the set screw and removed the knob. Now I can't get it
back on! There is a thin vertical pin that the knob goes down over and the set screw tightens against. The only problem is
that the pin slides up and down and I can't hold the pin up while placing the knob over it at the same time.
I assume that the other end of this pin has a gear which meshes with the RA train somehow. The pin also has a small cam
around it, I guess for feel while turning the knob. I've taken off the bottom base plate and the top cover plate (LX50) to
see if there is access to the pin assembly. No sign of the pin assembly. Any help would be appreciated.<<
I've had this same exact problem. Well, almost. My gear rod fell out completely as I was turning the RA the first day I got the
telescope. I spent about 8 hours trying to get the thing to work. I can tell you know that you're better off not worrying about it.
Simply because you'll never really use the manual RA adjuster. But, I know it's heart breaking to experience it, so here's what I
did to fix it.
First, you'll notice that the cam holds the gear rod (the pin) off center. Well, you have to pull the gear rod up as far as it can go.
Then, rotate the cam so the gear rod makes contact with the RA spur gear (so that the thinnest part of the cam faces away from
you). This is very difficult to accomplish. You'll have to unlock the RA clutch and rotate the fork arms so the cam turns the gear
rod easily so it meshes with the spur gear. Remember to hold the gear rod with your fingers. It has a tendency to slip down into
the gear housing.
When you find that the gear rod meshes nicely with the RA spur gear, then tighten the cam down using the little hex nut at the
base. Then, making sure the gear rod is stable, rotate the fork arms a couple of times and see if the gear slips down. If you see it
starting to slip down, then grab it and pull it back up. You want to make sure the gears mesh nicely (since you don't want them
to eat each other as you rotate the fork). IF THE FORK IS HARD TO ROTATE: then you've meshed them too tight.
When you're satisfied that the fork rotates easily, the gear rod is meshed nicely, and the cam holding the gear rod doesn't move
around or slip out of position, then attach (careful not to push the rod down) the RA knob to the gear rod. Then tighten the knob
on the gear rod using the hex nut in the knob. This will stop the rod from dropping into the gear housing. By the time I got this to
work, I'd eaten up the rod, the hex nuts and the cam. I called Mike at Meade and he sent me new ones to replace the one's I
mangled.
Like I said before, it's very disheartening to have this happen, but this knob is really not necessary. Just put a cap in the hole and
call it a day. You'll use the RA knob maybe 2 or three times and then never again. The hand paddle is easier to make the small
adjustments.
Subject: Fix for LX50 RA Adj. Knob Looseness
From: Patrick Lanclos <SkySgt
aol.com> Date: Aug., 1998
Just read the tip in the MAPUG Topical Archive concerning LX50 RA knob looseness and the problems other owners have faced
when trying to reinstall the knob. Please let me add my two cents worth to this topic.
I too had this problem with my LX50 and like most everyone else, I took the knob off to see if I could fix it. Of course, I had a
heck of a time getting it back on because of slippage of the shaft. Everytime I tried to slide the knob down over the top of the
shaft, the shaft would slip back down into the scope housing. This slippage didn't leave enough of the shaft protruding for the
Allen screw to grab hold of.
What I did to get the knob back on, was to go to my local Home Depot and purchase a 1/8" C-ring (I believe 1/8" was the size,
anyway, it was the smallest C-ring they had). I then took a pair of needle-nosed pliers and pulled the shaft up out of the housing
and held it there while I clipped the C-ring onto the base of the shaft, above and flush with the top of the offset cam that the
shaft protrudes from. This solved the problem nicely! The C-ring keeps the shaft from slipping back into the cam. I can pull the
knob off as many times as I want to, with no worries.
The only tools I needed were a pair of needle-nosed pliers and a "pocketsize" flathead screwdriver. To install the C-ring, I laid it
on top of the cam with the open end up against the shaft. I then used the flat nose of the screwdriver to force the ring onto the
shaft, making sure the ring stayed flush with the cam. This will require quite a bit of pressure, so be careful not to stab yourself
with the screwdriver.
When doing this procedure, be sure you are in a small sized room with very light colored carpeting or floors. The reason is, the Cring opening is quite smaller than the diameter of the shaft, and the shaft has no groove on it for the ring to slip onto. Needless
to say, to get the ring around the shaft requires some "elbow grease", but it can be done. The small room and light colored
flooring will enable you to find the C-ring again if it should go flying across the room (and it inevitably will). The C-ring is only
about the diameter of a #2 pencil eraser and will easily get lost if you are not careful. It took me 3 tries and 45 minutes to get
the C-ring on the shaft (about 40 minutes of the time was spent looking for the C-ring after the first two tries). Total cost of the
fix was $1.50 (the cost of the C-ring).
Subject: Magellan II Digital Setting Circles for LX50
From: David Bonnell
Brian Straight wrote:
> Does anyone have any suggestions re DSCs for an LX50. I'm
> currently considering the Sky Vector at $439. is it worth the
> price difference re the Sky Vector I or II? Are there better
> bargains out there?
I agree with Scott Strawn - I too have the Magellan II for my LX50, and, while I am not as effusive as Scott about it, it is
physically well engineered, and integrates with the scope. It does have the advantage of integrating the current handbox
functions into one pendant, and I find the control features better human engineered. In any case, you may need Meade support
to get the electronics and the motor upgraded to work properly if you try to control the scope as well as simply help you position
it. That will probably be easier if you intend to integrate Magellan. However, Lumicon products are extremely well thought out,
and tend to represent some of the best hardware solutions available. You won't be making a mistake to go that route, but it won't
be as "integrated" a solution.
As far as the Magellan II - getting it to work with your scope may be an eye-opening experience. There should be some
commentary in the archives on this subject, as it has been a recurring issue. But, I now feel that I can fairly reliably calibrate
Magellan in reasonable time, and that, with liberal use of the Sync function (which may not be available on the Sky Vector
(Meade's claims suggest not)), it is possible to roam the sky and get reasonable pointing results. Even the LX200 users need to
sync after major moves in many cases.
However, at best, I find that Magellan will get me within a 1 deg FOV on larger swings, once it starts to find things. The polar +
two-star alignment offered is a waste of time. Best is a good polar alignment, one alignment star in your first area of observation
(simply press the MODE button when asked for the second star). Then, find something within approx. 10-20 deg, and sync. It
shouldn't be too close, or too far away. This time of the year, I usually align on Vega, then sync on M57. What ever you do, don't
try to sync on two objects that are really close, or sync twice on the same object. Magellan can lose it entirely! If you need more
info, check out Nigel Puttick's comments. He really has the handle on Magellan.
An alternative - JMI has a similar system, and I have heard rave responses from owners. I personally have no experience, but
while I was still struggling with Magellan, I did think about switching! But, I was never convinced that the problem was Magellan,
as opposed to my technique (or maybe a scope mount problem). Magellan II still requires a polar-aligned equatorial mounting - it
does not work as an Alt-Az tool. Partly, this is because of the tangent arm Dec drive, which is not suitable for two-axis, all-sky,
powered pointing. You will have to do most of your pointing the old-fashioned way, unclutching the RA and DEC locks, and
swinging manually. Magellan II is designed to work successfully that way.
The main thing is, DSCs are no substitute for knowing your equipment, the basic techniques for setting up, and the sky - at least
for the LX50, you will have to regularly find (or identify) objects, and resync on each new find to retain enough accuracy (as
opposed to precision - Magellan precision is quite adequate for most uses) to reliably put faint fuzzies in the field. A good wide
field EP is also a big asset! Finally, if you are into Astronomical League clubs, be aware that, at present, using DSCs to find
objects doesn't count.
Speaking of Magellan II, it is well past time for new, better firmware - does anyone know if or where to obtain Magellan II
updates - or why Meade is not providing that support? I am convinced that Magellan is using a rather unrefined alignment
algorithm, and that Meade should be well aware that more robust alignment and sync strategies are needed. Otherwise, tools like
Sky Vector... will become the clear preferred alternative, despite the integration advantage of Magellan.
By the way - DON'T plan on running Magellan from the internal LX200 battery pack. It will do it, but rapidly drains the batteries,
and motor response gets sluggish fast. Plan on adding a 12V external battery. If you can find a small (tractor-sized) marine deepdischarge battery, or adapt a gel cell of the kind now common in UPS's, you will be much happier - I actually have a mediumsized standard Marine battery (it came with a carry strap) that cost ~$31 new. Radio Shack sells several styles of cigarettelighter receptacles. Nothing fancy is needed! You get juice to run the scope "forever," extra for dew heaters, atlas-lighting..., and
no more having the scope die in the middle of a session (which WILL happen if you try to run Magellan from the internal pack).
With Magellan and the LX50, simply plug in the 12v Battery using the supplied DC cable, and you're in business - no other
batteries needed. Making this work with a 3rd party DSC may be more complex - I would hate to travel an hour or two to a dark
site, get set up and aligned, observe for a few hours, and have the DSC die well before I was ready to quit because it's little 9v
battery ran out of juice. It's bad enough when my Telrad goes dead during a session!
Subject: Magellan I & II Alignment Stars
From: Alistair Symon <asymon
gushie.demon.co.uk> Date: Sept., 1998
The accuracy of the Magellan I and II is heavily dependent on the stars you
use for alignment. I have a in-depth discussion on my website on the
various ways you can obtain good accuracy. The URL is:
<http://www.gushie.demon.co.uk/digital_setting_circles.htm>
Note: should open new browser page over this one.
Subject: LX50 RA Drive Solution
From: Gary McKenzie
I have diagnosed the problem I developed with my LX50 RA drive last night.
I am posting this for others reference.
My original post was:
my 8" LX50 has developed a problem with its drive tonight.
It is OK at normal sidereal rate, and OK at 32x , 16x ; however 8x does not work when slewing to the east (west is OK). In
addition 2x in both directions is intermittent -- works sometimes, not others. Any ideas??
After disassembling the drive and running the motor unloaded I discovered that it was functioning correctly. All speeds worked in
all directions, hence the problem was not with wires, controllers etc. The problem was with the mounting of the motor/worm gear
assembly. The motor/gear is mounted via 2 screws to a piece of L-shaped aluminum. One of these screws is a pivot that allows
adjustment of the worms contact with the RA gear.. The other controls any tendency of the motor/ gear to twist away from this L-
shaped piece. On mine the screws had worked loose from the effect of torque twist of the motor - there is a surprising amount of
this, I was unable to stop the twist with my fingers -- repeated twisting had loosened the screws so much that they had both
stripped out their threads as well!! This allowed excessive torque twist of the assembly which caused the worm to rise onto the
RA gear and stall (hence the working in one direction where the torque unloaded the worm and gear).
At 32x and 16x the motor was sufficiently powerful to still run, but at 8x and 2x it simply stalled. As the screw holes were
stripped, the l shaped aluminum needs replacing. As Meade is along way from Australia, I am fortunate enough to have a friend
with a machine shop who is going to make a new part for me - this time out of stainless steel. I doubt the problem will happen to
me again.
Subject: LX50 Drive Upgrade
From: Gary Mckenzie
Just a note to advise that Meade appears to have introduced a new drive for LX50s. The main change is that the worm gear is
now brass instead of stainless steel. In addition the motor now has a small amount of epoxy glue attaching it to the worm mount
as well as screws. This stops the rocking of the motor that happened in earlier units when changing direction. The electronics are
6.1. As before placing a jumper on jp4 lets the scope startup in southern hemisphere mode (important for me). The Dec drive
now also works better (6.1????) My scope now has approx. +/- 15 arc secs of very smooth periodic error (previously it was more
than +/- 30 arc secs.) The image will stay on the cookbook 245 chip at f50 in 1/4 frame mode for the entire cycle of the worm!!!
- I did some Mars imaging last night. Previously I would have sometimes lost the planet in full frame mode!! I have a 16 1/3
geared Dec drive with a Blessing fix kit, and the Dec works fine with this combination for autoguiding. This is a VERY well
worthwhile upgrade.
Subject: LX50: Power Cord/Supply
From: Richard Clemens
I use a 12 volt Gel Cell to power my LX50 as the internal AA's do not seem to have enough juice for more than an evening. Last
night I broke the connector for the LX50 end of the supply and went looking for a new plug. The scope requires a 5.5/2.5 mm OD/
ID Coaxial DC Power Plug but the 274-1573A connector at Radio Shack does not have any strain relief and is the one that broke.
After shopping the store, I found part 270-029 which is a coiled cord for a Radar Detector with nice right angle strain relief plug. I
cut off the cigarette lighter end and replaced it with my own connector and it is a nice addition. BTW anyone else have problems
with the 6 AA's furnishing enough power?
Starfinder Dob & Magellan Issues
Upgrading the Starfinder Dob
Upgrading Starfinder Dobs-update
Starfinder Equatorial Mods -- 2 parts
Yahoo Discussion Group Link
StarFinder Polar Align
Magellan ROM Version Numbers
StarFinder Laser Collimation Setup
Magellan II Star Charting Software
Magellan II Operation Hints
Starfinder Rotating Rings Source
Meade Starfinder Contact Person
Starfinder 16" Discussion Group Link
Subject: Meade Starfinder 16" Dob--Upgrading
From: Michael Hart with additional comments from Ed Stewart <stargazer
skymtn.com>
COMPONENTS OF THE MEADE DOB-- 8-16"
I have experience with Dobs of this class and larger. As I recall, the 16" rocker box is made of high density particle board with an
overlaid and cured white coating on the panels. The altitude trunnions are solid cast nylon (the round discs attached to the scope
tube). The altitude and azimuth bearings look like Teflon but are probably high density polyethylene. This is important which I'll
explain later.
THE SYMPTOMS OF TIGHT DOB ACTION
The action of a Dob determines how well you can hand track and the maximum power you can use practically use. A well set up
Dob hand tracks so smoothly, you track unconsciously and effortlessly.
Mass produced and even semi-custom Dobs are set up for anticipated eyepieces and accessories. Generally the mass produced
Dob will have tighter action to allow them to work for a larger range of customer types and accessories. You can adjust the action
to suit your eyepieces and accessories.
Tweaking a factory Dob for silky smooth action is worth the effort. You have already tried some of the recommended tips such as
wax which as you found out, are not a permanent fix. The reason is the high density polyethylene pads scrape the wax away. You
can add Teflon pads used by the Obsessions to replace your harder, but less slippery pads, but Teflon is quite soft and does wear
down. The smaller the pad, the lighter the action, but faster wear. In addition, you will still get some stiction when the pad
conforms to the surfacein about a minute or less. You probably know the symptoms- when you stop moving the scope in azimuth
a minute or so, it takes much bigger push to get it going again. We'll talk about a MUCH better fix for the azimuth a little later.
THE SIMPLE FIX.
Replace the polyethylene pads under the altitude trunnions with Teflon, move the pads down to decrease resistance, up to
increase resistance. Remove the rocker nut and the rocker box from the ground board. Replace the pads with Teflon. Smaller
decreases resistance, larger increases resistance.
THE ULTIMATE FIX- Start By Balancing The Optical Tube
Now is the time to balance the tube with your heaviest eyepiece. This is important as we are going to lighten the action of the
altitude. The best way to balance the tube is to move the altitude trunnions.
This is somewhat difficult and the mirror box may end up too low in the rocker box. Another way is to add weight to the inside or
outside mirror box to tweak balance. Their are optimal places for the weight too, but it is rather difficult to explain. Essentially,
you want enough weight opposite and across the eyepiece and finder. Then add additional weight as needed behind the center of
the mirror or evenly around the mirror box. This method effectively counters the off axis weight of the focuser, eyepiece and
finder.
The result is the scope that has the same balance and feel in any position. If this seems difficult to understand, adding weight to
the rocker box is fine, you just won't be able to have the altitude bearings set lower for as light an action as the scope won't hold
it's position in some locations.
REPLACING THE TRUNNION BEARING PADS
Now, replace the high density polyethylene pads under the nylon altitude trunnions with Teflon. The lower the pads, the lighter
the action in altitude. Check balance again and secure the pads with small wood screws, I recall using a #2 brass wood screw.
Drill holes as the high density particle board won't take screws well without drilling. Countersink the pads so the screws don't
touch the trunnions, but use only one screw at this time because we're not done. Altitude bearing stiction needs to be corrected
and the altitude bearings surfaced to match the nylon altitude trunnions on the tube.
Use some 1" wide 100 grit sandpaper around the trunnions with the abrasive facing the Teflon pads. Move the scope up and down
to sand the Teflon to match the trunnion curve. Do this to both sides. Now remove the tube and place it on a couple of chairs.
Use 80 grit sandpaper to roughen the nylon trunnions. Don't worry about the sandpaper being too coarse as coarse sandpaper is
needed to cut into the nylon. Spend 30-45 minutes sanding each side.
The large Dobs often use ebony star Formica with bumps to minimize stiction. Your modified trunnions are better. Teflon from the
pads is eroded by the trunnions, filling the rough surface with Teflon making a Teflon to powdered Teflon surface that resists
stiction remarkably.
STIFFENING THE ROCKER BOX
Stiffening the rocker box increases the feel of the scope and improves hand tracking at high power. The tall sideboards of the
Meade Dob are stiffened by adding outside boards. It is tempting to use a 2 X 4, but the added thickness does not improve
stiffness much, but adds dead weight.
Use 4" by 3/4" hardwood such as oak and cut the same length as the side boards are tall. Place the board on the outside of the
rocker box and secure with wood screws through the inside and underside of the rocker box. Use a lot of screws as wood glue
won't readily adhere to the sideboard surface. Locate the boards a couple of inches or so toward the trunnions. Cut another piece
for the rear opening of the rocker with an arc that just clears the mirror box. Secure with screws as before.
IMPROVING AZIMUTH ACTION- Don't Use Teflon.
The big Dobs from high end companies such as Obsession use Teflon on the ground board that the rocker box pivots above. We
will NOT use Teflon here. First, remove the pivot bolt nut inside the rocker box and mark the bearing pads, then remove them.
Go to a bearing supply house or well stocked hardware store and buy three small precision bearings with shields. The size should
be 1/4" ID and the smallest OD available within reason. Pick up (3) 2-1/2" long 1/4" bolts of grade 5 or higher and six 1/4"
washers of a smaller diameter than the bearings. In addition, you'll need a 1/2 sheet of SMOOTH Formica, the smoother the
better. Look for split or damaged sheets which you can buy cheaply. Include 50 1/4" #4 flat head sheet metal screws.
Cut off the threads and the bolt head. Now, center the pin over the marks you made on the ground board around the pads you
removed. Use a router or Dremel to cut a slot pointing to the pivot bolt. Cut a deeper and wider slot for the bearings. The pin
slots should be deep enough to allow the bearings to hold the rocker box 1/8" above the ground board. Now, use a saber saw and
blade for laminates (a fine blade) and cut the smooth Formica the same diameter as the rocker box. Drill the center for the pivot
bolt and smaller holes around the outside circumference for the #4 flat head screws. Install the Formica on the underside of the
rocker box and secure with the #4 screws. The idea is the bearings will roll on the smooth Formica under the rocker box.
THE RESULTS
At the next star party invite a someone who owns one of the high end Obsessions or other high end Dob to view something
through your modified Meade Dob. Watch his jaws fall as he experiences fantastic feather light action from your Meade Dob.
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Todd--if you decide to go as far as Michael Hart describes, then you might as
well go all the way to a motorized tracking system that requires mostly the
same modifications--the DobDriver II. For a complete description of its
installation and suggested modifications of that installation, go to the link
AstroDesigns and select the "Installing the DobDriver II" button. I devised some dirt
protection to the ball bearing's track that you might find of interest. I
found that just one sand grain could bring the az system to a screeeeching halt--Ed Stewart
I have also installed a Dob Driver II and you are indeed correct about the grit problem, hence my recommendation the bearings
be on the ground board in place of the old bearings with Formica under the ground board. One bearing should be OK for the 16",
I used doubled bearings. I didn't explain, but the smooth Formica is needed because the coating in the Meade ground board won't
support the pressure in a small area. In addition, with the Dob Driver II, the bearings must be under the rocker box and the
Meade 16" ground board will probably have to be scrapped and replaced with marine type plywood such as Baltic Birch. This is
because the high density particle board ground board will not support the weight of the scope that sometimes SPANS the feet
with the Dob Driver II retrofit. Here, the groundboard supports weight. The originally bearing pads and my proposed bearings
reside directly on top of the feet. Here, no weight must be supported by the groundboard. I would say that having average to
advanced mechanical skills will improve the finished Dob Driver II installation, an important consideration. Mine was improved
with a quick release lever for the drive motor, replacing the knob.
I found smooth Formica worked better for the Dob Driver II as well by slightly offsetting the knurled drive wheel so the bearings
were in smooth tracks, while the drive wheel was it it's own track.
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In addition or separate from these modifications, the best thing I ever added
to my Dob was digital setting circles (DSC)--they really work fantastic! I
just about lost interest in the hobby because of the frustration in trying to
locate objects past the easy ones. Now I can easily find the next object in a
minute--look up next object number from my list, punch in number, move scope
to indicated position, and observe--almost as easy as a LX200! I use
Lumicon's SkyVector, which is the same box that Orion, Celestron and JMI use.
As to Meade's Magellan unit, there's been various praise and complaint here on
the list so suggest you ask for comment if you consider it.--Ed Stewart
I added the Lumicon SkyVector as well. For the 16" Meade, order a Coulter kit which includes a brass pivot pin if Lumicon lacks a
dedicated kit for the Meade. Maximum pointing accuracy is 6 arc minutes limited by the high res encoders. Careful installation
and adjusting of trunnions and a vertical stop must be done to achieve this. My personal Dob has an on board battery with LED
voltmeter and charger for electronics and dew heaters. An electric focuser is controlled from the Dob Driver control box that plugs
into a jack with all wires inside the scope and rocker box. A heated Telrad, heated 9 X 60 finder, heated secondary and cooling
fan rounds out the setup. In addition the Lumicon box is affixed near the eyepiece.
Subject: Upgrading Starfinder Dobs--Update
From: Bruce Rubenstein
I followed your recipe for upgrading a Starfinder Dob at the Mapug Topical Archive to upgrade my Meade 16. In general the
process described there worked exceptionally well, and I am very pleased. Thank you so much for providing this information.
Allow me to add a couple of my own comments:
Rather than using a jigsaw or sabersaw to carve the formica, I used a plunge router with a laminate trimming bit. The bit I used
cost $12 and produced a chamfered edge. Its ball bearing guide contacted the ground board all around without cutting it. The
router carved a channel right through the formica, obviating the need to cut the formica accurately to size before trimming.
For screwing down the formica, I used low profile pan-head screws. Countersinking the thin formica seemed too difficult, so I
avoided it. A problem arose once I assembled the completed mount, however, in that the tops of the screws chafed against the
ground board. As it turned out, clearance wasn't the problem. Rather, the chafing resulted from the ground board warping under
the weight of the scope. This problem was quickly solved by placing three "feet" on the bottom of the ground board as close as
possible to each of the three bearing assemblies. This way, the weight of the scope and rocker box transmitted straight down
through the bearings to the feet and straight into the ground. The feet must be placed within an inch or so of the bearings to
avoid warpage (I think. I didn't actually try moving them).
Once the chafing problem was solved, the scope could spin freely about its new ball bearing base. In fact, it spun too freely. One
small shove sent the scope into a near 360. Also, small adjustments produced subtle but annoying backlash, possibly caused by
deformations of the formica at the bearing contacts. Both of these problems were solved by adding small squares of Teflon
between the ground board and the rocker box. I used three squares, each about 1/8" high and 1/2" square, along the outer
circumference of the ground board. One Teflon pad was placed mid-way between each pair of bearings. When I tried to use fewer
than 3 Teflon pads total, the ground board deformed again, and the annoying chafing returned.
Subject:16" Starfinder Equatorial Mods --part 1 of 2
From: Jeff MacQuarrie <jamacq
erols.com> Date: Sept 2001
I have successfully autoguided the 16" Starfinder using a Cookbook CB245. The book and website contains a fairly simple circuit
that you can build that will allow the camera to autoguide. The only modification I had to make to the given circuit was to
duplicate the functionality of the hand controller for my dual axis corrector.
See the following on the Cookbook homepage:
<http://wvi.com/~rberry/cookbook/cookbook.htm>
For those interested in Starfinder mods, there is a Yahoo group that several of us started last year that now has over 140
members devoted to this scope. This group is devoted to discussions related to the Meade 16" f/4.5 Starfinder Equatorial, 16"
Starfinder Dobsonian and the Meade DS-16. Discuss upgrade modifications, imaging techniques and other topics related to this
scope.
<http://groups.yahoo.com/group/Starfinder16>
You can see both film and Cookbook CCD images that I've obtained with the Starfinder 16 at:
<http://members.aol.com/tchphysics/>
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Subject:16" Starfinder Equatorial Mods --part 2 of 2
From: Jeff Gibbons <Jgibleuler
aol.com> Date: Oct 2001
I am writing to let others know about some modifications I made to my 8" Starfinder Equatorial mount. I first purchased Rotating
Rings. They allow me to view conveniently but they are relatively heavy. I added 20 pounds of extra weight to the shaft and
eventually purchased the weight used on the 10" Meade Starfinder. The weight is much more convenient than gym weights and I
have to admit well worth the $100 or so for the item. As I added more weight I found that the scope did not track well. The
motor took a few seconds to get itself up to speed and was straining. Balance became crucial. I took the scope apart and found
that the nylon bushings were deteriorated, especially at the top of the RA shaft. I saw an article in ST which featured some
innovative optics on a SF mount. The bearings in the mount caught my eye. I tried to find someone who did this work, but I could
only find people who would "give it a try."
Eventually a chance contact put me in touch with a fellow who owns a firm which makes laser range finders for the military and
who used to make radio telescopes! He certainly understood what I needed. We agreed that new bushings would work so he
made replacements from oil impregnated bronze. I added a thrust bearing at the top of the RA shaft where it joins the Dec shaft..
A 1" id thrust bearing is hard to find so I settled on a metric bearing and a spacer. This bears the downforce of the mount in the
axis along the RA shaft. The bronze bushing bears the weight pushing down at 90 degrees from that.
With the clutch off, the thing spins like a propeller. It is smooth with very low friction and an incredible improvement over the
deteriorating nylon bushings. The motor jumps up to its proper speed and it tracks smoothly and accurately.
As an aside to all this I changed most of the screws, nuts and bolts from those used originally to ones with real Allen heads. I
recommend this in any case. Just be careful in tightening. When you have a real Allen head you can overtighten and strip the
threads. I also replaced all the washers with stainless and used two where possible. The original hardware will bend over time. If
you adjust your clutch frequently get washers for the clutch adjusting screws, there are only lock washers there and they chew
up the clutch plate if there is no protecting washer.
All of this was a prelude to getting a Magellan II. I felt that I really didn't to spend the money that unless the mount was
excellent. The improvements have maximized the mount so I will buy the M.II shortly.
I have also purchased the JMI DX3 with Motofocus which is outstanding. I also purchased the JMI Wheelie Bars so I could roll the
mount across the floor of my van. I just attached the JMI EZ Align which is excellent as well. It has an illuminated reticle which is
the best I've seen. I've had the mirror checked for its configuration and the tests confirm the viewing impression, it is fine. I had
the primary recoated at QSP with Enhanced II coating and had the secondary coated with Endurobright. The tube is flocked and a
fan is mounted at the rear. The fan blows out and pulls air in through holes in the tube just above the primary. The fan is
mounted in a Lumicon Tube Cover (with the center cut out) which a large rubber piece. The rubber provides insulation from
vibration and seals the tube so that the air flows as intended.
Next steps will be a longer tube to minimize the secondary along with a Protostar spider . I am leaning towards a Sonotube
because I like to tell my wife that it's only a "cardboard tube telescope".
These scopes have been around for 30 years so I'm sure that these changes are nothing new. I welcome ideas and corrections
from the other owners of these scopes. I'll let you know how the Magellan II works out.
Subject: StarFinder Polar Align
From: Mike Stute <mstute
compucom.com>
If you get those bolts too tight then the clutch doesn't work, but it will still track. With all the StarFinders, after you move the
mount by hand, it can up to a minute before the drive starts tracking again. I don't know why because I've never fully
investigated it, but I do know there is a lag time in most mounts before the nylon clutch grips again.
Two things are extremely important: balance and alignment. The DC motors are fairly weak, and a SF 10" fully loaded with
camera or CCD, motorized focuser, and 50mm guide scope can give the motor fits. In this case, loosen all the bolts on the clutch
plate, carefully balance the scope and mark the position of everything so you can get there again with minimal fuss (I use red
marks for astrophoto work and black for observational). You can just leave the mirror in the astrophoto position.
Rotate the scope so the shaft is horizontal, and move the counter-weight in and out until you get it perfectly balanced so it stays
in any position even with the bolts completely loosened.
Rotate the scope so the scope is completely horizontal and slide the scope back and forth in the straps until you get rotational
balance and it will stay in any position regarding rotation.
Then rotate it all over the place. If properly balanced it should stay put. Once you achieve that, tighten the clutch bolts so the
drive will engage, and mark all your positions.
This is tough because switching from a 12mm Plossl to a 20mm Nagler, and the difference in weight is enough to cause an
imbalance. Hopefully, it won't be too much.
Then as for alignment, make sure your a perfectly level and the latitude adjustment is right on. After that, standard 3-star
alignment should get you going.
Subject: Magellen II ROM Question
From: Tom <TheRone
aol.com> Date: Dec., 1997
According to Mike Liegh at Meade, the LX50 comes with two motor chip sets. An RA motor assembly stamped 500K should have a
thinner (~1/4" thick) chip labeled version 3.1. A motor assembly stamped 1K should have a thicker (~1/2" thick) chip labled
version 5.3. I have the 500K stamped motor assembly with the ver 3.1 chip and have not noticed any problems. Mike said that
some had problems due to the chips and motor assemblies being mismatched.
The correct chip would have a sticker on it that read: 35-4000-12 R 5.3. A scope with a 500K stamped motor assembly should
have a chip labled 35-4000-11 R3.1.
Subject: StarFinder Laser Collimation Setup
From: Mike Stute <mstute
compucom.com> Date: Feb., 1998
The following procedure is used to setup a StarFinder (Dob or EQ) to use a laser collimator (actually any Newt.). You first have to
do the mechanical setup and prepare the optics. Then learn the procedure for continued collimating.
1) You're dealing with your expensive optics here, remove all rings, necklaces, watches, and other jewelry.
2) Lay the OTA (Optical Tube Assembly) down on the a table so you can see the backside of the primary mirror mount. The
mount has three feet that contact the SonoTube. Meade usually marks one of these feet with a small red paper dot. If you don't
see this dot, then pick a mirror mount foot yourself an mark it with something that you can easily see later like a dab of red paint
(you want something permanent). Mark the side of the tube where the same foot contacts the tube so you can see the dot with
the mirror in place. Once again, Meade usually marks this with a red or orange paper dot. Whenever you put the mirror back in,
make sure you align the two red dots or whatever marks you've chosen.
3) Remove the primary mirror by removing the three bolts in the OTA at the primary end of the OTA. These bolts screw directly
into the mirror holder assembly so there are no nuts on the backside. The primary lifts out the back. Set it mirror side up and
observe every precaution.
4) Remove the secondary mirror. To do this, set the OTA on the ground with the secondary at the top. The secondary mirror is
mounted on a threaded rod. The rod is mounted through a hole at the intersection of the spider vanes and has two nuts on it.
One nut is on the mirror side, the other is what actually holds the secondary in place by screwing onto the threaded rod on the
other side of the spider vane. Using a small crescent or appropriate sized box-end wrench, loosen the nut on the back side of the
secondary. Once it's loose, reach through an opening in the spider vanes and grasp the BACK of the secondary. Make sure you
grab the back of the secondary or grab it at the top were the threaded rod protrudes from the spider vane. Be careful not to
touch the optics. Completely remove the previously loosen screw the pull the rod out of the spider vane mount by pulling the
secondary assembly down. Set it aside with the primary.
5) At this point, you have an OTA with no optics. Next remove the focuser. If you are still using the standard Meade focuser, it
has four screws that hold it in the OTA. Each bolt has a small nut mounted on the inside of the tube. They are easy to see if you
look into the tube from the spider vane end. Rack the focuser all the way out, remove the four bolts with a screwdriver and a pair
of needle nose to hold the nuts. Gently pull the focuser off the OTA.
6) Can take an hour or so to greatly improve the scope with a very simple modification. But this step is strictly optional. Take the
tube outside and remove the finder from its bracket. Get some dull black spray paint. Heat resistance paint, such as used on BBQ
grills, works great. Take a 9" piece of string and tie it around a pencil. Hold the other end in the center of the hole the focuser
was mounted in, and use the string like a compass to mark of an 18" circle around the focuser. Mask around this circle with
newspaper and tape, then paint the whole area around the focuser dull black. You'll get a lot less glare from that shiny white tube
in your peripheral vision. If you do this step, let it dry at least a day under a fan.
7) Now we'll prepare the optics. In this step we need to mark the center of the mirror while maintaining its reflectivity. The laser
is going to strike the secondary, bounce off it and hit the center of the primary. As part of one of the collimation steps, you will
adjust the secondary to make sure the laser strikes the exact center of the primary. One of the best ways to do this is to get
those adhesive backed rings used to reinforce holes in notebook paper, and place it on the center of the primary. This won't
cause a problem with your optics since the center of the primary is in the shadow of the secondary when properly collimated.
To find the center of your primary, start by respecting your optics. Keep everything off it. Fingerprints are nasty to remove.
Forming a triangle, the mirror is held to the mount by three clips. Using sewing thread, tape a piece of thread from each clip to
the two clips opposite of it. Keep the thread taunt by not especially tight. This forms a triangle of thread. Keep the tape and the
thread off your mirror. Using a ruler, measure the length of thread going from one clip to another. Note the center and mark it
with a tiny piece of tape. Do the same with another line of thread between another two clips. Now for each piece of tape marking
the center of a line, go to the post opposite and attach a piece of thread long enough to cross the whole mirror. Tape one end of
it to the mirror post opposite the center mark on the other side of the mirror (on top of everything else), and lay the remainder
on the table. Do this to the other clip opposite the other center marker. Now stretch the two pieces of thread across the mirror
and line them up with their respective center markers on the line opposite the clip they are attached to. Where the two lines
bisect is the center of the mirror. Mark it (another person is invaluable here) right under the intersection of the two bisecting
threads with a non-permanent felt tip marker. It doesn't have to be especially dark. This is the center of your mirror.
With tweezers carefully place the adhesive ring around the spot marked on your primary. The reinforcement ring's center hole
should surround the dot on mirror and the dot should be centered in the ring. Press the ring down firmly. Use some rubbing
alcohol (very little) on a Q-tip to gently remove the marker dot from the center of the ring.
You also need to find the center of the secondary. Since it's much smaller you can use a millimeter ruler and measure both ways.
You can't, of course, lay the ruler on the optics. I did this by mounting the secondary on my workbench so the mirrored surface
was face up and level. I carried my measurements a few millimeters above the mirror by hand, and marked the center with a nonpermanent marker. Even though you see the center of the secondary, it is only looking at the shadow of itself on the primary, so
once again, the small dot from the marker isn't a problem on the optics.
8) Time to square and face the focuser. Measure the outside diameter of the OTA up against the outer rim to get a good accurate
measure. Better yet, get some dry wall tape or some cash register tape, and wrap it around the tube, cutting it exactly to the
proper length so the two ends just meet. Fold the tape exactly in half to find the median. Or just use your measurement to
determine the center. Wrap the tape around the tube with the center fold centered over the eyepiece hole. Where the two ends
meet on the other side is the exact opposite of the tube. Mark it with a pencil. If you measured, make certain you keep the tape
the same distance from the end of the tube (make a lot of little measurements down the length of the tube) and determine where
the opposite side of the tube is.
Now measure from the secondary end of the tube to the center of the focuser hole. Let's call this number A. Now on the exact
opposite of the tube measure down the tube from the secondary end a length of A (where you marked earlier). Mark this on the
scope with a pencil. Your two lines should intersect. One showing half the distance around the tube from the center of the focuser
hole, and the other the distance down the tube to the center of the focuser hole. Force a needle or pin through the side of the
SonoTube until it just penetrates the inside so you can see it. This is the spot exactly opposite of the focuser. The focuser should
be exactly square to this. Mark this spot on the inside of the OTA with a dab of White-Out, white paint, or an adhesive white
paper circle.
While you have the focuser off, take some liquid, not gel, super glue and squeeze it into the exposed cardboard sides of the holes
the focuser fit into. Get it nice and wet in all four holes, all the way around the inside. You want the cardboard to soak up the glue
and reinforce a larger area then the hole. Since you're there, do the same thing with both sets of holes that the primary mirror
mounts into (both the visual and the photographic position). This makes the holes make tougher and less prone wear which will
cause wiggling of the focuser or mirror. Let this dry.
Put the focuser back on the scope, but only tighten the bolts tight enough to hold it square. Put your laser collimator in the
focuser and turn it on. It will project a red dot to the other side of the tube, hopefully directly on top of the white dot you placed
there. Now you need to start tightening down the focuser and either use the focuser adjustment screws or shims to fully tighten
down the focuser while keeping the laser's red dot on the white spot. Once done, make sure the focuser is nice and tight and that
the laser still projects it's dot on the white circle on the other side of the tube. The focuser is now square.
9) Calculating the offset. For Newtonian optics, it is necessary to offset the secondary mirror both away from the focuser and
towards the primary mirror to fully illuminate the edges of the field. This is due to the 45 degree angle of the secondary causing
one side of the light cone to be bigger.
To calculate this offset use the following formula:
S = secondary mirror minor axis
D = diameter of primary mirror
F = Focal Length
O = one half of the outside diameter of tube H = focuser height from the bottom to a fully racked in focuser
I = "in-travel" distance of focal plane above fully racked in focuser
L=O+H+I
offset = S * (D - S) / 4 * (F - L)
So for my 10" with a low profile Crayford focuser L is (all measurements in millimeters)
L =152.4 + 38.1 + 76.2 = 266.7
S is 60.198 (standard)
D = 254 (standard)
F is 1140 (standard)
So my offset is 60.1 ( 254 - 60.1) / 4 * ( 1140 266.7) = 3.3 mm
This offset is divided in half. One half is applied to move the secondary away from the focuser and the other half moves the
secondary towards the primary.
10) Re-center the primary. Replace the primary mirror by aligning the dot on the mirror with the dot on the tube and place the
mirror in it's normal position (I always used photographic). For non-StarFinder Newts it's important to make sure the mirror is
centered on the mount and mount is centered in the mirror box. With the StarFinder's, you can't adjust this. Meade does an
excellent job though. (I've done this procedure on about 12 different StarFinders and all are centered extremely well).
11) Square and offset the spider. If you have a four vane spider, you can usually hold the laser collimator on the surface of the
spider with the laser shooting through the hole the secondary normally mounts in. Hold it carefully so the spider is not
compressed. Make sure the collimator is level against the spider and see where the laser strikes the primary. BE CAREFUL, the
laser will reflect off the primary and back out the front of the scope if the primary is not aligned properly. Do it from the side and
hold something up in front of the scope first to determine where the spot lands outside the scope. You don't want it hitting you
directly in the eye. Turn on the laser. Look to see where the laser strikes the primary. If hits the center of the mirror in the
adhesive ring, you need to do anything except apply the offset.
To square the spider vane, you need to move the spider until the laser hits the center of the ring you placed on the primary
earlier. If this is off by more then 1/2", you need to check the primary mirror in the mirror box. The spider is held in place by four
screws into the tube. To move the spider, loosen the screw on the end of the spider opposite of the direction you want it to move,
and tighten the one in the direction you want it to move. Due one axis at a time, making small moves. Check with the laser often,
and keep going until the laser strikes the center of the primary. If the spider stops moving and it's not centered at any point in
this process the primary is not center in the OTA.
Once the spider is square you need to apply half the offset to move the secondary away from the focuser. Most Newtonians
mount the focuser on the same axis as on of the spider vanes. This is the case with all the Meade's I've seen (it's a good design).
For most 6" to 20" Newts this offset is small (around .5 to 3mm), so a couple of turns on the screw opposite of the spider
opposite of the focuser is all that it takes. Remembering you're applying half the offset, so in my previous example, it's 1.65mm.
Finish by loosening the spider mount screw on the focuser side of the vane by the same number of turns.
12) Replace and offset the secondary. This is the toughest part. put the secondary back in the spider and replace the outside nut
that holds the secondary in the spider vane. Tighten it to secure the secondary but make sure you can rotate the secondary.
Look in through the eyepiece. You should see your eye, the reflection of the primary on the secondary, and the reflection of the
secondary on the primary. It's all a bit of mirrors without the smoke and kind of fun to do. Now for the rest make sure your eye is
centered in the focuser. This is easiest to accomplish by using a 35mm film canister. Drill a small hole in the very end of the
canister. Most film canister have a little dimple on the bottom. Drill this out. Cut the canister below the rim that holds the cap on
and it will now fit in a 1.25" focuser or 1.25" focuser adapter. Look through this tiny hole. It will guarantee your eye is centered
on the secondary.
Looking through this perform the following:
A. Rotate the secondary until the reflection of the primary is centered all the way around.
B. Move the focuser in or out until the edge of the primary is just seen on the secondary. When the primary is centered,
tighten the secondary in place.
C. You should see your the film canister surrounded by the secondary, surrounded by the primary, all centered.
With that done, remove the film canister and place the laser in the focuser. Once again, it's important to realize the optics aren't
aligned and it's possible that the laser may shoot out the end of the open tube. BE CAREFUL. Look inside the open end of the OTA
to see the reflection of the secondary in the primary (your look at the primary) to see where the laser is striking the secondary
mirror. If it's right on top of the dot you placed on the secondary you only need apply the offset. Otherwise, you can adjust the
secondary. Out means towards the front of the scope and in means towards the primary. Move it out by turning the screw on the
secondary side of the threaded rod counter-clockwise and turning the nut outside the spider vane clockwise. Move it in towards
the primary by doing the opposite. To adjust left and right, rotate the secondary in the holder. When the laser strikes the
secondary on the dot, it's time to apply the offset.
You want to apply half the offset calculated in step 9 to move the focuser towards the primary. This means moving it in by
loosening the nut inside the spider and tightening the nut outside the spider. Once again this is a fairly small distance, so a few
turns is all it takes. To be very accurate, you can measure the distance between threads on the threaded rod, and how many
turns of the nut it takes to make a full rotation by counting the threads inside the nut. Otherwise, use a ruler to the best of your
ability held up to against the inside of the spider vane. Once the secondary is in place, check it's position again with the laser (it
should be slightly on the "out" side of the dot now).
You can now remove the dot from the secondary with a little alcohol and a Q-tip (use the weight of the Q-tip to do the job). On
large Newts (16"+) may no longer be in the shadow of the primary. We're nearing the end.
13) Adjust the tilt of the secondary. On the back of the secondary are three screws. These work like the wing nuts on the back of
the primary. It allows you to adjust the tilt of the secondary. Put the laser back in the focuser and turn it on (CAREFUL AGAIN).
Look inside the tube to see where the laser is striking the primary. At this point, the laser strikes the secondary, is reflected to
the primary, and is reflected back to the secondary. If the mirrors are way off, it may not hit the secondary the second time.
In this step the goal is to get the laser striking the center of the primary inside the ring placed there earlier. Using a Phillips screw
driver, gently adjust the three screws on the back of the secondary to get the laser striking inside the center of the ring on the
primary. The laser may still not hit the secondary again because the tilt of the primary is not yet adjusted. Just make sure the
laser coming off the secondary strikes the center of the ring on the primary.
14) Last step, adjust the tilt of the primary. Rack the focuser all the way in. Hopefully the focuser tube will stick out of the bottom
of the focuser. Take the cap from the film canister. Drill out the exact center to make a 1/4" hole. Place this on the end of the
focuser (1.25"). It will fit it perfectly. Place the laser in the focuser and turn it on. Since we haven't adjusted the primary, it is
important to be careful when looking in the scope. Look in the scope so you can see the bottom of the focuser. The laser will exit
the hole of the canister lid, strike the secondary, bounce to the center of the primary, bounce back to the secondary, and finally
hit the bottom of the film canister lib again. This means you should see a dot on the film canister. Remember (you've been
careful right?) the laser may be missing the secondary on the return trip and exiting the front of the scope. If it is, start adjusting
the wing nuts on the back of the primary until you see laser strike the secondary again. On the 10" and larger you can usually
look through the gap in the mirror mount to see the dot on the bottom of the focuser.
This is how the scope will normally stay after the first time. You are now rough aligned and have a red dot on the film canister lid
on the bottom of the focuser. The object is now to further adjust the primary until the red dot on the canister lid disappears into
the hole in the center. I always get my willing wife or a star party attendee to watch the dot as I move the adjust the primary.
With practice all you need is "left, right, up, or down" from your partner, and you'll be able to place the red dot in the center of
the lid where it will disappear entirely.
>From now on out you will probably only need to perform step 14, and occasionally 13 as the scope is jarred during travel or
setup. In 2 years of laser collimation, I have only done steps 13 twice (initial setup, and one other time). Step 14 takes about 30
seconds, and I do it at the beginning of every observing session, and sometimes a few times in the middle.
Now you have prefect Newtonian collimation in about 30 seconds any time you want.
Subject: Magellan II Star Charting Software
From: Joe Longo <sthnstar
southernstars.com> Date: Oct., 1998
If you have a Magellan you should run SkyChart III. SkyChart's user interface is ideal for scope support and field observing. The
latest version also prints superb finder charts, and even plots the scopes field of view on the chart. You an download a fully
functional demo from the skychart web site:
<http://www.southernstars.com/skychart> Note: should open a new browser window over this one.
Subject: Magellan II Operation Hints
From: M. Searle < msearle
west.raytheon.com> Date: Sept., 1998
After some teething pains, I've generally been quite happy with the Magellan II; I have a 16" Starfinder Equatorial, and it makes
life much easier when looking for faint objects. If one follows the directions (plus some hints) the M-II will put an object in the
field at 80X every time. Other products are less expensive, but the M-II is made-to-fit.
The Hints:
1. Check all of your (and Meade's) connections, especially the encoder connectors (solder 'em!). If you center a star, the raw
encoder counts (before you do an alignment) should always end up where they were after moving the scope around; this
will also show up any looseness in your mount or optics.
2. I use a one-star alignment, then sync to a star near your first object. Definitely use an eastern-sky, meridian star for the
first/only alignment star. Meade has a short list of alignment stars (30), but as far as I can tell the entire LX200 object
database is in there for syncing on. Doc Greiner's homepage has detailed database info/links. You can get away with using
any two of the three alignment steps in Meade's instructions (pole and two stars) if it's cloudy.
3. The encoder gear ratios (just the signs) differed from what Meade gave me; an hour of at-home experimenting using the
mount's setting circles to fake-align the system will tell you if the ratios are correct & give you good practice besides.
4. Make sure Meade gives you a "1K" R.A. motor (not a "500", as stamped on the metal gear housing). I've seen other posts
that emphasize the need for this without my really knowing why; Meade also acknowledges this & will send you a "1K"
motor without hassle.
5. The advertised "GoTo" function is supposed to slew the scope the final 2 degrees or so onto an object (but doesn't). Meade
will fix this "soon" in a new S/W release, but I prefer manually centering anyway to minimize fussing with the tangent arm,
etc.
6. The M-II doesn't actively correct (operate) the axis drives, but does display the true pointing coordinates (the Dec reading
will change more or less rapidly depending upon your mount's mechanical polar alignment). Meade's advertising and even
the manual are misleading on this feature.
7. Use an external power source (12V); it runs the motors faster and I got tired of buying AA batteries.
8. I have just tried the updated Earth Centered Universe program <http://www.nova-astro.com/> on a laptop; it worked well
with the M-II in the field. The M-II uses only three LX200 commands; ACK, :GR#, and :GD#. The serial port needs to be
manually enabled first.
9. I like being able to store your own objects; you can punch them in before an observing session.
Subject: Starfinder Rotating Rings Source
From: Jeff Gibbons <Jgibleuler
aol.com> Date: Feb 2001
I read that someone was looking for Rotating Rings for Meade Starfinders. Someone may have already answered this question
but they are available at Parallax Instruments. I've had them for about three years, they work well and really do eliminate the
problem of getting to the eyepiece. I use a bar stool for seating and rotate the tube to me. This makes viewing very comfortable.
Subject: Meade Starfinder Contact Person / Starfinder 16" Discussion Group
From: <Torq460
aol.com> Date: Dec 2001
For questions re: the Starfinder line of scopes we owners have a friend at Meade: call Paul McDaniel. He is far and away the most
knowledgeable about our scopes. See Meade topic for phone numbers.
Also be advised that there is an owners group on Yahoo dedicated to the 16" Starfinder DOB and EQ. Great,source of advice and
ideas:
<Starfinder16
Yahoo.com>
MAPUG is hosted by
LX90, LXD55, & ETX Specific Issues
International Meade LX90 Telescope Users Group & Website
LX90 vs. LX200
Differences in LX200 vs. LX90 OTA
LX90-- Pitfalls to Avoid
Janet Miller's Everything LX90 Website (many disassembly & repair tutorials) --outside link
LXD55 Topics
ETX Topics
Subject: International Meade LX90 Telescope Users Group & Website
From: Wayne Powell <wayne.powell
aerowood.com> Date: May 2001
Would you consider linking to our current web resource for the LX90 on the MAPUG-Astronomy.net home page: International
Meade LX90 Telescope Users Group or IMLTUG Archive & Mailing List:
<http://www.yahoogroups.com/group/lx90/>
Note: should open a new window over this one.
We have over 450 members and are in the process of establishing an online web site resource <http://www.lx90.com>. This
group is the first and largest international online user group of prospective and current Meade LX90 owners and enthusiasts.
Subject: LX90 vs. LX200
From: Janet Miller <LX90 Website>
In comparing the LX90 vs. the LX200, the optics should be the same. The LX90 doesn't have PEC (periodic error correction for
the RA drive), but it will accept an autoguider. The forks are little less substantial (probably a little better than the LX50s are). I
have no problems mounting a Nikon F at prime focus in regards to stability. The LX90 comes with the standard field tripod, but
no wedge. I've heard that Meade has finally come out with an adapter to mate the LX90 to the LX200 standard wedge though. I
had an adapter made for mine prior to them catching up to the demand.
The Autostar has been excellent for me, the latest update has some changes for the Accesory Port Module that the LX90 uses for
guiding, reticle and electric focuser. Finally, the GoTo accuracy is not rated to be as precise as the LX200.
Subject: Differences in LX200 vs. LX90 OTA --part 1 of 2
From: Janet Miller
The back of the OTA is different from the LX200. It's curved (somewhat sperical) with a small, flat cutout area for the focuser.
There's also 2 vertical screws just below the rear port for the Accessory Port Module to attach. The corrector end seems to be the
same. Mounting screws are the same as the 8" Lx200, as I have the Meade weight set and Losmandy dovetail mounted on my
LX90.
There's a pretty good image of the back of the OTA here on one of my web pages:
<http://m1.aol.com/kewtasheck/focuser.html> Note: should open a new browser window over this one.
The screws for the APM and the spherical back are pretty obvious in the picture at the bottom of the page.
-------------------Subject: Differences in LX200 vs. LX90 OTA --part 2 of 2
From: Wayne Powell <wayne.powell
aerowood.com>
IMLTUG LX90 User Group Moderator
<http://groups.yahoo.com/group/lx90>
Meade has been pretty specific with our group that the LX90 IS ABSOLUTELY NOT the same as the 8" LX200 OTA, though the
"optical system" is the same and theoretically they should perform the same.
The LX200 OTA has a significantly different "back end", compare pictures of the LX200 & LX90 Rear Port & Focuser assembly,
you'll soon spot the difference and be able to see if you received a mixed up corrector plate ring.
We've been charting significant numbers of QC problems from Meade as of late, perhaps nothing new, but seeing as their stock is
in the dumpster, I'm surprised (based on the number of formal complaints) that they haven't made a positive statement to
address the issue.
Subject: LX90-- Pitfalls to Avoid
From: Tom Heisey <THeisey
hs.ttu.edu> Date: 2001
I'm a fairly experienced amateur astronomer and a computer manager. One of my key reasons for purchasing the LX90 was for
public outreach programs, including satellite discussions. Naturally, tracking the ISS with the scope & video camera would be a
great crowd pleaser.
As a new computerized scope user, I fell into several pitfalls. I'd like to warn other newcomers about these problems:
1) #505 Kit:
I ordered the LX90 with the #505 cable set with the software, assuming that the software would be required to update the
AutoStar computer. WRONG. The disk contains a bundle version of Starry Nights and Astronomer's Control Panel (to control the
scope), but makes no mention of the updater program. Unless you want Starry Nights, save the $20 and by the cable kit only.
(Better yet, look at the 505 manual and build your own!)
The actual updater program can be found at:
<http://www.meade.com/support/auto.html>
and the 505 cable manual can be found at:
<http://www.meade.com/manuals/505ccs/index.html>
Mike Weasner has a quick diagram for making your own cable at:
<http://www.weasner.com/etx/autostar/as_cable.html> and
<http://www.weasner.com/etx/autostar/as_cable2.html>
2) Updater layout:
The updater program is poorly written, poorly documented, and a bit confusing to use. After getting accustomed to the strange
layout, it works OK, but could use some refining. Drag-and-drop updating is frustrating and it took me a long time to realize that
you had to drag-and-drop the file onto the button! (What happened to Windows programming standards?)
3) Upgrade problems:
One strong warning - Pause before your attempt to upgrade the AutoStar OS! I clicked the "Get update" and the system
supposedly downloaded the latest update, so I clicked the upload button. After 20 or 30 minutes of uploading, the AutoStar
showed I had actually stepped backwards from 22e to 21e! After a tech support call, I did a manual download and upload of the
22eh ROM, so all is well.
4) Updates erase drive training:
Updating the ROM seems to destroy the drive training, which left me rather disappointed and confused after my first update. I
wasn't sure what had happened and it took a while to find the remedy. However, a quick retraining session and the scope was
back to working great.
LXD55 Specific Issues
LXD55 SC-8 UHTC Sites --2 parts
LXD650 Mount Good for Imaging?
Subject: LXD55 SC-8 UHTC Sites --part 1 of 2
From: Mike Weasner <mweasner
mac.com> Date: Jan 2003
Andres Valencia wrote:
> If there are other MAPUG participants who would like to exchange information
> on the LXD55 mount or the SC-8 UHTC OTA, I'll be monitoring this list and
> will try to contribute my grain of sand.
I have started a LXD55 site to document my LXD55 8" SC experiences and provide a source of feedback, tips and links. This is a
companion site to my Mighty ETX Site, which has been online for six+ years. Have a visit:
<http://www.weasner.com/lxd> Note: should open a new browser window over this one.
I intend to support the LXD55 Telescopes Yahoo Group. I have been monitoring the group since I made the decision to acquire
the LXD55 8"SC. I recommend that LXD55 users sign up for the Yahoo Group.
-------------------------------------------------------Subject: LXD55 SC-8 UHTC Sites --part2 of 2
From: Richard Harris <rharris
elvis.com> The LXD55 Portal:
<http://LXD55.com> site is rich with information on the LXD55 scopes, with an on-line store for LXD55 related items including
a video for first-time set-up.
Subject: LXD650 Mount Good for Imaging? --part 1 of 2
From: Blair MacDonald <b.macdonald
ns.sympatico.ca> Date: Dec 2003
----- Original Message ----From: Mark de Regt
I am an experienced imager with the LX200. I have purchased a small APO refractor which I will piggyback on the LX200 for wide
field imaging. I am interested in also getting a relatively portable mount so I can take the little Tak to clearer skies and image.
The LXD650 mount is priced reasonably, especially used, and I was wondering if anyone has experience imaging with one. I will
be imaging at very low resolution/image scale, obviously, so I don't need the most perfect mount, but I was wondering, basically,
if this mount is comparable to the LX200 mount in accuracy, steadiness and reliability.
----- End of Original Message ----Mark: I use a LXD650 with an 8" Schmidt Newtonian mounted on it. The mount tracks well and works fine for astrophotography,
both CCD and film. With a 416XT, a Vixen 60mm guide scope and a 201 autoguider the mount is near capacity but works fine.
Balance is critical, if it is not perfect the mount will stall as the motor drivers overheat (this always seems to happen 19 minutes
into a 20 minute exposure). If you want to see some images let me know and I'll send you some.
---------------------------------Subject: LXD650 Mount Good for Imaging? --part 2 of 2
From: Ron Burch <Ronjonb
aol.com>
HI, Mark, I have had an LXD 650 for about five years. I have found it to be much more stable than the LX 200 mounts - it does
not "vibrate" in low breezes the way that fork mounts tend to do. I have been extremely pleased with the performance and
reliability. I bought it used; it had just been refurbished at the factory. It sits in the garage through extreme heat in the summer
and extreme cold in the winter, and starts up perfectly every time I use it. (I have used an 8" SCT on it - this is near its load limit
although the ammeter does not register pain, and most often use a Televue 85 mounted on a saddle with a guide scope). Even
with large, heavy image trains attached, tracking is very dependable - this includes the 8" SCT but it has to be balanced very
carefully. This mount is quite portable since the head is carried separate from the tripod -- I would guess that each weighs
somewhere around 35-40 lbs not counting counterweights.
ETX Topics
ETX Info Site URL
ETX/EC Repair & Tune-Up Page
ETX Repair Service
ETX Modifications
ETX Collimation Procedures
ETX70AT Computer Control Questions
ETX Astro Dual Axis Drive Corrector
Subject: ETX Info Site URL
From: Mike Weasner <mweasner
aol.com>
Contains large assortment of subjects and suggestions for using and improving your ETX.
<www.weasner.com/etx/menu.html>
Note: should open a new browser window over this one.
Subject: ETX/EC Repair & Tune-Up Page
From: Jordan Blessing <jblessin
worldnet.att.net> Date: May, 1999
I have put up a page dealing with common problems and solutions with the new ETX/EC. It contains repair and tune-up tips along
with about a meg of images showing the internals and repair procedures. I think many could well use it (unfortunately) if you
could find a place for it amongst the other "Meade Advanced Products".
ETX/EC Tune-UP Page: <http://home.att.net/~scopetronix/etxtu.htm>
Note: should open a new browser window over this one.
Subject: ETX Repair Service
From: Tim Crawford <tcarchcape
yahoo.com> Date: Jan 2003
I just received my ETX back from Arkansas Sky Observatory. Author and Professional Astronomer, Dr. Clay Sherrod does a
fantastic job of Super Charging, repairing and tune-up. My ETX scope had many problems with a lot of them being quite major.
His inspections and repairs are extensive and through plus you get upgrades to your Autostar.
I would urge you to contact him with your specific problem as your first option. A Description of the 102-point inspection
procedure is listed at <www.arksky.org/supercharge.htm>. Dr. Sherrod can be reached at <drclay
will also be surprised by his very reasonable pricing.
arksky.org>. I think you
FYI, for those of your unaware, Dr. Sherrod also provides his services for the LX line as well as all major brands of refractors,
SCT's and Newtonian telescopes. I also just received back my LX200 12" classic from Dr. Sherrod. With both of these scopes I
was very impressed with the very detailed commentary of what was repaired and adjusted as well as a report on the optical
performance and the drive system, after adjustments and repairs. Each Scope also had a Certification label attached attesting to
the Supercharge Service.
Subject: ETX Collimation Technique
From: M. Newton <mnewton1
bellsouth.net>
I succeeded in collimating my ETX. First, I took the focus knob off, 3 screws off the plastic rear cell, and I unscrewed the OTA
from the plastic rear cell. You'll find 3 sets of push pull screws on the back of the OTA. They tricky part is getting an eyepiece on
the back of the bare OTA. I used a VERY SMALL amount of super glue to TACK a Scopetronix SCT adapter (the one especially
made for the threads on the back of the ETX) onto the rear cell. I threaded a SCT visual back onto it and then inserted an
eyepiece. The scope went from nice views to SPECTACULAR views after correct collimation.
I know this may sound confusing, but it can be done.
Subject: ETX70AT Computer Control Questions
From: Dick Seymour <rseymour@wolfenet.com> Date: Jan 2004
> Could someone please advise me on whether it is possible to connect
> an ETX70AT up to a computer and use a planetarium program to control it?
> The scope has the AutoStar controller without the numeric keypad.
That's called the "494" Autostar. Yes, you can computer-control it. I've done it.
You need the Meade 506 cable/converter kit, which plugs into the AUX socket on the telescope base. Whether you can find a 506
kit -without- a software CD along with it depends upon dealer stock. The CD Meade used to package (which had Starry Night
Bundle edition) required three updates (two from Starry night, and one full ACP replacement ) before it would operate the ETX70
properly.
You might explore buying a 497 Autostar (-with- numeric keypad) on eBay or elsewhere... that will allow the use of a 505 cable
kit (which is merely two connectors and a piece of wire... you can build your own, or buy them for as little as $6 on eBay). The
497 gives you more objects, easier numeric entry, access to Meade's free updates, etc.etc.etc. for not much more cost than the
can-only-get-from-Meade 506 cable/converter set, which can NOT be home-built.
You might do well to join the yahoo discussion group:
<http://groups.yahoo.com/group/ETXASTRO/>
and (of course) visit Mike Weasner's ETX megasite:
<http://www.weasner.com/etx>
Subject: ETX Astro Dual Axis Drive Corrector
From: Jordan Blessing <jblessin
worldnet.att.net> Date: July, 1998
I would like you to consider adding my latest product, a dual axis drive corrector for the ETX Astro. I'm sure many ETX owners
would be interested. The web address is:
<http://www.weasner.com/etx/menu.html>
Note that there is also quite a bit of content there relative to the ETX, not just a product link.
MAPUG is hosted by
LX200 Astrophotography --Page 1
For Pictor Camera & CCD topics, return to Archive main page, right column.
LX200 Astrophotography Issues --Page 1
LX200 Good for Astrophotography?
Can the LX200 Deliver Precision Tracking for Imaging?
Can the LX200 Mirror Mount Allow Precision Tracking for Imaging?
LX200 & Beginning Astrophotography Questions
Piggy Back AstroPhotography
Guiding Techniques Articles Available
Helpful Hints for Astrophotography
LX200 Astrophotography Websites
Where to Process Film Images?
Film Camera Selection Criteria
Calculating f/ratio with eyepiece projection
FOV in 35mm Camera?
Back focus/JMI/Van Slyke Slide Mirror
New Evaluation Page of Filters
Go to Astrophotography Misc. Issues-Go to Astrophotography Misc. Issues--
Subject: Is the LX200 Good for Astrophotography?
From: Michael Hart
I felt the following private post to me may reflect a number of potential and current LX200 owners that may be discouraged at
trying astrophotography.
The LX200 is quite able to handle long exposures without modification. Arguably, the LX200 has the best price/performance ratio
of any scope and mount available today. Like many mass produced products, a few adjustments will improve results further. For
some of us (probably a small minority) LX200 owners, part of the challenge is getting results that compare to mounts and scopes
that are much more expensive.
A few of us tweak and fiddle with our scopes. This should not be construed to mean constant tweaking and fiddling is needed. For
example, MAPUG members are a very small minority of LX200 owners. Those that are in MAPUG that tinker with the LX200 are
still a smaller group- probably around 10-20 individuals out of many thousands of LX200 owners.
Some of us on MAPUG are pushing the LX200 design to the limits and more. Here, a few mods enable an inexpensive mount (a
relative term) to produce results of a much more expensive setup. In my case, I wanted to piggy-back an 8" f/2.5 camera lens on
my 12". The 12" has the same drive motors and gears as the much lighter 8". I also wanted to improve long exposure tricolor
CCD imaging from what I already have produced on my current scope with only minor maintenance. By improve, I mean produce
results to enable 90-100X enlargements of high S/N (signal to noise) ratio CCD images. This is of personal interest to me and
quite possibly only me.
An example of what the LX200 can do in it's existing form is on Doc G's website under CCD Imagers and Accessories, Color
Imaging Methods with the CCD Imager. Doc G's web site contains much detail about the LX200.
If your new to imaging with a telescope whether it be emulsion or CCD (I do both), I believe the biggest hurtle is gaining
experience and NOT the equipment. In fact, I recommend those starting in imaging start off with a plain camera, off-axis guider
and an illuminated reticle guiding eyepiece. Work on perfecting your techniques whenever possible and avoid getting caught up in
buying accessories you will later find you don't need. Accessories will not substitute for experience. Your acquired experience will
serve you well later as to what accessory is really needed for the desired results. Those with the financial means to purchase
whatever they want may have a steeper learning curve than others because it is quite easy for them to buy too much, too soon.
Don't let this happen to you.
Subject: Can the LX200 Deliver Precision Tracking for Imaging?
From: Doc G, Date: June 2004
Oh yes, OAGs (off-axis guiders) work. BUT, the guide star in an OAG is at the very edge of the field. Thus rotation will be about
the guide star and the stars on the opposite edge of the field will rotate the most. If the guide star is on the axis of the field, the
edge stars move half as much or less. All of these schemes have some problems of course. The very best way to image is to have
a very well aligned polar mount. I just came back from a week at New Mexico Skies where I used a Paramount ME that was very
well aligned. You could do 5 minute exposures at 4000 mm and get pin point stars with no guiding at all. The Paramount ME, by
Bisque, is the finest mount I have ever used by a great deal.
That is not to say that you cannot get fair results with a Meade fork. The LX200 12" in the Doc G observatory at the Madison
Astronomical Society dark site will give pinpoint stars without guiding when used with a Takahashie 106 mounted piggy back and
exposures are limited to 5 minutes. But I have worked on that scope for years and it is an exceptional example of a Meade fork
mount which is well tuned and well aligned.
In general, with the Meade fork mount, if you get under 10 arc seconds error (with a good PEC) over one turn of the worm (8
minutes) you are very well tuned. I did have a 10" LX200 at one time which gave only 5 arc seconds offer 8 minutes. That too
took very much tuning, tweaking and talking to the scope. (G)
For imaging with a Meade fork, I suggest very precise polar alignment, tuning the mount by cleaning the RA gears and lubricating
properly, and doing a very careful PEC. Almost no dec action should take place for the exposure period. A highly precise polar
alignment will allow for that to happen. You must align with the same total load of equipment as you use for imaging to within a
Kg or so. Attention to all of these mechanical factors will give you a fairly good imaging platform. Patience and care are required
to get these results. Fortunately the mapug archives are loaded with good information for getting the Meade fork mounts to work
fairly well. I have preached long enough about the mechanics of the Meade forks. With a lot of TLC they can be used for imaging,
but it takes a ton of TLC.
Subject: Can the LX200 Mirror Mount Allow Precision Tracking for Imaging?
From: Doc G,. Date: Oct 2004
Note on recent experience with primary mirror mounts in LX scopes.
I have recently had a good look at and spent some time tuning up a 16" LX 200 classic. (and several 12" scopes) I am assuming
that my experience with this scope reflects the design problems with all scopes of this type. I was well impressed with the
strength and fit of the mirror holder on the central tube and thus wondered where the mirror shift in this scope could be coming
from.
I fear that the mirror shift is coming from the basic flexibility of the central tube itself. This means that no amount of clamping of
the mirror carrier to the central tube will ever totally reduce mirror shift to zero. The entire weight of the mirror and tube
assembly is held at the base end of the tube. There is a strong connection between the central tube and the back plate of the
scope, but it is not perfectly rigid. I do not think you will ever be able to clamp a movable mirror in this arrangement perfectly
enough to eliminate all mirror shift.
The only way to clamp the mirror in place it to mount it in a holder that is a part of the back plate of the scope. This would of
course require a total redesign of the primary mirror holder. In fact, the mirror is so heavy and so poorly held by a light weight
spider assembly in this design that is simply not desirable for either holding the mirror fixed or for holding it without some
distortion of the mirror itself. It is time to face the fact that a scope with a movable primary mirror is not a high precision design.
This design is simply not used in professional telescopes nor is it even used in relatively inexpensive Newtonians and the like.
Another factor is the stability of the secondary. The mounting of the secondary on the corrector is flimsy at best. The secondary
shifts with scope position. That is a fact which also contributes to image shift with position. I am convinced, after this study of the
16" scope, that the design of the instrument is flawed for precision optical results.
Still another flaw is the design of the focus mechanism. There is a simply arm that pushes or pulls on one side of the primary
mirror mounting spider. This is an incredibly weak design and a poor way to move the primary mirror. It would require a
completely redesigned focusing means to fix this problem.
As I say, it is time to stop fighting the basic design flaws and use imaging techniques that get around them. These would include:
refocusing and re-collimating for each region of the sky being imaged; keeping exposures short enough so that the scope does
not move through very large arcs; re-focusing for even small temperature changes. These techniques may overcome some of the
design limitations. Then of course there are the problems with the mount that also need to be taken into account. It is tough to
image with these scopes for good reason. They are designed for viewing.
Subject: LX200 & Beginning Astrophotography Questions
From: Robin Casady <rcasady
scruznet.com>
Leigh Daniels wrote:
>I'm just taking the plunge into astrophotography and I have a quite a few
>questions. Given my usual observing location and a 7" LX200 f/15 scope,
>I'm primarily interested in planetary photography, although I'd like to
>try some deep sky stuff, too. I have an old OM-1 camera with cable
>release. I have Michael Covington's book on astrophotography.
For prime focus shooting you need to guide the photos on a star because telescope drives are not accurate enough for long
exposures unguided. For this you either need an off-axis guider, or a separate guide scope. Off-axis guiders can be a pain to use,
and separate guide scopes can have problems with flexure between the two scopes. You pay your money and choose your
problems. :-)
>I know I need a piggyback camera mount and an OM-1 T-Ring.
The Lumicon piggyback adapter is about the best you can get without going to a $400 Losmany dovetail system. It is very rigid
and can be adjusted slightly in altitude. The one Orion sells is not what is illustrated in their catalog. It is actually a stamped out
(rather than cast) bracket that would probably flex if the camera has much weight.
>I'm a little confused by the various adapters available. I see that Meade
>has a Variable-Projection Camera Adapter and that looks like what I want.
>The Meade catalog states that the Camera Adapter will also allow prime
>focus photography. Does this mean that I don't need to buy a #62
>T-Adapter? Is there a better variable camera adapter?
I bought the Orion variable adapter. It seems to be well made. I would recommend mastering prime focus photos before you go
to eyepiece projection.
For prime focus shooting I would recommend using a 2" adapter like the Orion #5272 that converts the SCT threads to a 2" back.
Then get a T-adapter that is designed for 2" backs. I like the ones Lumicon makes. They are short and vignette less than the one
Orion sells. With this setup, you can shoot prime focus. You can put a f/6.3 reducer in front of the 2" adapter. Or, you can use it
with a 2" diagonal for 2" eyepieces.
Before you settle on a T-adapter, think about focusing. Viewfinder focusing through the camera is not always accurate enough.
Read about knife edge focusing in Michael Covington's book. If you want to spend the money, the SureSharp works well. If you
want to do it yourself, you can jury-rig something up much more cheaply. Using the knife edge or Ronchi screen method of
focusing on a star will give you good focus for the moon and planets if they are near the star you focus on. Atmospheric
conditions or flexure make it advisable to use near by stars for focusing.
>Can I also use the Variable-Projection Camera Adapter with my ETX by
>inserting it into the eyepiece holder or do I need yet another adapter?
You probably couldn't reach focus because it is so long.
>Because my scope is f/15, it seems like the f/6.3 Focal Reducer might
>also be useful. Is this true? Is the Meade reducer OK or is there a
>better one?
A reducer is necessary for any deep sky photography. It is also necessary if you want to get the full moon into a 35mm frame.
The f/6.3 reducer will not give you f/6.3 because you are starting with f/15 and not f/10. If I remember correctly, it should bring
it down to around f/9.
>With the OM-1, an adapter of some kind and a focal reducer attached, do I
>also really need to buy the 7" set of counterweights? (I can't believe a
>set of weights lists for $140!)
If you do any piggyback shooting counter weights are an absolute necessity. I purchased the Orion Dovetail Counter weight
System because it is more versatile than the Meade weights. The one designed for 10" and 11" SCTs (Orion # 5152) fits the 7"
Maksutov. Just use one screw at each end and ignore the extra curved adapters. Nylon washers between the dovetail bar and the
scope are a good idea.
This balance system is a 2D system that lets you more accurately balance a piggyback camera at all angles of the telescope. I
added two small Jack Lalane weights to it rather than buy the Orion extra counterweights. You have to make bushings for the
Jack Lalane weights. I've balanced a medium format Pentax 645 with a 200 mm lens on it.
>Is the Beattie Intenscreen-Plus for the OM-1 worth getting?
I bought one, but should have returned it. A slight improvement, but not worth the cost. You should probably follow Chris'
suggestion of getting the 1-12.
>Is the Lumicon 2" rear-cell Deep Sky Filter a good idea?
No. Since you are starting at f/9, film is not sensitive enough for deep sky photos with this filter. I don't think it is very useful for
planetary imaging.
Subject: Piggy Back AstroPhotography
From: Greg Hartke <ghartke
clark.net>
Prime focus astrophotography, whether film or CCD, is such a challenging art that I thought it appropriate to remind possibly
intimidated beginners and lurkers how easy it can be to get rewarding astrophotos via the piggybacking of a camera with a
telephoto lens on, for example, an LX200. This is a great way to get started in astrophotography and is *really* easy with this
telescope. To accomplish this, I set up recently to do some piggyback work, paying attention to my techniques and equipment so
I could describe them to beginners.
First, the equipment I used:
10" f/6.3 LX200
Meade Superwedge
Tuthill Precision Polar Axis Finder
Losmandy 2-D counterweight system with extra 5# weight Meade Piggyback mounting bracket
Swivel-tilt piggyback adapter, Bogen #3232 (from Orion) Meade Series 4000 9 mm illuminated Reticle EP (eyepiece)
Nikon FM SLR camera
Nikkor 80-200 mm f/4.5 zoom lens
Cable release
Stopwatch
Foam dew shield (home made)
Rob Roy's LX200 joystick
A few comments about the equipment:
The Meade Superwedge has received its share of nasty comments. The truth is it's as rigid as only a cast unit can be, as all
recognize. The complaints arise from the less than precise altitude and azimuth adjustment mechanisms. This is really not a big
deal 'til you're making an effort to do a *perfect* drift alignment to the celestial pole, then it'll definitely have you talking to
yourself. (There's a lot of slop to be taken up when reversing directions in the adjustment process.) The unit would be
considerably improved if this were fixed. However, for the work described here, more precision is unnecessary. Alignment at this
level, I find, is very fast and painless.
The Tuthill polar finder is really not necessary but it makes it so easy to start the polar alignment process that I'm glad I have it
anyway. This device is, in essence, a plate with a rifle scope thru it with the optical axis of the scope precisely orthogonal to the
plate. The plate is bolted to the back of the wedge such that the polar scope would (hopefully) be exactly orthogonal to the base
of the wedge, hence parallel to the RA axis of the main scope. The center of the cross hairs in the polar scope is very precisely
offset from the optical axis so that when oriented correctly (a simple matter, determined from a table provided by Tuthill), the
cross hairs can be set exactly on Polaris leaving the wedge pointed exactly at the celestial pole. In practice, I've never found it to
work to a very high degree of precision even though I've tried to use it very carefully.
There are critical assumptions built into the device:
(1) The base plate of the wedge must be of exactly uniform thickness. The main scope is bolted to one side of the
base plate and the polar finder to the other. If the base plate of the wedge is not of exactly uniform thickness,
clearly the optical axis of the polar scope will not be orthogonal to the front surface of the wedge where the main
scope will sit.
(2) The RA axis of the main scope is obviously assumed to be exactly orthogonal to the base plate of the telescope
itself.
In mass produced items, I can't imagine either of these assumptions being true with any regularity to the degree necessary to
get very good polar alignment. Actually, I think a really cool device for SCT owners would simply dispense with the carefully
offset cross hairs and mount a simple finder scope with centered cross hairs such that its optical axis is exactly orthogonal to the
same kind of mounting plate as the Tuthill unit. Mount it the same as the Tuthill unit and center Polaris on the cross hairs. What's
the point? Well, without any extra equipment it's a real pain in the butt with the LX200 to do the initial rough alignment with
Polaris in the finderscope. The finderscope is always in a hideously uncomfortable position. With the initial alignment via the polar
scope on the wedge (well oriented and positioned for comfortable alignment), it's a very simple matter to fine tune the
adjustments to get Polaris in the finder, and thence in the FOV of the EP in the main scope. The bottom line is that I find the
Tuthill unit very well made but it can be (but isn't necessarily!) easily defeated by mass-production dimension errors. Here's irony
for you: I think it's hideously overpriced but I'm *really* glad I have one. Figure that one out!
Good balance is essential to the long term health of your telescope drive systems. Repeat that. Chant it. Adopt it as your mantra.
It's true. If you're going to hang extra equipment on your scope, you *must* have a 2-D balance system. The Losmandy unit is
*very* nice. I found the camera w/telephoto lens to be too heavy for the standard 2.5# weight so I bought the extra 5# weight
from Spectra. Perfect. Editor's Note: there are several designs for making your own 2-D Counter Weight System on the
AstroDesigns homepage.
When I bought my LX200 from the Nature Company, they included a bunch of extra items including the Meade piggyback
bracket. Works fine with the Bogen model 3232 swivel-tilt adapter I bought from Orion. I have to confess, though, I lust after the
3-axis piggyback mount from Losmandy. That would sure make composition easier. (A 2-axis mount like I have is a bit limited.)
One of these days I'm going to get one of these from Spectra.
I like the Meade Series 4000 9 mm illuminated reticle EP. Fortunately, I bought the version that is *not* battery powered. Mine
plugs into the LX200 control panel so that it's brightness can be controlled from the keypad. Very cool, and useful because you
can turn the brightness level down low for dim guide stars. (I have sensitive eyes anyway and don't need much illumination.)
As many of us have on this list, I made the dew shield from a foam pad I picked up at a backpacking store I frequent. The foam
is approx. 1/2" thick. I glued Velcro down the sides to hold it together when mounted on the scope and use a wrap of Velcro tape
to snug it around the end of the OTA. (This keeps it from winging away on the wind. Imagine my consternation the first time
*that* happened! Random neighbors also enjoyed watching me chase it. Added to my reputation, that's for sure.)
I also have a similar dew shield I made for the camera lens, then forgot to mount it for this session. Dummy. I hope no one else
makes the same mistake.
Any beginner that doesn't know about the LX200 joystick made by MAPUG's own Rob Roy is missing something important. There
are lots of people here who do without one but I'd be lost without mine. It's an inexpensive little mechanical contrivance (very
nicely made) that slips over the keypad and engages the NESW keys when pushed in the appropriate direction. I find it orders of
magnitude easier to use than the motion control buttons on the keypad. If I had to give up all other accessories and keep one,
this would be it.
Set-up:
Don't underestimate how long it will take to put everything together, particularly if you're working alone. Working at a leisurely
pace, it takes me almost an hour to gather and assemble all the bits and pieces for an evening's work. I like to do this well before
sunset which makes orientation of the tripod an interesting endeavor since you can't see Polaris. I first site the tripod, orienting it
by using the compass that came with the wedge. Of course, I move well away from the tripod (20 feet or so) to eliminate
magnetic effects from all that metal. (Don't forget to set the magnetic declination of the compass for your site! See the Meade
manual for details. It's a piece of cake.) Using the compass, I go directly south of the tripod and then orient the tripod along that
sight line. It doesn't have to be precise: The point of this exercise is to get the tripod positioned such that the available travel of
the wedge controls will not be exceeded when precise alignment is made. When satisfied with the orientation, level the tripod
(necessary for accurate LX200 refraction corrections). I use a small torpedo level I picked up for a couple of bucks from a
hardware store. The bubble level on the wedge itself is useless without recalibration.
The wedge is then bolted to the tripod and the scope mounted on the wedge. Mount the usual equipment (finderscope, diagonal,
and dew shield). You're now ready to mount the piggyback bracket. This is easily done by removing (in my case) 4 Allen screws
from the periphery of the rear of the OTA and using 2 of these to mount the bracket. The swivel head is then screwed to the
mounting bracket and the camera is mounted on the swivel head. You'll need to lock the dec and RA axes for this so make sure
the bracket and camera are approximately over the center of the fork so not too much force from the now-out-of-balance scope
is placed on the gears. Next mount the counterweight and release the dec lock to balance the scope. (You might just as well put
an EP in the diagonal for this.) Point the OTA straight up and screw the counterweight in or out until the scope moves the same
amount to the north and south in response to a small push. Next point the OTA horizontally, then move the counterweight up or
down it's track along the underside of the OTA until the scope is similarly balanced in this direction. You're done. See? Balancing
is easy with the Losmandy unit.
Now wait for it to be dark enough that you can see Polaris. (You can use the time to set your slew speed to less than the system
maximum to save wear and tear on the drive systems and check your telescope system clock.) I first use the Tuthill polar axis
finder (which only gets me close, but very conveniently does so), then I use the stock LX200 alignment routine. My experience,
though, is that it's easy to significantly improve alignment by then using Philip Perkin's once-popular iterative alignment
procedure. This methodology has fallen a bit from favor because inconsistencies in the telescope mechanics can keep it from
converging to perfect alignment. Philip himself now prefers a good drift alignment. Of course, he's correct: That *is* the best
method for precision alignment. However, my experience is that alignment with the stock Meade routine is not nearly as good as
might be expected and the iterative alignment improves it significantly in no more than a few iterations, with a total time
investment of less than 5 minutes (with just a little bit of practice). This works fabulously for piggyback photography where
ultimate alignment precision is usually not really necessary.
Philip's iterative alignment scheme is very simple. (I actually do this using the 26 mm Series 4000 Plossl EP that came with the
scope. This seems to be sufficient for me.) Command the scope to go to a star with a significantly different RA than Polaris. (I
used Pollux (Star 81), which is approx. 5 1/2 hours east of Polaris in RA and is close enough that slewing to it from Polaris is done
quickly.) Center the star using the NESW keys then sync by pressing and holding ENTER 'til the display says "coordinates
matched". Next command the star to go to Polaris (Star 19). Don't touch the NESW keys! Use the wedge controls to move the
center of the FOV of the EP (which the system thinks should be coincident with the position of Polaris) halfway to Polaris. (On rare
occasions, I've been far enough off at this step that Polaris wasn't in the FOV. Shame on me. I was careless somewhere along the
line. Simple solution: Use the finder scope for this step instead of the view thru the main scope. It works fine.) Now command the
scope to go back to Pollux. Center and sync. Repeat the procedure of commanding motion to Polaris, moving Polaris halfway to
the center of the FOV with only the wedge controls, then going back to Poleax, centering with the NESW keys, then Syncing. I
find that after about 3 iterations, Polaris is close enough to the center of the FOV that I'm ready to rock and roll.
I probably should use the reticle EP for the alignment, but what's the point? I use it for drift alignment, to be sure, but the
iterative scheme, as mentioned, is probably not capable of that kind of precision. No need to obsess here when it's unnecessary
and experience has shown me that the 26 mm EP is ample for this work.
The easy part: Taking the photographs.
Honestly, with the LX200, this is really easy. After I'm properly aligned, I usually point the scope at a star bright enough that I
can see it thru the viewfinder of the camera. I then adjust the camera mount so the star (centered in the scope) is centered in
the camera field. No worries about mis-aiming that way! I did all my shots that night at 200 mm and f/4.5. Before mounting the
camera, I put a small piece of duct tape on the camera barrel to hold the focal length of the zoom lens at 200 mm and another
small piece to keep the focus at infinity.
Insert the reticle EP. I find it useful to orient the crossed lines of the reticle in the cardinal directions. I then hold my keypad such
that the NESW movements of the joystick are parallel to the cross hairs. This way, when you use the keypad to move the scope,
a centered guide star always moves directly along the cross hairs. If the guide star drifts, say, to the left, I push the joystick to
the left to move the center of the FOV towards the star. It's very natural to guide this way.
I suggest when you open the camera shutter for an exposure using the cable release that you cover the camera lens while the
vibrations damp out. I just use my hand, although at various times I've used a piece of cardboard.
Now you're ready to aim and fire away. I did 10 minutes exposures of The Double Cluster (h and chi Persei), The Pleiades (M45),
the M36-M38 region of Auriga, M42, the area just south of zeta Orionis where the Horsehead Nebula lurks, and the Rosette
(N2237) in Monoceros. I didn't shoot longer than 10 minutes for fear of fogging the film. (My skies aren't bad but they're less
than pristine.) Experience will tell you what works for you and your skies.
The polar alignment must have been pretty good because I didn't have to do much correcting in declination. (Actually, this is
pretty typical when I do it this way but it does get better still with a good drift alignment.) It was quite easy to keep the guide
star in the center box of the 9 mm reticle EP. Actually, guiding like this is overkill when shooting with a 200 mm lens if your polar
alignment is as good as mine was, but it's always good practice. Guide stars are easy to find when doing piggyback photography
because you never have to move the FOV very far to find something suitable. Since the field of view of the telephoto lens is really
pretty darned wide (of the order of several degrees), moving the FOV of the main scope up to a half a degree hardly affects
composition.
Keep in mind I did all of this without training PEC, either. I figured beginners wouldn't need the added complexity so I tried to
keep it simple and omitted its use. In fact, this is how you get practice guiding so you can train your own PEC. Believe me,
guiding is an art that improves with lots of practice.
Conclusion:
Piggyback photography is an aspect of astrophotography that's easy to overlook but is a wonderful first step for beginners into
this arcane art. There are all sorts of fabulous subjects. In the appropriate season, you can shoot the North American and Pelican
Nebulae, M31, M33, lots of fun areas of the Milky Way in Scutum and Sagittarius, etc. You can learn a lot about your equipment
this way, get the practice necessary before moving to prime focus photography, and collect lots of neat photos along the way.
Experiment with film, especially color. It will all be valuable experience in the long run! If you decide to move on to prime focus
photography, you will have gone a long way in the development of the skills necessary to be successful. I read of owners who
have little scope experience and run out and buy an LX200 and CCD camera and then go not-so-slowly nuts trying to get
everything working, learn the rudiments of observational astronomy and telescope usage, while simultaneously trying to gain the
skills necessary to the art. I wonder how they ever manage: Taking it one step at a time is much less frustrating and can be quite
relaxing and downright fun.
Once you try doing this with the LX200, you can't help but be amazed at how easy it is. I've been an amateur astronomer for
over 30 years (in and out as time and location permitted, of course) so I remember the bad old days very well. Boy, was it
*hard* back then.
The best reason to own an LX200 is for its photographic capabilities; that's why I bought mine. If I were solely interested in
visual observations of DSOs, I'd get a good, fast 18" Dob, and maybe put encoders on it. (I've paid my dues starhopping over the
years.) It wouldn't cost much more than an LX200 and I'd have a *superb* visual instrument. If you've been intimidated about
doing astrophotography with your LX200, try some piggyback photography. You'll quickly build up a stock of good photos so you
can redecorate your house and wow your friends!
Subject: Guiding Techniques Articles
From: Philip Perkins
I've added three new articles to my web site which are accessible as follows: "Guiding Techniques for Astrophotography"-- A
beginners overview of guiding concepts and systems followed by a detailed description of guiding techniques based around the
LX200, GEG, and ST-4. Supplemented by photos and diagrams: <http://www.astrocruise.com/guide.htm> Note: should open a
new browser window over this one.
"Instructions And Tips For Using the ST-4 Autoguider"-- To supplement the above article, here is the excellent article on the ST-4
by James Janusz, which is reproduced with Jim's kind permission:
<http://www.astrocruise.com/st4tips.htm>
There's also a short article about the "Michael Stecker Astrophotography Competition": <http://www.astrocruise.com/msastro.
htm> All of these are also accessible from the front page. Hope they may be of some interest or use, and please let me know if
you discover any problems.
A good site for drift aligning:
<http://www.darkskyimages.com/gpolar.html>
Subject: Helpful Hints for Astrophotography
From: Chris Vedeler <cvedeler
and: Scott Tucker
ix.netcom.com>
Scott, and Chris have much to share about their experiences in astrophotography with the LX200.
Check their web sites for many hints.
<http://www.isomedia.com/homes/cvedeler/scope/guide.htm>
<http://www.darkskyimages.com/guide.htm>
Subject: LX200 Astrophotography Websites
From: Chris Vedeler
Note: new windows should open over this one as you select links.
Philip Perkins has probably the best images taken with an LX200: <http://www.astrocruise.com/>
Howard Anderson also has some of the best images taken with an LX200: <http://www.astroshow.com/>
Andy Steere has some impressive images too: <http://astro.umsystem.edu/andy/>
Of course if you are talking about the 16" LX200 Jason Ware is "The Man":
<http://www.galaxyphoto.com/index.html>
And last but not least, is my webpage: <http://www.isomedia.com/homes/cvedeler/space.htm>
For the super impressive, jaw dropping astrophotos, they are almost all taken with APO refractors or Schmidt Cameras. In terms
of image quality, and wide vistas a SCT can't compare.
Subject: Film Camera Selection Criteria
From: David Samuel <samueld
bigpond.net.au> Date: Dec 2001
I think that I was the one who mentioned the Topcon camera in reply to an earlier post.
The reason I mentioned it is as follows. About the year 1976 I was looking for a camera to purchase which I could use for
astrophotography as well as for taking everyday type pictures. My requirements for astrophotography were that the camera
should have at least the following features (not in any order of preference):
1.
2.
3.
4.
5.
6.
7.
8.
9.
Mirror lockup (mirror flip causes about 90% of camera vibrations - more in some cameras)
Interchangeable focusing screens (needed different types for astrophotography and every day photography)
Interchangeable viewfinders (needed different types for astrophotography and every day photography)
Interchangeable lenses (so that I could take the lens off before attaching the camera to the back of my telescope)
Total manual exposure controls (for both shutter speed and aperture)
Mechanical shutter mechanism (no need for batteries)
Good range of shutter speeds including the ability to leave the shutter open indefinitely
Accuracy and precision of shutter speeds
Quality (I intended to keep this camera for a long while and did not mind paying a little more up front for that
convenience)
The available cameras (in Australia at the time) I looked at were:
1. Olympus OM-1 (relatively cheap, but discounted this because of no interchangeable viewfinder)
2. Topcon D (satisfied all of my requirements mentioned above, a good camera overall, discounted this because I thought the
two camera companies mentioned below would be around longer and for the reasons that I decided to purchase the Nikon)
3. Cannon F-1 (satisfied all my requirements mentioned above, an excellent camera overall, discounted for the reasons that I
decided to purchase the Nikon)
4. Nikon F2 (satisfied all my requirements mentioned above, an excellent camera overall, purchased this one)
It finally came down to a choice between the Nikon F2 and the Canon F-1. I decided to purchase the Nikon F2 because:
1. It satisfied all my requirements mentioned above
2. Test reports in camera magazines indicated it had the more precise shutter speeds
3. The image in the viewfinder showed 100% of the image that would appear on the film. All the other cameras show about
90-something percent of the image. This would allow me to frame my images more accurately with the equipment I had
and give me the feeling that I had better control over my framing.
4. The Nikon F2 had a wider range of shutter speeds available.
5. The Nikon F series had a good reputation as a quality camera.
6. I am sure that there were other reasons which I have forgotten in the last 25 years.
The main disadvantage of the Nikon, Canon, and Topcon cameras at the time was that they were all highly priced (the Olympus
was much cheaper).
So finally to answer your question, even though I have not used the Topcon, I am fairly certain that it will do a good job for
astrophotography. Since you will be purchasing a second hand camera you should ensure that you can get hold of all the
accessories you will need with it. The accessories should include appropriate lenses (if you wish to do wide field
astrophotography), focusing screen, viewfinder, and attachment ring to the telescope. There are other accessories such as a
cable release and an attachment to mount the camera on the outside of the telescope tube (if you wish to do wide field
astrophotography) that are common to most 35mm cameras which will not affect the decision of which model of camera to
purchase.
What you will find hard to judge is the condition of the camera you purchase without being able to inspect it properly. This is
however the same problem when purchasing any second hand camera. Still for $50 the most you can loose is $50 plus the cost of
the telescope adaptor ring (specific to the camera you purchase).
Subject: Where to Process Film Images --part 1 of 3
From: Kevin Wigell <kwemail
twcny.rr.com>
----- Original Message ----From: "Phil" <psdisk@comcast.net>
> I know local places like Ritz and other small camera shops don't do a good
> job of developing our night shots. Can someone recommend a reliable place
> where I can send slides to have developed. A place that has a good
> reputation for this type of work?
----- End of Original Message ----I regularly have my print film developed at a 1-hour place at a local drugstore. The problem with developing astrophotos isn't
getting the film developed - it's getting them printed. Rarely will a photo shop print an astrophoto correctly. Developing the film
itself is a very standard process, and it's pretty hard to screw it up. The biggest danger in getting astrophotos developed (the film
part) is that they will cut right through the middle of your exposures when they cut the film. So what I always do is wait for the
film to come out of the machine and then tell them to just hand the negative right over to me.
Then I take the negatives home, cut them myself, and scan them myself using a film negative scanner. Then I can work on them
on the PC (in Photoshop or whatever), and either print them on a printer or post them on my web site (www.kwastronomy.com).
But you said your film is slide, which most 1-hour places can't do because it's a different process. You have several choices. One
would be to send your exposed film off to Tony Hallas (www.astrophoto.com), who is a professional film processor and
astrophotographer extraordinaire. He will do an excellent job developing and mounting your slides. Another option would be to
take your exposed film to a local professional film shop. These can generally be found in the yellow pages. They are specialized
photography shops and is usually their only business. Unless you live way out in the sticks you should be able to find one
relatively nearby. Then you can either explain to them that you have astrophotos and they should take great care in cutting the
developed film, or you can ask them to just give you the developed film uncut, then you can cut and mount the slides yourself.
--------------------------------------------------------Subject: Where to Process Film Images --part 2
From: "ScopeTrader.com" <rharris
elvis.com>
SnapFish.com if it's digital or film. I've been real happy with the results from there.
--------------------------------------------------------Subject: Where to Process Film Images --part 3 of 3
From: Gene Horr <genehorr
texas.net>
Tony Hallas is one of the best in the world, but you are likely dealing with mailing everything in.
My next choice would be a local custom lab. Unless they are experienced your initial results will still be poor but they will be
willing to work with you, redoing the prints until they get it right. They'll usually allow you to work with one of their techs so that
you can request the same person each time. It's more expensive, but not _that_ much more and in the end you will get great
results. Plus the negatives have the lowest chance of getting damaged.
Last of all try one of the local cheapo one-hour labs. One where you can actually talk to the tech yourself. The drug stores can
work well with these. Go during a slow period and bring a print to show the tech what you are looking for. Sweet talk them. Help
them by showing what is wrong with the prints. It will take longer than the pro lab techs as you are generally working with people
not too far up from minimum wage, but you can generally get them trained in a reasonable amount of time. The main problems
with this method are that the techs generally don't stay at the same place for extended periods of time and the treatment of the
negatives is often less than professional.
If you are in the learning stage go with the cheapo source unless you live around the corner from a pro lab. The faster
turnaround, convenience, and cost is IMO worth the somewhat larger risk and training factor. But if you are at the stage where
you are wanting to hang images up on the wall spend the extra time and money to go with the pro lab. You don't want to risk
ruining that perfect image because someone doesn't know how to properly treat a negative.
But ask around at your local club first. Someone may have already trained a tech for you <g>.
Another thought is to DIY. Even film positive processing is fairly easy nowadays.
If you aren't already a member you might want to consider joining the astro-photo-mailing list. It is an excellent source of
information for film imaging. <http://www.seds.org/mailman/listinfo/astro-photo/> at the bottom of the page.
Subject: Calculating F/Ratio with Eyepiece Projection
1. f ratio=focal length/aperture
2. With a reducer multiply the above by .63 (or whatever the reduction factor is for your reducer).
3. For positive eyepiece projection f/ratio=Mep*f
where Mep = the magnification of the eyepiece projection setup calculated as follows:
Mep = (D-Fep)/Fep where:
D = the distance from the eyepiece to the film plane (typically 100 to 150mm with a variable tele-extender).
Measure it with a ruler or tape.
Fep = the focal length of the eyepiece.
f = the f ratio of the telescope.
Here's an eyepiece projection example with an f/10 telescope and a 10mm eyepiece located 110mm from the film plane:
Mep=(110-10)/10=10
>From formula #3: 10*10=100
So the overall f/ratio for this setup is f/100, which is a good f/ratio to start with for planetary photography on film.
If you're using your Pictor instead of film, try using a 2X Barlow instead of an eyepiece. This is called negative projection. Don't
use a tele-extender...just slide the Pictor into the eyepiece holder of the Barlow. The f/ratio will be the f/ratio of the telescope *
the Barlow factor. In this case an f/10 scope will be f/20.
Subject: FOV in 35mm Camera?
From: Allen Ginzburg <alleng
sco.COM>
>Does anyone have handy an approximate field of view of a 35mm SLR camera when used for
>prime focus photography for a 8" LX200 f/10, 2000mm focal length, 200mm mirror.
If I remember correctly, the formula is
field size = 2*atan (film size / (2* flocal length)) * 60
Where film size and focal length are in mm and field size is in arcminutes.
In the 8" LX200 case at 2000 mm with 35mm film, the field size we get 60.2 arcminutes, or about 1 degree.
Subject: Back focus/JMI/Van Slyke Slide Mirror
From: R. A. Greiner
More info is available at my website
A new browser window should open over this page.
I have been working on a scheme to get very solid attachments for the LX200 which allow focus, mirror viewing use of a reducer
and use of any camera, photographic or CCD, all at the same time. I have found a solution which is, I think, worth sharing. I
have a 12" LX200 permanently mounted on a wedge. I wanted to be able to have mirror viewing and immediate return to the
imaging element. Additionally, I wanted everything very solid and with full 2" aperture for 35mm photography.
I have just received a very ingenious mirror box from Van Slyke Engineering. It is called the Slider. He has made a rock solid box
with a mirror that slides sideways so as to minimize the thickness of the box. This can be used with the JMI focusser, a focal
reducer, the mirror box and any camera, 35mm or CCD. and still maintain the 100mm back focus required by the Meade focal
reducer. It is 2" all the way. This is a wonderfully rigid and compact system. I can recommend it highly to imagers for all
purposes. As a additional note, I have also taken delivery of Van Slykes 26mm illuminated eyepiece. It is very nice even though a
bit expensive. His machinery is of the highest quality.
Van Slyke web page: <http://www.observatory.org/vsengr.htm>
Subject: New Evaluation Page of Filters
From: Leroy Guatney <lwlguatney
usa.net> Date: Apr 2002
Here's the direct link:
<http://home.earthlink.net/~ngc5139/SCI/filters.html>
Note: should open a new browser window over this one.
For now, heaviest emphasis is on colored filters. Other types have been covered elsewhere, but mine is the first I've seen on
these.
Astrophotography Issues continued on:
or
MAPUG is hosted by
LX200 Balancing, Loading Limits, & General Stats
LX200 Balancing Procedure
Simple Balancing Procedure
LX200 OTA Balancing --3 parts
Balancing with 3D System --2 parts
Symmetrical Balancing Device --2 parts
Balance at High Declinations
LX200 Max Weight Loading --5 parts
Weights of 10" & 12" Mounts & OTAs
Table of Scope Stats --outside link (Bill Arnett)
Note: for do-it-yourself balancing systems, visit AstroDesigns page on 2-D Counterweight Systems.
Subject: Procedure for Balancing the OTA --part 1 of 2
From: Doc G
For much more on the technical side of the LX200 and CCD imaging visit my website. Note: a new window should open over this
one.
Here is a technique that works fairly well toward getting near balancing perfection.
First the gross unbalance needs to be removed. I do this by pointing the tube and fork south and adjusting the Losmandy 2D bar
front to back so that the tube balances fairly well when pointed to the southern horizon. Then point the tube to the zenith and
screw the weight toward or away from the tube to get reasonably good balance in that position.
When this is done, the tube is close to balance about the Dec axis. Now you have to rotate the fork about the RA axis. If the load
on the telescope is reasonably well distributed about the RA axis, you will have reasonable balance. If the balance is off by quite a
bit you may have to move one of the attachments closer to the RA axis or add some weight on the light side to balance the tube.
If you repeat this process several times you should approach good balance. I recommend doing this by hand and not using the
Balance option since it is hard to evaluate when balance is obtained and the severe wobbling is hard on the drive.
Subject: LX200 Balancing Procedure --part 2 of 2
From: Jon Brewster <jon_brewster
hp.com>
> Does anyone have a basic lay-out (step by ..) On how to
> Balance the scope on a wedge in both axis?
I balance in 3D (2D DEC plus RA). To get more precision in balancing DEC, use the RA bearings for the out of balance telltale
since they have less stiction. See:
<http://www.proaxis.com/~sandstone/Astro/Modifications.htm#2-DWeightSystem>
for 2-D balance equipment description.
1. remove main dust cover from corrector plate (its very heavy). If the sun is still out, watch out! Make sure all observing
gear is on the scope.
2. set and lock DEC to +90 and move RA such that fork is
3. horizontal and unlocked then balance in RA with Velcro ankle weight (or something) on east (non-motorized) fork. A small
amount out of balance towards the East is OK to pre-load sidereal tracking.
4. leave DEC lockedat +90 and rotate in RA till the forks are vertical. Adjust 2D weight for least weight farthest out on spindle
using unlocked RA for telltale.
5. set and lockDEC to 0 while leaving RA alone (unlocked, forks vertical). OTA should be horizontal E/W now. Slide spindle
along OTA until balanced about RA in this configuration.
6. unlock RA and DEC and place OTA in many positions checking for balance. It should be perfect.
Subject: Simple Balance Technique --part 3 of 3
From: Ric Ecker <astroviking
juno.com>
I balance my LX200 using a combination of 2-D weights, slider weights, and dew shield (if needed). Whatever weight you add to
the back of the scope, i.e., camera, imager or large diagonal and eyepieces, you need to add weight to the corrector end. A
flexible dew shield works good for large back accessories.
Guide scopes or piggy-back cameras on top of the scope needs weights on the bottom of the scope. Equal weight on top must
have equal weight on the bottom plus, the distance from the main scope tube must also be the same, hence the 2-D weight
system. To begin balancing the system, point the scope straight up and loosen the Dec. lock. Move the 2-D weight in or out on
the all-thread rod, add or remove weights to get a good balance like a tetter-tauter. Once this is balanced you should be able to
move the scope in the forks and the scope should still point straight up. Move the scope level and move the weights forward or
backwards to balance. Your scope should now be in perfect balance in the forks. No matter where you put the scope (Dec. lock
loose) the scope will stay in that orientation.
Adding a pound weight to the Dec. arm will help balance the scope in R.A. Add enough weight to help the drive but don't try for
perfect balance because you need some extra weight on the worm gear so you eliminate any backlash or dead band. Add the
weight to the lower Dec. arm opposite of the Dec. motor.
I generally balance the guide scope first than add the cameras and dew shield. Light weight CCD cameras might not need the
dew shield. I carry enough weights to balance any accessories that I have.
Subject: Balancing LX200 with a 3D Balance System --part 1 of 2
From: Jon Brewster <jon_brewster
hp.com>
> Am I correct that when the scope is in balance and the Dec
> Lock is loose the scope can be pointed in any direction and
> stay there?
Yes, but you'll have to go to a 3D balance system. Usually, I have to add an ankle weight to the east fork arm. My full procedure
is:
1. remove main dust cover from corrector plate (it's very heavy). If the sun is still out, watch out!
2. set and lock DEC to +90° and move unlocked RA such that the dec axis is horizontal then balance in RA with Velcro ankle
weight on east (non-motorized) fork. A small amount out of balance towards the East is OK to pre-load sidereal tracking.
3. leave DEC locked at +90° and rotate 90° in RA till the forks are vertical (one above the other). Adjust 2D weight for least
weight farthest out on spindle using unlocked RA for telltale.
4. set and lock DEC to 0° while leaving RA alone (unlocked, forks still vertical). OTA should be horizontal E/W now. Slide
spindle along OTA until balanced about RA in this configuration.
5. unlock RA and DEC and place OTA in many positions checking for balance. It should be perfect.
---------------------------------------------
Subject: Balancing LX200 with a 3D Balance System --part 2 of 2
From: Dave Schanz <dave23sch
valleytranscription.com>
I found this very helpful to getting started balancing my scope:
<http://www.starizona.com/basics/balfork.html> Note: shoudl open a new browser window over this one.
Subject: Balance at High Declinations
From: Manning Butterworth <mbemailsubscriptions
earthlink.net>
It will seem more difficult to balance at high declination because the moment arm of your off-center weight (the guide scope in
this case) effectively becomes larger. When your scope is pointed straight up, (high declination) the moment arm through which
gravity can act is at maximum, so any imbalance is most noticeable there.
The solution is simply to find the right amount of weight placed in the right positions on the opposite side of the scope. I use two
Meade counterweight sets. I like their clean, low profile design which ensures they clear the fork base. I use one rail mounted on
the bottom on the opposite side from the declination drive and the other rail mounted on the bottom in the middle. I use one of
the weights on the offset rail to better balance the scope rotationally, but that weight also contributes to offsetting whatever is on
top of the scope. In my case, all the rest of the weights go on the center rail. Their position along the rail is determined mostly by
what is on the back of the scope. The amount of weight on the rail is determined by what is on the other side (top) of the scope.
If your guide scope is on a rail, you may (depending on the design) be able to adjust its position longitudinally along the OTA, but
its weight and distance from the OTA centerline are fixed. The product of those two numbers must equal the equivalent product
of the counterweights on the other side of the scope and their distance from the OTA centerline. If you use a counterweight
design in which you can adjust the counterweight's distance from the OTA centerline, you can change that distance or the amount
or weight or both, to achieve balance.
Bottom line, it sounds like you need more weight on the bottom of your scope. Point the scope up and add weights until it
balances. Then, point the scope at the horizon and position the weights longitudinally along the OTA so that it again balances.
Then, it will be balanced at any declination.
Subject: Dew Shield Counterweight
From: Scott Baker <scottb80
cts.com>
To balance my 10" with a dew shield, take a look on my web page under "LX200 Projects" to see how made a ring weight to fit on
the back of the scope: <http://www.starcrwzr.com/weight.htm>
Subject: Symmetrical Balancing Device --part 1 of 2
From: Doc G
Matt Considine wrote:
> It would seem that OTA balance could be more easily maintained
> with a counter-weight system that went *around* the tube,
> preferably towards the front. This would be in contrast to designs
> in which the counterweights are slung along a guide rail
> underneath the OTA. The advantage would be an ability to create
> a weight configuration that mimics what is at the eyepiece/camera
> end but provides symmetry about the pivot point of the RA/Dec
> axes. So, as one went to different sky coordinates, one wouldn't
> need to rebalance. Nor would balance get out of whack during a
> long exposure.
Again, Matt, you are excellently perceptive. The balancing of the telescope with weights requires that the added (balancing)
weight be of the correct weight and placed at exactly the right point in space. If a minimum of added weight is desired it is
necessary to have the weight move both along the length of the telescope OTA and in and out from the OTA axis.
If the weights are confined to rails along the length of the telescope, like the basic Meade rails and weights, is generally possible
to get balance, but it will usually require several weights placed so as to establish a virtual weight with the proper strength and
direction vector.
A 2-D weight system like the Losmandy and several others usually enables placing the weight at close to the correct position and
thus optimizes the amount of weight used.
You suggestion to be able to place the weight ahead of the front of the OTA is a very good one. Basically, when you add stuff to
the back of the OTA, you need to add weight to the front of the OTA. If you could move the weight more forward, you would need
a smaller weight. I have played with this sort of weight system. I added a rail to a 12" LX200 at the bottom and to the top. Each
rail extended about 6 inches in front of the front of the OTA. This indeed made it possible to get excellent balance with smaller
weights, thus reducing the load on the mount.
However, after considerable experimenting with different weight placements on these experimental rails, I found that the two
dimensional weight sets such as are available from Losmandy and others were very satisfactory.
My telescopes all have a Losmandy rail system on both the top and the bottom of the OTA. Then by judicious placement of
accessories and attachments on these rails, it is possible to get close to balance without added dead weight. Then a small weight
set can be used to tweak up the final balance.
In summary, I now feel that careful placement of accessories and a small weight set, such as the Losmandy set can give very
satisfactory results. Still, if you add accessories only to the back end of the telescope, which is quite reasonable with cameras and
CCD imagers and color wheels and the like, Then the very best place to put the weight is on a bar extending in front of OTA as
you suggest. I do not know of a commercial weight set system that provides this feature.
------------------------------------------------------Subject: Symmetrical Balancing Device --part 2 of 2
From: Matt Considine <matt
considine.net>
Balancing the tube of the 10" LX200 has always bugged me. With a camera body, Lumicon GEG, extension tube and ST-4
hanging off of one end, a dovetail bar+threaded weight hanging off the front struck me as a less-than-ideal solution. While I have
used this, it still struck me that as the scope worked through R.A., the balance point would shift, aggravating whatever
shortcomings the stock Dec bearings had to begin with.
A solution I came up with is "SymBaD" (symmetrical balancing device :) ). I picked up a piece of 3/4" melamine (sp?), about 24
inches to a side. This is a pressboard-like product with a smooth (laminated?) surface on each side. Any stiff piece of wood would
work, I'm sure. Out of this I cut a ring, with an inside diameter of 11 7/8" and an outside diameter of 16". In this I cut 16 halfinch holes, evenly spaced around the ring and at what would be a diameter of 14" if all the circles had been drawn before cutting.
At Home Depot, I bought a few packs of 1 1/2" corner braces (Stanley, IIRC). Taking 6 of these, I mounted these to the 6 holes
in the corrector-end of the OTA. Sliding the ring over the corrector-end of the scope, I marked the outlines and holes of the
braces on the ring. At the hole marks, I drilled through the ring, so that the ring could be attached to the braces with small bolt
+washer+lock washer+nut combinations.
Now, I took a bunch of 2" x 1/2" hex bolts and a bunch of 1/2" nuts, also found at Home Depot. I placed these around the ring as
symmetrically as possible to balance the above mentioned setup. (I also tried 3" bolts, but these added more weight, and I
wanted better "granularity" for adjusting the weights.) If I recall, 14 of the nut-and-bolt combinations were required. Using Doc's
measurement of the weights of the fork arms, I've got a 2.5 pound weight for the east fork arm (though Bruce Johnson's elastic
+scale approach seems intriguing).
I have yet to rigorously test this setup. It seemed that there was still going to be some unbalancing, but it (qualitatively) didn't
seem to be as much. And it made more sense to me to have counterweights organized symmetrically around the mechanical axis
of the OTA. If nothing else, it killed a rainy afternoon :)
Hope this helps someone. If anyone can see problems or improvements, please let me know.
Subject: LX200 Max Weight Loading -- part 1 of 5
From: Roger Hamlett <ttelmah
ntlworld.com>
----- Original Message ----From: David Samuel
> I purchased my 12" LX200 during the later half of this year and do have the
> steel ball bearings on the Dec. axis. I will be putting a Vixen DED108SS
> tube assembly on the 12". It is a 108mm f/5 refractor which weighs about
> 6kg-7kg (I am guessing and may be wrong by a couple of kilograms). The
> Losmandy dovetail system and rings will weigh 2.7kg (6lbs according to the
> Losmandy web site), and Meade told my dealer that the 12" is rated to take a
> maximum payload of 22lbs (10kg). This 10kg should include the
> counterweights, refractor, camera, etc. So I will probably be overloading
> the 12" a little bit. The LX200 is on a wedge (have not yet polar aligned it
> properly). I am not sure what effect the extra weight will have on the life
> or operation of the LX200 mount?
This is where reducing the maximum slew rate is critical. The standard fast slew, is pretty 'hard' on everything, especially when
accelerating and decelerating. The 'rated load', is (since it does not say otherwise, with the full slew rate still used. In terms of
the loads on the motors and gears, you can run with a lot more weight, without increasing the actual loads on the motors by
bringing this down. The 'caveat', is that it has to be set everytime the scope is used. I have a simple 'batch' file, that sends an
'initialization' sequence to the scope from the laptop, cutting the slew rate, and setting the time to an accurate clock. Glad you
already have the better bearings. Otherwise high loads can lead to accelerated wear on the shafts.
-------------------Subject: LX200 Max Weight Loading --part 2
From: Doc G
That is a lot of weight you are adding. I have always recommended no more that about 12 to 14 pounds of added equipment and
additionally a 3D weight set so you can balance this weight with significantly less added counterweight. With a 3D weight set you
can usually get by with less than an equal amount of weight in the counterbalance.
I think you are pushing the limit for the 12" since the OTA is already heavy. The mechanics of the 8, 10 and 12 are all the same.
Do your polar alignment with the added weight in place. The added weight will change the RA axis of the scope from the unloaded
position.
-------------------Subject: LX200 Max Weight Loading --part 3
From: Roger Hamlett <ttelmah
ntlworld.com>
First, in determining the max weight loading, are you working Alt/Az, or Polar mounted?.
If the former, you can go higher in weight, than with the latter. The problem is that when polar mounted, weight mounted up on
the tube, exerts a considerable torque between the two main base bearings. The bearings are strong, but eventually this can lead
to vibration problems. The next part is whether you can counterbalance the weight. Remember that the available moment arm
'below' the tube, to place a counterweight for masses above, is fairly short, unless the counterweight is going to foul the forks.
You _must_ counterbalance well, and because of the short moment arm, the counterbalance may need to be significant 'doubling'
the problem...
The next part is inertia. You can reduce the motor problems by limiting your slew speed (keeping the setting down to say 4,
allows a lot more weight to be carried, safely, than if the slew is left at it's default setting.
The next part, is how heavy the refractor is. Though some parts are 'fixed' (the lenses...), some designs are significantly heavier
than others.
The next part, concerns how it is mounted. Good rigid mounts, will add yet more weight...
Finally, there is a question on how old the LX200 is?. The newer ones, have needle roller bearings, for the Dec axis. This is a mod
that many people fitting a lot of weight have found necessary. So. If the 6" scope if carefully mounted, and reasonably light of it's
type, kept as close to the LX200 as you can. Then you are careful to counterbalance it well (2D counterbalance below the tube of
the LX), and keep your slew rates low, it is reasonable achievable, but you need to be 'considerate' of the LX, if you are not to
have problems...
-------------------Subject: LX200 Max Weight Loading --part 4
From: Doug Groesbeck
>
>
>
>
My concern is that as it is on a wedge, the whole weight issue
is distorted over to one side of the RA bearings. This together
with the extra work the RA motor has to do has made me
reconsider doing this.
I think that you need to look at this from two aspects. The first is the load to the drive motors. As has been noted elsewhere in
the Archives and member's websites, the LX200's motors and gearboxes seem flimsy and weak until you look at the final gear
ratio output -- that little assembly actually generates a fair amount of torque for its size! But you have to work within limits of not
overstressing it, so you must balance the load they have to move. If the load is properly balanced, there is no effectual change to
the amount of load that the motors are required to move; i.e. the amount of mass can increase, but balanced mass is effectively
naught when it comes to stress on the drives.
The other aspect is the amount of increased mass the mount must carry, and that's where I think that you'll start hitting some
walls. The 22lb. load limit that David mentioned as being the Meade recommended maximum load centers more around this
aspect. While it may be mechanically possible to put more mass load on the drives, the bearings (both Dec and RA) and the forks
have to bear that mass. The newer models with roller bearings in the Dec axis can negate some (even most, to a limit) of that
load with their better load/friction surfaces than other types of sleeve bearings. But on a wedge, the upper and lower RA bearings
are really going to be taking some lateral torque stresses that roller bearings aren't designed to take. There also may be some
flexure problems with the forks if the load gets excessive.
So it may be possible to put a total additional mass of 30-35lbs. on an LX200 *if it is properly balanced* without undue stress on
the drive motors. More than that may begin to overload the mount itself, though, to the point where it will eventually begin to
cause problems with the bearings.
-------------------Subject: Max Weight Loading --part 5 of 5
From: Greg Pyros <greg
>
>
>
>
gregpyros.com>
From: Edward Registrato
Is an 8lb weight (TeleVue 85 scope) plus a CCD (Meade 416XTE) too much
weight to piggy back onto a 10" LX200 scope which has the Meade under scope
weight system as the offset?
I use a TV-85 with STV autoguider piggybacked on my 10" LX200 with Pictor 1616XTE, color wheel, and flip mirror with no
problems whatsoever. But balance is critical when doing this.
What I did was to modify the stock Meade weight system slightly to make it a 2D system to balance the scope when aimed both
vertically and horizontally.
You can see the modification by going to my web site at:
<http://www.gregpyros.com/> and clicking on the "Customizations" link. Or direct: counterweight mods are on the second row
down on the right side. I've updated it a bit since the pictures, but you get the idea.
Subject: Weights of 10" & 12" Classic Mounts & OTAs
From: Doc G
My values are as follows:
10" mount (forks and base with electronics) = 34 lb.
12" mount (forks and base with electronics) = 36 lb.
10" OTA (f/6.3 version) = 28 lb.
12" OTA (f/10 with front cap) = 36 lb.
10" complete (f/6.3 version) = 62 lb.
12" complete (f/10 with front cap) = 72 lb.
I think the f/6.3 version is a bit heavier than the f/10 version because of the larger secondary structure. There are still some
minor discrepancies, but I would say we are close enough.
MAPUG is hosted by
Battery, Volts, Amps, Fuses, etc.--Page 1
EE 101--Basic Electricity Concepts
Battery Power Box Supply Designs --separate page
LX200 Battery Power Supply Cautions
Battery Information URLs
Battery Connectors
12-volt Battery Charger Recommendation
Deep Cycle Battery - What is the Real Capacity? --2 parts
Parallel Battery Charging
Reverse-Power Protection
Measuring Remaining Battery Power
12v Gel Cell Battery Charging Tips
Restoring a Gel-Cell
Operating the LX200 Classic on 15V
Reducing 18v Down to 15v
Adjusting Meade 18V Supply
Operating the LX200 Classic on 12 volt Battery Pack
Operating Classic on 12v Vs. 18v
Voltage Regulators--Short Primer
Fried 18V Converter
18V AC Adapter/Converter Problem
1812 Voltage Converters
Meade 12v to 18v Converter Alternative
Inverters & Batteries
DC Power Source & Inverter
Inverter Issues & Questions --5 parts
Power Supply Design URL
Power Supply Issues for LX200 Classic -- 3 parts
Standard LX200 Fuses
LX200 Power Cable Fuse?
LX200 Fuses Explained
Blowing a Fuse - Problem Solved! --3 parts
LX200 12V Converter Circuit
120V-12V Power Supply Recommendation
LX200 Power Supply (DC>AC vs DC>AC>DC)
Subject: EE 101--Basic Electricity Concepts
From: William Sommerwerck
It looks like I'm going to have explain some basic electricity.
Think of a rechargeable battery as a sort of huge wastebasket into which you toss ball bearings. If you hold the wastebasket
above the ground and let the ball bearings fall (or run) out, they can do work. Like demolishing an ant hill or making holes in
concrete.
The height of the wastebasket above the ground represents voltage (electrical potential energy). The number of ball bearings in
the wastebasket represents the capacity of the battery. Let's forget about voltage and think about capacity.
When we charge a battery, we are in effect moving electrons from a low energy state to a high energy state (just as moving ball
bearings from the ground to the wastebasket raises their potential energy). The larger the battery, the more electrons it can
accept, and the higher its capacity.
When we connect a load to a battery, the electrons move from a higher energy state to a lower state, doing useful work. The
battery poops out when we run out of higher-energy electrons.
One coulomb of charge passing a point each second is one ampere of current. If a battery has a capacity of 50 ampere-hours, it
can store 50 * 3600 coulombs of charge (180000 coulombs) at the higher energy level.
If we draw one ampere, the battery should last for about 50 hours. If we draw 10 amperes, the battery is good for only five
hours. And if we draw 100 amps, the battery will barely last a half hour. This should give you a rough idea of what the "capacity"
of a battery is. Please don't post messages saying that this is not a complete or exact explanation. I know it isn't. But it is
basically correct.
Subject: LX200 Battery Power Supply Cautions
From: John Hopper <JohnLX200
aol.com>
Batteries are often hooked in parallel, discharged together, and charged together without incident. Batteries also sometimes get
hot, boil, melt, or explode when being hooked in parallel for charging.
While there are dangers inherent in CONNECTING batteries in parallel, and other (typically smaller) dangers simply KEEPING
them in parallel, charging doesn't do much to add to those dangers. The main dangers are that a drained condition or internal
short in one battery causes it to become the target of current dumps from the rest of them, and/or a spark when connecting
them explodes the battery gases.
I don't think you will ever see a pack of (diesel, boat, golf cart, locomotive, etc.) batteries being disconnected and charged in a
different configuration than they were discharged in. THEY STAY HOOKED UP ONE WAY.
Even without any defect, spark, or short:
A serious danger occurs when CONNECTING the three 6V batteries in parallel after discharging them in series. This is mainly due
to the possibility that they are discharged to different voltages and one or two will apply an extremely high charging current to
the other one or two. This is one reason that batteries explode sometimes when you jump start a dead car battery. It really does
happen, and would happen more if people used heavier, shorter jumper cables!!
Discharging batteries in series and charging them in parallel IS A BAD IDEA, although if everything goes "nominally" as NASA
would say, and they are discharged from equal voltages down to other equal voltages, there may be no problem. This is far from
guaranteed, though, and some MAPUGers have been known to do downright dangerous things like tapping off 6V or 12V to run a
dew heater, CCD camera, or whatever, virtually guaranteeing unequally discharged batteries. In that case, they MUST be charged
separately or you're taking a real risk every time you hook them up in parallel for charging.
If you must go with an 18V battery pack, you could get an 18V charger if you don't tap intermediate voltages. If you do tap
intermediate voltages, charge them separately (or at least each group between taps if you know what you're doing.)
Subject: Battery Information URLs
From: Don Tabbutt <don
tabbutt.com> Date: Dec, 2003
For good information on batteries, try the West Marine web site. Mariners, especially long distance sailors, have battery demands
that we landlubbers rarely think about. West Marine is at:
<http://www.westmarine.com/> Should open a new browser window over this one.
From: Gregg Ruppel <ruppelgl
SLU.EDU>
Check out this web site for everything you ever wanted to know about batteries but were afraid to ask!
<http://www.uuhome.de/william.darden/>
Note: should open a new browser window over this one.
Subject: Battery Connectors
From: Doc G
At long last I have found some battery connectors that are of better quality than any I have used before. They are made by
Switchcraft and are superior in all ways to those from Radio Shack. And, to most of those on existing equipment.
Their catalog numbers are L712A, L722A for the plugs and 716K, S716K for the sockets. The former are with 2.5 mm pins and
the latter with 2 mm pins. The plugs are particularly nice. They have a larger than normal grip which allows the use of larger
gauge wire and they have a screw down locking ring so they are held firmly into the socket.
They are available from Newark and probably many other suppliers. They are not cheap, but they are very good. ($4 per part)
Those who are having trouble with these connectors might well replace troublesome versions with the higher quality ones from
Switchcraft.
Subject: 12-volt Battery Charger Recommendation
From: Gene Roeschlei <GRoeschlei
aol.com> Date: Jul 2004
I have one of the 'smart chargers' Vectron Model Number VEC 092 WM by Vectron. Details at:
<http://mastercatalog04.westmarine.com/0624.asp>. I did buy mine at West Marine but you can probably get a better price at a
number of outlets. This is undoubtedly the best battery charger I have ever had or used or heard of. I have the one that goes to
35A.
West Marine catalog has a lot of good information on lead acid batteries in their catalog. Be sure to read it.
Most common battery chargers (with essentially a transformer and bridge rectifier) only charge the battery to 75% or so. And
this I think is why a lot of people complain of not getting the calculated amp-hrs from their battery. This charger has three
separate charging parts to the charge cycle (all automatic of course) and will get the battery as fully charged as I have ever seen.
I use two 6 volt golf cart batteries in series and an Exeltech XP1100 inverter with great results. Pure sine wave output better than
the power line. This charger also de-sulfates batteries and I have restored several batteries which I would have in the past just
discarded.
Subject: Deep Cycle Battery - What is the Real Capacity? --part 1 of 2
From: Roger Hamlett <ttelmah
>
>
>
>
>
>
>
>
ntlworld.com> Date: Mar 2004
I am clear on the fact that batteries should not be run down
to the ground, so I want to distribute my loads well. I am
going to get another battery. Hopefully a 115 AH battery.
Here is what I am thinking of doing. Can someone help me
figure out how long I can run these things before I get
either of the batteries below 30%:
What I have to run is:
- Laptop: Dell Inspiron. The power supply says it consumes 4.5A.
It says that the supply can _deliver_ a maximum of 4.5A (probably at about 18v). This is different from the consumption. The
supply only has to deliver this when the laptop batteries are flat, and it is having to charge them at the same time as the laptop
is being used. You can keep the actual consumption of the laptop lower, using the options to switch the processor speed down,
keep the display dimmer, etc. etc.. Ideally, get a 12v supply for the laptop. These are available from Dell themselves, and
(cheaper) from a lot of third party companies (given that your unit has the higher current supply - there are two versions of Dell
supply, according to the Inspiron model involved, make sure that the supply you get is for the higher current unit). This gets rid
of the double inefficiency of converting to 120v, and then back down to 18v, and means that the whole system in this area is
running at the lower (safer if conditions are damp) voltage.
> - SBIG ST-7: From the SBIG website for the ST-7 it says: 5 VDC at
> 1.5 amps, ±12 VDC at 0.5 amp desktop power supply included. So
> which one do I use?
Again ideally, get the 12v supply. The same comment applies as for the laptop. The figures given are the _outputs_ from the
supply, which is having to deliver a maximum of 19.5W (5*1.5 + 12*.5 + 12*.5).
>
>
>
>
- Thousand Oaks digital dew controller: Unfortunately, their site
has very little info on current consumption and the unit has
nothing printed on its back. I'd be running a 10" strap, a Telrad
heater, and a 2" strap for EPs.
The unit itself, draws practically nothing. This is why it does not have a figure on it. It is the _straps_ that draw the power, and
the amount varies according to how high the heaters are set. Typically, a 10" strap, will draw perhaps 3A on full, while the
eyepiece strap (and the Telrad heater), will only draw about 0.2A at the same setting.
> Here's the site: <http://www.thousandoaksoptical.com/>
> - LX200: As advised, I'll turn slewing speed down to maybe 4?
Perhaps 2... I suspect the reason for the laboured sound, is that the _peak_ current delivery of the 1812 module, is less than the
mains supply. High speed is of no advantage really (if you are going to another part of the sky, the scope taking a few seconds
longer is not a great loss).
> That's it. I have a Coleman 800W inverter that does up to 7 amps,
> and I'll probably get another Coleman 400W that does up to 3.5 amps.
You do not need more inverter power here. If you are buying extra stuff, go for low voltage supplies instead, and get away from
running high voltages in the conditions round the scope, and the inefficiencies involved.
>
>
>
>
I was thinking of running the laptop and SBIG on one battery (to keep
them separate from the scope) and since they are the ones that consume
the most, run them on the big battery (115 ah) and the scope and
digital dew system on the other battery (the 75 ah).
>
>
>
>
>
Do you guys agree with this? Should I get the smaller coleman
inverter or another big one? They are both on sale right now. $29.99
for the small one and $50 for the big one.
Will this be the best use of these batteries? How do I calculate how
long I should run them before getting to 30% charge?
Work like this:
Take the quoted battery power, and _halve_ it. (this allows for the battery ageing, and the fact that you will be using it at low
temperatures), while also avoiding fully discharging the battery. So for the 115Ah battery, treat it as if it can deliver 57.5Ah. Now
work out the total power needed:
Laptop say perhaps (working at 3/4 the 'peak') 3A, at 18v = 54W. ST7 = 20W
Heaters = (take 3/4 power) 32W
Scope (look at an average between the 'peak,' and 'continuous' power, at perhaps 0.7A at 18v) = 13W
Assuming you have switched to using all '12v' inverters, instead of 'double' converting, then add these together, and
add an 'inefficiency' for the inverters at 20%.
Total = (54+20+32+13)*1.2 = 143W
Current (at 12v) = 143/12 = 11.9A.
The battery can then give about 5 hours.
In fact the figure for the laptop, heaters, and scope, are all higher than 'real.' My own Inspiron, only draws about 2A, provided
the internal battery is charged, while the heaters typically operate nearer to perhaps 30% power. I see more like 10 hours
operation, with a similar setup, on this sort of battery. The figure represents a 'worst case,' for a really cold night. However if you
work through the 'double inverters' (using the Coleman to go up to 120v, then down again to the voltages required by the
individual units), you would need to think in terms of: Total = 143*1.2 (to allow for the inefficiency of the second inverter) =
170W
Notice that this is still well short of what your 800W inverter can handle.
Battery current= 170/12 = 14.2A
The 'worst case life,' then falls to only 4 hours!... The same comment then applies that the figures are worse than real, but does
begin to bring home how much power is actually involved.
------------------------------------------------Subject: Deep Cycle Battery - What is the Real Capacity? --part 2 of 2
From: Bill Keicher <wekeicher
comcast.net>
The ampere hour rating is for a voltage of 12V. So it really is a measure of how much energy is stored in the battery.
75 ampere hours x 12V = 900 Watt hours
Including losses in the inverter which might be 20%, the energy available at 120V is:
80% x 900 Watt hours = 720 Watt hours
So at a voltage of 120V, the "Ampere hours" are:
720 Watt hours / 120V = 6 Ampere hours
The telescope, computer, etc. will require about the same amount of energy no matter how you change the voltage (aside from
inverter losses), so it is best to think in watt hours available from the battery as John has done.
Subject: Parallel Battery Charging
From: John Hopper <JohnLX200
aol.com>
Gene Horr writes:
<< But the current level/voltage charge curve should be the same for batteries of the same design but different
capacities. And if they are in parallel this will "force" them to always be at the same voltage level, which would
prevent overcharging. >>
In my opinion, this is the key point which people were missing, that once the batteries are successfully hooked in parallel and
have reached equal voltages with no current flowing between them, they are effectively one battery which can be charged and
discharged as one.
Furthermore, the charging currents will sort themselves out, and will be lower than if the same charger were used on either of the
two batteries separately. All the worries about a "high charging-current draw" by one battery somehow forcing current into the
other wasn't correct, as the presence of the second battery REDUCES the charging rate on each.
The only more important point is that INITIALLY CONNECTING two batteries in parallel is DANGEROUS. All the normal cautions
which apply to jump-starting a dead car battery should be applied, and it's STILL dangerous! A charged battery and a dead
battery are at significantly different voltages, and due to almost negligible internal resistance, the currents can be extremely high
when you connect them.
This is one reason why I prefer to use cheap, light jumper cables over expensive, heavy ones. A cheapo 8-gauge pair won't have
the same current-carrying and voltage-forcing effect as a "professional" 2-gauge pair. The smaller wire will support a larger
voltage drop across it (due to its higher resistance) at a given current than a heavy wire. Hence this will reduce the voltage seen
by the weaker battery, which in turn lowers the current. You're dumping more energy into heating up the smaller wire than with
the thicker wire.
A suitable resistor to put in series with the jumper wire between the last two terminals to be connected, is a 12v automotive
headlight. Typically they're around 2 ohms, 6 amps, 72 watts. Power = (Voltage squared / Resistance) = (Current * Resistance).
If you can see some light, and then it slowly dims until you can't see any more light coming from the filament, you know the
voltage has been almost equalized and there isn't much current flowing to the (formerly) more dead battery. Then I'd wait a
couple more minutes, remove the headlight and jump them together with less fear of a problem. Just make sure the light didn't
go out instantly due to being put across 24 volts if you connected + to - !!
Rather than actually try hooking up batteries with different states of charge, I'd charge each battery separately, check that they
took the charge OK, then follow the procedure above. Maybe with a couple of 50-foot 14-gauge wires and making the final
connection at the headlight, 50 feet from the batteries ;-)
Just remember, if you get the terminals mixed up, connect a dead battery to a strong one, make a spark where hydrogen gas has
been venting from the battery, charge too fast for the hydrogen to vent properly, or otherwise don't know what you're doing, it
really is dangerous.
The sulfuric acid in batteries can (and often, does) do bad things to delicate organic matter like eyeballs, lungs, and skin. It's not
the absolute nastiest acid in existence, but it's close enough that you've got to respect it and not take chances.
I've been playing with sulfuric, nitric, and worse acids since the age of 12, and have jump-started a lot of cars under all kinds of
circumstances, etc. I've never had a problem, but I do know other seemingly competent people who have had batteries explode
in their faces. I'm not sure how much of it was luck vs. knowing what I was doing, but I'm certain it wasn't exclusively one or the
other.
Subject: Measuring Remaining Battery Charge--1 of 6
From: Radu Corlan <rcorlan
profis.ro>
Guy Schwartz wrote:
> I use a Sears marine battery to power my scope remotely. What can
> I use to check/measure the remaining charge of the battery. I know
> that voltage is not the only thing.
In general, you can't determine the state of charge of a battery by measuring something on it -- it depends too much on the
charge history and general state of the battery.
When you start discharging a fully charged battery, the voltage goes down fast at first, to little above 12V. Then it goes down
more or less linearly to below 11V -- this is the portion where you get most of the charge. After that, the voltage begins to drop
at an accelerating rate (and you should stop discharging the battery!). If you knew the "turning points" of the discharge curve,
you could then determine the amount of charge, However, there's no way to reliably determine those, other than monitoring the
discharge of your battery in roughly the same conditions (discharge rate and ambient temperature) as when you use them.
Large UPS designers (I used to be one) would kill for a formula or something to determine the charge level; it just doesn't exist.
All you can know for sure about a battery is when it's fully charged (when it draws less than about 1A at boost voltage (14.4V) or
was kept a long time (>8 hours) at float voltage (13.8V) ) and when it's discharged (voltage less than about 10V).
I found that the best way to determine charge is to integrate what you take out of the battery, and compare that with the total
capacity (which you determine by doing a complete discharge). If you make the test discharge and the actual discharge at similar
rates (the battery capacity goes down when you increase the discharge rate) you can get pretty accurate results with this
method. However. if you change the ambient temperature a lot, all bets are off!
The best advice I can give is to monitor the voltage during the night -- you will get a feeling for what it means in time; To do
better is a lot of work, and not always possible.
------------------------------Subject: Measuring Remaining Battery Charge --part 2
From: Doc G
I have avoided this topic for years now. I appreciate Radu's response. For those who may have doubts, about his response, I will
be at least one person, who has also worked with batteries in industrial applications, to verify what he is saying. Measuring what
energy remains in a battery is exceedingly tricky. It can be done under the limiting conditions he describes. I usually suggest
charging the battery and then trickle charging to hold the charge until you are ready for use. Then monitor the voltage while you
use it and stop at between 10 and 10.5 volts.
----------------------------------------------------Subject: Measuring Remaining Battery Charge --part 3
From: Doug Azwell <deazwe
netzero.net>
I agree with your explanation. The most significant factor in battery capacity is the temperature, especially with lead-acid
batteries.
The driving force for battery activity is the chemical reaction that provides the charge. In lead-acid batteries, this is the reaction
of sulfuric acid oxidizing lead in the neutral state to a charge of +2. This reaction's activity constant changes by ~20% for every
change in temperature of 10 deg C.
This is why the capacity of a lead acid battery is significantly reduced on those cold nights. Just ask anyone that lives in Canada
about that, they will have plenty to tell you about car batteries on cold nights.
----------------------------------------------------Subject: Measuring Remaining Battery Charge --part 4
From: Don Tabbutt <don
tabbutt.com>
Try: <http://www.westmarine.com/electrical.html> There is much about batteries there.
----------------------------------------------------Subject: Measuring Remaining Battery Charge --part 5
From: Roger Thompson <rthompsn
nb.sympatico.ca>
Measuring the remaining charge in a battery is very difficult thing most of the time, you can't just use a voltmeter. What you
have to do is measure the voltage drop and current under load. This will give you some ideal as to where on the batteries
discharge curve the battery is currently at. Unfortunately, the discharge curve is seldom ever supplied with consumer batteries,
and it can vary considerably depending on conditions, discharge current, age, temperature, etc. at best you have to make a
judgment call as to the remaining capacity in the battery. Your best bet is to insure that the battery is always maintained in the
condition specified by the manufacture. The batteries should always come with some time of charging schedule and discharge
ratings, follow them for longest battery life. You can try to log the usage and over time you should get a feel for the condition of
the battery after use.
Be very careful about using the battery with unknown capacity, since a lower than normal terminal voltage can put any inverters/
converters you may be using, under severe stress, and can cause their failure.
----------------------------------------------------Subject: Measuring Remaining Battery Charge --part 6 of 6
From: Don Tabbutt
With you having said all that, still all you need is a voltmeter. When a deep cycle (marine type) battery reaches 10.5 volts under
load, whatever that load may be, it is discharged. This is the voltage level that is the standard in the industry.
To determine amp-hour capacity and reserve capacity, which are different tests, the battery is discharged with specific loads to
10.5 volts. These tests are what determines the content of the label stuck on the battery for consumers.
So stick a voltmeter on it, discharge it to 10.5 volts, and then recharge it. You should recharge it at 10 to 15 percent of the
battery's amp-hour rating. Thus a 100 amp-hour battery should be recharged at 10 to 15 amps.
By the way, lead-acid batteries have no "memory" like NiCads, and can be recharged from any reasonable discharge level. Just
don't discharge it to below 10.5 volts...you risk sulfating the battery and inhibiting its ability to recharge.
Subject: Reverse-Power Protection
From: Paul Goelz <pgoelz
eaglequest.com>
> I wouldn't give a passing grade to a student who designed
>something for field operation and didn't protect it against obvious
>environmental hazards, of which the most obvious is reversed power. (This
>can be done several ways without a 0.6-volt silicon voltage drop... a
>Schottky rectifier costs only 0.3 volt... there's a MOSFET circuit invented
>by Robert A. Pease that costs essentially nothing.) But it is very common
>for digital devices to be built without that kind of protection.
>When the warranty on my LX200 expires, I'm going to add protection ->probably a Schottky rectifier.
It's even simpler to add a reverse biased diode ACROSS the power input (i.e.., band connected to the positive input). A 3A diode
and appropriate fuse on the power input (there is one there already, I think?) will give you total protection and costs zero volts
drop. It's sole purpose in life is to blow the input fuse on reverse power application. And since silicon devices usually fail shorted,
you are protected even if you blow up the diode before the fuse opens.
I am going to add this sort of protection to my 2045D. The last time I had it out, I managed (in the dark) to plug my polarized
battery connector in backwards and blew up the input transistor. Thankfully, that was all that blew up! And it's even worse on the
2045D, because they use a battery holder with a "9V style" snap connector where if you attempt to snap the connector onto the
battery pack, there is nothing to prevent you from attempting to mate it backwards. The snaps will not mate but they will
certainly touch. If the cable is plugged in to the scope… POOF! As we say in the electric airplane community "You will let the
magic smoke out". (There is magic smoke in all electrical devices. If you let it out, the device won't work any more).
Subject: 12v Gel Cell Battery Charging Tips
From: Ric Ecker <rlecker
juno.com>
Gel cells need to be fully charged up when not in use to give a long service life, I have been doing this for years now with great
success, learning about batteries from battery manufacturers. plus keeping a few different UPS (battery back-ups) for systems
that can't go down. I use a 12vdc battery charger that puts out 12 amps, plus it will trickle charge, and I use a 1 ohm resistor 20
watts or larger in series. I can leave this arrangement on the battery at all times keeping the battery charged @ 14.2vdc. This
will allow the charger to be hookup to the battery all the time and you don't have to remember to disconnect it after a couple of
weeks. The resistor acts like a switch when the battery is fully charged so you can't over charge the battery.
Subject: Restoring a Gel-Cell
John McVey <jmcvey
hpbslq.boi.hp.com>
When the cell voltage drops too low because the battery is discharged or allowed to self-discharge, a insulative chemical can form
on the electrodes within the battery. This causes a high impedance state which makes it difficult to charge. It is, however,
possible to charge the cell by applying a higher than normal DC charging voltage which is carefully current limited. Many nice
laboratory power supplies are capable of this. You just have to seek one out.
Proceed as follows; this has always worked for me:
Set the output voltage of the power supply to 30 volts or so (even 20 will probably work, it will just take longer). Limit the output
current to 50ma or so. Now charge the battery until the battery is taking the full 50ma of current. This may take hours or
perhaps a full day. Watch the battery, it may start to get warm because you are reversing the chemical reaction that formed the
insulative layer in the first place.
Once the battery is taking 50ma or so you can reduce the power supply voltage to probably 15V and limit the current to the
Ampere-Hour capacity divided by 5 or 10. Charge the cell until its voltage has stabilized around 14.5V (I am assuming you have a
12V cell). Don't worry too much about overcharging lead acid gel-cells. They typically like trickle charging.
Subject: Operating the LX200 Classic on 15V
From: Robert Preston
A while ago I installed a JRC 7815A three-terminal 15 volt regulator (Digi-Key cat. no. NJM7815A-ND, $0.55 each) on the output
of my Meade 120VAC/"18"VDC power supply (It actually had a 20VDC output under load).
I then mentioned on MAPUG-Astronomy that slewing was slightly uneven when using the 15V regulated supply, so that the pitch
of the slew-whine would rise and fall noticeably during the course of a high-speed slew.
It now turns out that my regulated supply was putting out an average 13V, not 15V, and when I fixed the circuit so it really puts
out 15V, the slewing sounds just fine and I'm pleased with the 15V operation (and hope that it will make the motors, regulators,
and motor driver circuits longer-lasting).
The final circuit also includes three 6-amp diodes (Radio Shack) in series between the meade supply and the regulator input so
the input to the regulator is 17.5 volts and it doesn't run so hot. The regulator and diodes still are hot to the touch after an hour
of operation, but I think well within design specs. The regulator is on a little Radio Shack heat-sink for TO-220 ICs, and I drilled a
large number of 1/8 inch holes in the Meade power supply case to give better ventilation. The three fat diodes are attached to the
inside top of the case under the air slots so their heat goes right out of the case. Thanks go to Bill Miller and other mapuggers for
the diodes and holes ideas.
For those who care about details, I'll add the following explanation: When I initially installed the regulator, I omitted what I
thought was an optional 0.1 microfarad disc-ceramic capacitor across either the input or the output (can't recall which, now) since
it seemed that the huge electro- lytic capacitors in the supply and on the front panel of the lx200 made those little discs
unnecessary. When I initially checked it, that circuit did give 15V output, so I thought it was working fine. Later on, I added a
bunch of red LEDs as safety lights on the top of a stepstool/toolbox and had them plugged into the regulated supply. Imagine my
surprise one night when I saw the two dozen LEDs blink in intensity while running on my fancy regulated power supply! The
voltage of the supply was erratic, but mainly 13V, not 15V. Adding the capacitor (now there's a disc cap across BOTH the input
and output of the 7815A) finally fixed the problem.
Update: By the way, the 15V 1-amp regulator added to my Meade supply shut down from overheating, despite its little heatsink
and the 3 series diodes and my drilling enough ventilation holes in the Meade plastic case to make it look like it was shotgunned.
So I got a larger, metal case from Radio Shack and mounted the 7815 regulator chip directly against the aluminum case. Now it
seems to be happy as a clam, with the entire metal case acting as a heatsink. (I discarded the top part of the Meade plastic case
but installed the bottom part inside the new case as a holder for the Meade transformer and rectifier circuit).
Subject: Reducing 18v down to 15v
From Stan Thomas <thomas
cosmic.physics.utah.edu>
If I understood the original question you asked how to reduce the 18 VDC power supply voltage down to 15-16 VDC. The problem
with using a resistor is that the voltage drop across the resistor depends on the current. A simple way to achieve a constant
voltage drop is to use a series of diodes instead. Each diode will have a voltage drop of ~0.7 VDC. Therefore, to drop from 18
VDC to 15-16 VDC all you need to do is put 3 or 4 diodes in series between the positive (+18 VDC) supply and the telescope. The
diode should be rated for more than the maximum current the telescope will draw.
Just in case you are not familiar with diodes I should mention that they are marked with a dark band painted near one end of the
diode. The side with the dark band must be connected to the telescope side (right side in the diagram below) and the other side
connected to the +18 VDC side (left side in the diagram below).
Supply (+18 VDC)
+18 V -- diode 1 -- diode2 -- diode3 -- diode4 -- telescope +
GND -------------------------------------------------- telescope Telescope ( +18 VDC minus four times 0.7 VDC = +15.2 VDC)
Subject: Adjusting Meade 18V Supply
From: Dave Sage <dave.sage
canrem.com> June, 1996
If anybody feels that they really need to adjust the output voltage of the 18/12 converter, it is really a simple matter (detailed
below). I don't really think it should be necessary, but then I havn't experienced any problems with my scope either, and my
converter puts out 18.2Vdc un-loaded. For those of you who have converters putting out more than that then you should
probable have a look at fixing it. The voltage should not change significantly when the converter is loaded. The chip inside should
be able to put out 5 amps, although it may not have an adequate heatsink to do that. I would suggest you open your unit up and
check all solder connections. The circuitry design is sound but converters are built by a third party and are really very poorly
constructed. I found two un-soldered joints in mine and the chip legs bent improperly so that the part was not making contact
with the heatsink at all. I am not surprised that some converters have self-destructed.
In any case the output voltage is set by a simple voltage divider which takes the 18Vdc output and divides it down to 1.24 volts
to be compared by the reference voltage in the chip. The 1.24 volts appears on pin 2 of the chip with respect to the negative of
the supply.
Open the box and hold it sideways so that the 12vdc input is on the right, the 18Vdc output is on the left and the IC and heatsink
is along the top edge and more or less in the top right quadrant of the box. You will notice three blue resistors side by side
horizontally to the bottom left of the chip. The top two are the two which form the voltage divider. The third (bottom of the three)
is of no concern. The top one should have color bands brOWN, RED, YELLOW, brOWN, brown (1240 ohms) left to right or
reversed.
The center resistor of the three should have colours brOWN, BLUE, WHITE, RED, brown (16900 ohms)
For those that can figure out a resistor divider you will see that those two resistors across 18 volts will have 1.24V at the
junction.
In order to change the voltage to say, 15V should only require changing the top resistor from 1240 ohms to 1500 ohms (brown,
green,red). This should give approx. 15 volts.The designer has been careful to use precision resistors in the circuit to get as close
as possible to 18 volts and the output voltage changes quite a bit if the resistors are a bit off so a standard 1.5k resistor out of
you junk box may only give you marginal success. You may want to try 1.3k or 1.4k first to see what happens.
BE VERY CAREFUL CHANGING RESISTORS and be sure to measure the output before you connect the scope. Observe spotless
solder techniques. If pin 2 gets grounded the output of the converter will be VERY high.
I realize that a variable resistor could be put in place of the resistor but there are too many ways for an amateur to mess up this
connection and have the ability to make the output go to 30 or 40 volts or more. Also the pot could go bad and the voltage could
go that high without you knowing.
Subject: Operating the LX200 Classic on 12 volt Battery Pack
Ed Stewart, <stargazer
skymtn.com>
In watching the discussions on 12 volt vs 18 volt and dec motor failure, I noticed that one recent post tied the two discussions
together. He wondered if those running on 12v experienced less dec failures and noted there was less dec motor sparking when
slewing speed was dropped to a value of 6. From a past thread on experiences in powering at 12 vs 18 volt, there was
considerable concern about doing anything other than what Meade described in the manual, i.e., use 18v.
When another commented that he had been using 12v for a year with no problems (although it seems he did not have high speed
slew capabilities?), I decided to use the 12v gel cell that powers the DobDriver II on my 12.5". This unit was purchased at Target
dept. store in the camping dept. and has the label "Power Source" on it. Has a 12v and a selectable 12-9-6-3 volt recepticals, a
built-in light and a 6-amphr rating with fuses on all circuits. Cost $30 and weights about 5 lbs. I ran simulated observing sessions
with 3 power-ups, 20+ slews, and continuous tracking. After 5 hrs. total, the battery pack indicated low voltage, but the scope
still performed normally including high speed slewing (set at level 6). I shutdown and within 5 seconds tested the voltage--it was
11 volts!
As to dec failure, just listening to the mechanical sound at full speed vs a low setting of 5 or 6 indicates to me less stress, plus
the noted reduction in sparking, probably would result in less failures (?). I will continue to use 12v and will report periodically on
my findings.
I have since used the battery pack for several years with normal performance. Should the need for longer observing or additional
accessories require more capacity, then I will move to a small marine battery or wheelchair gel cell. Some advice on gel cells:
first, be sure to have a 1 amp or smaller fuse in the circuit; second, do *not* use an automotive battery charger. Instead, use a
trickle charger (one probably will come with the battery pack). Should a resistance build up to charging, use a very low rated
charger (100 milamps) over several days to reverse the chemistry.
Subject: Operating the Classic on 12v Vs. 18v
From: Doc G
I need to correct a comment I made on this issue. I stated that the keypad sets the speed of the drives by sending counts to the
motor circuit. This is correct. I also stated that the slew rate thus did not vary with voltage (when set from the keypad). However,
it is the case, as someone suggested, that the scope will move more or less rapidly with voltage changes, when the maximum
slew rates are selected. Or when the default rate is selected (this is the maximum rate). The reason is that the motors are
slewing as fast as they can for a given voltage under those situations. This means that the drive amplifiers are putting out the
maximum current possible under very fast slew conditions and they cannot keep up when the scope is on a lower voltage.
Never-the-less, the actual motion of the motor is still kept track of by the computer by its counting the encoder pulses. This so
the computer can tell the motor when to stop. If this were not the case, a slew overload would cause the scope to loose track of
where it is, and it does not. The apparent mode of operation does depend on how mechanically tight the drive is. So the observed
conditions might vary depending on the mechanical condition of the scope. Again, the LX electrical and mechanical mechanisms
prove more complex than they at first seem. This matter has been a controversial topic for years. The facts, as I understand
them, are that almost all of the LX scopes work well with 12 volts. However there are exceptions. Scopes that are tight
mechanically or have significant stiction require a much greater torque and thus a much greater motor current to get them
started as you have described. This requires higher voltage.
A solution to this problem has been for Meade to recommend a higher voltage, 18 volts, in recent years. This is in many ways an
unfortunate solution to what is basically a mechanical problem. This is why. With the higher voltage and a case of mechanical
stiction the motors can overheat or the transistor drivers overheat and burn out. With the lower voltage, you can more easily get
erratic running of the motors as you have observed. In order to solve the overload problem with the higher voltage, Meade has
added current limiting resistors to the circuit. You will find these described in the archives on recent board replacements. This is a
partial solution but not a perfect solution. It is a fix (add on)(after thought). With the present design it is hard to get off of the
horns of this dilemma. The best solution, I think, is to see to it that the mechanical system of the telescope is smooth and free
running. This can be done by insuring that the bearings are aligned, the scope is balanced and it is well lubricated. Unfortunately,
all of these problems go back to the original design, which is, in my opinion, fine for the smaller versions of this scope but
somewhat problematical for the larger scopes.
I really regret to report this analysis because it means that some LXs will give users problems. So it appears, that if you have a
tight scope, it is essential and worth the time to get it in the best possible mechanical condition. I have personally done several
things to my two LXs (a 10 f/6.3 and a 12 f/10). These are: to replace the declination bearings with roller bearings, carefully align
the axes, lubricate the bearings with the best grease, carefully adjust the motor/worm mechanism to give just the right tension
on the worm wheel, balance the scope carefully and use the 18 volt supply. I put in a considerable amount of time and constant
care to keep the scope running smoothly.
Subject: Voltage Regulators--Short Primer
From: Doc G
This is a short primer on power supplies which may be of some interest to those concerned about electronic equipment which has
both digital and analog sections, and particularly which drive transducers such as motors. This may or may not apply to any
particular piece of equipment since there are some alternate designs possible. (but not usually used because of problems with
cost.) I am not privy to the details of specific designs which may be of concern to MAPUGers at this time.
In general the power supply will have both +12 and +5 volt regulators for the voltage busses. The 5 volt bus is for the digital
parts of the circuit and the 12 volt bus is for the analog and higher level output and auxiliary switching electronics. There may be 12 and -5 volt supplies as well, as in the case of a PC, but these are not necessary for less complex digital/analog designs.
Additionally, the electronics may have semiconductor drivers for the output circuits that can withstand higher voltages. This is
particularly true if the outputs drive inductive loads like motors of most types. (either steppers or DC)
The 12 and 5 volt supplies are usually regulated with standard three terminal regulators like the 7812 or 7805 which are
integrated packages of high quality and low cost.
In order to regulate 12 volts, the regulator must have a voltage in excess of 12 volts by a few volts. Typically 3 to 5 volts. There
are some low drop regulators which will work with as little as 0.5 volts differential but they are not usually used in older designs.
Thus we see that there is no problem at all regulating the 5 volt digital power supply since the source is always substantially
higher than the 5 volts. But a 12 volt electronic regulator will typically start to run out of regulation capacity with less than a 3
volt drop. It will certainly run out of regulation when the source voltage is equal to the regulated voltage.
Thus it is prudent to advise that equipment with 12 volt regulators be operated with sources of at least 15 to 18 volts. This
straight forward design limit is the reason that manufacturers recommend voltages for the source at least a few volts higher than
that of the highest voltage regulated bus in the equipment. Of course if the source voltage is too high, there is more and more
power lost in the regulator itself. Thus it would be foolish to use a 24 volt source for a 12 volt regulator. In that case, the
regulator would dissipate a power equal to that dissipated in the equipment. This situation would double the heat sinking
necessary for the equipment, a costly design mistake.
At the same time if the source is the power mains, the voltage from the source will vary with the line voltage which might be well
over plus and minus 10% depending upon the policies of your power company. So a safely factor must be built into the design. If
the source is a battery, it should maintain a voltage about 3 volts above the regulated bus voltage. For a 12 volt regulated bus
that would be 15 volts or slightly more. A convenient voltage is 18 volts. A battery voltage as low as 13 volts might result in the
failure to maintain good regulation. This does not necessarily mean that the electronic equipment would fail immediately. But, if
the regulation is an important part of the design it might cause erratic operation.
An additional factor in designs which use inductive loads in the output is that inductive loads, especially switched loads, often
require voltages higher than the voltage used for the main circuitry. When that is the case, it is necessary to connect the high
side of the load to a higher voltage power supply and to use devices in the output stage that will handel both the higher voltages
and the spikes that result from switching transients. This is easily done in proper circuit design. If the drive voltage on the motor
is too little, the current will be too little and the motor will either stall or miss counts since it is the current which provides the
mechanical torque. Neither condition is desirable.
Thus it is often standard design for reliability purposes to have a source voltage higher than the voltage of the regulated supply
and to have enough voltage to drive the motors. The higher source voltage is of course not regulated nor does it have to be. The
above information is a very simple overview of power supply design. It is based on 40 years of design experience in electronic
and computer applications and instrumentation.
Subject: Fried 18V Converter
From: Richard Tabbutt <76367.3371
compuserve.com>
The Meade 12VDC to 18VDC converter is comprised of a simple switching regulator circuit, of which the LT1170 chip is the
"heart". This chip is definitely not a rectifier. Instead, it contains the switching transistor (hence the heat sink) and regulator
circuit. It controls (switches on and off) the current through the inductor located just below its leads, which then charges
(through a diode rectifier) the large capacitor located at the output. The ouput voltage is sensed by the LT1170 and controlled by
varying the inductor switching current. Voila! 12V in becomes 18V out.
If your converter is new, you should send it back. Otherwise, if you feel you can handle the desoldering and soldering involved,
try Radio Shack for the parts you need. They advertise that they can obtain almost any IC if you can provide a part number. Also,
I'd replace the output diode rectifier, as failure of this part could have caused the failure of the LT1170.
Subject: LX200 18v AC Adapter Problem --part 1 of 2
From: Brian Bond <brian.bond
blueyonder.co.uk> Date: Nov 2003
----- Original Message ----iship.com>
From: Christian Molnar <cmolnar
I just finished a power box, marine deep cycle battery inside a metal
toolbox with 5 lighter outlets on top and leads for my inverter.
I don't know whether this is just my paranoia but, since I just did this, I
noticed it. When I run my LX200 on outlet power (from the house) it is very
fast and there are only 3 LEDs turned on the indicator most of the time.
When I use this power box, you can tell it's moving slower and it is just
very different. There's more between 4 and 5 led turned on constantly and
it peaks every time it slews. The slews are more sluggish and the motors
don't sound like they do when the scope is plugged in.
Is this normal? I can't see how this battery wouldn't be powerful enough.
It's like a 75 amp hour boat battery.
----- End of Original Message ----There is a problem with one of the components in the Meade 12 - 18 volt convertor, where the off load voltage is 18 but when
plugged into the LX200, under load conditions, drops to 12 volts. The flyback inductor controlling the voltage change develops a
shorted turn over time (heat) and prevents the circuit performing as it should. Normally there is nothing wrong with the chip. My
internet site <www.brianbond.eu.com> has details of rewinding the inductor to clear the problem. This has always been the cure.
I've copied the relevant section below:
'Must handle at least 3 amps (Meade = 94 turns of 24SWG Enamel wire on original bobbin for 330uH, saturated in Polyurethane original fault showed low conversion once the chip had been changed - due to inductor turn short circuit)'
-------------------------------------------------------Subject: LX200 18v AC Adapter Problem --part 2 of 2
From: Damon Raphael <w7md
gci-net.com>
----- Original Message ----aol.com>
From: Bob Manley <RManley234
I have now confirmed that the thermal cutoff is in series with the transformer primary. I have also confirmed that it
has not blown. All fuses are in place, of the proper sizes, and not blown. I believe that your diagnosis is the correct
one- that there is an internal short in the secondary winding. The resistance of the secondary seems to be too lowonly about 0.4 ohms, after the resistance of the ohmmeter leads is subtracted from the total. This AC adapter has
been outside in my unheated and well ventilated observatory for four or five years, and I suspect that some
corrosion of the core or breakdown of the magnet wire enamel has taken place. It now appears to be unrepairable.
----- End of Original Message ----I think that your assessment of the cause of failure is correct. If the transformer was exposed to moisture, that would accelerate
the insulation deterioration. In a transformer secondary short, you would usually expect that the failure of an external component
would have initiated the insulation breakdown; that is, heating secondary to excessive current draw through the secondary
winding. If the other components are OK, then moisture is probably the culprit. If the primary had shorted, it would have blown
the thermal cutoff device. You tweaked my curiosity with your post because I have had some problems with my LX200 which
were power source related (as have others in the group). My AC Adaptor is branded as "SCEPTRE" made in China with a nominal
output of 18VDC rated at 2 Amps. This is the original unit which was supplied with my 8" f/10 LX200 purchased new in 1996. I
have had no problems with the unit and am always careful to protect it from the elements. I live in Tucson, Arizona where
moisture is usually not a problem.
I tested it tonight with my Fluke 77 DVM. The unloaded DC Voltage across the output is 21.3 VDC. I located the manufacturer/
supplier of the 18v converter at <http://www.gpelectronics.com/AC-DC.htm>, and it is still available from them. They have a .
pdf spec sheet online but no schematic. They do list it as an unregulated AC to DC power supply.
I opened the case and examined the contents. Of course your unit may not be similar to mine. I was curious to see whether it
used switching components or a voltage regulator of an kind. Voltage regulators are near the top of the checklist for common
component failures, one rung below electrolytic capacitors. I see the transformer, 4 1N5400 common silicon diodes, an
electrolytic capacitor 6800 mF, what is probably a resistor and a fuse. I did not remove the circuit board to see how the diodes
are hooked up but it looks like a simple voltage doubler circuit with a single capacitative filter stage.
There are no zener diodes, voltage regulator transistors or ICs and certainly, this is not a switching power supply (which would
add several levels of complexity and potential problems). In a more perfect world, you would be able to call Sceptre and order a
replacement transformer for a few bucks and the problem would be solved. You can give them a buzz and try it but they may not
speak English, may not provide replacement parts, charge more for the transformer than a new whole unit or refuse to sell to
you. Maybe all of the above or tell you to call Meade for service. I then downloaded the motherboard schematic from Doc's site
and checked to see what happens to the power when it goes into the telescope. I see that several capacitative filter stages are
added and there is a voltage regulator chip which converts 18 VDC to 5 VDC for the solid state devices. The way the LX200 is
designed, the filter and voltage regulator parts of what would properly be called an "AC to DC Power Supply" are on the
motherboard. The power transformer and rectifier parts are external to the scope. I was curious to see if a failure of a component
inside the scope could cause the transformer in the power supply to fail. I think not if the fuse in the Sceptre unit and the fuse in
the DC connector cable are proper. The series output of the motherboard section of the power supply is fused to protect the
motherboard and plugged in devices should there be a failure in the power supply.
It would have been nice if there was current limiting circuitry to prevent damage from low voltage situations. I wonder if current
limiting has been engineered into the newer GPS versions.
Subject: 1812 Voltage Converters
From: Ken Fields <KNSTARS
aol.com>
I fried two of the 12 to 18 volt Meade converters. I have switched to using 12v to 110v converters from Fries for about $40 or
$50. I use a big 120 amp. marine battery which handles the draw of that converter well and then I can use the regular 110 to 18
volt converters that come with my laptop and other equipment. Since I switched to that kind of power source I have had no
problems. I have it all hooked into a switch panel in the back of my truck so that I can turn on or off any line including a portable
worklite.
Also see: <http://obs.nineplanets.org/meade/1812/1812.html>
Subject: Meade 12v to 18v Converter Alternative
From: Ted Van Sickle, Date: Nov, 2001
Radio Shack has a very nice DC to DC converter that connects to automotive battery and by a switch selection provides an output
voltage of about 8 to 30 volts DC. It has a capacity of 30 watts which is just fine for an LX200. I have used it with a garden
tractor battery and it has run the scope for more than 30 hours with no sign of trouble or battery discharge. I don't believe that
the voltage is too important in this type of equipment, an LX200, but for those that are concerned with the voltage, this system is
perfect because you can set the voltage to whatever value you want in one volt steps. Also, I think that it cost $59.95 or
something near that price.
Subject: 12v to 18v Converter Source
From: Gary Giddings <garyg
wwwsite.com> Date: Nov 2001
Radio Shack has a very nice DC to DC converter, #273-1826, that connects to an automotive battery. It has a capacity of 30w
which is just fine for an LX200, 11-16v in and selectable 9-24v out (+-5%).
Subject: Inverters & Batteries
From: Paul Goelz <pgoelz
eaglequest.com>
>First of all, the mount. Unless you are slewing all over the
>place the mount draws very little power. I don't have any specs
My LX200 draws in the neighborhood of 400 mA tracking or slewing, with brief excursions to maybe 1A at the beginning or end of
a slew. This is at 12VDC. At 18V, I would guess it would be maybe 20-30% lower.
>Two inverters available at Walmart (cheaper) or Radio Shack (expensive)
>allow you to power your equipment without having to do anything
>more difficult than plugging it in.
Note the output of the inexpensive inverters is a two step square wave that has an RMS value of 120VAC. However it is not a sine
wave and may not run all types of equipment (especially ones with inductive components) satisfactorily.
So be careful when running expensive equipment from an inverter. I think a couple sensible precautions might be: Don't turn the
inverter on into a load... turn the inverter on and then connect the load. When you switch on the load, make sure it is running
correctly Many inverters have an output current limit that can prevent the output voltage from coming all the way up to 120 volts
when trying to start into a load with a high inrush requirement. This can result in a steady state condition where the output
stabilizes at a lower than expected (and very unstable) voltage.
Avoid powering expensive and/or difficult to repair loads that contain power transformers unless you are sure it is OK (like you
have tried it before and nothing went wrong). Look for a true sine wave output inverter if you want to be safe. I have not seen
one but I understand they exist, at a higher cost. My experiences with inverters have been less than satisfactory, and I would
rather power my field devices directly off 12VDC if at all possible.
Subject: DC Power Source & Inverter
From: Bill Arnett <bill
nineplanets.org> Date: Sept., 2000
Jchoroszucha wrote:
> I recently bought a used LX200.I did not receive a DC adapter with the
> purchase.My scope requires 18 volts DC. The Meade #1812 costs $100. I
> have a marine battery sitting around and was thinking of buying a 300 or 400
> watt inverter hooking it up to the marine battery. And plugging in my scope
> to the inverter since I already have a AC adapter with the scope. Any
> suggestions on this from any one if this will work? If it will draw the
> battery down fairly quick? I plan on getting some software down the road
> probably TheSky by Bis. I also don't have a DC adapter for the lap top so
> I thought the inverter would work for this to. The battery is pretty large I
> use it for a trolling motor I think it it has 700 crank amps. Don't remember
> and the inverter costs $50. Would welcome any comments or suggestions.
First of all, "crank amps" is irrelevant. That's a measure of the maximum short term output current which is important for starter
motors but not here; your LX200 plus a laptop, dewheaters and CCD cameras is unlikely go draw as much as 1/100th of that
much current.
What is important is the amp-hour rating of the battery. That (given that it's 12v) is a measure of its energy storage capacity.
And that's what determines how long it will run your setup. A "big" marine battery is usually 100 amp-hours or more. That is
enough to run an LX200 for weeks and a full imaging setup for several days.
Using an inverter instead of the 1812 is fine. It's a little less efficient but if you have a "big" battery you don't care. And it does
make it convenient to run other AC devices. I've run this way many times with no problems. (And I've had lots of problems with
the 1812, all of which were ultimately my fault but ...)
If you do get an inverter get one that puts out a "pure sine wave" output. The LX200 will probably work fine with a "modified
square wave" but a laptop or a CCD camera may not.
Subject: Inverter Issues & Questions --part 1 of 5
From: Dave Graham <hardware
stephejlwrote:
datasolaz.com> Date: Mar 2002
> First: Large batteries are Dangerous.
Yes, and bad things can happen fast. Some thoughts on making life easier and safer... Check out the battery accessories at a
marine supply house or boat store. Some items on my shopping list:
1. A polyethylene battery box. They have slip-on lids and usually a plastic web strap to hold the lid on. The lids are made with
channels that allow the cables to exit the box. They can help contain the acid if the battery is tipped beyond normal, and
the spatter that can result from over charging. They have handles molded into the case (sometimes a plastic rope loop and
handle) which make the battery much easier to lift and carry.
2. Battery terminals which attach to the posts like automotive clamps, but instead of going directly to a cable, They have a
stud with a wing nut for a ring terminal. Put ring terminals on the end of the cables, and you can attach them without
tools.
3. (More likely from an electrical supply house) A polarized connector rated for 50 amps, wired to very short cables going to
the battery. Keeps you from accidentally connecting the battery backwards, and eliminates the temptation to walk around
with long cables dangling from the battery. Put the female side of the connector toward the battery, especially if the
connector doesn't have protected male plugs. Eliminates the possibility of an accidental short circuit. Might want two (or
more, depending on how many charging options you desire) of the male connectors so one can be wired to your equipment
distribution rig, and the other(s) rigged for charging.
4. An in-line fuse between the battery and the connector. A 40 amp fuse will keep the wiring from a meltdown or fire (or
worse, a battery explosion, if you *do* somehow have a catastrophic short circuit. Downstream, wire an in-line fuse sized
for each individual device as close to the distribution point as possible so it protects the wire as well as the electronics.
5. #8 fine-stranded wire (or heavier if you like) for the cabling between the battery, primary connectors, distribution box, and
charging source. Fine stranded gives greater flexibility. The type of insulation also bears greatly on flexibility. RV and boat
houses usually carry a selection. Ask to see different types. You may be surprised at the differences. You can use an
automotive electrical system for charging if you also get ...
6. A battery isolator (boat or RV house). Allows the automotive system to charge both batteries, and keeps the telescope
battery from draining the auto system, and allows starting and stopping the motor during the process without problems. If
the battery box is well secured, you can run the charging cables to a location in your vehicle and charge while on the road.
The location does need to be adequately ventilated, since charging produces hydrogen gas, and you don't want your RV
becoming a Hindenburg....
The battery box you got at the boat store will come with hold-down clips that can be attached to the floor or other storage
location. They are for the strap that goes around the box to pass through, holding the battery securely in place. The bottom of
the case will have recesses keyed to accept the clips, adding to the stability. Measure carefully when mounting them.
Use terminals properly sized for the wires and the terminals. Again, the people at the supply house can guide you.
Hope this is helpful... You can't stress safety enough around high capacity batteries. A shorted battery can put out enough power
to melt very heavy wiring, and possibly cause the battery to explode. I've never been around one myself, but have seen the
aftermath of two such incidents. Kind of like a tornado...I don't ever want to be close to one...
--------------------------------------Subject: Inverter Issues & Questions --part 2
From: Doug Groesbeck <douggro
>
>
>
>
>
>
>
attbi.com>
The question is that can I run 2-400w converters daisychained together for an
effective output of 800w 110vac without damaging the converters. I have all of
my outlets in the observatory connected together so all I do is connect a
small length of 12ga extension cord with 2 male ends from the converter into
an outlet thereby energizing all of my outlets. What do you think? Can i plug
another 400w inverter into an outlet that is already energized by an inverter
to double to power?
I've followed all the responses thus far, and either I'm way off base or the rest of the folks missed part of your question. You're
energizing the outlets by running a cord between the battery-powered inverter, then tapping the other outlets to supply your
110v items. So far, no problem there.
You want to add another inverter to the mix to provide a larger load capacity and connect it to the outlets in the same manner.
Potential BIG problem there.
Unless you've very strictly paid attention to polarity coding on your wiring chain to the outlets, you could end up with crossed
polarity - the second inverter would feed a hot signal to the neutral side of the chain. Result: a direct short. Something will give,
most likely the second inverter you plug in - right as the bright sparks fly from the outlet. 110v outlets and switches have those
brass and aluminum finishes on each side to provide the reference for polarity - brass for the hot side and aluminum for the
neutral. You can in fact use either side of the switch/outlet for either hot or neutral, as long as the wiring is consistent on that
receptacle (though you should follow code and keep the hot side to the brass for polarity-sensitive devices).
The other issue mentioned by several others is the frequency timing of the power supplied to the circuit. Two sources operating
out of phase are going to make for some problems with consistent voltage.
So if you want a bigger load capacity on the 110v circuit, you're going to have to beef up the point-supply for the circuit. Consider
either a single higher capacity inverter, or a small generator to feed the circuit.
-------------------------------------Subject: Inverter Issues & Questions --part 3
From: Mike Dodd <mdodd
>
>
>
>
>
mindspring.com>
Not daisy chained (indicating series connection). You want to run the
outputs in parallel. This will keep the voltage the same, but increase the
load capability to 800 watts. I THINK you can do this with AC. I
know it works with DC. Come to think of it, there may be a phase
difference trying to do this. Can anyone else comment on this?
Never connect the outputs of inverters together in any way. If you need more power, buy a larger inverter.
-------------------------------------Subject: Inverter Issues & Questions --part 4
From: Roger Hamlett <ttelmah
ntlworld.com>
mindspring.com>
From: Mike Dodd <mdodd
> > Not daisy chained (indicating series connection). You want to run the
> > outputs in parallel. This will keep the voltage the same, but increase the
> > load capability to 800 watts. I THINK you can do this with AC. I
> > know it works with DC. Come to think of it, there may be a phase
> > difference trying to do this. Can anyone else comment on this?
>Never connect the outputs of inverters together in any way.
> If you need more power, buy a larger inverter.
To 'add' to this. If you are running 'normal' AC inverters, doing this, can give the same results, as 'crosswiring', between two
phases on a three-phase supply. The potential for damage is massive. There are AC inverters sold, which are designed to do this
- some 'off line' UPS systems, have a 'sync' connection, allowing the internal signal to be synchronized (for exactly this reason),
but this is only common on very large units, where the manufacturers assume that even more power may be needed. I have a
pair here, of 4KVA units, that do this, but the prices start at a couple of thousand pounds (and presumably similar in the US...).
You can (of course) 'parallel up' the incoming battery supply, to increase the time that the load can be driven for, but to get more
output power, the only simple solution is a larger supply. Remember there is nothing to stop you running different equipment
from separate supplies though.
> On the subject of two inverters I would be concerned about possible
> phasing issues between the two different
> 110v outputs.
Yes.
> I could be possible to have an interaction between two powered devices
> if they share any common circuitry outside of the input
> power supply, could be sorta like the ground loop from hell.
Shouldn't matter. In general, the equipment being talked about comprises devices with their own 'mains' power supplies. These
provide isolation between the incoming supply and the user (necessary...), and in doing so, prevent problems of this sort. What
you say _could_ apply, if you are dealing with directly 'mains driven' equipment, and then joining parts of the latter circuitry
together, but (fortunately), equipment that has connections 'available' to link to other kit, has to have these isolated from the
incoming supply (except the ground connection, which can be common between multiple supplies), to meet current wiring
regulations. The potential for normal 'ground loops' exists, but these would be the same if the equipment was on a common
supply. If multiple inverters are used this way, it becomes essential that the ground connection is made common (and _only_ the
ground connection), otherwise if there is a potential difference between the ground points, this potential will exist between the
equipment...
--------------------------------------Subject: Inverter Issues & Questions --part 5 of 5
From: Jimmy McGuire <jxmcguire1
ualr.edu>
By hooking AC power systems together, either in series or in parallel, you will let the smoke out of your equipment. This is an
event I've always tried to avoid. I suggest you avoid it also. If the outputs of two or more inverters are COMPLETELY isolated
from each other as verified by electronic test equipment, you MIGHT get away with connecting together the electronic equipment
being individually powered by separate inverters, but even that is quite risky, since the equipment and inverter internal
configurations are never guaranteed to remain in the tested config during all the operating modes.
Subject: Power Supply Design URL
From: Randolph Wilson <astro
rwizard.com> Date: Mar 2002
Assuming that the Pictor CCD camera expects "nice" power, and given the cost of a CCD, some refinements may be in order.
Radio Shack has a nice little book on power supply design, as do others. There are easy to implement solutions that provide
clean, well regulated power, as well as features to protect your expensive equipment from possible harm. Take a look at:
<http://www.national.com/parametric/0,1850,645,00.html> to learn about some of what is out there.
Subject: Power Supply Issues for LX200 Classic --part 1 of 3
From: Doc G, Date: Dec 2002
----- Original Message ----From: Bruce Gillespie<Bruce
pcb.co.za>
> my AC Adapter and Inverter got stolen a while back and
> I am trying to setup a new power supply system. What I would
> like to ask anyone who might have some advice on the following:
>
> - How tightly regulated must the 18V be? What happens if the voltage is
> - over? under?Peak current draw? (I figure 2 Amps)
> - Anyone with a suitable circuit for a transformer/rectifier/smoothing cap?
> - What type of fuse and what rating?
>
> I would also like to include a 12V DC to 18V DC Converter in the box
> for when I have to use the system remotely - and cannot locate an
> off-the shelf DC-to-DC component here. Any pointers to web sites of
> suppliers in the USA and reference to brand names / part numbers?
>
> I tried using a laptop PSU that put out 19V DC up in the bush during
> the recent total solar eclipse (when it was not cloudy that is) but I
> found it could not handle the current and kept resetting the CPU in the
> scope when slewing on both axes so I need to build a transformer based
> one that can handle the current.
>
> Also the scope behaved very strangely. I have been using it for years
> with satisfactory tracking and GoTo capabilities. But this time I had
> real problems. I triple checked GPS coordinates (23 01 deg. S, 329 05
> W), time zone, GMT time, alignment stars (tried a few different), did
> two star alignments several times, with the problem being really way off
> Goto's. Even after stepping to the targeted and Sync'ing it seemed
> clueless, didn't even track properly. For instance aligned on Canopus
>
>
>
>
>
>
>
and Betelgeuse, tried to GoTo Saturn and it lost the plot and slewed and
10 deg of course. Also some times it was giving a "Align Mismatch Check Stars" message during selection of 2nd alignment star although I
was 100% sure I had the right stars.
Could this be power supply related? (this was off that laptop PSU) Or
something else? Or am I missing something really obvious?
The voltages in the LX200 classic are regulated down from 18 volts. The digital boards work with 5 volts regulated and the rest of
the electronics uses 12 volts regulated. Only the drive motors use the 18 volts directly.
In the beginning the LX200 classic used 12 volts. It was found that the motors sometimes needed more voltage and they went to
18 volts. This was very inconvenient and then they had a lot of transistor driver burnouts. Later still they started to add a pair of
current limiting resistors to the motor circuits. This has apparently save most from a burn out problem. The motor currents are
limited to about 1.5 amps. This saves the motors and the driver transistors.
What this all means in that the LX200 classic should work well with anything from 12 volts to 18 volts. I would not go higher and
I would not let the voltage go below 12 volts. The regulation is not very important as long as it stays within this range. Rather
than use a 12 to 18 converter, especially the Meade unit, I normally stack three 6 volt batteries in series. This gives a convenient
12 volts for some equipment and the 18 volts for the LX200.
At voltages above 18 volts, the regulators in the LX200 get very hot. If you are already in a hot climate, it may be too much.
With a bell lubricated and well balanced LX200 you should be able to get reliable operation with 12 volts. Well charged batteries
will usually be at 12 to 14 volts.
I cannot comment about the other problems though I suspect they are not power supply related unless the voltage gets below 11
volts. Then everything can go bonkers. (G)
--------------------------------------------------------------Subject: Power Supply Issues for LX200 Classic --part 2
From: Jim Henson <jimh
bga.com>
ScopeStuff <www.scopestuff.com> offers the #1218 DC-DC converter for the LX200 Classic. It has internal over-temperature
protection that keeps it from suffering the heat related death that kills the Meade unit.
--------------------------------------------------------------Subject: Power Supply Issues for LX200 Classic --part 3 of 3
From: Hari Seldon
How about building a 18V battery pack out of three 6V cells. It works great for me and you will not worry about current draw or
voltage regulation anymore. If you use solar panels to charge the pack, you can opt for 6V panels to charge each cell separately.
In any case, if you opt for an AC2DC make sure that your output is regulated for higher voltage. The scope can take lower
voltage with no complaints. I believe peak current draw is around one amp. You should use a fast-blow fuse of 2 amps. There is a
2A fuse inside the control panel, but I believe it is not quite so 'fast blow'. Some time ago there was an incident in which the
onboard fuse failed to blow as fast as it should and blew a capacitor on the panel. Instead, it blew a couple of 3A I had in-line
from the battery pack.
If you insist on going the 12V battery route, then search the MAPUG-Astronomy Topical Archives to find the schematic diagram
for a 12-to-18 dc solution and build it yourself if you're handy at electronics. Otherwise look for a cheap unit from Scopestuff at:
<www.scopestuff.com>.
Subject: Standard LX200 Classic Fuses --part 1 of 2
From: W. Miller
In my 12" rev 4.3 Classic scope I use a 1-amp glass body fast-acting fuse (Littelfuse 3AG 312 series) in the fuse clip on the
power panel. In my 16v power supply I use a 3-amp fuse. The 1amp fuse is on the downstream side of the LX200 power panel
on/off switch. I first turn on my 16v supply and two large capacitors get charged through the 3-amp fuse. These caps (~10,000uf
each), one in the 16v supply and one in the LX200, take a huge surge of current to charge up to 16v. In fact my 16v supply's 8amp meter slaps over to full scale for an instant. Pushing all this current through a smaller fuse might cause it to blow. Then I
turn on the LX200 power panel switch and a smaller surge of current flows through the 1amp fast blow fuse. I haven't blow a
fuse since I set up this way.
Before this, I burned out my RA motor and Op Amps using only the 2amp slow blow fuse that came with the scope in the power
panel and the fuse inside the Meade 18v AC adapter. These fuses were too big. Maybe a 1.5-amp fuse in the power cord would
have blown, but I was not using the Meade cord. It is most convienent to change the fuse in this cord should it blow, but I don't
mind getting out a screwdriver. The power panel came from Meade with a 2,200uf minature electrolytic capacitor on it.
I upgraded my power panel cap to the type typically found in power supplies for switching circuits. It has bolt on terminals, low
internal resistance, and fits inside the LX200. I wanted a better capacitor since my 50ft power cord has considerable inductance.
Using 12 gauge copper cuts it's resistance down but does not reduce the inductance.
-----------------------------------------------------------------Subject: Standard LX200 Classic Fuses--part 2 of 2
Michael Hart
The Bussmann MDL 1.5 amp fuse is in fact a time delay "slow blow" type. The particular version you describe is known as a spiral
wound element. Older designs used two elements in series, one for short circuit protection, the other for overload protection. The
older design is more expensive but eliminates current limiting effects of a spiral wound design. The original two element design is
still available as an MDQ-1-1/2 amp.
Subject: LX200 Power Cable Fuse?
From: Mike Dodd <mdodd
mindspring.com> Date: Dec 2001
>The ends of the power cable fuse are stamped "250v" and
>"Buss MDL 1 1/2", respectively.
That's a 1.5A time-delay glass fuse. The Digi-Key part number is 283-2179-ND (5/$0.91), and the Radio Shack part number is
270-1022 (4/$1.99).
>The Archive implied that "MDQ" fuses - though more expensive >had two types of protection. Yet there wasn't enough of a
>discussion to suggest that one would be preferable over the other.
>Or that 1.5A fuses are too much, too little, or just right, given a
>particular setup.
Digi-Key does list some 1.5A MDQ fuses, but: 1) they cost $80.33 for a package of 100 (no single-piece prices), and 2) currently
there are none in stock.
I agree with Curt Tooley about not arbitrarily switching fuses. Many factors dictate the type and size of a fuse, and it's unwise to
second-guess the designer.
This is a no-brainer: You can buy 4-5 replacement fuses for pocket change. Replace it and see if it holds. If not, replace it again.
If it still blows, you have some other problem in the electronics.
Subject: LX200 Classic Fuses Explained
From: Michael Hart
>
>
>
>
>
>
>
>
>
>
>
>
I have looked into the fuse issue and the news in not good. It is a close
call between blowing the internal fuse and burning up the chip or even the
motor. The internal fuse is a pain to replace. I suggest using a
slightly smaller fuse in the line cord. It is a inconvenient when it blows
but it is easy to replace. Standard fuses do not burn out very fast unless
they are overloaded by 2 times or more. They have a time constant for
heating and melting. This whole fusing issue is much more complex that
you might at first think because of the several heating time constants involved.
There is no good solution since the fusing burnout and device burnout were
not coordinated carefully in the original design. Slow blow fuses and
semiconductors do not like to coordinate well. The semiconductors often
burn out faster than the fuses.
Doc G has a good understanding of overcurrent protection. I believe I can add a bit to this discussion and perhaps a solution:
Typical 1-1/4 X 1/4" fuses are available with at least four characteristics:
1.
2.
3.
4.
Non-time delay, non current limiting
Non-time delay, current limiting
Time-delay, non current limiting
Time-delay, current limiting
Certain fuse designs actually limit fault current to a value considerably less than the available fault current and operate extremely
fast- a few milliseconds. They do this in a rather complex and important way.
It is not unusual for a non-time delay fuse to be slower at reacting to overcurrents than time-delay fuses, depending on the fuse
and application. When designing in a fuse to protect a circuit we must consider many factors including available fault current,
running current, peak current, circuit voltage, minimum melt time, total clearing time, AC or DC, frequency, temporary overload
current, and the I2t rating of the weakest component in the circuit. These are off the top of my head- I'm sure there are more
considerations.
The problem in applying a single fuse is it must be have a continuous current rating that is adequate for the entire circuit load
while protecting individual components in the circuit. The fuse must react to short-circuits or overloads of different duration below
any individual component's I2t without blowing needlessly during acceptable short-duration overloads. Then if we are using
multiple fuses, we want the fuse to blow nearest the fault or overcurrent so that only the effected circuit is disabled. Finally, we
must weigh the added static component cost into the design. For most consumer applications, a single fuse is used primarily to
prevent fires while board level components are sacrificed.
Having said all the above, it might appear there is no simple solution to protecting the output driver chips. I believe Meade added
two power resistors to the motherboard to help. If the Meade mods isn't deemed adequate (I still use the old motherboard), I
believe there is a solution as follows, if there is really a problem to solve:
Protect the individual components using specialized high speed semiconductor fuses whose I2t let-through is LESS than the
components I2t rating. I have knowledge and access to military grade fuses not typically available to the public. These fuses are
very fast, used in redundant satellite, military and space applications, and may be quite small. Some require a magnifying lens to
install.
To spec out a specialized fuse for an individual component, I need:
1.
2.
3.
4.
5.
6.
Component I2t rating
Operating voltage
AC or DC
Peak running current
Peak cyclic current
Peak available fault current
Subject: Blowing a Fuse - Problem Solved! --part 1 of 3
From: John Teel <mapuglist
yahoo.com> Date: Aug 2001
Well I think I found the problem. As I said the fuse blows with nothing connected except the computer board (and the power
panel board). I saw that it uses a 3-terminal 7805 voltage regulator to power all the digital electronics. First thing I did was see if
the input of this device was shorted to ground and sure enough it is. According to Doc's schematics the 18vdc comes in to the
input of this device and the only other thing connected here is a capacitor. With the ribbon cable unplugged the input is shorted
to ground so that means it must be a faulty vreg or the input cap is shorted. Both of these would be very easy to replace.
However, I'm going to wait to see what Meade says. If they tell me to ship the whole thing back and wait 4-6 weeks then I
suspect I'll fix it myself. Ironically I design regulators for Texas Instruments and if Meade would have used a TI regulator instead
of Motorola this wouldn't probably have happened. Actually my money is on the cap being the problem and I've read of others
having problems with shorted caps.
Also I would think it would be safe to assume that nothing else was damaged by this short since it's at the input?
-----------------------------------------------------------------Subject: Blowing a Fuse - Problem Solved! --part 2
From: Paul Rodman <paul
ilanga.com>
On my new LX200, the in-line fuse blew out of the box. It turned out that the power brick was reverse polarity...
-----------------------------------------------------------------Subject: Blowing a Fuse - Problem Solved! --part 3 of 3
From: Emery Hildebrand <emeryh
earthlink.net>
Before turning my 1994 Classic LX200 8" (affectionately know as R2D2) on for the first time in 3 years, I decided to replace the
battery first. Something must have gone wrong, because the fuse blew instantly when I turned it on. I blew 2 more fuses trying
to see what could be the cause. Couldn't notice any problem at all. The scope booted-up fine as long as I had the power panel off.
I tried reinstalling the face plate with both the declination and hand controller cords disconnected, and it still blew the fuse as
soon as it was turned on. What a heart-sinking feeling! I noticed that the original fuse I took out was a 2-amp slo-blow. I thought
that odd since the manual calls for a 1-amp. Then I scoured the message boards and found that most LX200s seem to have 1.5
or 2-amp fuses there.
The next day I picked up boxes of 1, 2, and 2.5-amp slo-blow fuses so I could continue tracking down the problem. Having had
time to digest the situation was all it took. Since the mechanicals were smooth and free and I couldn't locate any obvious
electrical fault, I looked for the most likely location for shorting out. The worst spot was the obviously tight clearance between the
daughterboard that holds the fuse and the housing of the drive base. Before replacing the face plate this time I added a 6" strip
of electrical tape to both the edge of the daughterboard and the upper, inner surface of the drive base opening. For this first test
I used a 1-amp fuse.
Voila!!! it turned on without blowing! I cycled it several times and then ran it thru several polar alignment routines and then
slewed all over creation. No problem. During this process I kept an eye on the built-in amp meter and it never lit more than 4
bars - and only 4 bars briefly. Wow! It felt great not only finding the fix, but not having to return lil' R2 for service. I'm gonna
keep the 1 amp fuse installed since it's working. I have a gut feeling that the 1 amp will be adequate as long as I don't slew a
camera into the base... but that has only happened once in all the years of using R2 so I doubt it will ever happen again. Anyway,
I'll keep all those extra fuses on hand just in case.
Follow-up about a week later...
Last night was clear, dew-free and in the low 50s, so I took R2D2 out for a regular setup and checkout. It was the first real use
its' had in 3 years. After changing the battery it retained my site info but lost date and time so I input those, did a tight
collimation and crossed my fingers. It operated fine all night without blowing the 1-amp fuse. I guess that confirms the electrical
tape fix worked. My neighbor has a 10" LX200 that he also hasn't used in 3 years. When he first fired up, his fuses kept blowing
during the alignment procedure (but didn't blow immediately upon power-up as mine had). After similarly isolating his power
panel with electrical tape his also appears fixed. Strange coincidence - or is this a known problem?
Subject: LX200 12V Converter Circuit
From: John W. Downs
Summary on the Meade DC-DC converter, all Meade LX200 scopes will run on 12VDC - 18VDC. The processor board only sees
12VDC because of a on-board regulator. The motors run stronger at 18VDC, thus Meade made the change. The motors are rated
to 24VDC so no problem there. Focusers such as the JMI zero image unit runs at one speed when the LX200 is powered by
18VDC, and two speeds at 12VDC. If you have anymore questions on the converter, I'll be happy to answer them OT.
Subject: 120V-12V Power Supply Recommendations
From: Colin Haig
David wrote:
>I have been thinking on using a Computer Power supply to power
>my 208xt and Kendrick Dew System. The Power supply says it's
>12V DC is rated for 10A and 5V DC is 25A. Any one see any
>type of problem doing this?
Your computer power supply idea will work probably work fine, but a couple of tips:
1. Get an older style (non ATX) power supply, the kind used for AT-form factor boards. The ATX supplies need a couple of
things to sequence them on properly, and have soft-off.
2. It usually needs a load on the 5V side in order to work (the fan inside is usually enough for the 12V side). Usually the
necessary load is a few hundred milliamps. So, you will need like a 10 Ohm resistor that's good for at least 3 Watts. You
can also use the heat from this puppy as a dew heater ;-) or eyepiece warmer.
3. You should probably put the two systems on as far separate wiring as possible. I.e. connect them back at separate 4-pin
disk drive connectors, instead of bringing the wiring to a dual outlet at the scope. The Kendrick gizmo sometimes induces
noise in the line with the big on/off currents.
4. They really aren't well sealed for outside use.
5. The 208XT should be okay, but some other devices actually expect +13.8V from lighter sockets. For example, the PC23C
video cameras are fussy about input voltage because they have a built in 12V regulator that needs an extra volt or two to
get past it. The 208XT power supply has some switching regulators, and a 5V jobby, so I don't think its gonna be a
problem.
Subject: LX200 Power Supply ( DC>AC vs DC>AC>DC )
From: Gene Kahn
This has been covered from almost every direction but I had never seen any real number to compare using a 12VDC to
18VDCconverter compared to a 12VDC to 115VAC then 115VAC to 18VDC so I set up to do some comparisons of my own.
●
●
●
●
●
As a load I used 6 3ohm 25W resistors for a constant 1 amp
As a DC to DC converter I used a home built supply that runs on the standard LT1170 regulator
For the DC to AC, I used a 100 Watt inverter from Noteworthy/Toshiba
From the 12V source with the DC > DC the current was 1.66 Amps or 19.99 Watts in to 18 Watts out.
With the DC > AC > DC the source current was 2.08 Amps or 24.96 Watts in.
So if my setup/math is correct then the AC step wastes an extra 25% of your power.
MAPUG is hosted by
Power Box 12volt - 18volt - 110volt
for the LX200
by Jim Lowry <jim-lowry
Other designs:
att.net>
Field Power Box -- Alternate Design by Thomas Wideman
Alternate Battery Box Design by: Rob La Pointe
18 Volt Power Supply Design by Ray Wallace
Field Power Solutions by Larry Owens
12/18/120V Power Box Design URL by Danny Cobb
Telescope Power Box Design by Adrian Round (outside link)
-----A ONE PARAGRAPH "ABSTRACT'----Designed to provide portable power for the amateur astronomer. One 12 volt battery provides 12 volt outlets for various
accessories, 18 volts to power a Meade LX200, and 110 volt AC current to power an external clamp light with a 40 watt red bulb.
This lamp comes in especially handy when leaving a dark site in the middle of the night!
-----THE ACTUAL "TEXT EXPLANATION"----During the last year, I got very tired of lugging various "pieces" to provide all of the necessary power for a typical viewing
session. In addition to my main battery supply, I needed my Meade 12 to 18 volt converter for the LX200. But I also needed a
pigtail clamp when using a dew remover or 12 volt hair drier. Then there was always the question if the battery held enough
charge for the planned session.
With these problems in mind, I set about planning something which would hold everything in one convenient box - providing any
and all voltages that I would need. I also decided that 110 AC current would be a great added benefit. Thus the idea for my
"Power Box" was born.
EXTERNAL CONSTRUCTION
12 inch pine boards were cut to make a 12" by 12" by 12" box, with the sides actually being 15" to give clearance for dewy grass.
I simply screwed them together as well as gluing, except for the top board, giving me easy access to the inside unscrewing only
four screws. The wood was stained, and then triple coated with polyurethane to protect from moisture.
TOP PIECE
The top holds a one piece double switch, one acting as the main power switch, and the other to prevent accidental power
discharge if the external carriage bolts somehow get connected by a conductor. There are also two plastic capped cigarette
outlets - one for 12 volts and one for 18 volts. A standard radar detector coiled cord connects my telescope to the 18 volts. The
other is available for using my dew protection system. On top are also two carriage bolts. These provide easy clamp on access to
recharge the battery. The Radio Shack motion detector allows me to leave the telescope in the yard or on the porch to cool down,
without worrying that "uninvited" guests get too close. Finally I have a strong handle mounted in the middle for easy carrying.
FRONT PIECE
The front holds the Radio Shack 0 to 15 volt meter, and a standard wall mounted 110 volt switch and double outlet. This is
connected to the internal inverter, capable of providing 300 watt continuous power from the 12 volt battery. There is also a bank
of three identical switches. One powers the meter, which is direct to the battery so that the master switch does not have to be on
to check the power. A second switch activates the alarm, and the third is empty for possible future expansion. There are also
three standard cigarette outlets for extra accessories.
OTHER PIECES
Both the left and right pieces have a 3 inch square hole cut out for ventilation purposes, covered with standard mesh screening.
The 12 volt computer fan is mounted inside one of these blowing air out. This prevents any build up of heat from the inverter and
various converters.
My 34 amp hour battery was bought at a hobby supply store for around $80. The electronic pieces cost around $50 from Radio
Shack, and the 300 watt inverter was $69. I now have enough power for several nights of viewing without the dew protection
system, and at least 10 hours of viewing using all dew accessories. Charging the next morning takes less than one hour with a
standard automobile battery charger set to automatic.
Subject: Field Power Box
From: Thomas Wideman <twideman
earthlink.net>
Thanks to Jim Lowry for the great field power supply design in the Topical Archive!
I had to tinker, so I built a slimmer model and have put info about it on my site at:
<http://home.earthlink.net/~twideman/powerbox.html>
Note: should open a new browser page over this one.
Subject: Battery Pack Design URL
From: Pat Lanclos <SkySgt
aol.com>
I have yet another submission for you to consider posting on the MAPUG archive. It is a webpage I have developed showing and
describing a 12v battery system I made to power my telescope. Maybe some other MAPUGGERS will find it useful. The address is:
<http://members.aol.com/planclos/index/battery.htm>
Note: should open a new browser window over this one.
Subject: Battery Box Design
From: Rob La Pointe <m81
pacbell.net>
Hopefully, the images will speak for themselves or contact me.
Subject: LX200 18 Volt Power Source
From: Ray Wallace <ray_wallace
juno.com>
One of the problems LX200 owners have is finding a reliable system that produces 18 volts DC to power their telescopes. The
common solutions on the commercial market seem to be DC to DC converters for about $100 a piece that are overpriced and
inadequate for the application. Another alternative is gel cell packs. They can suffer from inferior quality components and circuit
design. After having a $100 DC to DC converter burn out, I made an 18-volt system that is both inexpensive and, electrically, as
good or better than anything I've seen commercially available.
It uses 2 car batteries. One is in my car, the other one I bought at K-Mart for about $35. I bought 3 x10' long, light duty,
extension cords for a few dollars a piece, and 3 sets of alligator clips made to connect to car battery terminals also at K-Mart.
From an electronics store, but not Radio Shack, I bought an ECG970, a heat sink and a 1k ohm, 10 turn, pc mount potentiometer
and a plastic box to put the regulator assembly in. The ECG970 is a positive variable voltage regulator. The potentiometer
connects between the output and ground pins of the regulator and allows it's output to be varied between 2 and 35 volts.
Also, this particular regulator provides up to 3 amps output. Plenty of power for the telescope and any accessories. The 2
batteries are connected in series with one of the extension cords to produce 24 volts. The extension cord and alligator clips on
one end of the regulator box should have their polarity marked (+-) for quick reference. The positive (+) clip is connected to the
positive battery terminal that has 24 volts output. The negative (-) clip is connected to the extension cord coming from the
negative (-) terminal of the battery. The lead on the other end of the regulator is connected to the telescope.
During the initial setup, I monitored the regulator output while I operated the telescope motors in fast slew. I adjusted for about
18.25 volts. Plenty of power for any motor operating scenario. As for pro's and con's: The con's are I switch the batteries every
week or two using the car to keep the batteries fresh and charged. That's about a 5 minute job. The pro's: clean DC with plenty
of power. No worries about burn out (the regulator or a motor or motherboard).
Subject: LX200: Field Power Solutions
From: Larry Owens
I use a home brew power system, that actually fits into a computer bag. I setup the 10" LX200, set the power bag under the
scope, pull out the 18v wire, plug in the dew heater (20w) and optionally the computer and I'm set. I use this system even when
AC power is available, because since everything is in the bag, it's more trouble to find extension cords, set out the power supply
and there are of course more things to trip over. I even have room in this bag for binocs and a flash light or 2, but it's pretty
heavy.
The power system consists of a lawn tractor lead-acid battery and a 150w continuous (200w for 5min) power inverter from Radio
Shack. Attached to the battery is a cigarette lighter type receptacle, wired directly to the battery with the + terminal of the
battery covered with a plastic protector. I then have a "Y" adapter plugged into this to power my DC dew heater and to plug in
my inverter. Into the inverter I plug the Meade 18v power supply (which I keep in the bag permanently - just pull out the wire)
and the laptop when necessary.
To charge the system, I attached two 50w 4 ohm resistors in parallel for current limiting to a smaller DC receptacle. I plug my
15v laptop power supply into this and it charges the system nicely overnight. During charging the resistors get warm to the touch
when the battery is low, and after a few hours the resistors are cold to the touch indicating no more current flow and a complete
charge.
I've used this system for about 3 months so far, and have used it continuously for as long as 8 hours, with lots of slewing, dew
heater on full 20w and a couple of hours of computer. Do not yet know how many hours I'll get out of this since I've never run
the battery down.
I considered using a higher wattage inverter, but the 150 watter doesn't even get warm under the load. Since it will handle 200w
for as long as 5 min, and since slewing is an intermittent high current activity, I think this is more than enough.
Cost: The inverter was $79, the battery was $39, I had the computer bag, and various connectors and components no more than
$15. I also had a suitable charger which could be built for another $20 or $30. My investment: $133.
Subject: 12/18/120V Power Box Design URL
From: Danny Cobb <dndcobb
bellsouth.net>
I have yet another 12/18/120V Power Box design, download a Acrobat PDF file by clicking here.
MAPUG is hosted by
Battery, Volts, Amps, Fuses, Cables, etc.
--Page 2
Cables and Connectors
Treatise on LX200 Plugs
LX200 Electronic Improvement--Resister Upgrade
Grounding the LX200 and Computer (separate page)
Electrical Connector Compound
PC-->LX200 Serial Connector Diagram
Dual Serial Ports and USB Laptops --5 parts
Connecting a Computer to a Telescope --link to outside page
Dual Serial Connection for LX200
Cable Construction URLs
Simple LX200 Serial Cable Assembly
LX200 Serial Cable Construction
Easy Serial Cable Construction
LX200 Serial Cable Construction --link to outside page (Bill Arnett)
Serial Cable Pin Out
Tester for RS232 Port
RS232 Aux Port Location & Use
Wiring Control Panel Aux Plug-In to Power Accessories
Power Panel/Cable Problem Solved
LX200 (classic & GPS) Circuit / Schematic Diagram URLs
iMac to LX200 Connection
Power Connectors / Cable Management URL
LX200: What to do with Ceramic Resistors
AC Power Supply Voltage Reduction
Return to:
of Battery, Volts, Amps, Cables, Etc.
Subject: LX200 Cables/Connectors
From: Doc G
Technical Note on Plugs and Cables for the LX200 Classic (may appy to GPS)
Many of the control signals on the LX200 are carried by telephone type connectors known as modular plugs/sockets. These are
usually 4, 6 or 8 pin plugs/sockets. These signal cables can be extended to at least 100 feet and often much longer. I have tested
cable lengths up to 150 feet for the following cables. All 232 Serial cables including the computer to LX200 cable, the serial cables
to the various imagers and the keypad cable.
Some of these cables are available in complete form from Radio Shack or Newark Electronic supply houses. Cables over 25 feet in
length will have to be custom made since none are generally available. A standard handset coiled cord will work for the keypad.
This is a four wire cable with 4 pin Modular plugs at each end.
So called modular jack extension wires have a 6 pin modular connector at each end but are generally only a 4 wire cable. These
will work for any of the purely serial communications ports but will not carry ground and power signals since these signals are on
pins 1 and 6 which are not connected.
Custom cables can be made to any length by purchasing bulk 4 or 6 wire flat modular telephone cable and attaching plugs to
each end. The cable and plugs are available from Newark electronic supply or possibly other suppliers that stock telephone
supplies.
In order to attach the connectors, a special crimping tool is needed. There is a Telco tool that will crimp both 4 and 6 pin
connectors which should be considered. It is plastic and thus for light duty use. But it is only $18. With the proper crimping tool
the connectors are very easy to apply. Without, it is all but impossible.
It is possible to put the connectors onto the wire in two orientations. A right and a wrong way. You must get this correct. When
the cable is a standard cable, the color coded wires will go from left to right at one connector and in the opposite direction on the
other when the connectors are looked at side by side pointing in the same direction.
Viewed another way, the connectors and wires go straight through with no twists when laid out straight.
NOTE: the cable that goes from the imager to the CCD socket on the LX200 IS NOT a standard cable. DO NOT substitute for the
coiled cable supplied. A special cable of greater length can be made but do not attempt this unless you are sure of what you are
doing. If a new cable is made, the connections must be EXACTLY like the coiled cord cable supplied for the purpose. This requires
a cable with a twist and one pin removed at each end.
The modular plugs/sockets are made to carry low currents and like all plugs should be worked from time to time to keep down
oxidation on the contacts. Regular use, plugging and unplugging, should not cause problems and will generally be good for the
connectors.
Signal circuits are often called "dry" circuits because they carry little current. Even slightly oxidized contacts can cause problems
in "dry" circuits. Thus, if these plugs are seldom used they should be worked from time to time to keep them clean. Standard
contact or switch cleaner can be used but excess should be wiped away.
Recently there have been complaints about declination drive intermittent electrical problems. Many do not realize that there is a
second plug on the inside of the fork where the declination cable plugs in. This plug should also be worked from time to time as
well and cleaned.
The declination cable carries motor power, ground and DC supply power as well as the two signals from the encoder of the motor
shaft. Interruption of any of these signals will cause a dead or runaway declination drive depending upon the type of fault.
--------------------------------------------------------Subject: Radio Shack Power Connector
From: John Mahony, Date: Jun 2005
The connector that attaches to the scope is Radio Shack size N, 5.5mm OD, 2.5mm ID. Size L is 5mm OD, 2.5 ID, so it's close
enough that you'd probably get a connection, but it will be more reliable with size N.
Subject: Treatise on LX200 Plugs (may appy to GPS)
From: Doc G, Date: Sep 2001
This note is a short treatise on plugs on the LX200 and pin numbering conventions. There has been some confusion about pin
numbering on the plugs on the LX200. This is because Meade manuals seem to differ from standards used by others. I hope to
clarify this situation in the following.
My convention and what I think is generally used by the electronics industry is as follows.
Take the example of a 6 pin RJ connector. From the front of the socket (which is female) and with the keyway at the bottom
there are 6 pins at the top which I designate from the left to the right as 1, 2, 3, 4, 5, 6. When the socket is drawn on a flat sheet
as in a schematic circuit diagram, this connector is normally drawn as though it has been flattened. Thus the pins will be show
next to each other in a single line and labeled in the order 1 through 6. This seems to me to make perfect sense and is the
convention I use.
Now when viewed from the back of the socket with the keyway still at the bottom, the picture becomes less clear. From the back
side there are two rows of wires coming out of the socket. There is a top row and a bottom row of 3 wires each. The top row is
offset to the left from the bottom row by a half space. The wires are colored, but to use colors is folly since different
manufactures use different colors. But, using the above convention, the bottom row from right to left becomes 1, 3, 5 and the top
row becomes 2, 4, 6. This is of little consequence to the user since the user sees the front of the socket. The circuit board
manufacturer sees the back side and gets it wired correctly.
So in summary, I have taken the viewpoint of the user and numbered the pins in the order that you see them from the front of
the socket with the keyway down.
I have wondered why the Meade manual shows the pins in line and gives them the numbering from right to left 1, 4, 2, 5, 3, 6.
That is from the front with the keyway at the bottom. Their chart shows the correct function of the pin to go with their numbers.
But why the strange numbering? Apparently they have numbered them from the back as follows. From right to left the numbers
are for the bottom row of 3 wires 1, 2, 3 and for the top row of wires 4, 5, 6. This would make the pin numbers from the front 1,
4, 2, 5, 3, 6. From the viewpoint of the circuit board maker this convention is sensible since it corresponds to that used for other
two row straight connectors. So it is one choice of conventions that is correct. Most two row straight connectors are drawn on
circuit diagrams just like IC pignuts. But sometimes from the top and sometimes from the bottom of the board. (one needs to be
careful here) However, the RJ connectors, like edge connectors, are usually shown as one straight line of pins on a schematic.
But I find it strange when viewing the socket from the front. In any case, I think it wise, from the users viewpoint, to label the
pins with the actual function rather than with pin numbers. Thus I will try, in the future, to do this. Never use colors of the wires
since for both the sockets and the flat cables have no established convention for these colors or their order.
With this convention, the pins from left to right with the keyway at the bottom will be called: For the CCD socket: NC, Ground,
West, South, North, East. And, for the RS-232 socket: +12 (18) volts DC, Ground, Aux. serial out, PC receive data, PC transmit
data, Aux. serial in.
For the RS-232 cable this is the correct convention for using a normal RS-232 PC cable and a normal D to RJ adapter.
With this convention, there is no confusion about pins numbers but rather a clarity of what function each pin carries. I am
currently working on new circuit diagrams for the LX200 scope and am trying to get everything right. This is a big job. The
current diagrams on my web site are not perfect but are a good start. More later.
Subject: LX200 Electronic Improvement (Classic)
From: Don Tabbutt <don
tabbutt.com>
Meade has improved the motor circuits on the main board of the LX200. "New LX200 main boards now include overload resistors
that prevent motor burn out" is the quote from their Main Board Installation Addendum.
For those interested, R-4 and R-9 on the main board have been replaced with 10 watt 8 ohm ceramic resistors. These new
resistors are mounted on the side of the base with a metal clip and double sided tape. They are then wired back to the main
board to the holes previously occupied by the smaller resistors. The mounting point in the base is the rectangular gap on the right
side (looking from the bottom, face plate down) forward of the main board. Heat transfer goo is also put on the resistors where
they contact the side of the base.
Subject: Electrical Connector Compound
From: Ray Mote <rmote
rain.org>
Ah, the trusty Dow Corning "4 Electrical Insulating Compound". That's good stuff, and a tube can indeed last you for decades -I've had mine for around 20 years now. It also works well for preventing moisture intrusion in coaxial cable connections outdoors,
but does take some care. (For those who want to run cables from scope outside to computer or VCR inside.)
Basically, you want to put enough of the DC4 into the connector so it will displace *all* the air when you mate it with the other
connector. If you plan to leave it set up for anything longer than a week or two, or if it might rain, consider the additional steps I
use. Wrap the entire connector junction area with electrical tape, starting out on the cable on one side and proceeding to the
cable on the other side. Don't be stingy with the tape; use about 50% overlap. Then cover the wrapped joint with a good layer of
synthetic silicone sealant (clear sealant will make it easier to find the tape end later for unwrapping!). Let it cure and you're in
business. I've undone connections like this using "UHF" (PL-259 type) connectors after over five years, and they came out looking
like new! (Anyone who has ever seen these screwball connectors in their normal oxidized state after a year or two open to the
weather *knows* how bad they can be. I do know from personal experience that this little trick works quite well.
Another item that works well on connectors is Stabilant 22A (my little 15 ml container says). It's actually a contact enhancer, and
the local 2-way radio folks use it on microphone, speaker, antenna, etc. connectors for high reliability. Made by D.W.
Electrochemicals Ltd./Ltee., 97 Newkirk Road North, Richmond Hill, Ontario, L4C 3G4, CANADA. These guys locally swear by it,
but I don't know if they use that on *permanent, outdoor* connectors, or if they add an additional wrap & silicone sealant, etc.
I generally use Caig Laboratories (San Diego, California),"DeOxit" spray on various indoor connectors, switches, etc. It's also a
contact cleaner/lubricant that works *very* well.
Subject: PC-->LX200 Serial Connector Diagram
From: Clark Williams <S.I.G.H
ix.netcom.com>
Jim Schissler wrote:
> I can't find the wiring diagram for the PC serial port to LX200 serial port.
First remember that this thing is an RJ25C (6P6C) connector and NOT an RJ11 (4P4C) connector. So you may have trouble
finding the right part. Fry's electronics does have DB9 to RJ25C connectors, or you can buy an RJ25C and wire it up with a crimptool and a soldering iron.
DB-9 Pin RJ25C Pin
1 N/C
2 5 RX on the PC side
3 3 TX on the PC side
4 N/C
5 4 Ground
6 N/C
7 N/C
8 N/C
9 N/C
As you can see it is only a 3 wire serial communication.
The RJ25C has the following layout (shown with the clip away from you). In case you are wondering the numbering is
consecutive, from the left, skipping every other pin, then starting again from the left, again skipping every other pin.
Subject: Dual Serial Ports (Classic) and USB Laptops --part 1 of 5
From: Bill VanOrden <bill
beevo.com> Date: Dec 2001
Check at <www.cyberguys.com/> (use the keywords USB SERIAL in their search engine on the site), or call 1-800-892-1010.
Most specifically you are looking for a USB to Serial adapter #104-0475. $35US
I got a new IBM notebook and found it had no serial ports and I use the notebook at work to interface with onboard automotive
computers and ALL the scanner software works with the serial ports! The company that makes the scanners tried a bunch of
these type adapters and this was the only one that functioned in all situations with all the available software.
I use it with SkyMap Pro and my LX50, it works perfectly.
---------------------------------------Subject: Dual Serial Ports (Classic) and USB Laptops --part 2
From: Randy Wilson
You wrote:
> I have a single cable like this, and it does work very well.
> What I was trying to do, though, was find a way to have more than 1 serial
> port added to the laptop (so I could control the LX200 and a focuser ). I'm
> still puzzled how folks do it now - even older laptops only had 1 serial port.
Easy, just use more USB to Serial adapters. I have multiple Keyspan adapters supporting a label printer, eprom programmer, pic
programmer and a basic stamp prototyping board all off the same USB. Note that some software (for no good reason) only
supports COM1: thru COM4:
You wrote:
> I may do that, Randy. I was thinking that there would be a conflict with
> the various adapters, but if not (and I only need 2 com ports), that may be
> the way to go. Mike
I can't promise it works in all situations and with all adapters. The stuff I'm doing runs under windows - if you have software that
cheats and talks to the hardware directly it would be a problem. I had one piece of software that arbitrarily limited the max com
to 4, but the vendor fixed that for me the same day that I called. My adapters are Keyspans. I'm not even using the "official"
serial port version, I'm using the "PDA adapter" because it was cheaper. I've used them on Macs and PeeCees. Not the best thing
I ever saw, but adequate.
---------------------------------Subject: Dual Serial Ports (Classic) and USB Laptops --part 3
From: Rick Sheve
Keep in mind that most, if not all of these adapters are for Win98 and above. They will not work for Win95, or none I have found
thus far.
---------------------------------Subject: Dual Serial Ports (Classic) and USB Laptops --part 4
From: Michael De Santis
I was finally able to get the device to work properly by changing the port default settings in control panel. I had to change the
com rate to 57600 and flow settings to "hardware". For whatever reason, this now lets the multi port hub work perfectly. Go
figure.
---------------------------------Subject: Dual Serial Ports (Classic) and USB Laptops --part 5 of 5
From: Michael Gartland
The one I have is made by Socket Communications, Inc., 510-744-2700, it is a one port Serial I/O card P/N SL0700-004. They
also make one with two ports, if you need to add that many more. It includes the plug in adapter cable that mates with the
standard Serial plug...I would sell you mine, but I may need it again. It's called a Socket I/O PMCIA card, outputs to a serial cable
that becomes a second serial port on your laptop. Of course you have to have an open PMCIA port to plug it in...comes with the
drivers and everything. One serial port for the autoguider, one parallel port for the CCD, and another serial port for the LXD650
telescope control in Megastar.
Subject: Dual Serial Connection for LX200 Classic
From: Marc Castel <mcastel
idirect.com>
I reread the old post for the LX200 serial splitter on the Topical Archives and found that it was not mentioned that the second
serial tap should also use the ground on pin 4. This may be why there were a few glitches. I've been using the "dual serial"
splitter with the Sky V on one port, and my own custom program on the second port (for focus, initialization, reticle, etc.) which
operates flawlessly providing you don't switch to long format scope positions before going back to the SKY V (otherwise it will
loose contact with the scope). My COM splitter is a Radio Shack 6 wire RJ45 splitter adapter ($4) which I took apart cut several
internal wires and re-soldered them according to the LX200 manual such that I can plug identical DP9 to RJ45 plugs into either
splitter outlet to access either of the two "multiplexed" serial ports as desired. The sets for each serial connection are:
LX200 RJ45, Description , from RJ45, to RJ45, DB9 Pin
Serial A
pin 2 Misc. Serial out Grn wired to Grn 2
pin 6 Misc. Serial in Wht wired to Wht 3
pin 4 Ground Yel wired to Yel 5
Note: cut unused Red, Blk, Blu wires on RJ45 Male side (set 1)
Serial B
pin 5 PC Receive Red cut & rewire to Grn 2
pin 3 PC Transmit Blk cut & rewire to Wht 3
pin 4 Ground Yel wired to Yel 5
Note: cut unused Grn, Wht, Blu wires on RJ45 Male side (set 2)
I'm pretty sure that the color coding is standard but double check your wiring. Note that the LX200 Female RJ45 port has the
color order reversed from the Male splitter adapter so don't get mixed up. Also make sure that Pin 1 from the LX200 (+12V DC)
is disconnected from everything by clipping and sealing the Blu wire coming from the RJ45 Male splitter side.
Double test the connection all the way to each DB9 pin side to make sure everything is wired correctly before connecting the
LX200 to computer or you may blow your serial chip!
Subject: Cable Construction URLs
From: Michael Schwarz <michael
schwarz.org>
The following site refers to an ETX cable, but when I went from an ETX to an LX200, the same cable worked with a regular
telephone wire:
<http://wastelands-observatory.factspot.com/etx-serial.html>
Note: should open new browser window over this one.
Subject: Simple LX200 (Classic & GPS) Serial Cable Assembly
From: Steve Stilwell
Often people ask for advice constructing a serial cable to operate their LX200. I hope this helps those who don't want to decipher
wiring diagrams or try to figure out which side of the connector they are supposed to be looking at. etc. Forget the soldering iron
and special tools! You can easily construct a serial cable with 2 off-the-shelf items:
These 2 parts are available at Fry's Electronics
* DB-9 to RJ11 connector - $2.89, Part# ADM-9F6-GR
* 6P6C twisted pair patch cord for data (25') - $3.99, Part# DC-506P-25P (or -25SV)
(Note: No one at Fry's knew they had these items so you may have to hunt on your own.)
Assembly Instructions:
In the plastic "connector" bag there are two items; a plastic connector body with 6 colored wires hanging out of it and a black and
silver connector with numbered holes in it. First, you are going to push three gold-colored metal connectors attached to three
colored wires into the correct numbered holes in the silver and black connector end...
1.
2.
3.
4.
5.
6.
7.
8.
Push the Yellow wire connector into connector hole number 5
Push the Red wire connector into connector hole number 2
Push the Black wire connector into connector hole number 3, then assemble the connector...
Cover each of the 3 remaining colored wire connectors with electrical tape and shove them down into the plastic connector
body.
Push the black and silver connector end down onto the opening in the plastic connector body until you feel that it is seated.
Now, plug it in...
Make sure everything is turned off! Plug the fully assembled connector into the back of your computer.
Plug the 6P6C twisted pair patch cord into the back of the fully assembled connector.
Plug the other end of the 6P6C cord into the RS232 port on the front panel of your LX200.
You are done!!The fully assembled cord cost you $6.88 + tax to purchase and no longer 20 minutes to assemble.
Congratulations!!
These instruction worked for me to produce a fully functional serial cable to control my LX200. Proceed at your own risk. I do not
guarantee this will work for you and will not be held responsible for the affect of these parts, instructions or the finished cable on
your equipment.
Subject: LX200 (Classic & GPS) Serial Cable Construction
From: Tom Skinner
If you want a serial cable from your computer to your LX200 it won't get much easier than this:
From Radio Shack:
279-422 for 25 feet, 6 conductor, RJ12 on each end $7.99
276-1538 for a 9 pin, female D-Sub connector
1.29
276-1508 for a metal hood for the D-Sub
2.19
That's $11.47 plus tax.
1.
2.
3.
4.
5.
6.
7.
Make sure your computer has the male part serial connector (I've never seen a female here).
Cut off one RJ12 and strip jacket back 1/2 inch.
Strip 1/8 inch off the green, yellow and black wires. Ignore the rest.
Solder the green wire to pin 2.
Solder the yellow wire to pin 3.
Solder the black wire to pin 5.
Attach the hood to the D-Sub and you're in business.
You can save money by 1) buying a shorter cable, or 2) a cheaper hood. These parts are also available from radioshack.com.
Prices are lower and you might not pay tax but you pay a couple of bucks for shipping.
Subject: Super Easy Serial Cable for LX200
From: Dave Kelley
This version of a serial cable is neat, clean, requires no soldier and can be assembled in under a minute.
I got both parts from Radio Shack.com for $10.98 plus tax
279-0422 25' 6C Mod-Mod SL (the cable)
9500285 DB9F-RJ11 Adapt (the connector)
This is one of those adapters where you simply click the wires into the holes you need them in for your particular project. There is
an RJ-11 connection on the adapter so the cable remains intact, plus this gives you an option of having a shorter or longer cable
as the situation changes.
On the adapter identify the row across the widest part of the connector...these should be pins 1-5 and marked as such if you look
close enough. Put the following wires in:
2 - Green
3 - Yellow
5 - Black
Cut off the Red wire
Push the pins in until you feel or hear them seat. Then snap the head on the shell and you're done.
Subject: Serial Cable Pin Out
From: John Linse
Serial Cable Pin Out:
Pins for a 9 pole cable are as follows:
2- receive date
3- transmit date
5- signal ground
Pins for a 25 pole cable are as follows:
2- transmit data
3- receive data
7-signal ground
Pin 4 is RTS (ready to send)
Subject: Tester for RS232 Port
From: Doc G
It is called on the tester an "RS232 Mini-Tester". On the package it is called "RS232 Line Analyzer, the Radio Shack number is
276-1401.
It has 25 pin D connectors on each end so you will have to get RJ to 25 pin adapters. These are also standard. Note that you will
need two 25D or RJ adapters. One with a male D25 and one with a female D25. The checker has two D connectors. A male and a
female.
Subject: LX200 Classic RS232 Problem/Aux Port -- part 1
From: Jim Henson <jimh
bga.com> Date: Nov 2002 <www.scopestuff.com>
John, pins 5, 2, and 3 are the correct ones for the D9.
If you can't get the primary port to work, it is worth trying the secondary port wiring before shipping the scope off. The ports are
susceptible to damage from nearby lightning while there is a cable plugged in. If you have never used the RS232, lightning
damage is unlikely.
The common failure of the RS232 port is the MAX-232 chip on the main board. It is not socketed, but can be replaced and is
commonly available. I installed sockets for that chip on the ones I have serviced, as they are a known failure point and not fun to
unsolder even with the correct tools.
John wrote:
>We have had a 12" LX200 for several years. It has operated with no
>problems but we have never tried accessing it with the RS232 port. We
>have a special alumni open house for our homecoming in 12 days and we
>decided that since our department is regularly remote observing with
>large telescopes, we would do a demo of remote observing using the
>LX200 and ACP2 and/or The Sky. I made up the cable as described in the
>Meade docs as corrected by Doc Greiner and so far we are unable to get a
>response after trying two laptops and a desktop, all of which had known
>good ports. Any suggestions?
>If our RS-232 port on the Meade is dead, is there a common failure mode
>that we might try to repair?
---------------------------------Subject: LX200 Classic RS232 Problem/Aux Port -- part 2 of 2
From: Gregg Ruppel <ruppelgl
SLU.EDU>
The RS232 on the base of the LX200 actually has two separate pinouts for 2 separate ports, both of which do the same thing. All
you need to do to access the second one is change the cable. The best diagram I have seen is on Bill Arnett's site at: <http://obs.
nineplanets.org/meade/cable.html>
I blew my primary RS232 (lightning or hot plugging) and have been using the secondary one for several years.
Subject: Wiring Control Panel Aux Plug-In to Power Accessories
From: Ray Wallace <raywallace
altavista.com>
Here is a description of a LX200 Classic scope mod. I did several years ago. I wired the aux. plug-in on the control panel of my
LX200 to power my palm-sized VCR. I did a resistance check on the connectors to find 2 that didn't connect to anything. I then
hard-wired them to the 18 volt telescope power connector on the control panel. I arbitrarily chose one wire for positive (+), the
other for negative (-). It is very important to note that I wired to the terminals of the power connector. So, the power for the
aux. plug-in is before the control panel fuse so the fuse won't blow and the panel is safe! I have an external positive 9.6 volt
regulator and fuse in a box. I plug one cord into the aux. panel for power, and the other cord into the camera. With this
arrangement I don't have the excess weight of a battery pack on an already burdened system, and I have unlimited power to
take my time with the setup.
Subject: Power Panel/Cable Problem Solved!
From: Wayne Watson <mtn_view
sirius.com>
I reported having lots of trouble with the plug/connector combination on the power panel, and have spent a considerable amount
of time trying to discover why the power goes off when I wiggle the power cord near the plug or the plug itself. I tried just about
everything.
One of my astro buddies came over with at alternate DC power supply and cable just in case it might solve the problem. It took
about 1 minute to discover the problem. If you look at the way the wires are connected to the plug, my whole plug rotates while
the wires are fixed in position. That is, the finger like piece of metal to which one of the wires is attached is free to turn around as
one turns the black sleeve of the plug. This results in the freely turning metal finger as providing the contact with the metal on
the plug, and not very well. I'm sure it needs to be soldered to the metal on the plug.
Earlier I had noticed that this might be the problem, but had no information on whether it was correctly attached. When we saw
his power plug and compared it to mine, it seemed we might be on the right track. I've been operating for over an hour with my
power supply and his cable without any power outages.
Subject: LX200 (classic & GPS) Circuit / Schematic Diagram URLs
From: Doc G & B. S. Jones <b.s.jones
bham.ac.uk>
I have compiled the circuits for the Classic LX200 telescope into three parts which can be easily downloaded. These are not
official circuits but might be of interest to some users. Thanks to Mr. B. S. Jones for providing the circuits. They are at my
website. Note: should open new browser window over this one.
Take a look at Jones' website for more information on the classic:
<http://www.eee.bham.ac.uk/joness/lx200/index.htm>
Also check out these links for LX200 classic schematics:
<http://www.ccdguy.com/lx200/lx200pp.htm>
<http://www.telescopeservice.com/lx200.htm>
For the LX200GPS schematics, <http://www.telescopeservice.com/lx200gps.htm>
or they're also in the Yahoo LX200GPS Group's Files area in the "LX200GPS Schematics" folder. You have to join the group to
access them: <http://groups.yahoo.com/group/lx200gps//files>
Subject: iMac to LX200 Connection
From: Chris Vedeler cvedeler
ix.netcom.com
Kevin White wrote:
> If the RJ connector on the back is a modem or printer port and can be selected
> as the comm port under your program then you're correct in thinking that an
> RJ to RJ cable is all you need, except the wiring will most likely be
> incorrect. Therefore you need to cut it in the middle and cross connect.
> The Apple web site should be able to provide you with the pin outs for the
> iMac RJ socket, if not try a MAC user group. You only need to worry about
> three wires, Ground, Send (TX) and Receive (RX).
> The serial to USB sounds problematic and I would avoid this path.
> Anyhow, hope this helps and maybe some experienced Mac users may have
> more detailed advise????
Kevin, the iMac's are a whole different animal than the older Mac's with the serial DIN8 connection. The RJ11 jack on the iMac is a
56k internal modem (i.e. it is talking in analog modulation not digital), and so is not a RS232 port. USB to serial is the only
option, and should work fine. I just set up 61 iMacs as student computers where I work, so I know them pretty well.
Check out: http://www.Zones.com sells a converter for $60.00
You will then need to make your own cable to connect from the USB to serial adapter listed above to the LX200. Detailed
instructions can be found at: http://obs.nineplanets.org/meade/cable.html
I have used the above instructions to make a cable, and it works great. I have never tried to connect my LX200 using the USB to
serial converter so I can't verify first hand if this will work. I can tell you that theoretically it should, as the converter is designed
to work with all the older Mac printers and modems which are RS232 devices.
Subject: Power Connectors / Cable Management
From: Kevin Dougherty <PLEIADE0
aol.com>
I'm convinced I've spent about as much time trying to ease the setup process as I have actually using the scope....as much of a
challenge as getting great images, I think....
A lot of discussion recently around the sturdiness of the power connectors got me thinking about another approach to speeding
up setup and I just installed a 6 conductor standard trailer hitch wiring harness to carry power to the scope and all its accessories
(which are mounted either on the scope or tripod and transported on a modified 'Stewart Sled'--see AstroDesigns via the Home
button). The beefy connector provides for a single step hook up and eliminates the concern around the normal Meade connectors
loosening -- they stay in place all the time now. I've placed a couple of pictures on my web site.
See my Astro Web Site at: http://members.aol.com/pleiade0/astro/
Click on the 'Cable Management / Power Connections' link on the updates section of the Welcome page.
Note: should open a new browser window over this one.
Subject: LX200 (Classic): What to do with Ceramic Resistors --part 1 of 2
From: Jim Tury <tury
erols.com>
Craig Tupper wrote:
>I got my LX200 electronic guts returned from Meade today -- without any
>reassembly instructions. Wouldn't be a problem, except they added a couple
>of ceramic resistors to the motherboard, hanging off long wires. I read
>they've been doing that for a few years now. There is a little aluminum
>clip that looks like it is supposed to hold the resistors, and a couple
>little plastic pads with adhesive on 1 side that look like they should be
>involved somehow. It's not at all clear how the resistors should be
>oriented and inserted into the clip, or how to keep the clip/resistors from
>rattling around in the base. Maybe I should just duct tape them to the inside.
The resistors fit into the wings of the W shaped bracket and then the double sided tape adheres the now-bracketed resistor
assembly to the inside wall of the aluminum base casting. There may or may not be some silicon heat transfer grease (don't
remember from when I did mine) included to help transfer heat from these new drive current limiting resistors to the casting wall.
-------------------------------------------------------------------------------------------------Subject: LX200 (Classic): What to do with Ceramic Resistors --part 2 of 2
>If I correctly understand your discussion the two ceramic resistors are
>actually supposed to have a thermal adhesive that attaches them to the
>base to help dissipate the heat they generate. This is according to the
>instructions that Meade sent me when I had to replace the PCB to my scope.
>They even sent the adhesive. However I found, and I thank that you will
> to if you try to use their adhesive that it has the adhesive properties of
>10W-30 motor oil. I could not get it to stick. I ended up using silicone
>adhesive as you suggested.
>If you can find a good thermal adhesive somewhere I would use it.
>mikemca wrote:
> >On my 10" LX200, the little metal clip that holds the two ceramic
> >resistors is fastened to the inside of the base casting by two
> >little dabs of silicon adhesive (at least that's what it looks like)
Mike -- Whoa! The white stuff from Mead is actually a "heat conducting" silicone grease(paste). Yes it won't stick.......It's to be
smeared like butter just on the face of the resistors, carefully, so you don't get it an the center bar of the heat sink where the
double sided sticky tape goes.
Then (after applying the double sided sticky tape to the center bar of the heat sink), peel off the second side of protective film on
the sticky tape and without getting the white stuff on the sticky tape, carefully and with significant pressure, stick the assembly
to the sidewall of the base compartment. Test it by tugging on the leads a little bit to make sure it is nicely stuck to the base.
Subject: LX200 AC Power Supply Voltage Reduction
From: Mike Dodd <mdodd
mindspring.com>
I was tweaking my 8" LX200 Classic and decided to measure the output of the AC power supply. Instead of 18V under a
moderate load (300 mA), I saw about 22V. Even with a 2 amp load, it was 20V instead of 18V.
I attribute this to the high line voltage at my house (believe it or not, anything up to 130VAC is within spec, and ours is right at
the 130V mark; we use light bulbs like there's no tomorrow).
Anyway, the Meade power supply is completely unregulated - just a transformer, a diode bridge, and a 6800uF capacitor. So
naturally the output voltage is going to be high.
I decided that 20-22V was too high, so I dropped it by adding four diodes inside the power supply. (I've seen the Topical Archive
article on adding several in series with the output, but I wanted to keep things clean.) After adding the diodes the output voltage
ranged from 17V under full load to 18.5V under minimal load. There are effectively two diodes in series, producing a drop of
about 1.4V total (in a bridge rectifier circuit, only two of the four diodes conduct at any time).
For each of the four diodes, I unsoldered one end and bent the diode up. I then soldered a second diode in the PC board hold,
being careful to keep the same polarity as the original. Finally, I soldered the other end of the new diode to the end of the
original diode. I used 1N5400 diodes, rated at 3 amps.
ŸŸŸŸ
MAPUG is hosted by
LX200 Grounding Issues
Grounding the LX200 and Computer
Electrical Grouding Between Scope & Camera Question
LX200 Grounding --10 parts
RS232 Grounding Problem?
Subject: Grounding the LX200 and Computer
From: Doc G
<cfrye
ix.netcom.com> wrote:
>
>
>
>
>
Doc G. said to make sure that the telescope and the computer are separately
grounded. That's real good advice but how does one do that. Both the Meade
120VAC/18VDC power supply and the laptop computer power supply only have
2 prong plugs, not three. How do I ground a two prong plug to the copper
rods I have driven into the ground?
Unfortunately many DC power supplies like those you get at Radio Shack for $10 or the one from Meade for $70 do not have a
correct 117 volt power plug. They are cheap, generally imported units, and they are not designed for outdoor use. I doubt if they
are even legal for outdoor use. Certainly not approved. You will always find a disclaimer that says something like "do not use
outside." The SBIG power supply DOES have a three prong power plug.
This becomes a bit silly since if you normally use the scope outside. And on dark often damp nights. So what to do?
Here is what I do. NOTE: This is not a suggestion and I am not responsible for anything whatever that happens electrically to the
scope or operator.
I always use a 117 volt socket that has a Ground Fault Interrupter (GFI). You can get these on power strips and on extension
cords. I ground accessories to the telescope and to the tripod with a bit of wire and a ground lug or clip. I also plug all 117 volt
things, LX power supply, computer and ST imager supply into the same power strip.
I do not pound a rod into the ground. That would only be necessary if you were viewing during a thunder storm and wanted
protection from lightening.
-------------------------------More from Doc G:
The flared plug is a substitute for the three prong plug, more or less. The idea is that the plug can only be put into a socket one
way. This keeps the hot side and the neutral side of the power line in correct order. But, and it is a big but, This only works if the
sockets you plug into have the hot and neutral to the correct pins. Most modern homes and buildings that are competently wired
have this correct. Now the neutral wire, the white wire, is neutral and not really ground. The green wire is true ground and is
grounded to the metal parts of the socket and to the round pin that is ground on a three prong plug.
The neutral is connected to ground at the fuse box in a house or building. Under normal conditions the neutral is close to ground
in potential. But under short circuit conditions the neutral line which is shorted to the hot line jumps up in voltage to half the line
voltage. Thus it is under the stress conditions of a short circuit that you get a half-hot neutral line. The green ground on the other
hand is supposed to protect the user from things like this. If the socket or plug is wired wrong of course, the neutral is actually
hot and vice versa.
So, in summary, the safest power lines, cables, extensions etc. are those with three wires and a well grounded green wire.
Subject: Electrical Grouding Between Scope & Camera Question --part 1 of 2
From: Roger Hamlett <ttelmah
>
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ntlworld.com> Date: Nov 2003
I use to power my LX200 Classic from a 12V car battery (without
the 12-18V converter, it's an 8") and my laptop computer from another
12V car battery (with a converter). The scope and laptop are connected
via the RS232 line.
I also have a SBIG ST7 camera powered from the battery to power the
scope. And the camera is connected to the scope for autoguiding and
to the laptop via the parallel line.
So far nothing has fried. But considering the scary electrical design
of the LX reported in the Archives, I am having doubt about my
connections. I would be very grateful for your comment about it.
The power requirement of the LX200, is 12 to 18v. A 12v battery, is OK, provided it is well charged, and the connections are
good, but there is little 'margin'. If the battery voltage starts to fall, the motors can lack the torque to actually reach their target,
stall and overheat. This gets worse with the larger scopes, where the loads are greater. So, _provided_ your battery is well
charged, and the scope is kept well balanced, there should not be a problem.
The second difficulty with the LX200, is that it's 'chassis ground' connection (which also connects to the RS232), is connected to
the top of the 'current sense' resistor. Hence if your laptop, and the scope were on the same battery, and your laptop was not
using a converter (most of these provide isolation), you could end up with the scope current being drawn through the RS232
ground. You look to be OK here, since you have both a separate battery, and a converter module. The same 'ground' signal, is
also present on the 'guide' port, with the same potential problem. It sounds as if what you have is 'perfect'. The ST camera, and
the laptop, share the same 'ground', and are powered from one battery, while the scope is on the other. If you put a voltmeter
between the -ve terminals of the two batteries, you would find a small voltage between them, which would vary as the scope
draws more/less power. Keeping the scope on a separate battery, ensures that this does not cause a problem.
------------------------------------------------------->
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As long as you keep your two car batteries connected in
parallel i.e. positive to positive, negative to negative you have
nothing to fear. The converter to your laptop will supply the
laptop needs; and any voltages that occur on the port pins will
be correct and referenced to the "same "ground as is every other
device you are using. Even if you isolate the batteries there is
little chance of a 'cookout' however strapping the two batteries
together forces all to have the same ground reference. And if you
were to power your LX200 from the mains converter you could still
tie your (one) battery ground to the scope/fork ground as this would
ensure a perfect ground reference. Just remember that the negative
terminal of your battery is your ground reference.
--Doug
NO!... Do _not_ do this. You risk damaging the equipment.
The 'key' is to understand that the LX200, does not use battery negative as it's 'ground' reference. It has a sense resistor (used
to feed the display showing the current drawn), between the -ve connection, and the 'ground' connection on the RS232 plug, and
the CCD plug. If you join the battery -ve connections, and attach an un-isolated device to one of these ports, you risk the power
being drawn through this connection, rather than through the power connection. This is how you can blow the RS232 port, or the
guide system...
This is the big 'LX200 caveat,' when wiring.
---------------------------------------------------->
>
>
>
>
>
If I understand correctly, I should not connect the Pictor 201
Autoguider and the 16" LX200 to the same 12V battery because I risk
blowing the LX200 Guider port or the Pictor, right?
Is there another way to solve this problem apart from carrying around
two 15kg car batteries?
Yes. You are OK, if the laptop has an isolated converter driving it, and if the camera is using a relay box or opto coupler. It is a
really annoying 'feature' of the LX200, which is why there have been so many posts about it in the past.
----------------------------------------------------Subject: Electrical Grouding Between Scope & Camera Question --part 2 of 2
From: Doc G
----- Original Message ----From: Bostjan <ac0
email.si>
> Thank you so much Doc and Roger for your info.
> I am now starting to realize what has probably burned my 16" LX200 main
> board _FOUR_ times...
> Let's suppose I short the 0.1 ohm sensing resistor as you mention.
> Will I then be able to connect the LX200 and the rest of the equipment
> (Pictor 201 etc.) to the _SAME_ 12V car battery without the risk of
> burning something?
>
> The reason you get half the current indication is that you are partly
> shorting out the current sensing resistor. That is the bad part of this
> whole circuit problem. Some users have simply done away with the current
> meter by replacing the 0.1 ohm sensing resistor on the circuit board with a
> short circuit.
> This connects the battery plug ground directly to the true
> circuit ground which is the metal part of the base. The internal ground
> for the electronic circuits board is established through the screw that
> holds the board in place. It is the one going through the voltage
> regulator chip.
> The latter connection method is also very bad circuit design tactic.
> This is indeed a crummy design and has caused many problems over the years.
> I hope they have done better with the GPS version.
> The LX200 "classic" is dead, long live the "classic."
That is certainly a good solution to grounding problems. You will loose the current indicator, but it is generally useless anyway. It
will indicate a gross overload due to mechanical jamming of the mount. In the case of such an overload, the fuse should protect
the scope. The current indicator is also used during a dynamic balancing operation suggested by Meade. That balancing technique
is also a very bad idea, in my opinion. It greatly stresses the drives. Simple two position static balancing is adequate.
It is quite astonishing that the original design was issued. I have designed electronic equipment for over 50 years and such a
design has never been considered proper in the electronics industry.
Subject: LX200 Grounding --part 1 of 10
From: Doc G
Ed Fitzgerald wrote:
>
>
>
>
My questions have to do with proper grounding procedures for the LX200 and
accessories. The MAPUG topical archives treat this briefly, with the
following suggestions:
a) Plug everything into the same power strip.
Good advice!
> b) Use ground fault isolation receptacles.
Absolutely good advice!! Called GFIs.
> c) Use clip leads to ground the scope and tripod to true AC ground.
Nice if you can do it. A good site should offer this capability.
More comments from Doc G ---First , let me say that I am very sorry that you asked these questions. That is because I am now
going to get into trouble with all faithful MAPUGers and especially the devoted inner circle. These are my opinions based on 50
years of electrical and electronic design and industrial consulting. Please do not take them personally.
The Meade electrical and electronic design is at best non-standard, primitive and incorrect. The LX seems to be a collection of
outmoded designs and parts and has been modified, sort of fixed and otherwise kluged into working (sort of) over the years. It is
due for a major electrical and electronic revision. That said, I will try to answer some specific questions.
> From my perspective, I don't think this subject has been adequately
> addressed. I have the following questions:
> 1) What physical parts of the LX200 is true ground.
Ah yes "true ground" is elusive in the LX. The main body of the telescope might be expected to be "true ground" but it is not
unless the DC power cable is plugged in. Otherwise the body of the LX floats. Neat Eh? The grounding of the body of the LX
seems to be through the battery connector plug which has three terminals and shorts two of them together when the plug is
inserted.
Now a word about this power plug. It is an abomination. It is the most poorly designed cheap and crummy plug ever invented
since the ubiquitous RCA jack used on audio equipment. It is a loosely fitting sliding contact which is prone to being intermittent.
BAD PLUG!! Never the less, like the RCA audio plug it is everywhere since it is cheap, cheap, cheap!!
I have thought about replacing this plug with a "real plug that had a solid ground for years but it is not easy to do this since the
control panel is firmly pressed together and glued in the finest tradition of electronic design.
> 2) Is this ground the same as the 18-volt return line?
So the answer is sometimes. The body of the LX is connected to the 18v DC
return (ground/negative) line when the power plug is in place and happens to make good connection.
> 3) Is this ground the same as Pin #4 on the 6-wire RS232 modular connector?
This ground, which? Actually yes, the ground pin in the 232 connector is the circuit ground within the control panel. The 232
signal probably goes directly to the computer board where there is a 232 send/receive chip. This connection is through the short
flat cable going from the control panel to the computer board.
By the way, notice that this short cable has a makeshift shield around it. It is quite amazing that such a shield should be
necessary. Computers have very long cables inside without shields. This is indicative of an after thought because the thing did not
work for some unknown reason and was "fixed" with the shield.
> 4) Can I access a convenient grounding point on the scope with clip leads?
There simply is no convenient grounding point. You have to add a "body" ground by adding a tapped hole and ground lug or
clamp. This can be easily done on the control box chassis. All of the "body parts" of the LX are connected together via the
bearings and so forth. Notice that all of the several connector "ground" parts on the control panel are in fact insulated from the
panel except through the circuitry. Thus these should not be used as places to connect external grounds.
> 5) Why does the tripod have to be grounded?
I see no reason to ground the tripod if the body of the LX is grounded properly. In any case it will probably be connected to the
body of the LX through the big bolts holding the LX onto the tripod.
> 6) Do I need to have a separate ground connection for my laptop? Its AC
> adapter (like the Meade) doesn't have polarized AC prongs (where one prong
> is wider than the other).
When the DC adapter does not have a ground pin and is not polarized, there will not and must not be a connection from the ac
side to the DC side. There may be and likely will be some ac leakage current however. Thus it is good practice to ground the DC
output side of the adapters together. This is normally done through the connecting cables such as the 232 cable.
However, note that cables like the 232 cable are not designed to be hot plugged. Only special cables which are designed for hot
plugging should be hot plugged. The 232 cables and any RJ type connectors and also the crummy battery cables are not to be hot
plugged.
Often there is a considerable leakage current or a surge of current when adapters are plugged in. This surge may be strong
enough to destroy a 232 chip which is not fully protected. None of this equipment should be hot plugged.
Static electricity is also a serious problem. Even after a person "discharges" himself by touching a ground on the equipment, just
shifting position can cause a renewed potential difference that can cause serious static discharge damage.
> 7) For many field trips, true grounded AC receptacles are hard to come by at
> good observing sites. What is a good grounding setup for these cases?
Well, I would say that grounded and ground fault protected plugs ARE available at a GOOD observing site. The Madison
Astronomical Society has a dark site with many outlets at pads and ALL are grounded and ground fault protected. A site that does
not have such outlets is not a good observing site even if it has good skies. ;-o
Now if you really want to find more problems, just start to add CCD imagers, and all kinds of other electrical toys to the LX and
you have a REAL grounding nightmare. Most of this equipment is of marginal electrical design in my opinion. But some, like the
SBIG imagers actually have a true and continuous ground. Amazing that this stuff works at all!
-------------------------------Subject: LX200 Grounding --part 2
From: David W. Bonnell <Bonnell
nist.gov>
I will throw in my two cents worth here, noting the Doc has really covered the ground well (as always), but a couple of concepts
may still be unclear to some.
(1) All DC grounds should meet in one place. A good choice, when using multiple devices that are interconnected is to do as Doc
suggests, tap a hole in grounded "body metal" somewhere, put in a screw, and make sure a wire from each device's "ground"
potential is attached here (or nearby "electrically"). Note that you will need to ascertain just where to get that ground from some
devices. An inexpensive multimeter from Radio Shack is a good way to explore for possible problems. Do remember that many
devices are deliberately designed not to have grounded cases (for static isolation/protection), and you need to be careful just how
you arrange to "ground" them. If a "continuity" test (with power supplies off) shows a low resistance connection to your central
DC ground, you may be OK, at least as regards power ground loops. Note that for almost all DC equipment, it is NOT necessary
for that ground to be "earthed." The DC voltages involved are all too low to be dangerous, and "earthing" a DC ground can be a
marvelous way to pour current into the ground. Using the AC "ground" is a really bad idea -(2) AC "ground" should NOT be mixed with DC ground. It is very common to have several volts of "hum" on the neutral wire, and
sometimes even the green ground, if there is one, whether from a generator (e.g., battery-powered inverter) or even good mains
wiring. This hum is not often good for DC devices using 5 volt signals. If you need a good AC ground (and don't have one), a
couple of feet of rebar, sharpened at one end, and driven into the ground can be a good ground. Put a hose clamp or something
similar at the top (out of the ground) end, be sure to wire brush or sand rust... off the rebar metal (and the hose clamp!), and
use the clamp to attach a substantial (at least 16-18 gauge, better is 10 or 12 gauge) wire (can be bare copper, or whatever - in
a pinch, heavy fence wire or something will be better than nothing), and run it to a ground pin on your AC supply (could be the
case, or look at any receptacle - the center screw hole is supposed to be ground!). Then, your ground fault receptacles will not
only protect against current carrying grounds, but will insure those grounds are earthed. It is possible for ungrounded GFI gear to
suggest no fault, until YOU make the ground. If you don't have GFIs, and let the power supplies float, you are asking for it. Any
AC-using device should either have a ground wire, or be totally isolated (greater than 20 MOhms) from any of the AC Pins
(except, perhaps the green ground pin). Floating AC supplies are a pain, but do generally have a polarized plug. Be sure your AC
source has the wide pin as neutral! and things should be fine. Doc's comments that ungrounded AC supplies are OK ungrounded
is generally good advice for commercial hardware.
If you are using multiple AC sources (ugh!, bad idea), be extra careful, and be sure that they are either completely isolated, with
the grounds joined. It's also a good idea to at least be sure that the neutrals are both near ground potential! It is not uncommon
for different AC receptacles to be miswired interchanging hot and neutral. A real opportunity for serving smoked equipment.
Sidebar: It is generally good practice NOT to run DC, AC, and signal wires near each other. Often the biggest mistake made in
setting up an installation (whether observatory, or a big night at a favorite site) is to conveniently bundle all wiring together in
parallel runs. In general, having cables fanned out (the usual haphazard way they fall is good), and AC as separated from DC and
signal wires as possible will avoid many "glitches." Trying to compensate for nearby AC is possibly one of the reasons for extra
shielding on external computer wiring.
(3) Where Doc talks about "hot-plugging" he is referring to making or breaking a connection with power applied. Bad idea for
anything you are not SURE is designed to allow it. Plug in everything, then apply power. If a power source fails, better to turn
everything off, make the power source change, and then repower everything. A pain, but cheaper and quicker in the long run
than sending fried electronics back to Meade or whoever!. If you are not SURE your laptop or whatever will last on internal
batteries, hook it to the main power at the beginning. Interestingly, much general electronics today is designed to survive hot
plugging (for instance, the old saw about unplugging the laser printer I/O port cable without turning off power is almost never a
problem where everything is plugged into good house or business wiring). Hobby (which includes a lot of Astro-stuff) devices are
often of a lower standard, and will die easily. Even good commercial stuff can be hurt by the vagaries of outdoor wiring. Thus,
Doc's advice to avoid "hot-plugging" is really good advice, regardless of how you are set up. Those who don't need this advice will
know what I mean.
-------------------------------Subject: LX200 Grounding --part 3
From: Ed Fitzgerald <fitzgerald
msn.com>
Doc - Thanks a lot for the detailed and pertinent input. I couldn't test ground points on the scope (since it is being repaired) but I
tested my laptop. I found that there is a screw hole for some aux connector in the back which is at the same ground as Pin 5 on
the DB-9 serial COM port connector. The hole is one of two on either connector side that you'd normally run screws into to hold
the connector in place. I could run a grounding strap from this screw lug to an AC ground point on the power strip. If I also
ground the LX200 and then tie a serial cable between it and the laptop, do I end up with a ground loop? Also, I found in the
MAPUG topical archive that the 18-volt DC power return is tied to ground through a 0,1-ohm resistor (so they can measure
current draw). Hence, this point is not a true scope ground. My gut feel tells me that it's best to ground everything I can.
Mark - The AC adapter for the laptop is essentially the same as the one for the LX200, except that it puts out 15 VDC instead of
18 VDC. In neither case are the AC prongs polarized. I thought that the transformers would provide isolation, but this evidently
isn't strictly true - especially for in-rush current when you plug something in. If you think about the transformer-coupled DC
output of the adapter, the question is "What sets the absolute voltage of the two DC lines, +18 V and DC return?" I think this has
something to do with capacitance between the transformer primary and secondary for turn-on transients and then leakage
resistance from the primary to secondary - at least in lieu of any other constraint on these voltages.
I think my solution at this point is as follows:
1.
2.
3.
4.
5.
Plug everything into one power strip with GFI receptacles.
Take the battery out of the laptop and always use AC power.
Connect all serial cabling before applying power.
Connect a special grounding strap from the computer to AC ground on the power strip.
Connect a special grounding strap from the LX200 to AC ground on the power strip.
The remaining question is getting a good ground point on the LX200
-------------------------------Subject: LX200 Grounding --part 4
From: Doc G
I have just checked, by taking the thing apart and measuring it, the above comment about a 0.1 ohm resistor in the ground
return lead from the internal circuit ground and the return lead to the external power supply. It is also the case that the reticule
ground is returned to the internal circuit ground and the 232 plug ground is also returned to the internal ground.
Thus, the return lead to the power supply which is the negative side of the supply is slightly below in potential than the internal
circuit board voltage. This potential depends on the current drawn at the moment. For a current of 1/2 amp it would be 0.05 volts.
This means that the return lead to the power supply is not at the same potential as the ground lead pin at the 232 port. This
means that the ground on the computer should not be connected to the ground on the LX external power supply. I have normally
run my LX and my computer from the same battery with a common ground and not had trouble. But I should be shorting out the
0.1 ohm resistor by doing this. Probably the external wiring resistance is larger than the 0.1 ohm resistor. There is really no
reason to measure the current this way since it could be measured in other better ways that do not screw up the ground system.
This is strange and unconventional design in my opinion. I would say it is odd and stupid design. I am really baffled by such
design. I no longer feel confident in making predictions about the LX electrical design. I think at this point, I will resign from
saying anything further at all about the LX electrical system.
-------------------------------Subject: LX200 Grounding --part 5
From: Bill Ezell <wje
sii-nh.com>
This isn't quite true; check out the front panel power schematic on my astro page. The negative (or sleeve) of the power
connector is NOT ground. There is a (small value) resistor between it and chassis ground. This is used to provide the currentsense for the little LED current meter on the front panel. Consequently, if you short the DC connector 'ground' to chassis ground
(which is also the circuitry electrical ground), you'll lose the current meter output. This isn't any big deal, and it won't hurt
anything.
However, if you start plugging in accessories, aren't using a scope supply that doesn't have an isolated DC - (which the brick
does), then you can potentially set up a situation where the ground voltage levels can differ by several hundred millivolts
between things. Again, this isn't a disaster but it can certainly introduce electrical noise.
In my setup, which is permanent, I use a DC supply for the scope whose outputs are isolated from any other ground, and use
the scope frame as system ground. All of the ground pins in the various external connectors are (more or less) at this level, since
the main board in the scope does eventually tie to the scope base casting.
-------------------------------Subject: LX200 Grounding --part 6
From: Doc G
Ron Wagner wrote:
> I presume this is more about ground loops then grounding? I don't suppose
> that an AC isolation transformer on the equipment would help?
You make a distinction which should be considered. The discussion has been mainly about the local ground, ground loops and the
like among the various power bricks and equipments. These grounds are for the sake of reducing noise in the system and
insuring that the various equipments can communicate among themselves at digital the level.
The secondary but very important issues has been grounding equipment to a true earth ground. -- nominally, the neutral of the
ac power line is grounded at the main fuse box. A third wire has been added to improve the ground to the true earth ground.
Grounding to a true earth ground is mainly a matter of safety. An isolation transformer can be used to interrupt the ac ground on
the output side of the transformer from the house ground. I such a case, the output side of the ac system will have a neutral and
a hot side which is nominally determined by the equipment connected to it. Such transformers are usually used to eliminate noise
and power system spikes from getting to the equipment.
So, one should pay attention to both sorts of grounding and isolation. The various suggestions made in the bast day have been
good ones. Do both. Good grounds among components of the system and a single good ground to the true earth ground if
possible.
-------------------------------Subject: Further Thoughts on Grounding --part 7
From: Bill Ezell <wje
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sii-nh.com>
My gut feel is that I should ground the laptop and let the serial cable
carry the laptop's ground over to the LX200 Obviously, one would have to
be very careful to connect the serial cable first before powering up
anything. I would appreciate comments on this approach. I fried my serial
chip once, and I'd like to avoid doing this again.
If you're using an isolated supply for the scope (the brick that came with it), then you can use the scope frame for ground. This is
electrical ground as far as the scope electronics are concerned. If you're NOT using an isolated supply, then don't. You can see a
simple schematic of the LX200 front panel power supply layout in the astronomy part of my web page-<http://www.duckpond.mv.com/> Note: should open a new browser window over this one.
Normally, the RS232 common pin is tied to electronics ground, so you really don't need to separately ground the LX200 anyway.
The brick is isolated, so unless you get it wet there's no path from the AC supply to the scope. (it's isolated by a transformer
that's part of the supply)
-------------------------------Subject: Further Thoughts on Grounding --part 8
From: Ric L Ecker <rlecker
juno.com>
Ed Fitzgerald" writes:
>I have fabricated a GFI receptacle box and separate grounding wires so >that
>I can ground my laptop and the LX200 to AC ground at the receptacle >box.
You don't need to ground your Laptop because it's already has an isolation xformer built into the computer. It is basically still
seeing battery power and/or power supply power which is isolated. When ever hooking up the LX200, Laptop or anything that's a
computer, always have the power off and better off unplugged. If you forget to install or want to install a serial connector or dec.
motor cord always power off to do so. GFI will only work on plugs that have a ground connector. If you plan on making your own
ground you must be very careful and get everything polarized to prevent problems. On the GFI outlet the round plug will be the
ground while the small slot is the Hot side of the 115 vac and the larger slot is the neutral. Most plugs (two prong) we have today
are polarized so they go in one way. This plug will not work with the GFI unless you modify the plug which is defeating the
isolation already built into the electrical device, as the transformer for the LX200. Remember that the LX200, Laptops, CCDs all
run on battery power or (basically) a battery eliminator (transformers). Your home PC has a good ground and a GFI is designed
to work with this type of product.
-------------------------------Subject: Further Thoughts on Grounding --part 9
From: Ed Fitzgerald <fitzgerald
msn.com>
Ric --Your point about only changing or setting up cables while un-powered is a good one. Even if you do this, there may still be a
problem (like the one that fried my RS232 chip) depending on the sequence in which you power things up. Both my LX200 and
Toshiba laptop are powered from "bricks" with un-polarized AC plugs. Where this puts DC ground in (say) Pin 5 of the DB-9 serial
connector depends on leakage resistance between the transformer primary and secondary in the brick. During power turn-on, this
ground reference may be initially determined by stray capacitance in the transformer.
As a test, I plugged my laptop (two-prong un-polarized plug) into my power strip and then measured the AC voltage between the
true ground in the power strip and the Pin 5 ground on the DB-9 connector at the back of the laptop. I got a reading of over 50
VAC. A similar test on the LX200 (using the ground pin of the RJ-25 RS232 connector) showed a much smaller voltage. This
voltage difference can cause a momentary current surge through the serial cable during power-up until the voltages equalize.
My present approach is to ground the laptop to power strip ground using a separate ground cable and then let this ground be
carried over the serial cable to the LX200. If I use my Pictor 201XT autoguider, it is powered by a separate brick and can get the
ground reference from the CCD front panel connector on the LX200, which in turn is set via the serial cable and laptop ground. In
this way, I have one ground reference point.
-------------------------------Subject: Further Thoughts on Grounding --part 10 of 10
From: Ric L Ecker <rlecker
juno.com>
Ed Fitzgerald writes:
>Actually, I measured a resistance of about 1 ohm between the LX200
>front panel screws (i.e., case) and ground as seen coming out of the RS232
>connector, so case is close to ground, but there isn't a dead short
>between them.
I think folks here are confusing earth ground to neg. dc voltage or common which are different and somehow some are making it
the same, they are not in this case. Earth ground is in reference to what??? Earth ground is a very archaic reference point
considering the makeup of soil and the aggregate of the soil, moisture, salts and the like. Grounding can be a very serious
problem depending on what part of the country you come from and what type of ground system you are talking about. A rod
driven 6 feet into Terra Firma is not necessary a "good" ground. A proper ground screed cover several thousand sq. yds. is
sometime considered a poor ground depending on the soil and age of the ground. What type of instrument would one use to
consider a ground to have a resistance of 1 ohm in reference to the panel screw of the LX200. If grounding is a problem like the
instance of the ruin serial port of the LX200 I would consider the use of better voltage transformer (brick) that had no leakage
current. Most are so well isolated that leakage current seems strange to me and must be an isolated case. A scope that sits on
rubber feet does not need to be grounded and if you have leakage current coming from your (brick) just replace it, I'll bet the
problem goes away.
P.S. That's why it has an Isolation transformer in the (brick) power supply.
Subject: RS232 Grounding Problem?
From: Roger Hamlett <ttelmah
ntlworld.com> Date: Oct 2002
----- Original Message ----From: Paul Goelz wrote:
>I use TheSky with CCDSoft V5.00.070 to control my camera and LX200. For
>some time, I have been having intermittent problems getting the telescope to
>move in one or more directions using the direction buttons on the focus
>panel of CCDSoft. Usually the problem will go away when I disconnect the
>RS232 wire running from the computer to the scope, massage the ends, and
>plug them back in.
>This sounds like a hardware problem to me. Do I need to spend a ridiculous
>amount of money buying a new telephone-type cord from Meade or one of its
>suppliers, or is this cable available at Radio Shack?
>
>
>
>
Before you go too far, make sure you do not have a ground loop or potential
difference between the two ends of the RS232 connection. I have seen the
LX200 do some strange things in the face of less than perfect grounds or
leakage currents.
Good point. In the case of the LX200, it is not 'less than perfect grounds,' that are the problem, but the fact that the internal
ground of the scope, is offset from the incoming supply ground, through the current sense resistor (silly design...). Hence if you
have a 'perfect' ground on the RS232, and no isolation, the system will attempt to ground the supply, through the RS232
connection. Ouch...
Provided you use something like a laptop, on it's own _isolated_ power supply, then the small offset voltage can be dealt with by
the isolation provided by this, but if instead you switch (say) to using battery supplies, with no isolation provided, this becomes a
problem.
MAPUG is hosted by
Carry/Storage Cases & Covers for LX Scopes
Carrying Cases for LX200s, 90s, & 50s
Carrying Cases for LX200s, 90s, & 50s in Europe
Modification to Military Computer Case
Desert Storm Scope Covers Sources
Best Scope Cover in Humid Climate
Black & Decker Wheel Toolbox as Carry Case for 10"
Subject: : Carrying Case for LX200
From: Tony Mehle, Mahoning Valley Astronomical Society
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I just got a 10" LX200. I have saved all of the packing. On occasion,
I expect that I will want to take the telescope a fair distance (over
the mountains, where the skies are not cloudy all night), although I do
not expect that I will want to take it on an airplane. Is there any
point in buying a carrying case for it, since it is too big and heavy to
carry like a suitcase anyway, or should I just put it back in the foam
in the box when I want to take it a distance?--Mark de Regt
Mark--I am still using the deluxe Meade cardboard box in my 3rd year since getting my 12" LX200. I got a roll of clear contact
paper and "laminated" all of the outside surfaces of the box, then reinforced the corners with clear weatherstripping tape, which I
touch up as needed. I always use the box when driving to the observing site. This has held up thru dew filled nights and even
some snowy ground contact, as I put the box back in the van after setting up to minimize environmental degradation.
Subject: LX200: Cabbage Cases Carrying Case for 8"
From: Evan Zucker
I bought an 8" LX200 last month. After much research, I decided to have a custom carrying case built by Cabbage Cases <http://
www.cabbagecases.com/> in Columbus, OH. Total cost was $264.12, including $20.12 for UPS ground. It took 6 days (Friday till
Thursday) from Columbus to San Diego.
The case arrived yesterday, and my wife (who bought me the telescope) and I are pleased with it. We decided not to glue the
foam to the case because it appears to fit snugly. The case has built-in wheels, an extension handle and the top of the case lifts
off via 4 latches and a handle on either side.
When I put the top on there is a slight gap -- perhaps 1/8 inch -- between the top and bottom, and so I press down on the top
and close the latch. I was wondering whether compressing the foam in this manner is a good thing or a bad thing. Cabbage Cases
says that's exactly what they were aiming for, and I'm inclined to agree with them that this provides a snug fit for the scope.
The only problem was when I opened the shipping carton. As I always do, I used scissors to cut through the sealing tape.
Unfortunately, there was no gap or packing material between the top of the carton and the case, and so I gashed the top of the
case. Naturally, I wasn't pleased about this, even though it's just a cosmetic gash.
I talked to Mike Hannah at Cabbage Cases about this, and he said nobody has complained about this problem in the past 15
years. I asked him how he thinks I was supposed to open the carton. He said I should have pulled the tape off. I don't think
that's feasible. A better alternative is probably an Exacto knife where you can have the blade extend just slightly from the handle.
After I contacted CC a second time about this, they were very apologetic and offered to make up for it. They said customer
service and word of mouth is very important to them.
I suggested that Cabbage Cases warn customers about this to make sure they don't do what I did. Since you've been forewarned,
you shouldn't have a problem.
I recommend this case and Cabbage Cases. If you're interested in getting an estimate from them, be sure to ask for Mike Hannah
and mention my name (Evan Zucker) and my Order No. 42645 so you can get the benefit of the work they already did on my
case.
Subject: LX200: Carry Case for 10"
From: Jeff Schotland
I placed my order for a an ATA Style case yesterday (10: LX200), I have
decided to go with the case from Atlas Case Company. The following information was provided in their quote:
"A fabricated ATA Case with your dimensions of 36"L x 23"W x 17.5"H, no foam, white exterior, removable 3" lid, recessed
casters. 3/8 plywood & all recessed hardware cost would be $410.00. Shipping cost is $13.80 for RPS ground. Build time on this
case would be two weeks from time of order."
I decided to go with the Atlas Case for the following reasons:
1. Their quote (while not the most detailed) was for what I asked for. I received seven quotes, two quotes I received were for
the wrong dimensions! Or contained options that I had not specified.
2. 3/8" plywood construction, Yes this case will weigh more empty, but should withstand lots of shipping/travel. And should
provide as a sturdy seat with appropriate cushions.
3. SHIPPING CHARGES $13.80 for an object of oversize dimensions and a weight near 60 lbs. I can't think of any astronomy
related product that I have purchased that has shipped for so little! I received quotes as high as $80.00.
Atlas Cases <http://atlascases.com/>
Other quotes:
Harnel Cases <http://www.harnelcase.com/>
A&J Cases <http://www.ajcases.com/>
Calzone Cases <http://www.calzonedealer.com/>
Cabbage Cases <http://www.cabbagecases.com/>
Star Cases <http://www.starcase.com/>
Subject: Custom Carry Cases
From: Chad Reynolds
I was surfing the web and noticed a discussion on your website concerning carry cases. We offer custom case solutions for all
types of applications, with a minimum order of one. If you have any questions concerning our company, please contact me or
visit our website at: <http://www.cyber-case.com/> or 1-800-268-6000 x221
Subject: Carrying Cases Source In Europe
From: Jean-Luc Luczak
I have seen that the "maison of astonomie" in Paris seems to supply some cases for the OTA, equatorial table and tripod. They
have a web site:
<http://www.maison-astronomie.net/> where you could query a catalog and also send an email.
Subject: Modification to Military Computer Case
From: John Hopper <JohnLX200
aol.com>
Here are some comments base on my experience and that of a few others as well:
1. There are two versions of the 10" case, and possibly a couple additional variations on the exact configuration of mil foam in the
cases. The foam variations don't matter for anyone doing it your way, as you removed it all. However, the bottom piece (your top
piece) in most cases (pun intended) has a hard plastic accessory bin, complete with nylon lashing straps. I'm not sure how hard it
would be to remove it, I presume that either your case was the version without this, or you'll provide the answer to that
question! Note: all of the brand-new ($150) 10" cases have the interior accessory bin, while the used ($100) 10" ones are still
available with or without it. None of the 8" ($90) ones have the interior bin, just two different foam configurations. Their weights
of the two 10" versions are 45 and 52 pounds, but that's only due to differences in the amount of mil foam in them rather than
the bin weight itself. Once the extra foam is removed to a level where you can compare apples to apples, the difference becomes
only around 2 pounds. The bin is along the long side of the case, and in fact eliminates the need for extra foam in that direction.
2. The interior accessory bin wouldn't work very well upside down, as that would put its opening facing downward, sort of hard to
load.
3. While using the larger top piece as the bottom is tempting, especially with those ridges looking like feet to keep the case off
the ground, I generally don't recommend it to people for these reasons:
A. You'll note that trying to put the Meade foam all the way to the bottom of it, required trimming the length of the Meade foam
due to the taper of the case which is much greater on that piece than on the shorter but more square real bottom. The same
would be true right-side-up on the top, except that nobody leaves 4" of military foam in the bottom, therefore the top of the
Meade foam doesn't have to go all the way into the most tapered part. And if you do want to trim it a little, it would be on the
thinner Meade foam piece, rather than the big one.
B. When I first left a bunch of these cases outdoors in the rain, then opened them, I found out that if you have them right-sideup, then it's much less likely that you'll let any water into the case when opening a wet case...or if you have a case with a bad
seal, bent rim, or whatever. Right-side-up water problems are rare even with a minor case problem, but upside down you had
better make sure the case is still airtight and that you don't open it wet.
C. You really don't need to use the ridges as feet, as it's not getting wet anyway, and if you drag it on pavement, the wear gets
spread across the whole bottom of the case rather than just the feet...unless you add wheels or drag them on the edge. Either
way, they're pretty tough as you say, I've never heard of one wearing through from dragging. D. I think that part of the reason
the handles are on the bottom, is so you're not holding the weight of the contents (scope, in this case) by relying upon the
latches. Then again, the 12 latches are overkill and plenty strong, so you're right that it's OK to do so, from a practical standpoint.
4. Adding wheels, or anything else to the outside of the case, makes it beyond the size limit which UPS will ship (air or ground,
doesn't matter) and the same is true of FedEx Ground. FedEx Air will still take it, but obviously that isn't cheap. So I recommend
that any exterior mods be easily removable if you might want to ship the case at reasonable cost. Note: on the 8" cases, wheels
would only move it from "Oversize 1" to "Oversize 2", but on the 10" you're already at the extreme limit of "Oversize 2".
5. Anyone wanting to use your method which removes all the mil foam, can get one of a limited number of foamless used 10"
cases I have, for $60-$80 depending upon condition. These are cases which had been left open and wet at some point in their
life, and I've had to rip out the moldy foam and pressure-wash them. Similarly, if anyone doesn't need latches on every side (e.
g., for adding a hinge instead) or doesn't mind cleaning up rusty latches, removing near-unremovable labels, sanding off spray
paint, or having various other minor/moderate flaws, I have other bargain cases of every description (and price!) available culled
away from what I've been selling at the normal price, that could be made presentable with a little labor. For example, if someone
wants to try sanding and painting a case with Meade-blue epoxy paint, you might as well take one that could use sanding and
refinishing anyway, at a bargain. Or if you want to add a hinge to replace 3 latches, you might as well take one missing 3 latches,
etc.
5. I'll have to try a hacksaw on the foam sometime. I've never cut the Meade foam, but I've cut a lot of the mil foam. I normally
use a heavy serrated kitchen knife. Mildly serrated, not one with fine teeth, just a slightly wavy serrated edge. It works great, but
when cutting slices of the mil foam, especially on the tough 8" case's version with a near-solid foam block 20x30 inches in cross
section, the knife must actually be removed a few times to cool off!! It's real fun making two cuts meet exactly 10" deep inside
the slice. Usually I just get it close, then hack at the remaining line down the middle, from the end.
Subject: Desert Storm Scope Covers --part 1 of 2
From: Dave Schanz <dave23sch22
home.com>
I haven't seen this site mentioned yet in this thread but they do have something that appears to be similar to the Desert Storm
cover that might suit your needs. I don't own one and have never seen one in person so I can't vouch for their quality.
<http://www.casesandcovers.com/> Note: should open a new browser window over this one.
-----------------------------------------------------Subject: Desert Storm Scope Covers --part 2 of 2
Editor's Note: also try: <http://www.telegizmos.com/> and Nite I's Visual Astronomy Accessories,
<http://www.niteis.com/NiteIsNiteScape.shtm> Note: should open a new browser windows over this one.
Subject: Best Scope Cover in Humid Climate --part 1 of 5
From: Mike Wyatt: As a follow up to the below request. I also live in Florida and have installed a pier on the south side of my
home. I'm not allowed (homeowner's association) anything like a shed or even semi-permanent cover (box) to cover my pier and
scope. What I'm trying to do is cover the scope pier with something like a Desert Storm cover, include a small light bulb to keep
the inside temp above the dew temp and add a chemical dehumidifier inside and seal the cover at the lower pier tube above the
ground with tight bungee cords wrapped around the cover and pier tube. I know I'll need to change the dehumidifier chemical
often (plan on getting some of the "rechargeable" packs). I also plan on covering the scope with a plastic bag, then a plastic grill
cover, then the Desert Storm type overall cover, just in case the Desert Storm cover leaks during our frequent rain showers here.
Comments, experiences and general information regarding this "attempt" are requested.
---------------------------------------Subject: Best Scope Cover in Humid Climate --part 2
From: John:I was wondering given the high humidity here in Florida if a Gortex cover, tailor made for the tube/dewshield
assembly would have any benefits in stopping everything dripping after a couple of hours. I have a Kendrick system arriving in
the week but this will obviously only keep the optics clear. Does anyone have any knowledge of blanketing the OTA in any fashion
and its usefulness, if any.
---------------------------------Subject: Best Scope Cover in Humid Climate --part 3
From: Tim Cantwell: I saw a great idea by a friend of mine that might help. He had two 33-gallon trash cans glued to gather at
the openings. He cut the bottom out of one can which allowed them to be placed over the pier, wedge and some electronics which
were permanently attached to the pier. Under the trash cans he had a small 25-watt, red light bulb to control humidity
One modification he made after time was to cut a small hole in the trash can. This hole was in the area of the light bulb. The hole
was covered with a piece of Plexiglas to allow a visual indication of the red light from his back window to insure it was working.
Perhaps in your area you might want to add some kind of covering (plastic, nylon, etc.) which is attached to the bottom of your
pier, when the trash cams are in place they can be brought up and tied to the bottom of the trash cans. This may help with
humidity and other critters found in south Florida.
---------------------------------Subject: Best Scope Cover in Humid Climate --part 4
From: Dave Schanz <dave23sch
valleytranscription.com>: I have my 10" LX200 permanently mounted on my wedge and pier
here in Michigan. I leave it outside all the time. I went to the local shop that makes covers for boats and had them make me a
waterproof canvas cover. It's cylindrical shaped, has a long zipper on one side with a Velcro flap over the zipper and a draw string
sewn into the bottom so I can draw it tight. It's about 72" long and 3' in diameter and it ran me about $130. It works great, stays
flexible in our cold winter months and is impervious to the weather. I keep a 40 W bulb in a safety light on a timer stuck in the
base of the wedge to ward off the humidity. Although it has never appeared to be necessary, I cover the scope first with a cheap
plastic deck chair cover, then cover it all with the canvas cover. I keep the canvas cover snugged up against the concrete pier
with a bungee cord. It all works like a charm for me here in MI.
---------------------------------Subject: Best Scope Cover in Humid Climate --part 5 of 5
From: Clark Williams <S.I.G.H
ix.netcom.com>: I don't want to violate any of the advertising taboos on MAPUG, so first I have
to say that I own a company that makes telescope covers, now everyone will know that they don't have to read any further if
they don't want to.
There are several different kinds of covers out there, but if you are interested in seeing our covers, pop over to our website. Nite
I's Visual Astronomy Accessories,
<http://www.niteis.com/NiteIsNiteScape.shtm>
You don't want to use Gore-Tex. The Gore-Tex people will also tell you the same thing. When I did my research on fabrics for our
Nite's Capes one of the things I did was to look into Gore-Tex. Gore-Tex works because there is positive pressure on the inside
and relatively negative pressure on the outside of the fabric. Now if you want to stick a light on the inside it might generate
enough heat, but humans tend to give off about 2400 BTUs per hour. That is a lot of heat. And if the light ever fails, the
waterproof nature of the Gore-Tex will no longer work. So you might look into other fabrics.
Subject: Black & Decker Wheel Toolbox as Carry Case for 10"
From: John Mahory <jmmahony
hotmail.com> Date: May 2004
This came up on the LX10 group a couple days ago. Here's summary of a couple messages from a guy who found an alternative
(note that the LX10 is an 8" SCT, so you'll have to check if your 10" LX200 will fit):
"I work in Home Depot, and while walking around the store one night, I stumbled upon this AWESOME tool box! It's got HUGE
rubber wheels, AND a metal telescopic handle. This box is DEFINETELY large enough for the LX-10 (with plenty of room for
accessories!)
And the best part is, it's only $54.00!!!! However, you'll have to add your own lining / foam / whatever.
And, the fact that it's got large enough wheels (to easily roll over damn near any terrain), and a telescopic handle..... This link is
EXACTLY what the toolbox looks like(see below), only the one we sell, is a bit larger in size. But, this will give you an EXACT idea
of what it looks like. <http://www.acehardware.com/product/index.jsp?productId=1340673"> or click on Speciality Toolboxes.
MAPUG is hosted by
LX200 Collimation -- Page 1
*Also see Star Testing & Optical Quality topic (includes how-to make an artificial star for testing)
Maksutov Collimation/Optical Issues --2 parts
Daytime Optical Alignment Procedure
Collimating an SCT with a Cheshire?
Simple Collimation Technique
New Collimation Page Ready
Advanced SCT Optical Adjustments
Maintaining SCT Collimation
Collimation Demonstration Webpage URL
Collimate With or Without the Diagonal? --7 parts
Decreasing OTA Cool Down Times for collimating/testing --6 parts
Ronchi Grating Used to Re-Position Secondary Rotational Position
Secondary Mirror Rotating?
Secondary Mirror Description/Optical Alignment
Centering the SCT Secondary
Tri-Lobed Stars Fixed?
LX200 Corrector Plate Glass?
GoTo Page 2 of Collimation/Optical Issues
Subject: LX200 7" Maksutov: Collimation Issues --part 1 of 2
From: Robin Casady <rcasady
scruznet.com>
Leigh Daniels wrote:
>With all this talk of how much collimation has improved performance, I
>started looking more critically at my new LX200 7" Maksutov. When I look
>at the inside-focus and outside-focus rings generated by looking at
>Arcturus or Vega, they look quite symmetrical. I tried Robin's daytime
>look-down-the-front test and things looked pretty good there, too. When I
>have a star in focus, however, the diffraction rings around the Airy disk
>are significantly brighter on one side than on the other. This is not the
>result of bad seeing.
>I suspect that the scope requires some minor collimation but the LX200
>manual says no collimation is required for the 7" Mak, so I have no
>instructions on how to collimate my scope. The ring holding the corrector
>plate has three large-head Allen screws. Next to each of these screws is
>a tiny, countersunk, headless Allen screw.
>Now, my questions:
>1. Why would Meade say no collimation is required for the Mak?
The Mak should hold collimation better than the SCTs and it is a bit tricky to collimate. It is easy to go too far and get lost (not
know which way to go to correct). I speculate that they figured there would be more frustration generated by people trying to do
it themselves then there would by some having to send the scope to Meade.
>2. Could the imbalance in brightness of the in-focus diffraction rings be
>the result of bad collimation? If not, what might be the cause and the cure?
I could be. There might be other causes, but it could be collimation. did you remove the star diagonal? Did you rotate the
eyepiece to see if the bright area rotated? Did you try another eyepiece? Were you using at least 300x? If yours shows an Airy
disk with rings, that is pretty good. If it is out of collimation that is causing this it is very slight and would need only a very small
adjustment.
>3. Can I *safely* collimate the scope myself and if so, does anyone know which screws to use for collimating?
What is safe? You could make it worse and not be able to get it as close as it is. Then you would have to send it back to the
factory and hope they got it right.
Because my only other option was to return the scope to Meade, John Piper told me how to collimate it. It is very much like
collimating a refractor. There are three sets of push/pull screws around the edge of the corrector. Each set has two screws, a
capped screw and a set screw. When both are tight, the corrector cannot move. To make an adjustment you must loosen one and
tighten the other. Make very small changes. In your case, make them as small as you can.
ALWAYS KEEP TRACK OF WHAT CHANGES YOU MAKE. You should always be able to undo what you have done in case it gets
worse. If you lose track and get way off, you may have to use the sight-down-the-front technique to get you close to collimation.
If I remember correctly, the area that is dark relates to the part of the corrector that is too close to the eyepiece. I could have
that backwards, and remember that the image is flipped. Best to see which direction causes improvement and which makes it
worse. It is easy to get confused. Take notes.
The capped screw pulls the corrector towards the eyepiece. The headless set screw pushes the corrector away from the eyepiece.
>4. Would I follow essentially the same procedure as the one outlined in
>the manual for the SCTs or is a special procedure required for the Mak?
There are similarities but it is not the same.
-----------------------------------------------------------------Subject: Daytime Collimation Method for Maksutovs --part 2 of 2
From: Robin Casady <rcasady
scruznet.com>
Bob Middleton wrote:
>Is there a better way to reach good collimation besides just eyeballing the
>doughnut of the out-of-focus star image. I know there are commercial aids
>for Newtonians, but what about aids for a 10" SCT? (LX200) Other tricks or tips?
There is a daytime method that works for Maksutovs, and I assume would work for SCTs.
Look down the front of the scope from a little ways away, perhaps about 10 ft. The exact distance is determined by what you see.
Right around the secondary you should see a dark ring. Move closer to the scope until the dark ring is lined up with and almost
completely obscured by the secondary. It is best to set up a white card with a 1/8" hole at this position so that you can come to
this position easily after making an adjustment, and the reflected image in the scope is white. You should see: the secondary, a
narrow dark ring, a white ring, a dark ring, a white ring.
The first dark ring around the secondary is used to insure that your eye is looking straight into the scope. If it is not concentric
with the secondary, move the card with the viewing hole until it is lined up. If the first white ring or second dark ring are thicker
on one side than they are on the other side, you need to adjust collimation.
This technique was demonstrated to me at Chabot Observatory's ATM workshop by Kevin Medlock. It seems to work pretty well
on the 7" Maksutov. It may not give you the ultimate collimation on the faster Act's, but it should get it close so you can do fine
tweaking on a star.
One thing I found helpful was to set up a white card 8.5 x 11" or larger with an 1/8" sighting hole in the center. I used a photo
light stand and clamp to hold it vertically in place. This reflected white into the scope to give the best contrast between bands and
it allowed me to find the proper eye position easily and quickly between adjustments. BTW, the mirror position should be where it
will be focused on a star in your normal viewing setup.
Subject: Collimating an SCT with a Cheshire?
From: Rod Mollise <RMOLLISE
aol.com> Date: Jan 2002
<spectrumsoft televiso.com> writes:
I'd be curious to find out how many folks collimate their SCTs with a Cheshire instead of doing a star test, or in addition to a star
test. As you know, conditions often make it difficult to perform an accurate star test-based collimation, although you can usually
get pretty close. Would a Cheshire give me better collimation?
No. Not often. Usually a Cheshire yields miscollimation...both due to the nature of SCT optics and to the fact that it's quite normal
for the system not to be _quite_ concentric with regard to the rear port.
However, I've discovered a rather painless way to collimate your scope indoors. Just get a hold of a string of Xmas tree lights.
You know, the modern kind with the small, clear colored bulbs. I found that one of these bulbs placed a decent distance away
(not critical) produced nice diffraction rings in an SCT! Experiment with different colors. You might want to pose the bulb of
choice in front of a black piece of cardboard. It might also be helpful to dim the thing down a bit with a dimmer or variac. Works
amazingly well. No fuss, no muss.
Subject: Basic Collimation Technique
From: George Malyj
>>>>... when the seeing is good and the scope has reached thermal equilibrium, take that extra couple minutes to
further tweak the collimation screws so that the high-power (>250x) Airy disk of an *in-focus* star is at its centered
best...<<<<
>>It sounds simple enough, but trying to make adjustments and ensure they are visible on an in-focus star does
not sound so simple.<<
It's actually fairly easy once you've done it the first time and know what you're looking for.
Basically you need a good seeing night (so that the Airy disk isn't boiling) and at least 35-40X per inch of aperture. I use a 6mm
Clave Plossl yielding approx. 420X on my 10" f/10, and usually select a star of 2nd or 3rd magnitude that is at least 60 degrees
above the horizon. Starting with a medium-power eyepiece, go ahead and first do the out-of-focus centering of the "hole-in-thedonut", confirm with the high-power eyepiece, then rack the high-power eyepiece into best focus finishing with a
counterclockwise turn of the focus knob (to prevent image shift). If the seeing is steady enough, you should be able to see at
least one bright ring and one or more additional fainter ones around the central point of light. Move the star around in the
eyepiece field of view from center to edges and note how the orientation of the Airy rings relative to the center disk changes.
What you strive to end up with is perfectly concentric rings around the center Airy disk when the star is in the very center of your
high-power field of view. Start with an extremely small nudge on a single collimation screw to see what changes. You'll note that
the star will move and will need to be recentered in the field of view before making any additional changes. Under near-perfect
seeing conditions, you may even be able to go one step further. The rings could be as centered as best you can tell, but the
center disk seems slightly smeared or elongated in one direction; the final adjustment would be to make the central Airy disk
itself as round as possible. Don't be discouraged if don't get a perfect disk, as a combination of excellent unstrained optics, ideal
seeing, and a scope at ambient temperature all need to exist at same time.
Anyway, once you've done this, pop in one of your low-medium power eyepieces and go check out globular and open star
clusters, and Jupiter or Saturn if high enough in the sky. It makes a difference. And if both seeing and transparency are superb
that night, you'll really appreciate what your scope is capable of showing you.
Subject: New Collimation Page Ready
From: Sylvain Weiller <sweiller
free.fr> Date: Nov 2003
I have just finished the translation of my French page on collimation.
It's at: <http://sweiller.free.fr/collimation.html>
I hope you will enjoy it. I had many good comments. People telling me it helped them much in that hard known enterprise. I
hope it will help you too getting better images more easier than before.
Subject: Advanced SCT Optical Adjustments
From: Michael Hart
PREFACE
SCT optics are often criticized as mediocre as compared to refractors and other less complex optical designs such as a Newtonian.
This reputation is due, in part, to the rather complex optical design which if not properly adjusted or figured, may inhibit ultimate
performance. It is often assumed that if the image is not so good, the optics and/or the SCT design is at fault. This is unfortunate
because the SCT is arguably a very compact, readily available, reasonably priced and versatile design with an enormous selection
of accessories.
Serial optical manufacturing methods have the potential of producing consistently good optics. It is quite possible those whom
own what may be described as less than excellent optics actually do have good optics whose full potential may be realized with a
bit of adjusting. I should point out that there are vastly different words used to describe an observation using the same telescope.
Some will use superlatives while others see the change more like the difference between 97 cents and a dollar.
Sometimes, a SCT with rather good optical potential does nor realize it's full potential in the field. This may be so because the
telescope is not adjusted properly both mechanically and optically. Specifically, the focuser, corrector orientation, corrector
positioning, secondary orientation, collimation and very rarely, a loose primary can result in less than optimal performance. As a
result, the user may conclude they have poor optics, which may not be the case. Of course, another telescope where the optics
are properly adjusted will likely perform better, confirming (in error) the user's conclusion about the original optics. Then of
course, excellent optics look bad before the telescope is at thermal equilibrium and/or during average-poor seeing.
In addition, the SCT optical potential is sometimes criticized because inside and outside diffraction patterns are not identical. This
is often so because the tester and/or the collimation & optical orientations were done using the SCT focus knob. Those that have
removed most of their image shift through procedures I described elsewhere are likely to see close to identical inside and outside
diffraction patterns. Those with a higher amount of image shift can still enjoy good optical performance with a few workarounds.
BACKGROUND
For precision optical alignments and repeatability in a SCT, it is best to avoid using the SCT focus knob for inside and outside
focus changes or at the minimum, finish focus in the optimal direction described later to pre-load the focus mechanism. Use this
same focus procedure for viewing and imaging as well. An even better method is to roughly set focus in counterclockwise
direction to pre-load the focuser. Those with the 12" should pre-load the focus mechanism clockwise due to the mirror spring. Use
a reticle eyepiece with a barrel extension (if needed) secured by double screws to adjust inside and outside focus distances. The
JMI NGF-S is likely to have insufficient travel for these purposes. I use a special SCT threaded accessory manual focuser for this
purpose.
For optimal diffraction patterns as well as precision optical orientation adjustments, do not use a focal reducer or diagonal. A focal
reducer is likely to effect the sharpness of diffraction rings and visibility of the airy disk and a diagonal is likely to be a bit out of
collimation. It is conceivable, though somewhat rare, that the secondary of a SCT may become loose. It is also conceivable the
corrector may become loose as well, though this may not be as obvious. If the SCT has optics where the secondary is orientation
sensitive, the full potential of the scope will not be realized if the orientation is not restored to the factory position. However,
improper secondary orientation may not severely effect viewing, especially under typical seeing.
It is assumed the reader has good knowledge and experience with SCT collimation procedures, which are not covered in detail
here. Those that attempt star testing with the help of a textbook will find real diffraction patterns will not match the examples
contained in most textbooks. Experience and good seeing are most important. I repeat, EXPERIENCE AND GOOD SEEING ARE
MOST IMPORTANT, especially at this stage.
It is possible to improve upon factory corrector/secondary index settings, though I believe this requires a VERY experienced
observer and excellent seeing to do so as the differences are very subtle. It is also possible the corrector may move under a
normally tight retaining ring if the cork spacers have become permanently compressed. The symptoms are a slight change in
collimation which is likely to go unnoticed and slight corrector movement under the corrector retaining ring. This may result a
gradual loss of the corrector index position. Meade usually marks the corrector orientation. However, a few may not be marked,
so the procedure below will restore factory orientation of the corrector.
If the reader is not experienced with collimation procedures and star testing, it is recommended the secondary/corrector
orientation be left at or near the factory position. I have recommended rather coarse (10 degree) adjustments which, in the
eyepiece, are adequately fine.
LOOSE SECONDARY REPAIR WITHOUT CORRECTOR REMOVAL
The standard procedure for correcting a loose secondary is to remove the corrector and tighten the secondary retainer while
holding the secondary cell on the outside. It is possible to tighten a loose secondary WITHOUT corrector removal. This is useful
for secondary orientation adjusting described later. Here's how:
To prevent accidental primary mirror damage, point the optical tube horizontally (in case the secondary falls out). To tighten,
firmly grasp the secondary cell and pull AWAY from the corrector while simultaneously turning the secondary cell clockwise.
To loosen the secondary cell, pull AWAY from the corrector while simultaneously turning the secondary cell counterclockwise This
will method will be useful for adjusting the secondary indexing or adjusting the secondary orientation as described below.
SYMPTOMS OF INDEXING ERRORS IN THE CORRECTOR & SECONDARY
Adjust collimation and star-test under excellent seeing without a diagonal or focal reducer. Check inside and outside diffraction
rings, Are they up to your expectations? Check planetary views. Do they seen to lack contrast and punch? Check focus. Does the
telescope seems to focus a bit softly? If you have some or all of the above symptoms, you may have an optical set whose
secondary is orientation sensitive and/or a corrector that has moved from the from the factory orientation.
USING THE STAR TEST TO ADJUST THE CORRECTOR AND SECONDARY
With the corrector, a good place to start is to remove the corrector retaining bolts. Use the procedures for adjusting the
secondary orientation while turning the corrector in the front casting. You will likely need to remove two or three cork spacers
from top corrector edge to allow corrector turning.
Since Meade doesn't index the secondary, and I'll bet you didn't either, you will need determine the secondary's orientation to
your optics. Do this on a night of excellent seeing. You may need to patiently await for several months for a really good night, but
the following just can't be done unless seeing is quite good, such as well after midnight and just before dawn. It is possible to
equal or exceed original factory secondary orientation placement using the star test as the arbiter.
You will want an assistant who can rotate the secondary 10 degrees or so at a time while you observe the diffraction patterns.
You will likely need to tweak rough collimation when the secondary is rotated. You will want a fast and efficient method for rough
collimation to speed things along. Here's how:
Using a straight-through reticle (no diagonal), outside defocus a centered star (move the mirror forward by turning the focus
knob counterclockwise). This will enable you to see the shadow of the Allen wrench and your finger. Use your finger and point to
the elongated diffraction rings. Have your assistant place the Allen wrench on one of the three screws with the handle sticking
straight out nearest your finger. Tighten (turn the screw clockwise) to move the airy disk (and the diffraction rings) toward the
shadow of the wrench. Recenter the star in the reticle.
When you find a location that looks good, have your assistant mark it. Continue on- you will likely see other areas that are good.
Have your assistant mark them. Now, have your assistant go back to the marked locations. Compare them against each other.
Pick the best one and tighten the secondary and place an indexing mark for future reference.
POTENTIAL RESULTS
If you have completed all the above checks and adjustments, you are likely to want to see the results. Pick a time of excellent
seeing with the scope at thermal equilibrium. Try a bit of planetary observing. Don't be surprised if your planetary views are very
good. You will know this is so when under good seeing, higher powers display more details. Under good seeing, I observe planets
at 800X and more on my 12". If the seeing supports higher powers, the aperture of a SCT really brightens the image. The airy
disc is clearly visible with circular diffraction rings that look close to identical both inside and outside of focus. It is likely that stars
seem to snap into focus at pinpoints that easily allow reticle powers of 800-1200X, useful for excellent PEC programming while
providing sharp stars at lower powers for manually guiding.
Subject: Maintaining SCT Collimation
From: Michael Hart
BACKGROUND
Reports from this list indicate that some need to tweak collimation frequently while others do not. At first, this sounds like a
paradox. However, my notes tend to indicate that some may want and need to tweak collimation more frequently than others
depending on how the scope is used and under what conditions it is used. However, after several thousand hours of CCD and film
imaging on SCTs (and other scopes), I have found collimation to be one of the lessor hurtles to produce good images. It is
important to put efforts in the areas likely to require attention (such as mount stability, alignment, focus, and guiding) and
minimize efforts worrying about other adjustments that have less an impact on the final results so that imaging does not become
needlessly difficult.
For general astrophotography and CCD imaging, critical collimation does not severely effect image results until one starts to
approach the theoretical resolution of the optics. Typical seeing of 4 arc-seconds experienced by most does not allow one to
record details at the theoretical resolution of the optics. As a result, critical collimation does not result in visibly better images
because image blurring caused by seeing hides slight collimation errors and other optical anomalies.
I must say that with 1 arc-second seeing, any optical anomalies really start to become evident. Field flatness and other
aberrations are now apparent to the experienced imager. That mega-special accessory now produces or worsens distortions if it is
not optimally corrected for the position of the spherical primary SCT mirror. Good collimation is noticeable under excellent seeing.
**NOTE: I want to caution those that are checking collimation with a dew cap in place that if the cap is slightly askew, even a
slight blockage of the clear aperture will result in flattened diffraction rings on one side.
COLLIMATION FOR VISUAL WORK
Visual work requires different considerations. Visually, the eye and brain act as a signal processor combining several images,
discarding the bad portions of the image while retaining the better portions, then assembling a composite image. With observing
experience, the human signal processor is programmed to see more detail while discarding what is not relevant. Likely, most of
us have been to star parties where an experienced observer sees things we cannot. We may not be able to easily surmise
whether the experienced observer is exaggerating or is really seeing what he reports until we gain similar observing experience.
Here, excellent optics will help with nice visual images under good seeing, but somewhat less so under typical 4 arc-second
seeing experienced by most. Often, Cassini's division is used to "test" the collimation and resolution. However, Cassini's division
is an example high S/N ratio (contrast), not resolution, because we aren't really resolving it, even though we believe we see it, so
the results may be somewhat misleading.
COLLIMATION REQUIREMENTS FOR GENERAL IMAGING
Quite frankly, imaging is often less demanding of optical quality than visual work because using amateur equipment, the signal is
diluted with noise of atmospheric blurring, reddening produced by absorption of shorter wavelengths (extinction), and a host of
other factors. In this example, the benefit of precision collimation and diffraction limited optics is buried in the noise produced by
other sources.
COLLIMATION REQUIREMENTS FOR HIGH RESOLUTION IMAGING
When we are imaging resolvable extended objects such as the moon and planets, it is possible to produce images with an
apparent resolution exceeding the theoretical limits of our optics. In this case, precise collimation increases the signal to noise
ratio (contrast) resulting in a image that appears to be more resolved, when in fact it is not really.
The moon is a great object for high resolution astrophotography because it's contrast and brightness provide the high S/N ratios
we need to record fine details at or better than the theoretical resolution of our optics. This is why the best lunar images are not
taken during a full moon where the lack of shadows reduces contrast and resulting S/N ratios. Some of the best lunar images
have been and are made on small telescopes of 16" or less, many are with SCTs not noted for high Strehl ratios. These scopes
are looking through relatively small columns of air resulting in images less likely to be exhibit less contiguous blurring at typical
amateur locations as compared to a larger aperture telescope.
With the case of SCTs, the secondary obstruction and subsequent contrast losses are small as compared to the overall S/N ratio.
However, good collimation increases the S/N ratio of the individual point sources that make up the extended object and thus
apparent resolution. In this case, a small collimation error can produce enough loss in S/N ratio that apparent resolution is
reduced by 30-60% or more. In fact, the resolution has not decreased as much as it would seem (as determined by viewing close
double stars for comparison), but the loss of contrast makes it appear as so.
CAUSES FOR SCT COLLIMATION LOSS
It would seem that maintaining good to excellent collimation is a good idea. Newtonians often loose collimation as the weight of
the diagonal increases deflection of the spider vanes when pointing away from the zenith. Newtonian primary mirrors may also
move a bit in their cell. A counter weighted secondary and/or thicker spider vanes helps.
SCTs such as the LX200 that tend to loose collimation for mechanical reasons that are quite correctable by the user. I often
transport my LX200 and collimation remains generally quite good. A SCT can be prone to excessive collimation losses from a
number of sources such as corrector movement in the front casting, excessive secondary cell clearances in the corrector,
excessive primary mirror tilting (image shift) excessively loose secondary collimation screws and differential optical tube
expansion/ contraction, optical tube looseness, as well as a loose primary mirror. If all the described sources are controlled,
collimation in a SCT remains good without frequent adjusting.
PREVENTING EXCESSIVE COLLIMATION LOSS
Corrector movement (more common in larger SCTs) is controlled by adding thicker cork shims to the corrector edge, compressing
the cork just before insertion. This allows even corrector expansion but stops gravity from shifting the corrector under the
corrector retaining ring as the optical tube is moved across the sky.
Excessive secondary cell clearance in the corrector is controlled by adding masking tape to the secondary cell circumference for a
snug fit. This also helps prevent secondary loosening and movement during temperature changes.
Excessive primary mirror tilting (image shift) is minimized with a somewhat slippery and viscous lubricant. I have been testing a
new lubricant that appears better than anything I've used to date. The image shift on my 12" LX200 was reduced to a few arcseconds in cold and warm weather- not enough to effect collimation except for the most severe imaging requirements.
Excessive loose secondary collimation screws is minimized by tightening all three completely, then adjusting collimation by
loosening the desired screws. This helps to prevent the secondary mirror from moving slightly during thermal and mechanical
stresses.
Differential tube expansion is controlled by waiting to start an image until temperatures are stable and/or the use of gentle heat
may help. The tube may expand a bit on one side due to differences in cooling rates. This causes collimation loss, focus loss, and
guiding errors when using a guidescopes. I have observed this anomaly in the Land Mode. Invar rods will control tube expansion,
but are not used in commercial or any known amateur SCTs (other than Schmidt cameras) to my knowledge.
Optical tube looseness should be rare in Meade SCTs because more recent models (as reported by John Downs) are cemented to
the castings. Loose primary mirrors should also be rare. Meade uses a cork gasket that allows for expansion/contraction and a
rubber O-ring (or silicone rubber) to grip and hold the mirror on the baffle tube. My observations in the Land Mode indicate very
little image shift and collimation loss result from the Meade methods of securing the primary mirror to the slider tube. Attempts
to support the primary in the thinned upper sections as often done with full thickness mirrors are likely to result in astigmatism
and should be avoided.
CONCLUSION
Good SCT collimation is always desirable and should be quite easy to maintain in most SCTs in good mechanical adjustment.
Those that find they must constantly adjust collimation may want to review a few of the items described above. Those with
critical imaging requirements may want to check collimation more frequently; however, only slight collimation adjustments should
be required.
Subject: Collimation Demostration Webpage
From: Robert Preston
Mssr. Legault has a page that provides wonderfully clear demonstrations of the effects of different amounts of miscollimation on
lunar and planetary images:
<http://perso.club-internet.fr/legault/collim.html>
Note: should open new browser window over this one.
There is essentially no difference between the images on that page that simulate perfect collimation and those that simulate
slight miscollimation (as evidenced by slightly asymmetric in-focus diffraction patterns at high mag.) So I'm not going to worry
about this non-problem, personally. But Legault says that it is his experience that a large fraction of amateurs who use reflecting
telescopes are using BADLY miscollimated scopes, and suffering severe image degradation as a consequence. That's unfortunate,
if true, since it's so simple to fix the collimation with in-and-out-of focus star testing. It's in the LX200 manual, even. It seems
very worthwhile (and extremely simple) to check the diffraction pattern at every observing session, and fix it if it's badly off.
Subject: Collimate With or Without the Diagonal? --part 1 of 7
From: Richard Shell, Date: Jan 2003
The basic problem is that manufacturers (and we) assume a diagonal mirror needs to be placed at an exact 45 degree angle for
perfect centering. And, that assumption is true. However, the proper angle is only relative to the mirror's location. If you just hold
up a diagonal and look at it, just trace the path from where the center of the eyepiece is to where the center of path of the exit
attachment tube is. It is at that point where the mirror should be placed for perfect collimation. And, if you look at where the
mirror is actually placed in the diagonal, you can easily see that it rests at a 45 degree angle, but at a significant distance below
the point of intersection. This distance varies from manufacturer to manufacturer depending upon their design and the thickness
of the mirror itself, but none of the mirrors even come close to that ideal point of intersection.
So basically, one has two choices to fix the problem: 1) leave the mirror at a 45 degree angle but move it upwards to the proper
point, or 2) change the angle of the mirror to compensate for the overshoot distance. I am sure someone who still remembers
high school trig could formally develop a formula relating this distance to angle change, but it's really not necessary.
The problem is that diagonal manufacturers do neither - and for a number of reasons: moving the mirror upwards requires
making it smaller to accommodate the original diagonal housing. In this case the field of view is reduced. The other alternative is
to redesign the housing and make it significantly larger to accommodate the same size mirror. And, since many manufacturers
have been using the same dies and molds for decades, there is not much chance of that happening.
On the other hand, placing the mirror in the same offset position but at an angle would center the image and preserve the field of
view. But here again, most diagonals were designed with mirror guides cut into the mold that allow the mirror to be simply
plopped in place with no movement during assembly. Unfortunately, the mold makers all assumed a 45 degree angle. And
probably for a good reason: diagonal mirrors themselves come in various thickness ranging from 1/4" Pyrex to 1/8" god-knowswhat. And since they change mirror suppliers at will, it would be difficult for them to commit to a certain mirror specification when
designing a mold.
In developing the Series I focuser, I tried all sorts of solutions and ran into all of the problems above. The fact of the matter is
that diagonal manufacturers do not pay this problem much attention -- mainly because in visual use no one notices that there is a
problem. And visual use is probably 95% of the diagonal market. And of the 95%, probably 95% of that are beginner scopes with
1/4 wave mirrors.
In the end, however, if I were a conscious and informed diagonal user, I would much more worry about the flatness of the
mirrors rather than mis-positioning of the mirror as far as diagonal quality is concerned. If you are to take full advantage of
excellent optics manufactured to 1/15 or 1/20 wave, it makes no sense at all to simply plop in a diagonal with a 1/4 or 1/8 wave
diagonal mirror. But unfortunately, those are usually the types of diagonals included 'free' along with an otherwise excellent
telescope.
I hope this explains diagonals a bit and explains why anyone in their right mind does not use a diagonal when imaging.
When collimating a scope, just keep in mind that (in a SCT) all one is doing is aligning the secondary mirror with the primary
mirror to have a perfect diffraction pattern. The moral is: (1) nothing one can do with a diagonal can overcome this
misalignment. Just remember the Hubble fix. It required addition of corrective optics, not just realignment. For a diagonal to
overcome initial miscollimation, its surface would need to be optically designed to reverse the damage. And the common 'flat'
surfaces of diagonals are not going to do this; (2) using a diagonal during the collimation procedure can only add to the problem,
not reduce it. In practical terms, however, it makes little difference if one collimates with or without the diagonal in place, as long
as the primary and secondary mirrors are in proper alignment; (3) there is a difference between optics being collimated and
images being on center at the exit of the final eyepiece holder. A bad diagonal (even a cheap one) will not alter the collimation of
the optics significantly, rather shift the entire collimated image off center at the exit point;
(4) to check the degree of shift, simply put an astrometric or crosshair eyepiece in the diagonal and center a star. Then, remove
the diagonal and insert the same eyepiece. Refocus, and you should be able to measure the difference in position. (Don't be
surprised if the star is not even within the field of view!)
STELLAR TECHNOLOGIES INTERNATIONAL <http://www.stellar-international.com/>
--------------------------------------------------------------Subject: Collimate With or Without the Diagonal? --part 2
From: Eugene Lanning
It would appear to me that what we can learn from this thread is
a) Diagonals do not necessarily have the mirror at 45 degrees
b) Diagonals do not have the mirror center at the centerline of the eyepiece holder and the eyepiece
c) No to diagonals are probably identical, due to manufacturing tolerances.
Therefore even a) and b) are generalizations
d) The offset in using a diagonal is on the order of a couple of arcminutes (undocumented)
e) Collminable diagonals are not commonplace
f) No information on the diagonal optical properties is readily available... what is the surface tolerance of the standard issue
Meade diagonal 1/10 wave?, 1/20 wave?, what percent of light is transmitted? Indeed, what *are* the appropriate performance
measures vs. what are just advertising ploys?
It would seem that we have treated the diagonal as a convenience item, and ignored it as an optical item. People spend a lot of
time to learn/master their eyepieces, and spend a lot of money on them too. Then we place a diagonal, of which we know little, in
front of it and go onward.
--------------------------------------------------------------Subject: Collimate With or Without the Diagonal? --part 3
From: Don Tabbutt <don
tabbutt.com>
I've followed this thread for a while, and here's my take: if the scope is not collimated on the optical axis, then it is not
collimated. That's why for critical collimation you use high power and a reticle eyepiece to make sure the star is at the center of
the optical axis, and keep recentering it every time you tweak a collimation screw.
If you were to collimate the scope through a diagonal that is several minutes off-axis, then in effect you have miscollimated. I
would never collimate any telescope through any diagonal.
--------------------------------------------------------------Subject: Collimate With or Without the Diagonal? --part 4
From: Taras Hnatyshyn
From: Charles Crapuchettes:
First, there are 4 elements, not 3: corrector, primary, secondary, eyepiece. (Diag merely folds path to eyepiece.) All
4 need to be collimated for ideal performance, but that requires rotational freedom at 3 points and translational
freedom at two points; we don't have that, and would be hard pressed to use it if we did. (It's hard enough to
explain what is seen and what to do about it for the one adjustment point we have; explaining 5 interacting
adjustments, each with 2 degrees of freedom, would be impossible.)
So, with the one adjustment you have, adjust for all the imperfections you can adjust out. If you use AltAz, the
diagonal probably doesn't need to be rotated, and collimating with the diagonal is best for visual work. Even
equatorial, for most visual work the diagonal is probably on one side, and probably collimation is best with the
diagonal where you use it most; but this is a statistical argument about how one individual uses the scope, and the
optimum answer varies. For CCD work, using the CCD to make the observations would be the most accurate, but
probably painfully slow.
But, because there's not enough freedom to adjust out all the imperfections, a perfect collimation is just not possible.
It is 5 elements. You are forgetting the detector - the human eye or a CCD device. If you are wearing glasses, that lens is
another element. When I first tried to collimate my SCT, I used my right eye without glasses to collimate, and I ended up
correcting for the astigmatism in my eye, but my photos couldn't get a sharp image... oops.
Now, when I want to collimate my LX200, I use a SAC-IV or an electronic eyepiece, to take the eye out of the equation. Then
again, I do a lot of photographing/imaging, so I do not usually use an eyepiece to collimate, except to get close after a bumpy
trip.
--------------------------------------------------------------Subject: Collimate With or Without the Diagonal? --part 5
From: Ed Stewart <stargazer
skymtn.com>
John Mahony wrote:
> The whole point of the thread (at least the recent parts) has been what to
> do if the diagonal is misaligned (usually) and (not as often) if you're going to
> be keeping the diagonal in the same orientation. Then is it better to collimate
> through the diagonal, for best image in the center of your actual field of view...
I'm still not convinced-- if you collimate straight thru to get the best possible images with the 3 elements within the OTA
(corrector, primary, & secondary) then the these elements are in their optimal positions to produce the best possible images that
they can. If you then introduce a misaligned diagonal and one that has no adjustments, then the only adjustable element is now
the secondary. If the secondary is adjusted to compensate for the diagonal's error(s), then it follows that the optimal collimation
of the OTA elements will be lost. The diagonal is just folding the light cone which if it has become miscollimated. then it seems to
me that the images will be degraded. My logic says collimate straight thru, let the diagonal fold the light cone as it will, and the
image may be off center to the eyepiece, but that is better than mis-collimating.
--------------------------------------------------------------Subject: Collimate With or Without the Diagonal? --part 6
From: Roger Hamlett <ttelmah
ntlworld.com>
This brings to mind, one aspect of collimation that hasn't been mentioned in this thread. Start with the fundamental concept
already outlined, that collimation of the SCT, involves aligning the optical axis of the secondary, with that formed by the primary,
at the point where the test is being made. Unfortunately, in an SCT, there is no guarantee that the baffle tube (along which the
primary moves to focus), is actually aligned perfectly with the primaries optical axis. Because of this, collimation will only be
exact, when the primary is at the position on the baffle tube, where the secondary adjustments are made. As you focus in/out,
and the primary is moved along the baffle tube, if it's optical axis does not align to this tube, there will effectively be a small
amount of lateral shift relative to the secondary, bringing back collimation errors.
Hence the 'best' collimation, setup, has to be to have the focal distance, where it is actually going to be used. This then is the
'downside' of trying to collimate without a diagonal. It is also why when setting a scope up for CCD imaging, using a focal
compressor, where the effective focal plane is very different from the default 'visual' position, it may be necessary to re-collimate
at this focal point for the best results.
Now collimating with a diagonal present, simply implies that the centre of the eyepieces FOV, will almost certainly not align with
the centre of the baffle tube. As has been pointed out above, there is no guarantee that this is actually the centre of the optical
axis of the scope anyway!. However as Doc G has pointed out, this does not prevent collimation for the best diffraction pattern
(the pattern still shows the same directional offsets, as it moves away from the centre of the eyepieces FOV, which still allows
good collimation to be achieved).
Hence, I would say that the 'best' configuration, would be to collimate as you intend to use the scope, and not to worry about any
error in the diagonal. Separately, it is (of course), nice to have a diagonal that produces an exact 90 degree reflection,
perpendicular to it's mounting face (which then should imply the FOV will remain on the same part of the sky as it is rotated), but
given the small angles concerned, achieving this is not easy.
The problem I am talking about comes from internal mechanical errors. This is where the baffle tube (the actual tube on which
the primary slides for focus), is not aligned to the optical axis of the primary. The problem here is that if you place the primary at
(say) 300mm spacing from the secondary, and tilt the secondary to get good collimation, then refocus the scope by moving the
mirror forward to give an increase in the back focus distance (a 200mm increase in back focus, will involve moving the mirror
forward about 40mm), then if the internal tube is angled by 1 degree (say) to the axis between the primary and the secondary,
the main mirror will effectively move sideways by 0.69mm. This will completely destroy collimation. Hence if you collimate at the
rear port, then add a diagonal, and have to refocus, you will once again have lost collimation.
In the context involved, there is really no such thing as 'collimation' of a diagonal. Unfortunately, some posters are talking about
the alignment of diagonals, so that they produce a centered refection, as 'collimation.' The word collimation, implies aligning the
optical axes of elements, so that they are coincident with the axis of the incoming light path. A plane mirror, doesn't actually
have an optical axis. If an SCT, is collimated (primary, secondary, and corrector are all aligned correctly), you can stick a
diagonal in and bend the light to any angle you want, with no effect at all on this collimation. However if in doing so, you change
the focus required, miscollimation may well result.
The sole possible effect of the misalignment of the diagonal (from the optimal 45 degrees, with it's surface intersecting the
junction of two lines, one through the centre of the eyepiece hole, and the other through the centre of the incoming hole), is to
move the viewpoint away from the optical axis. As has already been pointed out, the same unavoidable mechanical errors imply
that this axis is already not in the centre of the baffle tube anyway!...
If there is an optical 'doubt' about the diagonal (producing astigmatism or some other similar distortion), the _best_ way to
collimate, would be to add an extension tube to the rear port of the scope, so that the light path is the same length as it would be
with the diagonal present, and collimate like this.
---------------------------------------------------------------Subject: Collimate With or Without the Diagonal? --part 7 of 7
From: John Mahony <jmmahony
hotmail.com>
Let's assume a best-case scenario as far as OTA is concerned- the axes of the corrector, primary, secondary, baffle tube, and rear
opening are all coincident. If you put an EP in the center of the rear opening you'll get perfect diffraction rings around a star at
the center of the field. If you move the EP off center, the collimation pattern deteriorates. But it has been my experience that you
can then adjust the tilt of the secondary and improve the pattern considerably. Not quite perfect as before, but to just about
anyone except perhaps a professional optician, it appears to be a good collimation pattern. Stars in the center of the EP field of
view have even, concentric diffraction rings, and the view at focus improves considerably.
A poorly made diagonal can produce three errors1) The image is offset relative to what's seen through the rear opening.
2) The light cone hits the EP field lens at an angle.
3) Wavefront distortion due to a poorly figured flat.
The last two we'll have to live with if we want to use that diagonal that evening. So we're left with the off-axis image, which, just
as before, we can improve by adjusting the secondary. And you can't argue with an improved view, if that's what you want. So I
collimate through the diagonal if I will be using that diagonal (in a situation where I won't be changing its orientation, which
would give a offset relative to the center of the rear opening).
Doc said there's only one correct position for the secondary, but I suppose he was referring to just the three optical elements of
the OTA. Another poster said that the thought of anyone collimating through a cheap diagonal makes him cringe, but there are
situations where it makes sense. When I go back to imaging or astrometry, I re-collimate straight through. I see no reason to
cringe.
Subject: Decreasing OTA Cool Down Times --part 1 of 6
From: Anthony Kroes <akroes
venomtech.com>
Not sure about checking for optical quality, I just look through mine!! I've never 'star tested' a scope so it could be that or a
combination of things. That said, I think an hour is NOT be sufficient cool-down time for a 10". Folks have posted here previously
about times of up to 2-3 hours to ensure full cool-down depending on the size of the scope (larger-longer, all other things being
equal).
1-1/2 hours seems about right for my 8", and the 12" can take 2 hours or more. Of course that all depends on how much warmer
the scope was from outdoor ambient when you brought it outside or opened your observatory. Your observatory (if you have one)
also makes a difference, especially on a dome, because there is less sky visible to help draw down the temp of the scope - thus
longer stabilization times, roll-off roof=faster cool-down. How fast the temp outside is dropping (or rising) as the night progresses
can also affect the cool-down times, particularly if it is a fast drop.
I not hip to the nuances of thermodynamics, so please excuse my numbers - I know there are other factors here...but simply, for
example, if your scope cools off 25F degrees/hour and it was 60F degrees warmer than outside to begin with, like bringing a
scope from a 70F degree house to a 10F degree Wisconsin winter night, you are looking at a 2+ hour cool-down. If the temp
outside is also dropping by 3 degrees/hour it would stretch out to over 3 hours. That's why I leave the scope in the obs - it is
usually close enough to ambient to do serious observing in an hour or less. Editor's note: to decrease these times, read on...
-------------------------------------------------------------Subject: Decreasing OTA Cool Down Times --part 2
From: Scott Oates <SOates4616
aol.com> Date: Jan 2003
Doc G suggested using a large fan blowing air across the optical tube to assist cooling. I have been using his method ever since. I
find the cool down time for an 8" OTA to be 45 min and a 9.25 right at 1 hour. All it cost was $10 at Wal-Mart. It does not require
pumping dust into the OTA and it works! I use a 14" oscillating fan blowing over the OTA. No internal fan. I have a small
observatory and I leave all my equipment (camera, etc.) attached. Just the fan moving the air around works wonders.
-------------------------------------------------------------Subject: Decreasing OTA Cool Down Times --part 3
From: Kevin Wigell <kwemail
twcny.rr.com>
Regarding cooldown times, for some time I've been toying with the idea of putting an electronic temperature sensor inside the
OTA to allow for reading the actual interior temperature. This could be done with an inexpensive, wired, indoor/outdoor type
thermometer (such as sold by Radio Shack and others), or (preferably) by putting a wireless temperature sensor inside that
sends a signal to a remote unit. With the wireless unit, I'm picturing sticking the transmitter inside the OTA with velcro or sticky
tape so it wouldn't be loose inside the OTA.
Does anyone have any idea on whether there would be room for such a transmitter inside the OTA, say behind the mirror? The
transmitters are usually a little bit smaller than a deck of playing cards. And if there is room, is there an easy way to get it in
there? Also, would the weak signal from the transmitter would be able to penetrate the OTA?
-------------------------------------------------------------Subject: Decreasing OTA Cool Down Times --part 4
From: Bill Arnett <bill
nineplanets.org>
Kevin Wigell wrote:
> Regarding cooldown times, for some time I've been toying with the idea of
> putting an electronic temperature sensor inside the OTA
I did that using one of the Oregon Scientific units that has the sensor on the end of a short wire which is intended for immersion
in water. It was just the right size to fit thru the shipping bolt hole.
-------------------------------------------------------------Subject: Decreasing OTA Cool Down Times --part 5
From: Tom Mote <pytom
texas.net>
If I'm not mistaken, Robert Haler, at Lymax, <http://www.lymax.com>, sells an "SCT Cooler" device that blows filtered air
through the "eyepiece hole" of your catadioptric telescope and brings its interior temperature to essentially the ambient outside
air temperature in a relatively short period of time.
-------------------------------------------------------------Subject: Decreasing OTA Cool Down Times --part 6 of 6
From: Anthony Kroes <akroes
venomtech.com>
If you are the handy type, there are plans on the internet <http://www.starcrwzr.com/cooler.htm> for making a similar "SCT
Cooler" device yourself out of PVC pipe fittings and a computer fan.
Subject: Ronchi Grating Used to Reposition Secondary Rotational Position
From: Dennis Persyk, Date: Jan 2003
>
>
>
>
>
>
>
From: Mark C
I noticed the "Easy Tester" for sale on the ScopeStuff site. It is a Ronchi
grating mounted in a standard 1"1/4 eyepiece mount.
<http://www.scopestuff.com/ss_jspe.htm> Would this be useful
in trying to determine the optimal rotational position of the secondary
and or corrector. Some LX200 users have had secondary come loose, or
the corrector and have found no indexing marks to help in re-orientation.
My mentor and neighbor, Jack Schmidling <http://schmidling.netfirms.com/ez-testr.htm> is the maker of the EasyTester. He
said that one could optimize rotational orientation of the corrector plate with his device.
Subject: LX200 Secondary Mirror Rotating?
From: John Rostoni, Date: Aug 2001
I had a similar problem of the secondary mirror rotating out of position several years ago with my 10". Here's what I learned...
If you call Meade about it, they want you to return the scope for realignment (which is not the same as collimation). They really
didn't want to talk about either what they were going to do to get the secondary back in position, or what I could do to do the
same thing. I figured I had turned the secondary about 15 degrees at the most, and could most likely get it back close to where it
started.
A talked to a few more people (John Piper might have been one of them), and finally got a single detail about the process - the
rotational position of the secondary is adjusted within a 5 degree band about an "optimal" point. I have no idea what test is used,
or what the tech is looking for while rotating the secondary - that is, I have no concrete information on what the effect of rotating
the secondary is on the image quality.
With this information in hand, I decided to do some "qualitative tests". I removed the corrector/secondary (yes, this is really the
only good way to retighten the loose secondary housing), and removed the secondary baffle, releasing the secondary from the
corrector. A quick inspection showed several things - 1)the hole in the corrector is significantly larger than the secondary housing,
making it difficult to recenter the assembly, and 2) there were no alignment marks anywhere on the corrector or secondary
housing the marked the "correct" position. I did find an abrasion on the edge of the corrector that seemed to be similar to an
indentation on the rubber gasket of the secondary. I marked both of these points on the outside of the corrector and secondary
housing (so I could use them when the scope was reassembled. I added a few shims to keep the secondary centered in the
corrector, and put everything back together.
I spent several nights going through a collimate/check-the-image/turn-the-secondary process. Each time I recollimated, I
checked for focus patterns on either side of focus, in focus star images throughout the field, and for some reason, color artifacts.
That was about all I could think of that would be apparent under viewing conditions.
The final result was that unless the secondary was off by at least 90 degrees, no significant image changes were apparent. Minor
changes, yes...but none that would say, "wow...that's perfect!" or "Geeze...I broke it!" I also consider the proper centering of the
secondary to be more critical that minor changes in the rotation position (just a guess, really). I finally got the alignment back
where I was getting the best images.
Well, that's my experience. I'm not assuming that EVERY scope would have the same sensitivity to these adjustments. I'm sure
there are quite a few on both sides of my single sample. After all, a sample of one is not enough to make generalizations.
Subject: Secondary Mirror Description/Optical Alignment
From: Jim McMillan, Date: Feb 2002
I'd like to respond to your query regarding the secondary mirror by sharing a bit of my experience with it. Like you, I was
curious. So, after using my scope for a couple of years (and out of warranty), I fiddled with collimation. I think I got it fairly
close, but the focus just didn't want to "snap" into place. I bought the Kendrick SCT collimation laser. What I determined by it
was that the optical and mechanical alignment of the OTA wasn't exactly the same.
I also had heard that the secondary hole in the corrector was a bit bigger than the secondary holder. I reasoned that I could
move it to try to get better optical/mechanical alignment. So, off came the corrector. To my surprise, I discovered that the
secondary mirror was not centered in the holder. Apart it came. The secondary mirror is actually glued to an aluminum disk into
which the collimation screws screw. At the center of the aluminum disk is a hole which the secondary pivots on. Still thinking I
could improve my optics by getting everything centered, I pried the mirror from the aluminum disk, centered, and reglued it. I
used a couple of layers of black electrician's tape around the secondary holder so that it fit snugly - and centered - into the
corrector.
I put everything back together and....the astigmatism was so bad, my stars were now diamond-shaped. I could barely make out
medium-sized craters on the moon. The next day, I called Meade and (sheepishly) told them what I did. Ollie explained to me
that part of the process of setting the optics for each scope when it's manufactured is to align them such that they compensate
for the inevitable mechanical misalignment of the OTA. In other words, the fact that my secondary was not centered - both in the
corrector and in the holder - was on purpose. Ollie said I'd have to send my scope back and they'd "repair" it for the standard
$500 fee - or install new optics for $550.
After many, many hours of trial and error, I was able to restore my optics back to where they were - and maybe even a bit better
because I had so much practice at collimation. But, I think it was more a matter of luck than skill.
So, my suggestion regarding fiddling with the secondary is to be very careful what you do - and be very sure to mark it such that
you can return it to its original position.
Subject: Centering the SCT Secondary
From: Richard Jordan, Date: Feb 2002
Like Jim's scope, my old Meade 10" SCT (2120) just didn't seem to be up to par. After a careful collimation, higher power (180X)
terrestrial views were "muddy", 4-6 mag stars showed a bit of coma and planetary views were unsatisfying, even on nights of
good seeing. Collimation changed depending whether the scope was inside or outside focus.
Suspecting a tilted primary mirror and/or a decentred secondary mirror, I used a machinist's caliper to check whether the plastic
secondary holder was centred in the casting holding the corrector. I found that it was only slightly off-centre, so I shimmed it to
the centre of the casting, recollimated and tested. There was no improvement in the image.
I made a sight tube out of a 35 mm film canister and inserted it in a 1-1/4" visual back and checked the centreing of the
secondary baffle, secondary, and the slider tube. The assembly was significantly off-centre. I re-shimmed the corrector to
centralize the circles as seen through the sight tube and recollimated. Still no joy.
Next, I rechecked the position of the secondary holder in the corrector holder casting and found that on one axis the secondary
holder was off-centre by .5 mm. I re-shimmed the corrector so that the caliper made the same sliding fit between the secondary
holder and the casting. After collimation, this time success! On the other axis, the secondary holder is 2.5 mm off-centre relative
to the casting!
For the first time and after 7 years of frequent use, I saw what is passing for the GRS on Jupiter these days and the scope split
Zeta Orionis. Contrast and sharpness of focus was significantly improved. Zeta Orionis had always been just a burning blob. My
terrestrial test object (the print on a distant hydro transformer label) shows a noticeable improvement. Collimation is the same on
both sides of focus.
In this instance a .5 mm centreing error caused a very noticeable image deterioration. There was a most definite element of luck
involved in this procedure, but it was a most worthwhile effort.
Subject: Tri-Lobed Stars Fixed?
From: Gene Chimahusky <lynol1000
yahoo.com> Date: Mar 2003
Civil twilight brought clear and extremely steady skies. The last 18 months my scope, under very high power, has exhibited trilobed stars. I had queried a possible cause and the best that could be offered was pinched optics, as in the secondary adjustment
screws too tight. Over that time I had tried multiple times adjustments with the screws and was never able to resolve the issue.
The optics over this time have never seemed extremely crisp, not snapping into focus, so I also went looking for possible
solutions to that.
I decided to play with the rotation of the corrector plate. I removed the bezel and clearly marked and matched were the Meade
alignment marks. I started with 5 degree changes both CW and CCW. To make a long story short I ended up with 10 degrees
CCW and it seems now my lobes are gone, I have a circular airy disk with a well defined circular first diffraction ring.
I replaced the bezel and tightened everything down, gave final tweaks to the collimation screws and everything stayed put, much
cleaner, crisper, and now things do seem to snap much easier into focus.
These adjustments were all made at 600x and 800x, 10" f/10 with 2X barlow , 6.4 and 9mm eyepieces done straight through.
Note I could bring the lobes back and/or loose crispness with certain rotations of the corrector (obviously for the crispness) ,
including at the original Meade matched marks. The roughly 5 degree rotation changes brought noticeable differences at 800X
and steady seeing.
Maybe the corrector versus the mating surfaces are not 'perfect' and the corrector warps slightly?
Subject: LX200 Corrector Plate Glass?
From: Bill Keicher <wekeicher
comcast.net> Date: Apr 2004
----- Original Message ----From: Michael Blaber
> I believe the 12" LX200 classic corrector plate was made from BK7
> glass (also the 16", but not the 10" and smaller), while all the new LX
> GPS scopes appear to have "water white glass" corrector plates. Does
> Meade still use BK7 for the 16" GPS? How does the BK7 differ from the
> "water white" glass?
The 2002 and 2003-2004 Meade Catalogs specify BK7 glass (borosilicate glass) used in the corrector plate of the 7", (Maksutov
Cassegrain) LX200 GPS telescope. Meade specifies "clear float glass" for the corrector plate used in all of the Schmidt Cassegrain
LX200 GPS telescopes. BK7 glass is an optical grade glass available from Schott Glass and others. Achromatic doublet lenses are
often fabricated with BK7 as well as a flint glass. BK7 has an optical index of refraction of 1.509 at 582 nm, has a high optical
transmission, can be selected nearly free of bubbles and inclusions and has an index of refraction uniformity of about 1 part per
million. BK7 glass is composed of 66% silicon dioxide, 12.4% boron oxide, 8% sodium oxide, 12% potassium oxide, and ~1.6%
other chemical components.
Unfortunately, "clear float glass" may imply a commercial grade of glass used in windows! Pilkington describes typical clear float
glass as having an index of refraction of 1.523 at 582 nm and being composed of 72.6% silicon dioxide, 13.9% sodium oxide,
8.4% calcium oxide, 3.9% magnesium oxide, 1.1% aluminum oxide, 0.6% potassium oxide, 0.2% sulfur trioxide, 0.11% iron
oxide (Fe2O3) ( as known as soda lime silica float glass). Pilkington "Optiwhite" float glass is a low iron oxide float glass with a
visible light transmission of 92%, reflection of 8% (uncoated) in a 1/8" thick sheet. "Optiglass virtually eliminates the green cast
inherent in standard clear float glass" (implying "water white" glass). The polished edges of "Optiglass" float are noticeably
colorless compared to standard float glass. The glass can be selected to be nearly free of inclusions. This glass is probably
cheaper than optical grade BK7.
The mirrors are made of Pyrex glass (optical transmission is obviously irrelevant here).
My guess is that Meade is using the equivalent of Pilkington Optiglass in the Schmidt corrector plate. The corrector plate is thin
and this is probably a good choice in this application. The Maksutov Cassegrain telescope has a thicker corrector with significant
optical power and requires an optical grade glass.
GoTo Collimation Page 2
MAPUG is hosted by
Star Testing & Optical Quality
Be sure to see the discussion of cool down times in the Collimation, page 1, topic
Artificial Star for Testing --7 parts
Spherical Aberration 101
Optical Quality Testing: Ronchi Lines?
10" f/10 LX200 Mirror Measurements
Calculating Focal Length for a SCT --4 parts
Optical Defects Simulation Software
Subject: Artificial Star for Testing --part 1 of 7
From: Tom Whicker <burt
mercury.interpath.com>
To those who continue to have optical problems, and in fact to all Meade owners who are curious about how good their optics are,
I strongly urge you to do an ARTIFICIAL STAR TEST! Burt Whicker and I had similar problems with his new 10" but could never
really get a definitive look at a star test because the atmosphere was always a problem. You can't get a clean diffraction pattern
so you always blame it on poor seeing.....even on the best night, the pattern jumps all around. It could never be photographed
for later reference.
So we made an artificial star and in 5 minutes had all the answers we needed! Now, there are published methods in Sky and Tel.
and other places that can get complicated.....about making the pinhole small enough, about locating it many hundreds of feet
away so as to not induce spherical aberration into the test. But believe me when I say that a simple pinhole in a piece of tinfoil as
close as 40 feet will show a good star test with rings and an Airy disk. And it is *Rock Stable* if you set it up inside your house or
garage. It is no problem to photograph with an eyepiece projection set-up. It is easy to video-tape with one of the little mini-cam
video cards. Then you have a permanent record of your scope's condition. When Meade sends the scope back to you after
repairs, you can compare A to B.
Here's how to do it: Get some aluminum foil. Cut several pieces about 4" square or so. Stack the pieces and flatten them nicely
together. Place on a flat surface. Take a sewing needle and put a hole through the stack, such that the needle barely pierces the
bottom foil. You now have a range of hole sizes. Select a pinhole that looks good....you can start with the larger ones and as you
get the process under control, work to the smaller (and dimmer and harder to find with your scope....) as you progress.
Take a 12" square piece of cardboard and put a 3" hole in the middle. Tape your foil pinhole onto the cardboard. Tape the
cardboard in front of a 75 watt utility lamp with frosted bulb. Put the lamp at the end of a darkened hall, etc. We only had about
36' for our first set-up and it worked fine.
Use a low power eyepiece to get it centered and then work up to your highest power plus barlow if you have it. You should easily
see the intra and extra focal diffraction rings and a good Airy disk at focus. If you get no patterns, go to your next smaller pin
hole, etc.
Note: Finding the pin-hole with your scope can be surprisingly difficult. It will be about a Mag. 7 star. It helps to paint or draw a
big cross hair guide pattern on the tin-foil. Then you can leave a little ambient room light on to allow you to find the cross hair
pattern and follow it to the pin hole.
Now of course at this close range you are inducing a good bit of spherical aberration into the test. Not to worry. Once you have
the technique down, you can take the rig outside and set it up with 300 or 400 feet or more range. Even better, find a warehouse
or school gym to set up in.
But even at close range, the test will clearly show the kind of astigmatic problems and problems of irregular surface figure that
are common in SCTs. Our particular scope produces a Mercedes Hood Ornament at best focus. It is a non-symmetrical three
pointed star with several other smaller lobes that add up to a contorted pentagon pattern. It is about 2.5 arc seconds in size at
best focus. On either side of the "focus" it changes to rings that have large lumps where the points of the stars were.
With a stable indoor star, you have all the time and repeatability you need to methodically rotate the corrector plate, or the
secondary, or tweek the collimation, to try and isolate your problem. For us, nothing helped, so likely a poor surface on the
primary or corrector.
I really hope that many of the Mapug will do this test! If you go back through the archives, you will see again and again people
reporting star tests that look like "wheels with spokes", "flairs", "dandelions", "flower petals", "Mercedes Hood Ornaments",
"Chrysler Hood Ornaments"! But every time, the Meade owner ends up saying...."Well, the seeing was not too good, so maybe
that was the problem..."
Some Final Suggestions: If you can, place a second pin hole at a distance of .1" from your first. This will give you a reference
scale that will allow you actually calculate the size of your aberration in terms of Arc Seconds. It also means that if you take a
photograph or a CCD image of the star test, then you will have a scale mark so that later tests can be accurately compared.
A good way to make two pinholes at .1" spacing is to get a piece of pre-punched printed circuit board from Radio Shack. The
holes are in a .1" grid. Also, try set up a second scope with diffraction limited optics as a side-by-side comparison. We used my
old Criterion 6" Newtonian. It will immediately show you what you are supposed to be seeing 8^)
Update: Just a quick note on artificial stars. It is a bit of misconception that one needs a really tiny pinhole....especially if you are
planning only to use the star for collimation (and not for the more demanding requirements of testing for spherical aberration,
etc). A typical pin-prick into aluminum foil that gives you a 100micron (0.1mm) hole is fine for collimation use. In fact, smaller
holes become very dim and are hard to use in daylight. Also, you can use the artificial star at a fairly close range (ie 40 feet) to
do the collimation....since you are just interested in the centering of the optical axis....and not worried about how your diffraction
pattern may or may not show spherical aberration from the unusual closeness of the star.
To really test your scope, you need to move the artificial star at least several hundred feet away. If you want it to be smaller than
your "Airy" disk, use a rule of thumb that 1 arc second is equivalent to about a 1 million to 1 ratio of star diameter to star
distance.
So if you want a 0.5 arc second test star.....put your 100 micron pinhole at about 700 feet distance. Such a test star is the best
(and in the real world....the only practical) way to get a rock-stable view of your diffraction pattern. The sky will never be stable
enough....even on the best night...to allow you to photograph (or video...even better) your diffraction pattern as a function of
focal travel. But with the artificial star, you can get a repeatable photo-record of your performance to compare with later scope
tunings .....or after it returns from a Mead service trip!
--------------------------------------------------------------------Subject: Artificial Star for Testing --part 2
From: Ron Hendrickson <Ron_Hendrickson
vul.com>
Jeff--I also have a 10" LX200 and I have experienced some of the same frustration you seem to be having. I am a relative novice
in astronomy (3-4 years) and it has always seemed to me that much of the advice and info from books is contradictory and
confusing when it comes to checking optics.
However, my advice (use at your own risk!) is:
1. Use a good quality Plossl eyepiece that will give you a least 300 power for collimating and star testing.
2. Don't use a Barlow for star testing.
3. The size of our scope does make atmospheric turbulence a problem. The books say that you should get a good in-focus star
image looking at a mag. 2.0 star. With a 10" scope, this is too bright in my opinion for almost all sky conditions. I think a mag.
4.0 or 5.0 star will give you a much better chance of seeing a good Airy disk with diffraction rings. The double double in Lyra near
Vega is a real good choice right now, as it is high in the sky and about the right magnitude. But even so, I have only seen a good
Airy disk and rings (partial) just once when the skies were very steady. I talked to a guy who has a 12" LX200 scope who is very
experienced and he says the seeing only permits a good Airy disk about 2 or 3 times a year. (We live in San Antonio, TX)
4. Purchase a cheap (about $8) Ronchi plastic tester and check your scope. They come with directions and made me feel much
more confident about my scope. The test showed good straight lines, just like they are supposed to be.
5. If possible, compare your planetary views with those from a known telescope of good quality. This was difficult for me until I
met a friend who has a 100mm Takahashi refractor. Its star images were beautiful mostly because of its excellent optics, but also
because of its relatively small aperture (compared to your SCT). But when observing Mars side by side a few months ago, my
LX200 showed more definition than his excellent refractor. He commented that he was impressed with the Meade optics, even
though its star images were not that good that night.
6. Wait at least two or three hours for your tube currents to die down before collimating or star testing. The books say one hour,
but that isn't long enough for me. Also, most importantly, make sure the ground you are set up on isn't giving out heat waves. I
found that any type of asphalt, concrete, hard surface, etc. is going to mess up your view for hours. You will swear that it is your
scope until one night you set up on grass and see the difference.
7. I guess big apertures can be a curse, but its still worth it in my opinion.
-----------------------------------------------------------------Subject: Artificial Star for Testing --part 3
From: Frank Loch <floch
early.com>
If you have access to a CCD imaging camera, you can use this to great advantage for collimating.
The procedure is to image your collimation star with your CCD camera on to the monitor. Center the collimation star in the image
box To do this, I take a fine tip magic marker and mark the center of the image box with a small cross hail mark .
With the collimation star centered, defocus to make the star image almost fill the image box. Now the image is big and stable and
you can easily see the rings and the airy disk and the "out of collimation" positions.
Now tweak the collimation screws and re - image. Note the alignment changes. Repeat this, enough times until you have the airy
disk centered. If the star moves off your center marks keep recentering it until the scope is collimated and the star and airy disk
are both centered.
This has worked nicely for me and improved my images a lot. You may want to scrub off the marker cross hairs at this point.
Mine are so small, I leave them in place permanently as I then also use them for a center reference for all my imaging work, and
they don't bother me in my other applications.
---------------------------------------------------------Subject: Artificial Star for Testing --part 4
From: Chris Vedeler <cvedeler
ix.netcom.com>
I also have a 10" LX200. I had it for a year living in Spokane before I ever saw a defraction ring around a star. Seeing makes all
the difference in the world when star testing. Some places don't get good enough seeing to star test but a few nights a year. I
live in Tucson Arizona now, and frequently see very nice concentric rings in my out of focus star images. When I lived in Spokane
the image would dance and shake too much to ever see them. I thought it was my optics because each time I would try and star
test, I would get the same result.
Another thing that might be contributing to your poor star test performance is using a Barlow and a wide angle eyepiece. That is
a lot of glass the light must pass through. Keep star testing as simple as possible. Sometimes I don't even use a diagonal. Simple
eyepieces like a good Plossl work best. 362X is OK with very good seeing, but if the image wavers like you said, it is probably to
much for the seeing. Vega and Arcturus are pretty bright to do star testing especially with poor seeing. Polaris is about the right
brightness, but it is a double star which can make the out of focus image look strange.
I went though a stage of wondering about the optical quality of my scope too. I've relaxed a lot though. My scope does about as
well as the seeing most of the time. There have been a few nights where it might have helped to have better optics, but I can
count those on one hand in 2 years. I wanted a large refractor until I looked through one (7" Meade APO) side by side with my
scope.
----------------------------------------------------------Subject: Artificial Star for Testing --part 5
From: Gary McKenzie <aquarius
netspace.net.au>
Jeff, All of the conditions you describe could be caused by turbulence, however bear the following in mind:
1. Before star testing make *absolutely* sure that your scope is as perfectly collimated as possible. You do not *need* to use a
collimation tool with an SCT, although you can use either a Cheshire eyepiece, or an autocollimator eyepiece to come close, the
final tweak will *always* have to be done on a star image.
2. There are very, very few nights - and locations - where you can profitably use 360x and not see horrible images. For most
times 200x is a reasonable limit, and 250x or so on a fairly good night. 3. Star testing should be performed without a diagonal
mirror or prism in place, since these will *possibly* have some effect on the image.
4. A *bad* star test can be the result of a dud eyepiece, so before believing that your scope is bad, check it out with several
eyepiece/Barlow combinations.
5. Most experienced testers would not have a dew removal system since it *can* cause some deterioration in images, or cause
thermal effects that mimic bad seeing, particularly if the temperature differential between the scope/ ambient air temp, is large. i.
e. if the heater is turned up too much.
6. Get someone who is experienced to star test the scope for you, then get someone else to check it out again, then maybe 3 or
4 others, average the opinions and you will probable be *somewhat* close to a true idea of your scopes performance.
An easier method is to make or buy a Ronchi testing eyepiece--see <http://schmidling.netfirms.com/ez-testr.htm>
If you don't know how to use one, e-mail me and I'll try to help, but basically if you see straight lines when the Ronchi is used in
your scope alone, then your scope is *possibly* OK, if there is ANY curvature of the lines then the scope is BAD and get onto
Meade straight away. To confirm that your scope is good, insert the Ronchi eyepiece in a GOOD Barlow and view the lines, if they
are still straight then you have a very nice scope even if the star test is not perfect. The star test is so sensitive that any scope
will fail it (well at least the 60 or so that I've looked through will)
-----------------------------------------------------------------Subject: Artificial Star for Collimation --part 6
From: Gary McKenzie <aquarius
netspace.net.au>
I was just browsing the Topical Archives and found that a simple method of collimation that I use was not mentioned so I thought
it might be helpful. I got sick of trying to do it at night, and could never make a pinhole in aluminum that seemed to work so I do
it the following way:
Get a piece of wood, paint it flat black, glue a 1/4 inch ball bearing to it. Hang it from tree, or fence etc. position your scope 1020 meters away such that the sun is behind you as you look at the ball bearing. The ball bearing will have a nice glint on it that
makes a perfect artificial star. Focus on it and collimate. The star doesn't move and you don't get a crick in the neck, you don't
have to worry about seeing (provided it isn't too windy and you are on a grass surface.) Note that you can't star test your scope
this way as the close range induces spherical aberration, but this doesn't affect the collimation process.
-----------------------------------------------------------------Subject: Artificial Star for Collimation --part 7 of 7
From: Ric Ecker, <rlecker
juno.com>
I use a projector bulb which is very similar to an automotive bulb, mine operates at 6 volts. This is placed in a aluminum housing,
the bulb is 4" away form the eyepiece. The eyepiece is an old ortho 6mm which acts as a star projector. The unit can be placed at
least one mile from your scope and makes a fine airy disk. Not really much to it, very simple. I use 6vdc nicads to power it. P.S.
make sure the eyepiece aligns with the filament of the lamp.
Subject: Spherical Aberration 101
From: Roger Hamlett <ttelmah
ntlworld.com> Date: Dec 2002
----- Original Message ----> I am aware that many SCTs will show some spherical aberration on the
> inside/outside focus star test. My question is how much is typical for
> the LX200? I am familiar with Suiter's ratio test and am wondering if
> his limit of 3.0 is applicable to the LX200? Is a factory rematch of
> the corrector to mirror feasible if a scope is outside that limit? I am
> happy with the focused image I get in my LX200 for visual viewing but
> wonder how much better it might, or should, be. And yes, I do my star
> tests with a well equilibrated and collimated scope under rare steady
> skies; and no, I have not removed the corrector but did buy the scope used.
>
> Is splitting Zeta Ori a good test of a properly aligned and corrected
> LX200 10"/10? Other suggestions?
The SA shown on an SCT, varies according to the spacing of the primary/secondary mirrors. Since this changes to achieve focus,
this gap is actually controlled by the position of your eyepiece/camera. There will be just one point with corrected SA. The
location required to achieve this, is rarely where the eyepiece normally sits!. Hence you can adjust SA, by changing the length of
your optical train, and refocussing. If you experiment, with an eyepiece very close to the scope, and then add extension tubes,
you can generate a figure for the point where your scope is corrected. With this figure, you can try to lay out the optics when
working to keep close to this length, and minimize the problem.
An SCT can only be properly corrected at one point, so even if the entire optical train was refigured to suit your diagonal/
eyepiece, as soon as you changed anything, and had to refocus, the aberration would reappear. As an example, my own LX200,
had the 'optimum' point, slightly further out than the spacing produced by a 1.25" diagonal, but slightly closer than the spacing
with a 2" diagonal. However in both cases, the error was tiny. However when the focus distance is really pushed by using a
Crayford focuser, F/3.3 compressor, filter wheel, and camera, despite the 'field flattening' properties of the compressor, the
aberration became unacceptable (to me). Running without the Crayford, shortened the optics enough for reasonable results.
Subject: Optical Quality Testing: Ronchi Lines?
From: Bill Dougherty <bd5572
yahoo.com> Date: Jan 2003
Spherical aberration only measures the scope performance at one point in the image plane, exactly in the center which
corresponds to the optical axis of the instrument. If you are interested in splitting close double stars or viewing planets, it (along
with on-axis chromatic aberration) becomes the primary consideration because you are only interested in the center of the field
of view. However, even if the scope is perfectly corrected for spherical aberration, it can still suffer from off-axis aberrations -coma, astigmatism, lateral color and field curvature to name the usual suspects.
For purely visual use, field curvature can be somewhat compensated for by the accommodation of the eye. You automatically
change the focus of your eye lens to adjust to the different focal planes of the center and edges of the field of view. Since all
SCTs have some degree of field curvature anyway, the designer will often accept a fair amount of field curvature and concentrate
on reducing coma and astigmatism instead.
For photographic use, a flat field becomes very important. CCD sensors are flat, and bending film to match the radius of the field
is not practical as a rule. In actual practice, the available adapter tubes and external focuser used will place the camera sensor at
a particular point along the optic axis. You will then use the coarse focus knob to move the main mirror to achieve approximate
focus at this point. Fine tuning of the focus will be done with the MicroFocuser or other external focuser, or with fine movements
of the coarse knob, for example, using the RoboFocus system.
Using focal reducers or expanders will generally require shifting the coarse focus point considerably as well. The point to bear in
mind is that you will rarely be adjusting the primary focus of the scope to exactly match the optimum or 'design' point. A secure
and stable attachment of the camera, and the ability to achieve and maintain an accurate focus at that point are more important.
By all means continue to test and use your scope in various ways. You will learn a lot and may even find a problem that requires
attention. Just bear in mind that the SCT is a complex system, and tests such as the Ronchi require a good deal of care and
experience if you need conclusive results. Actual star testing may in fact be more accurate for a beginner, since there are fewer
variables to manage. Moreover, as others have pointed out, that is what really matters when the light hits the electronic,
chemical or biological sensor.
The "Easy Tester" is listed on the ScopeStuff site. It is a Ronchi grating mounted in a standard 1"1/4 eyepiece mount.
<http://www.scopestuff.com/ss_jspe.htm>
Subject: 10" f/10 LX200 Classic Mirror Measurements
From: Matt Considine <matt
considine.net> Date: Apr 2001
I've dug up my notes that I took when I had the OTA in the cellar for flocking. At that point I ran a quick Ronchi test to look at
the primary, measure the ROC and take other measurements on the corrector/secondary cell. The Ronchi lines were straight to
the edge.
Given the distances involved, I had to use a steel tape measure and some measured dowels to try to get a decent measurement
of the distance between the grating and the mirror surface without risking a scratch to the mirror itself. When all was said and
done, I ended up measuring the distance from the mirror surface *just outside the baffle tube ring* to the Ronchi screen plane,
as well as from the edge of the mirror to the Ronchi screen plane. (I measured to the Ronchi plane so as to keep everything
linear).
I got two measurements of the ROC for the primary : 39.89302" and 39.91338" I'll take the average of the two and use 39.90".
That would get us an f/2 spherical primary.
However, taking into account the central obstruction (= 3 19/32" diameter of secondary baffle cone) gets you an effective f ratio
of 2.72.
For the secondary, I measured the distance from the center of the surface to the top of it's baffle cone (straight up), as well as
the distance from the edge to the top of the baffle cone (*along* the cone). Converting this latter measurement to "straight
up" (the cone seems to flare out by about 31/32"), taking the difference between as the sagitta and solving for R in sagitta = R sqrt(R*R - d*d)
(where d = the diameter of the secondary = 2.625) yields a ROC of 22.06 or an f ratio of 4.20.
Multiplying the two f-ratios together to get the approximate t-ratio for the systems yields 11.4 - which, if I recall, meshes well
with what has been measured by people from images. Of course, this does not take into account any power imparted by the
corrector plate, which I think is 1/2" thick. (For some bizarre reason I never wrote that down...)
>From this info, combined with a spacing measurement when the scope is at focus, one could solve for the ideal corrector profile,
enter the design into OSLO (or some other package) and then figure out what the effect would be of various changes to the
optical path or additions of other known optical elements.
If anyone has any comments, corrections, suggestions, etc. to the above, I'd love to hear them. This was by no means the most
rigorous analysis, as I lack some of the equipment to do such a thing. And there may well be errors in the above analysis/
approach. But I hope it is helpful to someone.
Subject: Calculating Focal Length for a SCT-- part 1 of 4
From: Gene Horr <genehorr
texas.net> Date: Aug 2002
Barre Spencer wrote:
> Could someone please explain how the focal length of a schmidt-cassegrain telescope
> is calculated. I have 10" SCT and have always wondered how it is done.
Well, this is not an easy task due to the Cassegrain design. Since the secondary is a "magnifier" (has a negative focal length) the
total system focal length is dependent upon the distance between the two mirrors. Since these units move the primary mirror to
focus changing EPs or camera adapters will change the focal length. So all you can do is measure the FL of a particular
configuration.
For me the easiest way is to take a photograph, measure the distance between two stars, calculate the angular separation then
with these two numbers calculate the focal length. Of course this will be limited upon how accurate the star positions are. And
how accurate your measurements of the photograph are. And only gives you a number for that configuration.....
If you _know_ the FL and AFOV of an EP you can use this to measure the FOV and from that calculate the FL. Again, just for that
configuration and just that particular EP. But the first two variables are rarely known accurately enough as you are stuck with the
chicken or the egg problem. To measure the FL and AFOV of an EP you need to _know_ the FL of the instrument.
The focal length for the Cassegrain systems is supposed to be the stated amount when set up for 35mm film use with the
standard SCT camera adapter. So in your case it should be 2500mm at that point. If you make that assumption then you can
measurer your EPs and from there measure different configurations. But you are starting with a number that may be several
percentage points off.
Confused? You should be....
-----------------------------------------Subject: Calculating Focal Length for a SCT -- part 2
From: Gene Chimahusky <lynol1000
yahoo.com>
I have found the following publication to be helpful in SCT focal length calculations:
<http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/BRAYOBS%20PUBLICATIONS.html>
Scroll down and the PDF: "Calibrating The Effective Focal Length Of Catadioptric Cassegrains With Moving Primary Focusing" A lot
of math up front and reasonable graphs further on in the publication. The paper from Brayebrook Observatory site can look a
little daunting from the math end of it, but the graphs they also supply make life much easier.
I am not sure of the design spec Meade used for the SCT as far as where the image plane has to be in order to get the F10 stated
focal ratio.
Let's 'assume' it is with the visual back attached to the tailpiece and no diagonals or other things attached. Insert the 25mm
eyepiece and focus on infinity. This will define the location of the image plane for 'F10'.
Now if we look at the graphs in the publication and find the line for the 10" SCT, we can read the graph and find if we move the
focal plane back 3 inches the scope will now operate as if it is an ~F11.2 or 112 inch focal length.
So if you are using a 25mm eyepiece it is not 100x but 112x. Using a 9mm give 311x versus the native 277x. Now how can you
get into the situation of shifting the image plane back 3 inches? Add a Crayford type focuser.
Things get even worse if focal reducers are entered into the picture. If you look at Doc G's page:
<http://www.MAPUG-Astronomy.net/ragreiner/opticlens.html>
Here Doc gives an example of a Meade 0.63 reducer that needs the focal plane 148mm behind the tailpiece. Now 148mm is ~6
inches so reading the graphs we really start at F12.2. The actual focal reduction is ~7.7 versus the 6.3 expected. We can get
back to the F6.3 by varying the spacing of the focal reducer to the CCD slightly but the math requires using the rough ~F12 as
the basis.
These are not meant to be 'exact' numbers but only illustrate the point. You exact focal length may vary
--------------------------------------------------Subject: Calculating Focal Length for a SCT --part 3
From: Roger Hamlett <ttelmah
ntlworld.com>
On the SCT design, the secondary mirror, as well as reflecting the light, also acts like a Barlow, narrowing the angle of the light
cone, to give the final effective focal length. The actual result, depends on the spacing of the two mirrors, so with moving mirror
focussing, the effect will change according to where you want to focus. Hence if you attach a focal compressor, and have to alter
the focus of the main scope to use this, the focal length of the main scope will be changed by this, altering the overall effect.
It is possible to calculate the actual focal length, if you know the focal lengths of the two mirrors, and the spacing, but is not
normally done (especially since on a normal SCT, you rarely know the mirror spacing...). The normal practice is instead to
measure the effective focal length (rather than to calculate it). You can measure the focal length of any scope, by timing the
transit of an object across a known distance. The 'easiest' method normally is to use the field stop of an eyepiece (measurable
with a micrometer), and a star near the celestial equator. If you aim at this, with no motor drive, the time taken is related to
focal length.
The stars basically move at approximately 15 degrees per hour = 0.00416 degrees per second. Given the field stop _radius_ (half
the diameter), the effective viewing 'angle' of this, with a given scope, is theta=2*tan-1(radius/fl). If you rearrange for fl (focal
length), you get fl=radius/tan(theta/2). So if you time a star across a 20mm diameter field stop, and it takes 90 seconds, you get
theta = 90 * 0.00416 = 0.375 degrees. This then gives fl = 10/tan(0.375/2) = 3050mm. This can be done for any eyepiece or
camera combination, to give a good measure of the actual focal length. You can do a similar thing by using a measure of distance
at the focus (such as the pixel size of a CCD), and an object of known angular size/separation (a pair of stars), and measuring
the number of pixels this separation gives.
-----------------------------------------------Subject: Calculating Focal Length for a SCT-- part 4 of 4
From: Don Tabbutt <don
tabbutt.com>
For most purposes, the stated f/ratio is close enough.
Subject: Optical Defects Simulation Software
From: Gene Chimahusky <lynol1000
yahoo.com> Date: Jan 2003
A nice simulation program that can induce currents, pinch, turbulence and more:
<http://aberrator.astronomy.net/>
MAPUG is hosted by
LX200 Collimation --Page 2
*Also see Star Testing and Optical Quality topic (includes how-to make an artificial star for testing)
Laser Collimators for SCTs?--5 parts
Using the Kendrick Laser Collimator
Laser Collimation Eyepiece for SCT?
Laser SCT Collimator? --Stay with Star Test
Collimation On Axis of Symmetry?--5 parts
Collimation Using Two Telescopes?
Collimation Screws for f/6.3
Collimation Thumbscrew Replacement Procedure
Bob's Knobs Collimation Screws --11 parts
Field Flattener Requires Re-Collimation?
GoTo Page 1 of Collimation
Subject: Laser Collimators for SCTs --part 1 of 5
From: Doc G
A considerable number of persons have posted me about their problems with the use of a laser collimators to collimate their SCT
telescopes. There are a number of caveats that have to be applied when trying to do this operation.
The posts have related mainly to erratic results when the tube holding the collimator is a tube which screws directly onto the back
of the telescope or another such as the 2" eyepiece tube on a JMI or other Crayford type focuser. The underlying issue is holding
the laser in the exactly correct position when attempting collimation. There is a certain amount of sag in the tubes holding the
laser device with all methods. The tubes might not even fit tightly enough to insure that they are parallel to the optical axis of the
telescope. A burr or bubble of paint might skew the tube position.
Unfortunately, an essential requirement for collimation is that the laser beam be exactly lined up with the center of the optical
axis of the telescope. If the laser holding tube sags or is skewed in any way, the laser beam will not line up correctly. This effect
is quite obvious with most focusers. Even a tube screwed directly to the back of the telescope might not be perfectly aligned with
the optical axis of the telescope. The alignment required when making optical adjustments is very critical and might not be
attainable in some cases.
When the laser beam is not perfectly aligned, the collimation obtained will not be correct. This is a serious problem. While some
have reported good results, many have reported varying results when the laser device is removed and reinserted or varied results
when the holding screws are tightened more or less. Sometimes just tightening the tube or the holding screws a bit seems to
change the results significantly.
I do not have an answer to these problems. I am simply warning users that great care has to be effected in order for the laser
method to be reliable and consistent. It is quite attractive to have such a device but it may not work well in all cases. What I do
know is that the real star method, as recommended in all optical books, always works. It should be used as a final check and it
must be the final arbiter of correct collimation.
-------------------------------------------------------------------------------------------------
Subject: Laser Collimators for SCTs --part 2
Richard Seavey wrote:
>Doc, Why do you believe that the telescope optical tube mechanical axis is
>coincident with the optical axis? I thought that the optical axis of the
>primary mirror was not well defined and was unstable with respect to the
>tube mechanical axis. What am I missing?
Ah!! You are very perceptive. I have been waiting for someone to mention this issue. It is true that the primary might not be
mounted so it exactly lines up with the mechanical tube. It might be off center or it might be tilted. You are absolutely right. It
might even saunter around a bit as it is moved to focus the telescope.
But if this is the case with an SCT there is nothing you can do about it short of dismantling the telescope and lining it up with a
careful optical method. This would be possible. I have not tried it on a Meade SCT. Then you could use the back plate to adjust
everything else. Generally there is nothing you can do about this sort of misalignment so we have either to do nothing, or make
the assumption that the primary is Ok and proceed from there.
If the primary is really badly mounted, the telescope probably will not collimate well but will instead be compensated by moving
the secondary. I would call such an SCT not too good. A very few will have telescopes, like the standard CAS which has primary
adjustments. I have stated in my articles, that we have to start with some assumptions about the quality of mounting of the
primary. It seems that so many of the Meade SCTs do indeed reach very good collimation, so I think, and hope, it is safe to
assume that they do a rather good job of setting up the primary.
So you have indeed found the fly in the ointment as it were. I wish you had a good solution for this problem. Even better, I wish I
had a solution.:-) I do not.
----------------------------------------------------------------------------------------------Subject: Laser Collimators for SCTs --part 3
Paul Goelz wrote:
> >At this point I am suggesting that the tube used to hold the laser be screwed
> >very firmly to the back plate of the telescope. I am also making an experimental
> >mounting tube with a generous flanged foot and a very tight fit to the laser
> >device to insure that the tube is mounted exactly parallel to the telescope's
> >optical tube (the optical axis of the telescope)
> > Doc G
>
>
>
>
>
>
>
This has always bothered me.... If you screw the collimator to the back of
the scope, aren't you at the mercy of the orthogonality of the rear
surface of that port? Does anyone take care in manufacturing so that the
surface is orthogonal? And of course, as soon as you screw anything else
to it to mount an eyepiece, all bets are off!
My vote would be to use the 2" version and put it in whatever will
eventually hold your eyepiece.
I have promised I would not comment further about "the C word." But this post is about the telescope tube itself and not about
"c."
You are quite right, also, about the question of orthogonality of the back plate of the telescope with respect to the primary mirror.
But what else can we get our hands on easily. If we do not want to dismantled the OTA, we have to use the back plate and
assume that the manufacturer has mounted the mirror and the slider tube orthogonal. If this is not done, all bets are indeed off.
We would have to rebuild the OTA.
But to the second point, I would not vote with you this time for the following reason. Perfect alignment of the OTA itself is a
property of the OTA and has nothing to do with the focuser, external tubes, eyepieces or the like that you fasten to the back of
the telescope. All of that stuff is simply to look at the aerial image that the OTA has formed at the opening in the back of the OTA.
So, if you use a twisted or sagging collection of stuff on the back and then try to make your OTA perfect through this stuff, it will
not be so. It will reflect the defects of the attached accessories and will thus be inherently maladjusted.
-----------------------------------------------------------------------------
Subject: Laser Collimators/Optical Adjustments --part 4
From: Doc G
Paul Goelz wrote:
>>So, if you use a twisted or sagging collection of stuff on the back and then try
>>to make your OTA perfect through this stuff, it will not be so. It will reflect
>>the defects of the attached accessories and will thus be inherently maladjusted.
>But, but, but.... isn't the idea to take all this sagging mess into
>consideration by keeping it in place while you tweak the "C" thing? In
>other words, what's the point of doing the "C" thing if you then add the
>sagging stuff afterwards?
No, No. No! It is perfection of the image that the telescope forms that is the issue. The perfection of the aerial image (called the
real image) that the optical system generates at the opening at the back of the optical tube is dependent only on the quality and
alignment of the primary and secondary mirror. (and in an SCT the corrector plate) (A focal reducer might be a part of that
optical system, but that is a secondary issue.) No amount of twisting and turning the additional tubes will fix a maladjusted OTA.
(Optical elements can fix symmetrical aberrations as described below)
It is the job of the visual astronomer to look at the aerial image with a magnifier of some sort (the eyepiece). The eyepiece may
affect the total image quality, but it has nothing whatever to do with the quality of the image that the telescope forms. There are
some minor issues, like an eyepiece might have a curved focal field that matches the curved field of the OTA or not, but these are
other issues not related to the basic quality of the image that the telescope optics forms.
When additional optical elements are added to the telescope, they would ideally be designed to minimize or even fix aberrations
in the original optics. But it is a rare telescope that has additional optical elements designed in this way. (Some high quality
refractors do. Probably the most famous example if this sort of "fix" is Hubbell, where spherical aberration was fixed with added
optical elements)
When one puts a film or CCD at the point where the OTA forms the real image, you capture the real image. Again the fact of the
photo surface being placed correctly has no effect whatever on the quality of the real image formed by the telescope itself.
The telescope does not know, nor does it care, if you are going to look at the image through a magnifying glass or a microscope
or intercept it with a film or a chip. Normally adjusting the primary and secondary are the only controls one has over the quality
of the aerial (real) image in an SCT. (or possibly the corrector plate if it is flawed.)
This might at first sound a bit philosophical, but it is not. It is basic to understanding optical systems and things like cause and
effect. Again, I am sorry to go on so long and to sound so darn pedantic, but science has some immutable principles and the
above example is one of them.
----------------------------------------------------------------------------Subject: Laser Collimator for SCTs --part 5 of 5
From: Howie Glatter <howieglatter
mindspring.com>
Whether we collimate a SCT with a star test, or with a laser collimator, we use a collimated beam of light (parallel rays), and
arrange things so that the beam is directed along the telescope's optical axis. Using a real or artificial star, we do this by placing
the star in the center of the telescope's field of view. When using a laser collimator, we must also arrange things so that the
beam travels along the telescope's optical axis.
With a Cassegrain, this can be done by checking the centering and angular alignment of the telescope back fittings. This includes
the threads machined on the telescope's back casting, the axis of the threads or inside diameter of any additional adapter,
focuser or holder threaded onto the back casting, and the alignment of the laser collimator, itself, with the final cylindrical I.D. of
whatever adapter, or combination thereof, is being used during collimation.
Significant flexure of these parts under their own cantilevered weight is a variable misalignment, which is an even worse problem
As far as I can see, the solution is to check and repair as necessary all telescope back misalignments, and minimize flexure by
using shorter, lighter and stronger components for collimating.
It's not necessary to use a long adapter tube with a side cutout to observe the reflected central beam on the collimator face. In
most cases the collimator face, with the reflected central beam impact visible, may be seen from the front of the telescope, by
double reflection in the primary and secondary. This may be the best way to view the collimator face, as you can adjust the
secondary screws while you are viewing the beam impact. If you view from the front of the telescope, you can use a short and
inexpensive 2" to SCT thread adapter.
To check the back alignment, you must first check the centrality of the back opening with respect to the tube. Place a collimator
or eyepiece in the holder and slide it so that some of it's outside diameter is showing, before clamping it. Extend a reference
backwards from the main tube's outer surface using a straightedge held parallel to the tube's axis. You will have to use a strip of
material of uniform thickness as a spacer between the straightedge and tube sheet metal so that the straight edge clears the
back casting. Then measure all around between the straightedge and collimator O.D. It should be uniform. The secondary should
similarly be checked for centrality by measuring all around between the secondary mount and the inside of the front tube casting.
Hopefully, the secondary will be centered in it's mount ; if not, this must be corrected or compensated for. Then, the back's
angular alignment can be checked by seeing if the laser beam strikes the center of the secondary.
Using a single beam collimator, the beam centering on the secondary must be judged by eye (viewed by reflection in the
primary). Using a holographic collimator, you can see if the target pattern is centered on the secondary.
Subject: Laser Collimation Eyepiece for SCT?
From: John Mahony <jmmahony
hotmail.com>
>From: Oscar
>Has anyone ever heard or used a Laser Collimation Eyepiece for the LX200 ?
>I found a website that shows the different types of Laser Collimation
>eyepieces. They look very impressive. <http://www.digitecoptical.com/>
First, the collimation eyepieces are a completely separate product from the laser collimator. And while a reticle consisting of a
bunch of concentric circles could be used to judge collimation, you could just as easily go closer to focus, which exaggerates any
asymmetry. If the image is too small to see easily, use higher power. If your scope's mount is difficult to use at high power, just
remember that with the concentric rings in the collimating EP, the out-of-focus star image has to be perfectly centered to judge
by the circles.
The laser collimator looks like it might actually work, but not as well as a conventional star test. It has the same problems the
other "alternate collimation methods" have. For most SCTs, the mirror will shift so much when aimed horizontally that the
collimation will be worthless. At one of my club's public events in August, there were still a few visitors around when Mars rose
around midnight. Since we didn't expect our visitors to stick around until 3 am to get a good view, we all immediately aimed our
scopes at Mars, near the horizon. My collimation was suddenly terrible. I fixed it with the tube nearly horizontal, but then later
when I aimed it back at higher objects, it was terrible again. Maybe the mirror lock in the GPS scopes will reduce that problem,
but for other SCTs, collimating near the horizon is worthless.
A common reason I hear for why people want to be able to do a daytime collimation with a near target is too avoid bad seeing.
But collimating better than the seeing allows is also pointless. It won't help to have perfect collimation in bad seeing. Seeing
limits collimation and viewing in the same way, and the point of collimation is to produce a cleaner star image- measured directly
just as you view it. Put those together and it means that collimating better than can be measured through the seeing doesn't give
you a significant advantage.
Finally, a daytime collimation on a near target means that the mirror is on a different part of the baffle tube. Unless the baffle
tube is perfectly aligned, the mirror will be slightly displaced to the side when it is moved back for a close focus, further
interfering with collimation.
I used to think that the reason so many people put so much effort into finding alternate ways to collimate is that they had been
misled by experiences with Newtonians, where a full collimation is complicated enough to be intimidating to a beginner. But I see
so much of this that I'm starting to think that the real reason is that collimating an SCT is _too_ easy, removing some of the
mystique of their high tech hobby.
Subject: Using the Kendrick Laser Collimator --part 1 of 2
From: Doug LePage <xuxek
apcn.net>
----Original Message----Tim deBortoli wrote:
Yesterday I finally had the chance to try out my Kendrick Laser Collimator on my LX50 10". It was snowing out so I
was limited to my basement and the maximum distance from scope to artificial star was approx. 51-52 ".
I first tweaked collimation on the artificial star until I was convinced it was perfect. I centred the star in a 12mm reticle. Replaced
the visual back with the laser and followed the instructions. After the procedure I rechecked the diffraction ring pattern on the
artificial star and found that collimation was off. The rings were off-centre towards the bottom of the field of view. Once again I
tweaked my collimation and repeated the process only to get the same results.
I had the OTA on its Superwedge and on the tripod. The OTA was balanced. The laser was firmly attatched.
My first question is why isn't it working - it seems many people are gettting good results with this device and Kendrick typically
makes quality products.
My second question - why go through the process of centering the laser's halo of light on the artificial star? If the scope is
perfectly colllimated using the star then why not attach the laser, turn it on and mark on the spot where the return beam strikes
the face of the collimator. Would this not be where it will have to return to in the future if you are to be perfectly collimated
again?
------------------------------------------------Tim, It isn't perfectly collimated until you get the beam's halo centered over the artificial star. Merely centering the star in your
reticle does not collimate the scope, you are centering the laser along the scopes optical axis by doing this. I gotta tell you that I
didn't achieve really good collimation until I did several things that I will describe for you.
I had no luck with the close focus distance of 50' I use 150-200' I guess that it is difficult when it's snowing outside....it's 83 here
in Miami. I shoot it down the street to a vacant house. You should wait till the thaw it will be worth your while.
Take the scope off the wedge per Jim's instructions on his web site
<http://www.kendrick-ai.com/> (Note: should open a new browser window over this one.)
and place the OTA on a table or other sturdy support... get the weight off the forks. People say there is a flexure problem with
the OTA ... Doc G could explain this better. I was ready to pull my hair out until I had the patience to do it slowly and
methodically after many e-mail's to Jim K. MOST IMPORTANTLY!! I don't know how long you've had your laser but originally Jim
didn't include a paper target. If you have one disregard this part, but I use a box with a halogen bulb inside and a sheet metal
front painted with FLAT WHITE Krylon or similar product and small hole drilled in it. I could never see the halo on tin foil, which
was the original instruction. If you follow this you should see a dramatic improvement...I sure did.
--------------------------------------Subject: Using the Kendrick Laser Collimator --part 2 of 2
From: Doug LePage <xuxek
apcn.net>
Tim deBortoli wrote:
How exactly do you centre the artificial star/target in the scope with the OTA lying on a table or whatever -especially if the target
is 150' away? And how do you know when the halo is focused well enough and when it is centred on the target? My finder scope
wasn't useful for this at 50'. I can't see that a pair of 10x50 binocs. are going to allow you to accurately centre the halo.
Tim,
I just walked back and forth until I got it right but an assistant would be helpful for this. I used small sand bags and duct tape to
hold it in position but I heard others say that they made a wooden cradle. Bottom line is that you really need to see (up close)
what is going on and the best way is the walking.
Subject: Laser SCT Collimator? --Stay with Star Test
From: <Carailway
aol.com>
I have a 12" LX200 that I haul around in my pickup and I collimate it every time I setup. It only takes a few seconds, and I can't
think of any reason to use a Laser collimator. Unless there is something drastically wrong with the SCT there is only one element
to adjust, the secondary. A quick look at the defocused blur circle and a tweak if necessary, then with higher power take a look at
the diffraction pattern, if the seeing is steady enough center the Airy disk in the diffraction rings. If seeing is bad then seeing will
probably be the limiting factor. But always go for as perfect as you can get so when there are moments of good seeing you will be
ready for it. After collimating a few times you will learn the tricks of the trade and it's so quick you will wonder why you ever
looked through a misaligned scope.
Editor's note: a number of members wrote to agree that the star testing method was superior to any of the lasers, including the
Kendrick.
Subject: Collimation On Axis of Symmetry? --1 of 5
From: Michael Sparks <sparksmd
zoomnet.net>
I purchased a Kendrick SCT rear cell version laser collimator. I followed the collimation instructions precisely. The final position of
the reflected beam is about 0.25" from the center if the grid. A friend of mine who also owns a 12" LX200 also purchased the
Kendrick's SCT collimator. He however purchased the NGF-S version. After several attempts to collimate his LX200 using the
laser collimator attached to the NGF-S he discovered that his view through the eyepiece was very fuzzy. The only way he could
improve the clarity through the eyepiece was to continue making random adjustments to the secondary mirror until the target
was very clear. After this adjustment the reflected beam was not even on the grid. Only some of the diffraction rings could be
seen near the edge of the grid. Unfortunately we live about 100 miles apart so we haven't been able to get together to swap
collimators. We have discussed this problem extensively on the phone and reviewed Doc G's and Ed Stewart's archives.
The question we keep coming up with is, "When performing a collimation are you attempting to collimate with respect to position
of the eyepiece/CCD or attempting to put the light cone and focal point right dead center of the optical axis?" In other words,
with an NGF-S, flip mirror and CCD hanging off the back of the rear cell it is difficult to determine if the CCD chip is orthogonal to
the optical axis. It probably is not due to flexing. In fact by attaching my laser collimator to the NGF-S via the SCT adaptor I
could get the reflected beam to project anywhere I wanted to on the grid just by adjusting the three set screws that attach the
NGF-S to the rear cell.
If the purpose of collimation is to line up the light cone and focal point to coincide with the optical axis, how can you verify that
the eyepiece/CCD is orthogonal to the optical axis, or does being orthogonal to the focal point important? If the purpose is to
place the light cone and focal point orthogonal to the eyepiece/CCD position, then is it better to collimate from the end of the
optical train where the eyepiece/CCD would be positioned and would include the flex caused by the weight of the train?
-----------------------------------------------------Subject: Collimation On Axis of Symmetry? --part 2
From: Doc G
I have now worked with three laser collimators. These include the Kendrick, the Glatter and the LaserMax. (one paid for, one a
gift and one on loan)
The LaserMax instructions say right up front that it is designed to collimate Newtonian telescopes and not SCTs. It produces a
central spot and a grid similar to one of the others. It is well built and offers similar abilities to the others.
I have seriously tried all three of them on two different LX SCT instruments. The results vary. I believe this is because of the
inability to adjust the collimator to be parallel with the optical axis of the telescope in a reliable manner. I no longer believe that
laser collimators can be expected to align an optical system with two movable optical surfaces, especially when one of them is not
adjustable.
I have not been able to verify collimation except with a real star and have not gotten consistent results with any of them. I now
believe that results are sporadic and an illusion based on luck in some cases.
I now believe that the traditional way for aligning the optics is to use a real star with the telescope focused at infinity. This is the
traditional tried and true way to do this job. It is described in all books about the optical properties of telescopes. Even then, with
one adjustment on a two element telescope the results are a compensated optical path and not necessarily a well collimated
telescope.
-----------------------------------------------------Subject: Collimation On Axis of Symmetry? --part 3
From: Michael Sparks <sparksmd
zoomnet.net>
Doc, I apologize for burning bandwidth here but I read your site. I think you missed my question of which the answer is not
clearly defined in any archive I have reviewed.
What I am trying to learn or understand has nothing to do with using lasers as collimating devices. I apologize if I did not make
that clear in my original post. What I am trying to learn is when collimating a scope is the intent to align the light cone/focal point
with the optical axis so that it is coincident to the optical axis, or is the intent to align the light cone/focal point to be orthogonal
to the resting position of the eyepiece/CCD which due to flexure probably is not orthogonal to the optical axis. Or is the intent
something totally different as far as the geometry of collimation goes?
My thought which is totally speculation is that it is more important to collimate so that the light cone/focal point is orthogonal to
the resting position of the eyepiece/CCD. This way the light striking one side of the CCD has traveled the same distance as the
light striking the opposite side of the CCD. Or does it? Because of the convex surface of the secondary mirror maybe the
geometry of the light path is more complex than I have assumed.
-----------------------------------------------------Subject: Collimation On Axis of Symmetry? --part 4
From: Doc G
Ah Yes! I now understand your question. It is a very good one. The issue of collimation which is discussed extensively in
telescope optics books requires that the optical elements each or which has an axis of symmetry be aligned with each other.
Collimation has nothing to do with the nature of the receptor, be it film, CCD or an eyepiece. An eyepiece is generally used to
inspect the real image field of course.
Many things can go wrong. If the optical elements are made in such a way that they are not symmetrical about a single axis
there will be serious aberrations. You depend on the glass pushers to do this job well. Many of them do a fine job.
Assuming you have good glass (mirrors) many things can go wrong with the way they are mounted. They might not all be
centered on the same axis and/or they may be tilted with respect to the desired optical axis (which is also the mechanical axis of
the optical system). Thus when aligning perfect optical elements, you have to move them laterally until the centers of curvature
are on one axis and then you have to tilt them so that their axes are on the set optical axis. Not only parallel, but coincident.
Generally the owner of the telescope, especially an SCT, has no control over the centering of the primary nor the tilt of the
primary. It has to be taken for granted that the primary is well set in the optical tube and centered with respect to the corrector
plate. The only adjustment possible is the position of the secondary. If everything else was lined up, the owner can move the
secondary in such a way as to point it along the optical axis of the primary.
It is impossible to get perfect collimation unless the primary has been well aligned by the manufacturer. Generally, the exact
position of the secondary in the lateral direction will be changed when the secondary is tilted. This limits the perfection of the
collimation. The best that can be done is to "compensate" the alignment to give as good a star image as possible. Such a
"compensated" alignment may be near perfect collimation if the owner is lucky enough to have a telescope with good optics that
were correctly installed.
The key words here are to adjust the secondary until the real star image looks as good as possible. Criteria for "good" images are
in many books on optics. I recommend Suiter or another books on modern telescope optical design for the details.
I do hope that this answers some of your questions. As to the issue of the film or CCD plane, it is also required that they be
orthogonal to the optical axis of the telescope. This is usually quite easy to do compared to the original collimation process. The
image will be most perfect on the optical axis of course. There will still be coma and curvature of field even with excellent optics.
Some designs are better than others in this respect.
-----------------------------------------------------Subject: Collimation On Axis of Symmetry? --part 5 of 5
From: Tom Wideman <twideman
earthlink.net>
I use the Kendrick laser for the NGF-S. I cannot speak to the very specific question you ask; however, I'll just point out that Jim
Kendrick has updated the instructions for use of his collimators, and I think they're a little more help now. Jim pointed them to
me recently while I was discussing another issue with him, and I think the instructions have improved.
To reiterate what you already know, the main problem is that the mechanical axis and the optical axis may not be the same.
I'd recommend against your friend making random adjustments. I used the target, then also used the target to do a regular
"star" collimation, and made fine adjustments kind of using both methods from there. I initially had the problem Jim mentions
(see the new instructions) in which reiteration worsens collimation. I spent some time switching between methods, finally got
what I thought was the best collimation, and marked the laser face with the paper ring. I'll point out that this may be somewhat
compromised by collimation at the shortest focus distance instead of on a real star at a realistic focus range as Doc mentions.
I've found that the Kendrick unit takes a little apprehension out of the collimation on-site, and adds convenience, but I'm still
playing with it. My overall impression of methodologies is probably the same as Doc's, but the laser adds convenience, perhaps at
the cost of "perfect" collimation. In fairness, I must also add that I haven't had enough experience with it to speak conclusively,
I'm just sharing my opinions of the experiences I've had so far. All things being equal, I think I would rather have spent the
money on an Everbrite diagonal. ;) I do not say this in any way negatively about Jim's product, his quality and support are
excellent and I give Kendrick my highest recommendation; I just am not convinced yet that the laser methodology delivers the
bang for the buck that I'd hoped for.
Subject: Collimation Using Two Telescopes? --part 1 of 3
From: Bill Keicher <wekeicher
comcast.net>
Bill Keicher wrote:
> Some of us have more than one telescope. Has anyone ever used
> one telescope to collimate a second telescope?
>
>
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One telescope ("the collimator") could be setup with a high
magnification ratio, say 400X, and an attenuated, low power laser could
be run into the telescope eyepiece and the laser beam would be expanded
to fill the main aperture with laser light. Assuming that this telescope
was already collimated and focused at infinity, this telescope (the
collimator) would produce an artificial star available to collimate the
second telescope. The second telescope aperture would have to be smaller
than (or equal to) the telescope aperture used to produce the artificial
star for proper collimation. The telescope adjustment could be made
inside with the telescope apertures adjacent to each other. One would
have to be careful in using a neutral density filter to attenuate the
laser since looking into the scope being collimated would be like looking
directly into the laser beam.
> The main disadvantage is that the telescope used as the collimator must be
> collimated and focused at infinity. Could this process "bootstrap"
> the collimation of both telescopes? Anyone ever try someting like this?
William McCarthy wrote:
>>If you have a laser why not just point at a plane white surface not too far away.
>>The reflected image will still be a coherent parallel beam i.e. an artificial star.
William, If you point a laser beam from a laser pointer at a diffuse, white surface it will produce a spherical wavefront after it
reflects off of that surface and you will have to focus the telescope on the white surface (say, 150' away). You would be forming a
magnified image of a laser spot that is a few millimeters in diameter. You can't collimate a telescope using this technique because
the laser spot is too big and the source is only 150' away. If you point a laser at a specular surface (a mirror) then it will just
return a parallel, narrow beam back to you. Illuminating a small curved, specular surface, for example a ball bearing, with a laser
(or the sun) is a step in the right direction but it is still only an rough approximation to a star. A parallel beam as large or larger
than the aperture of the telescope being collimated is necessary. The laser beam has to be expanded. If you run the laser beam
into the eyepiece of a telescope focused at infinity then the light coming from the telescope will have a near planar (or flat)
wavefront. Stars produce plane wavefronts so using a laser this way is as close as you can get to simulating a star. The
advantage of this technique is that you should be able to do the collimation inside and atmospheric turbulence won't be a factor.
How do you produce a large parallel laser beam? If the laser's beamwidth is 2 mm in diameter, then you would need an angular
magnification of at least 100X to fill a 200 mm telescope aperture. For an F/10, 200 mm telescope, a 20 mm eyepiece would be
needed. The laser should be centered on the eyepiece and aligned with the optical axis of the telescope. If the telescope has a
central obscuration (secondary mirror), then the laser beam coming out of the telescope will have a hole in it. This large beam
could be put right into the telescope (a few feet away) to be collimated. Once again, caution should be taken since looking into
the telescope being collimated this way is equivalent to looking directly into the laser so the laser beam intensity should be
reduced with a neutral density filter on the eyepiece and by using a magnification greater than the minimum (say 400X instead of
100X on the collimator). A video camera could be used to view the diffraction pattern to make this technique safe.
By the way, simply running a laser pointer into the eyepiece of an SCT (magnification same as above) and looking at the "donut"
beam reflecting off of a white surface a few feet away will tell you if you are in need of collimation. An SCT badly out of
collimation will produce an asymmetric "donut". This technique would apply to any telescope with a central obscuration. This is a
very easy test to perform. Crude focus (at infinity) can also be gauged by measuring the diameter of the donut. The diameter of
the donut should be identical to the telescope's aperture and should not change appreciably over a short distance.
---------------------------------Subject: Collimation Using Two Telescopes? --part 2
From: John Mahony <jmmahony
hotmail.com>
I've run into too many cases of newbies convinced that the standard collimation method is difficult, and looking too hard for
alternatives. Recently I heard from one who made the mistake of buying Kendrick's SCT laser collimator. The most basic
understanding of how a scope forms an image immediately shows that Kendrick's method has nothing to do with collimation.
Spending $185 on a worthless product can take the fun out of experimentation in a hurry.
Your method avoids two of the counterarguments against daytime collimation. Yours has the focus set at infinity. The others have
the focus set very close, so the primary is moved far back. So if the baffle tube is not perfectly straight, the mirror will move
laterally a bit as you move it forward to focus at infinity for night-time use. Also, it is claimed that daytime collimation avoids bad
seeing, but you can easily get turbulence across the distances normally used in daytime collimation. In your method, the two
scopes can be literally face-to-face.
---------------------------------Subject: Collimation Using Two Telescopes? --part 3 of 3
From: Bill Keicher <wekeicher
comcast.net>
An SCT primary mirror shouldn't shift if locked and not subjected to shock. The primary mirror should remain in place regardless
of gravity induced torques caused by changing the position of the telescope. By the way, the indoor collimation technique could
be used to carefully measure how much the primary mirror shifts as it is locked in position.
Subject: Collimation Screws for f/6.3
From: Tom Wideman <twideman
earthlink.net>
I have a 10" f/6.3 LX200. The collimation screws for this are very long (3.25") and there is minimal clearance between the
secondary housing and the end cap (or solar filter) -- about 0.15" to be roughly precise (a new term).
I checked McMaster-Carr <http://www.mcmaster.com/> as someone suggested, and found the following item:
(Stock# 91833A118) 18-8 SS Round Knurled Thumb Nut 6-32 Screw Size,
Partially Threaded, 3/4" Head Dia, $ 3.17 Each.
This knurled nut has a "T" profile with the top of the "T" 3/4" across and 1/8" thick, and with the stem (the vertical part of the
"T") 1/4" long and 1/4" across. It is tapped 6-32 in the stem portion.
Since the stem, being 1/4" long (total height 3/8"), was too high to clear the end cap, I trimmed the stem portion down to about
3/32".
I used a piece of 6-32 stainless steel all-thread, trimmed to the proper length, for the collimation screw, and secured the nut onto
the all-thread with Lock-Tite.
I set up an artificial star and collimated the scope to see how the thumb nuts worked. The thumb nut profile is quite close to the
secondary, so gripping isn't easy (not really problematic, but I don't think it would be possible with gloves). However, I think I
still prefer it to dropping my Allen wrench on the corrector plate. I feel it will be a worthwhile change.
If the clearance is higher (1/2" or so) on the f/10 as Andy indicated, this technique could be used on that model without having to
trim the thumb nuts down (the screw is also much shorter).
Thanks again to whoever provided the URL for McMaster-Carr -- besides the thumb nuts, I got some teflon for my binocular
mount, and an in-line GFCI (plugs into an outlet, I can plug my cord into that and protect myself -- thanks to whoever
recommended that, by the way) and some other tidbits that I don't think I could find locally.
Subject: Collimation Thumbscrew (Bob's Nobs) Replacement Procedure
From: Allan Keller
I ordered and received three replacement collimation thumbscrews from Bob's Nobs at:
<http://hometown.aol.com/rkmorrow/myhomepage/>
to replace the Allen head collimation screws in my 10" f/10 Meade LX200. I developed the following simple procedure to prevent
damage to the scope and to ensure that the collimation did not become so far off that I would have trouble collimating the scope
after the screws were changed.
1. Prior to removing any screws, be sure that your scope is collimated. If it is not collimated then take the time to get it
reasonably close. Collimation procedures can be found at here in the MAPUG Topical Archive. Just type "collimate" in the search
engine on the homepage to be directed straight to the relevant page(s).
2. Once you have collimated your scope, use a low power eyepiece with a large field of view, focus and center a bright star in the
eyepiece's field of view. Leave the low power eyepiece in place until you are finished exchanging all three screws.
3. After you have centered the above star in the eyepiece, carefully center the same star in the crosshair's of your finderscope.
Double check do be sure that both images are centered. THIS IS IMPORTANT! If you do not do this step, you may waste a lot of
time collimating your scope after changing a screw.
4. You may now begin the process of removing and replacing the collimation screws with the new thumbscrews. REMOVE ONE
SCREW AT A TIME! If you remove more than one screw at a time, you risk having the secondary falling out of it's holder and
landing on your primary mirror. Once the stock screw is removed, carefully insert the thumbscrew into the hole and turn
clockwise until the threads have engaged. Continue turning until the thumb screw just begins to feel snug.
5. Check to be sure that the bright star is still centered in your finder scope. Next, looking into your low power eyepiece, begin to
tighten the new thumbscrew until the star is centered in the eyepiece. Double check until you have the star centered in both
scopes. This will return your scope to a state of near collimation and help ensure that you don't end up with your collimation
totally lost.
6. Repeat the procedure above for the next two screws.
The new collimation thumbscrews are of high quality stainless steel with knurled edges. They work very well. No more lost Allen
wrenches in the dark! I highly recommend them.
Subject: Bob's Nobs Collimation Screws -- part 1 of 11
From: Bill Arnett <bill
nineplanets.org>
Yesterday I installed a set of "Bob's Nobs" on my 12" LX200. I wish all modifications went so easily! But now I'm a little unsure
about how much force to apply to the knobs ("Nobs"). The resistance they offer seems to be very nonlinear. For most of their
range they turn very easily, so easily that I feel like they're doing nothing. But then they abruptly get pretty stiff and a quarter of
a turn after I felt like any more force would not be a good idea. So there seems to me to be a very small range in which to work.
I managed to collimate OK by repeatedly tightening one and loosening the others. With the original screws and an Allen wrench I
was probably using a lot more force and driving the screws past the point that seems inadvisable with the Nobs. So, am I right
that I shouldn't turn them very hard?
(BTW, I have an awful time trying to collimate. I can get close but the in focus image of the diffraction rings dances around so
much that I can't see if it's really concentric. I suppose I'll just have to wait for better seeing.)
------------------------------------------------------Subject: Bob's Nobs Collimation Screws -- part 2
From: Gene Horr <genehorr
texas.net>
Bill Arnett wrote:
> But now I'm a little unsure about how much
> force to apply to the knobs ("Nobs" :-). The resistance they offer seems to
> be very nonlinear. For most of their range they turn very easily, so easily
> that I feel like they're doing nothing. But then they abruptly get pretty
> stiff and a quarter of a turn after I felt like any more force would not be
> a good idea.
This is exactly how it should work. You're actually doing it correctly now. There is a central pivot point against which the mirror
cell should rest. So your adjustments should always be loosen two and tighten one.
Very, very few SCTs are shipped with the collimation tightened up. Whether this is on purpose or not I have no idea. But because
of this many people (myself included for many years) thought that the "loose" condition was normal.
IMO you should tighten them down just to where you feel the resistance. Past that point and you may start applying stress to the
mirror.
------------------------------------------------------Subject: Bob's Nobs Collimation Screws -- part 3
From: Greg Hartke <ghartke
clark.net>
Bill Arnett wrote:
> (BTW, I have an awful time trying to collimate. I can get close but
> the in focus image of the diffraction rings dances around so much that
> I can't see if it's really concentric. I suppose I'll just have to
> wait for better seeing.)
I had the same trouble and hardly even trusted my ability to collimate on a star - I could never use sufficient magnification to
really believe that I had decent collimation. Then I learned of the joys of artificial-star collimation. It turns out that it's *really*
easy to collimate at high mags (I use 500x which is all I can get with the EPs etc. that I have) using any spherical metal object
placed in the sun at a reasonable distance. I went to the hardware store and found a polished metal knob of approx. 1.75"
diameter that works fine. I put it in the sun (on a stake with a cardboard backing) maybe 150 to 200 feet away and have at it.
It's so easy you'll wonder why you ever bothered to try it with a real star. A smaller target would probably let you place it closer
but the distance mentioned above is easy for me. Try it!
Editor's Note: also see "Collimation Method Using Artificial Star" on Star Testing Page.
------------------------------------------------------Subject: Bob's Nobs Collimation Screws -- part 4
From: Greg Hartke <ghartke
clark.net>
Bill Arnett wrote:
>
>
>
>
>
>
clark.net wrote:
ghartke
>... I put it in the sun (on a stake
> with a cardboard backing) maybe 150 to 200 feet...
> Doesn't it have to be well past the point at which the scope focuses
at "infinity"? I'm sure one of our optics gurus can figure out the
minimum distance given the focal length and f ratio.
Not when collimating at or very near focus. What you'll find when the target is not at infinity is that the diffraction rings are not
the same inside and outside of focus - as I recall you're seeing an image that's spherically aberrated. Fortunately that doesn't
mean anything when you're collimating with the image right on the optical axis. The rings will still be concentric as long as the
target is centered. As a practical matter, you need only be far enough away from the target for the scope to focus. I like to get
the target a fair distance away anyway but I've known users to collimate on a target much closer than what I use.
------------------------------------------------------Subject: Bob's Nobs Collimation Screws -- part 5
From: Philip Freeman <Philip.Freeman
MW.Boeing.com>
Since this question keeps popping up, maybe this item info should be stored in the Topical Archives.
For the f/10 telescopes: McMaster-Carr (www.mcmaster.com). Part number: 91746A128.
"#6-32 Size x 1/2" Long 1/8" Height 3/8" Diameter 18-8 Stainless Steel Knurled Head Flat Point Thumb Screws". It was about
$10 for three screws after shipping. Might need some spacers, or trim the length of the screw down a bit.
For the f/6.3 telescopes: Bob's Knobs seems to be the best choice. There are some unusual aspects of the 6.3 screws (long and
slender, rounded underside) that makes finding a replacement difficult. If you want to go the DIY route, by some thumb screw
heads and Locktite them onto some allthread. This information is in the Topical Archives.
------------------------------------------------------Subject: Bob's Nobs Collimation Screws Clearance -- part 6
From: Bob Morrow <RKMorrow
aol.com>
I noticed there are some questions about clearance between Bob's Nobs and the dust cover of some of the Meade scopes. The
10" f/10, 12", and 16" SCTs have no clearance problems, but there are some issues associated with the 8" f/10, 8" f/6.3, and 10"
f/6.3 scopes. These three models have a dust cover that essentially rests against the secondary housing when it's installed.
The instructions supplied with the Nobs suggest "contouring" the cover by pressing on the inside to bulge it a bit to obtain
clearance. This is actually very easy to do, and you can make the cover flat again just by pressing the outside of it against a flat
surface. I was able to get plenty of clearance on my 10" f/6.3 by doing this. For the 8" scopes, I include a set of stick-on bumpers
that can be attached to the inside flat of the dust cover against the rim. These allow the cover to sit a bit further away from the
end of the OTA to provide clearance for the Nobs. Bumpers really aren't needed if you're willing to contour the cover instead.
Nobs for both f/10 and f/6.3 8" scopes are low-profile to minimize their height above the secondary housing while providing
enough surface to grip them for adjustment.
BTW, Nobs for each Meade scope model are different, and the threaded part for f/6.3 models is much longer than that used in
f/10 scopes. That's because the secondary mirror is much closer to the primary so a steeper (shorter focal length) light cone can
be obtained between the secondary mirror and eyepiece. One scope I haven't yet tested is the new LX90 with its plastic dust
cover. Of course, that cover can't be contoured. I'm awaiting word from buyers of Nobs for this scope on how the dust cover fits
with Nobs installed. I'd be happy to answer any questions directly, either on the list or via private e-mail.
--------------------------------------------------------Subject: Bob's Knobs Collimation Procedure --part 7
From: Rod Mollise <RMOLLISE
aol.com>
Mark writes: Should I just snug them all down, then gently collimate, being careful not to take any one out very much? Later,
when I collimate again, should the first step be to tighten, until snug?
Mark: No. Snug em down to start with as Bob says in his instructions. Thereafter, to collimate, always _tighten_ a screw. Only
when you can't tighten it easily should you switch to its opposite number(s). Loosen the opposite screw or screws slightly, and
you will be able to continue in the proper direction with the original screw. If you do this, you'll never have a problem with any
screw being loose.
---------------------------------------------------------
Subject: Bob's Knobs Collimation Procedure --part 8
From: Mike Dodd <mike
mdodd.com>
Andy Heath wrote:
>...is there anything I can do during daylight that may give me a head start?
Yes. Check out Bob's Knobs Web site at:
<http://hometown.aol.com/rkmorrow/myhomepage/> and look toward the bottom of the page for a link to the installation
instructions (148K PDF file). This has directions for a preliminary collimation by looking in the corrector lens of the scope. Photos
are included, so you know what to look for. I performed this when I bought my Nobs, and it got pretty close.
--------------------------------------------------------Subject: Bob's Knobs Collimation Procedure --part 9 (disassembled secondary photos)
From: Anthony Kroes <akroes
venomtech.com>
I put mine 'very' finger tight and have no problems with collimation. I have Bob's Knobs on both my 8" and 12" LX200's (both
classics). I have had the secondary assembly on the 8" completely apart to see how it ticks and the collimation screws go into an
aluminum plate that is glued onto the back of the 3/4" thick secondary.
I am not an engineer nor an optician, but it would seem to be that it would be pretty difficult to stress something that thick using
such a short radius (center pivot to collimation screw) when only using finger pressure, but someone here please correct me if
you can!
Check out the pics (click them to see a larger version) of the disassembled 8" secondary at:
<http://www.cdo-astro.com/Telescopes/Lx200/Secondary/Secondary.html>
---------------------------------Subject: Bob's Knobs Collimation Procedure --part 10
From: Roger Hamlett <ttelmah
ntlworld.com>
Anthony Kroes wrote:
> I am not an engineer nor an optician, but it would seem to be that it
> would be pretty difficult to stress something that thick using such a
> short radius (center pivot to collimation screw) when only using finger
> pressure, but someone here please correct me if you can!
The question is how much distortion is necessary? If you look at something like the floor of your house, it is normal for the
construction codes to specify the required beam sizes, to accept a deflection in the centre, of perhaps 1/300th the span under full
load. If you put a small chair in the middle of a room, the distortion is so small that it is normally undetectable. However if this
floor, was a mirror, the distortion made by even such a single object, would be enough to take a perfectly 'figured' set of optics,
to a point where it would probably be no longer acceptable. A distortion of just 0.1um, would be very significant. Now when you
'tighten' a bolt, the increase in force you feel as it tightens, occurs as materials distort. The friction you feel, is a result of the bolt
itself going into compression, the surfaces of the threads carrying this force, and generating friction.
If you work on optics, just having a small hair, under the centre of a piece of 2" thick glass, not only lifts the glass (as you'd
expect), but also bends the glass itself...
_Gentle_ finger tight (perhaps a few oz/in of torque), is what the unit is designed to have. If it feels 'tight', it is almost certainly
too tight. The real 'pity', is that Celestron (or Meade) don't specify a torque for the bolts, so that they can be set to the same
level that was used when the scope was originally adjusted. I have seen a Meade scope, where the bolts were tightened to a firm
finger tight, and there was a visible 'pinched' effect on the optics, when collimating.
---------------------------------Subject: Bob's Knobs Collimation Procedure (caution)-- part 11 of 11
From: Dennis Williams <drwicu812
comcast.net>
Bob's Knobs are truly wonderful to use compared to the allen wrenches ...what were they thinking? Small wrenches in the dark...
A word of warning though, snug is plenty tight. The plastic secondary cell is not very thick and can easily be cracked from
overtightening with the allen wrench or fingers on Bob's Knobs. Been there and done that. Got a new cell from Meade, because I
cracked all three screw holes. I cut apart the cracked cell and was amazed to see such a small cross sectioned area around the
screw holes. I took it apart after about six months of not being able to keep my scope collimated and found the cracks...they are
very hard to see, need a magnifier to notice. The plastic is Delrin (I think) which is a good tough easily machined thermoplastic...
a very good choice but just too thin in the critical places.
I hate to think how many scopes are out there with cracks in the secondary cell and cause the owners to doubt their knowledge/
ability of collimation procedures (as I did). The worst is not fully utilizing fine telescopes. Just be careful about overtightening
when the temperature is low.
Subject: Field Flattener Requires Re-Collimation?
From: Doc G
>
>
>
>
>
>
>
>
>
Dr. Michael Blaber wrote:
I have a question about whether it is necessary or expected to
recollimate when using a field flattener. I star-tested and
collimated my LX200 and it looked superb. However, after
installing the Meade F/6.3 field flattener, and looking at the out of
focus diffraction pattern, it was clearly no longer collimated.
Should this be expected? Can the field flattener affect the
collimation like this? Is expected the you will need to
recollimate upon installing the field flattener?
I believe your result is not unexpected. You must consider that the application of a focal reducer/flattener is an extreme change
in the telescope optics. The base telescope has carefully designed optics, we hope, that give a focal length of say 1500 to 3000
mm. The focal reducer changes this focal length by a factor of one and one half to two times. Thus the "strength" of the optical
system is at least half dominated by the optics of the reducer.
This means that the optics of the reducer are as important as that of the prime telescope optics. This gives one pause when
adding a reducer. The reducer can re-introduce all of the aberrations that have been designed out of the telescope in the first
place.
The very best telescopes have a reducer specifically designed for the optical system to which they are being applied. Helter
skelter application of an optical element of such strength to an OTA is chancy at best. I would experiment with placement of the
reducer. It may well be that the reducer you are using is not perfectly centered or has de-centered elements or any of many
other problems. You might also try another sample of the reducer.
My comments are simply to warn those who use either reducers or extenders (Barlows) that they are greatly modifying the
characteristics of their optical systems and should do so with caution.
GoTo Page 1 of Collumiation/Optical Issues:
MAPUG is hosted by
Daytime Observing/Alignment
with the LX200 (classic)
Subject: LX200 Daytime Observing/Alignment --part 1
From: Allen Ginzburg <alleng
sco.com>
Daytime Alt-Az alignment of an LX200 Classic is quite easy:
The only thing to make sure of (possibly the night before) is that the focus is correctly set to infinity with a relatively wide field
eyepiece. I use the 26mm on my 10" LX200.
1. Set up the scope so that it's facing approximately south. That is, when you are facing the control panel, you are facing
south.
2. Accurately level the base. Use a torpedo level on the top of the OTA and adjust the tripod until you can rotate the OTA 360
degrees while keeping the bubble centered.
3. Set the DEC axis at zero elevation. I use the level on the OTA for this. It's more accurate than the setting circles. Use a
builder's bubble-level sitting along the top of the tube. (And once you've done this the first time, loosen the lock and adjust
the Dec circle so that it is dead on. Subsequent leveling jobs will then be easier since you can start close to right; but you
still need to use a level.)
4. Use a compass to point the OTA as close as you can to true south. Remember to correct for the magnetic variation in your
area. In California it's 17 degrees to the east of magnetic. Make sure both the DEC and RA axis are locked. It's useless to
put the compass near the scope. I just hold it out in front about a meter and sight along the compass to align the OTA.
This is the hardest part of the whole operation. It's also not that important to get it exactly right -- if you are very close in
Dec then you can find your first object by searching in azimuth only; this is a lot easier than searching in both dimensions.
5. Power up the scope and make sure the date and time are set correctly.
6. Make sure your location is set to a known site with the correct coordinates.
7. Select some bright object like Venus, Jupiter, or the Moon. Leave all the lens covers on and do a GoTo that object. The
scope will move somewhere close to the object.
8. MAKE SURE YOU ARE NOT POINTING NEAR THE SUN. Take off the lens covers from the finder scope. Your object should be
visible. Center it using the keypad.
9. MAKE SURE YOU ARE NOT POINTING NEAR THE SUN. Uncover the main tube OTA and center the object using your prefocused eyepiece. Then sync (by holding down the enter key).
After that you can GoTo any bright object. I can view any 1st magnitude star, Jupiter, Venus, Mercury, and Mars with no
difficulty. In certain parts of the sky (away from the sun) even less bright stars are visible). Splitting the double star Castor is
easy, even in full daylight. Whenever I do a GoTo, I put the lens cover back on the main OTA just in case it might cross the Sun.
Then I verify that it's pointing somewhere at least 15 degrees from the Sun before uncovering it.
-----------------------------------------------------------------Subject: LX200 Daytime Observing/Alignment --part 2
From: Bill Arnett <billa
znet.com>
Use the "zero star alignment procedure" (OTA level and pointed exactly due south at power up). Then slew to a bright star or
planet (Venus works well now). You'll be off a little but you can probably find it in the finder scope. Center it up and sync on it by
holding down the Enter key until it beeps. Now you should be able to slew to any of the alignment stars and see them in the
eyepiece. Do a two star alignment as usual and you're off to the races!
The zero star alignment assumes the tripod is level so make an attempt to get it close. A magnetic compass is sufficient for
finding due south if you know your local magnetic deviation.
-------------------------------------------------------------------Subject: LX200 Daytime Observing/Alignment --part 3 of 3
From: Mark Buettemeier <markbue
microsoft.com>
Daytime viewing and full use of GoTo is quite possible and fairly easy with an LX200. I have done it many times and have viewed
Venus, Mercury, Mars and dozens of bright stars.
The trick is that you need to properly set up the scope for a zero-star alignment. I have only attempted this in AltAz mode. I
think Polar mode would be nearly impossible unless you setup the scope the night before and leave it out all night.
To set up zero-star alignment in AltAz mode, you must start with a VERY level tripod, the optical tube perfectly level and pointing
directly opposite of the control panel, the control panel pointing directly to true north, not magnetic north. (Thus, the optical tube
is pointing to true south and is perfectly aligned with the control panel -- the little line on the base of the RA assembly lines up
with the little line on the control panel). Furthermore, the correct date and time and offset from UT must be entered into the
scope and your correct Lat. & Long. information for your current location. Once you have done all these things, power up the
scope.
A GoTo at this point should get you VERY close, if not dead on, to the selected object. Best alignment will be achieved if you can
fine tune the alignment on a bright star, planet or the Moon and then re-sync the scope to that object. If the Moon is up try doing
a STAR 903 GoTo. Fine tune the alignment using the arrow keys and then press and hold ENTER. Venus, at the right points in its
orbit, is also a good fine-tune alignment target since it can sometimes be seen in the finder scope and some times even naked
eye. Remember that as you GoTo further from your original alignment object you may start to loose accuracy and may need to resync.
WARNING: Although the LX200 software will prevent a direct GoTo to objects too near the Sun, it will not avoid slewing past the
Sun on its way to a target. This means that it is possible for the image of the Sun to transit inside the eyepiece and/or finder
scope. Stray sunlight from the eyepiece could be projected into your eyes or the eyes of nearby observers. For this reason, it is a
good idea to cover the aperture of the scope prior to starting a GoTo in the daytime.
MAPUG is hosted by
De-Rotator & Guiding
De-rotator & Guiding Discussion
Modification to Use with NGF-S
Field Derotator Experiences
Subject: De-rotator & Guiding Discussion
From: Doc G
The following is a long note on guiding and de-rotating. It is an accumulation of thoughts and posts I have made during the past
several months. Also discussed is the use of two or more tubes for guiding and imaging including considerations of wedge
mounting, de-rotating and piggy back camera mounting. The several possible cases are discussed in detail starting with simple
cases and going to the more complex.
These are my own thoughts based on calculations and experience with pointing my two telescopes over the past two years. I
hope they do not deviate too much from others experiences or reality.
The first thoughts on guiding are for cases where a camera (imager) is used piggyback and the main tube is used for guiding, the
main tube is used for imaging and a separate tube (telescope) fastened to it is used for guiding or some such combination. This
does not preclude using several imagers on several tubes with a guider on another tube all on the same mount and possibly all in
use simultaneously.
The advantage of using a separate guider is apparent to anyone who has ever used an off-axis guider. The separate guider tube
can be of fast focal ratio so as to get a bright guide image, its axis can be adjustable and so be moved a bit from that of the
imaging tube so as to center the guide star on the guider chip and an independent, stand alone guider chip can be used in its
independent operational mode. It is very convenient to have guider and imagers independent. Of course the ST 7/8 offers
additional options. I have not yet used the ST 7 in the guider mode so this arrangement is not discussed here.
To start with I assume accurate POLAR alignment. Assume that the guider finds a star and is working correctly. This situation
insures that the guide tube, is pointed at a star and locked onto it. This is the most straight forward setup and is relatively easy
to establish when a reasonably fast guide tube is used. I use a C5 on my 12" LX200. If polar alignment is not excellent, some
rotation of the field will take place. Also assume for this simple case that the atmosphere causes no distortion of the celestial
sphere. This assumption is not quite correct, so this issue will be discussed later. For the ideal case described, the declination is
fixed and the telescope needs only to track the R.A. perfectly. There will be no de-rotation required and a de-rotator is not
needed. If the telescope moves precisely in R.A. no guider correction is required either. Now assume that the telescope does not
move precisely in R.A. Naturally it doesn't because of the worm drive defects. The LX200 has a fine system for correcting periodic
worm drive defects which can reduce them from 50 arc seconds to 3 or so through a training program. Even then the guider may
need to make some corrections to the RA drive rate. This has been done manually in the past and now, with a guider, can be
done automatically. If there is no distortion of the celestial sphere by the atmosphere, then the guider tube can be pointed at a
declination or R.A. other than that of the imaging tube and guiding will still be perfect.
This is true since the undistorted celestial sphere in its entirety moves with the same angular rate in R.A. everywhere. Also note
that the above assumes that the guide tube and the imaging tube are rigidly held together with respect to each other.
Considerable care must be exercised to insure mechanical rigidity of the tubes. A counter example is given by suggesting that this
scheme will not work with the guide tube pointed at the pole star. And sure enough it won't. So what is wrong? It is this. The
effective length of the guider telescope is longer when it is pointed at a guide star that is moving the greatest linear amount for a
given angular motion of the celestial sphere. This linear amount is proportional to the sine of the angle from the pole to the
declination being guided upon. Thus when pointing the guide telescope at the pole star. The motion of the star is nearly zero and
the guider fails. To get the best accuracy with the above conditions, the guider should be pointed to a declination at 90 degrees
to the pole. Then, the guider will be locked to the celestial sphere where the linear motion of the guide star is great and the
guiding will be accurate and all will be well. Even if the polar alignment is perfect and the guider is perfect there is a complication.
That is the atmosphere. Except at the zenith, the atmosphere distorts the position of the stars in the celestial sphere as it is seen
from the telescope position. Thus as a star moves from near the horizon to a position higher in the sky and again toward the
horizon, its motion is not perfectly regular in angular rate of R.A. nor does it maintain exactly the same declination.
The amount of this deviation is quite small. The Meade telescope has a first order correction for this effect in its computer. This is
why the correct latitude and longitude must be entered into the computer to insure refraction correction that relates exactly to
the local horizon and thus insure accurate pointing. Thus it is clear that the guide tube should be pointed somewhere near the
position of imaging tube. If they are close together they both see the same atmospheric distortion and the guider will make the
required R.A. and declination corrections. But the two tubes do not have to be exactly axial aligned. Usually, imaging is done
away from the horizon because of light pollution anyway so the atmospheric distortion is usually not a great consideration. This
distortion is usually masked by "seeing defects" in the atmosphere in any case. In summary, polar mounting eliminates the
principle tracking defects and is thus very attractive for imaging. Several tubes can be pointed from the same platform and all will
function well with a single guider. A separate but important consideration is the focal length (more importantly, the effective focal
length) of the guider tube compared to that of the imaging tube. The guider cannot point more accurately than the angle
subtended by one pixel within the guider image and may not be that good. Thus, the focal length of the guider tube should be
similar to that of the imaging tube. It is usually recommended that the guider be at least 1/2 the focal length of the imager. For
example, I use a C5 (fl=1300) for my 10 inch f6.3 (fl=1200) and also on my 12 inch f10 (fl=3000).
I feel this is an adequately long guider focal length. Any shorter focal length imaging lens such as a typical piggy back camera
would normally use is then easily guided. Now, what about the Alt/Azm mounting for which celestial field rotation is a problem
when imaging. Normally a de-rotator is necessary. The rate of de-rotation is a complex function of the R.A. and declination to
which the telescope is pointed. A table of de-rotation rates is attached to this note. The table is normalized and so the numbers
must be multiplied by the local rotation rate which is 15.2 X cos(latitude). Also, values above 80 degrees are not given since they
become very large. A MATLAB graphic of this data is available on request. (very large file about 300K) The formula for the rate of
rotation of the star field is rate = (const.) X cos(latitude) X cos(azimuth) / sin(zenith distance) The rotation only goes to
zero at azimuth 90 and 270 degrees (due East and due West) and on a line connecting these points. Even on this line the rotation
becomes singular (infinite) at the zenith. At the pole the rate is 360 (approx.) degrees per 24 hours. At other points the constant
must be calculated for the observers location. The rate of de-rotation required is seriously large so that only very short exposures
are possible. Depending on you desire for perfection, only a few seconds up to a minute for some pointing directions. If the derotator is working correctly is will take care of all the calculations and turn the de-rotator at the correct rate as long as it knows
where the telescope is pointing.
I am told that the de-rotator on the 16" Meade does this operation very well. (Note that I have not use one.) Note also that the
telescope must be leveled and the correct location entered so that the telescope knows exactly where the pole star is. This is
because the de-rotation is calculated on the basis of the known R.A. and declination and azimuth distance. So, the Alt/Azm setup
cannot be more "sloppy" than that required for polar alignment. There are severe limits to the use of a de-rotator. The guide star
must be in the field of the de-rotator and be de-rotated with the field being imaged. An off axis guider will work if it is rotated
with the imaging camera. But off axis guiding is already difficult and with the guider rotating as well may require a triple jointed
neck. The ST 7/8 cameras solve this problem by mounting the guider chip next to the imaging chip Thus it rotates with the field
and will correctly guide when using a De rotator. This is a excellent idea but it does not solve the problem of field rotation in any
other tubes or piggy back imagers that may be on the same platform. If a series of short exposures is satisfactory, a single chip
could be used as a part time guider. Appropriate software would be required and short exposures would be necessarily
acceptable. But single long exposures have better signal to noise ratios. So using a chip to share functions as a guider and imager
does not seem like a good idea. Again, the shift and combine method used by SBIG is a good, if partial solution to this problem.
There are also software image processing techniques that might be applied. In summary, if the guider points the telescope to the
correct R.A. and declination and tracks a guide star accurately and the telescope computer knows the value of the pointing
position, it will calculate the correct rate of de-rotation.
The guider tube and the imaging tube need only be aligned to the accuracy and with the rigidity required for the polar guiding
case. But conversely, they need to be set at least with this accuracy and not less. Considerations for atmospheric distortions and
cetera are the same for either setup. Neither Polar nor Alt/Azm setups are much simpler each than the other to achieve the same
accuracy. In one case you need the wedge and in the other the de-rotator. One case is a well known solution the other, currently,
somewhat unknown. It is my opinion that for a permanently mounted telescope the polar mount is the least problematic. That is
because it is a simple, well understood and versatile solution to imaging guiding. For a moveable telescope that has to be reset
for each imaging session I still think the polar wedge solution is the best. Alignment, leveling and the like are not that much more
demanding for polar as for alt/azm setup I believe. I have chosen not to use a de-rotator and have opted for a wedge for both my
permanent and trailer mounted telescopes.
Thus the following opinions by be somewhat biased. The de-rotation is limited to the main tube for which the de-rotator is
designed. The piggyback image is not de-rotated. Use of a separate guider telescope is not possible. De-rotation does not work
well near the azimuth because the rate of rotation becomes very large. At the zenith, the Alt/Azm mounted telescope is rotating
rapidly on the fork axis in order to guide and the de-rotator is turning rapidly in the opposite direction to correct field rotation.
The clearest part of the sky, at least 30 degrees wide, is lost to imaging. Of course the pole region is lost to many mounted
telescopes. But it is not of much great interest in general. The de-rotator is just another complex mechanical mechanism with
bearings motor, computer software and the like which can fail to work precisely. Some autoguiders seem to work best when the
pixel axes are lined up with the axes of the telescope. With the de-rotator in the guiding path the situation is constantly changing.
Which is I think not a good idea.
Again the ST imager software reduces some of these problems. My final conclusion is, do not use a de-rotator on a small
telescope which can be easily mounted on a wedge. Since this was written, Meade has come out with a de-rotator for the LX
scopes. I have chosen to pass on it for some of the above reasons and others mentioned below. There is considerable added
extension to the rear of the telescope (about 75 mm). The attachment uses the standard Schmidt thread which is of small
diameter (internal tube opening of about 34 mm) which vignettes 35 mm format. It would be fine for CCD chip sizes. For imaging
that requires guiding, it must be done with an off axis guider that rotates with the imager. Or, of course, the ST 7/8 two chip
method. In the case of the Meade LX series, the PEC does not work in Alt Asm mode. The angle of exclusion at the zenith is
stated to be as large as 40 degrees from the zenith limited by the physical arrangement of the tube and or fork. There are in the
instructions implications that one could get somewhat closer. I must point out that I have only looked this unit over, measured it
and weighted it. I decided not to go the way of de-rotators so I do not own the unit and have not used it. Those interested in the
field rotation problem when using a telescope in Alt/Azm mounting might find the following calculations interesting. I have
calculated the rotation rates using the formulas given in Meeus The primary reference is Meeus, Astronomical Algorithms. Chapter
13, using the concept of the Parallactic Angle, explains rotation. The discussion is quite brief and thus not a clear as it might be.
A more convenient formula which is very easy to tabulate is: Angular rate of rotation = (a constant) X cos (azimuth
angle) / cos (altitude angle) The constant is the angular rate of rotation of the earth times the cos (local latitude). For my
location, Wisconsin, the constant is about 11.3 degrees per hour. One must be careful with this equation since there are several
singularities. i.e. points where the cos goes to zero. The singularity causes a line of zero rotation going from 90 to 270 degrees
azimuth, which is due East and West. This line intersects the zenith but at the same time the values of rotation at the zenith are
infinite since the cos at zenith is zero as well. The tables, calculated with MATLAB, are attached at the end of this note. The first
table is for altitudes up to 80 degrees and the second for angles from 80 to 89 degrees. Rotation at the zenith, 90 degrees
altitude, cannot be calculated.
Conclusions from the tables that follow. The rotation rate is smallest pointing East or West and largest pointing North or
South for a given altitude. When pointing at an altitude of 60 degrees, the rate of rotation can get to be 2 times normal (the
constant in the equation above). At 80 degrees, the rate can go to 6 times normal drift rate. Above 80 degrees, as shown in the
second table, the rate can get very large. The telescope is rotating on its vertical axis in order to track while the de-rotator must
rotating the opposite way to de-rotate the star field. This is not to say that the problem of de-rotation is impossible but only to
point out that movement of the telescope and de-rotator are fast and must be very accurate when pointing near the zenith. That
is why, I believe, de-rotators are not generally used at pointing angles closer to the zenith than about 20 degrees or more. But,
the best seeing is often at the zenith or at least high in the sky where de-rotation is the most difficult.
The following table is for de-rotation rates below
80 degrees alt. The values are normalized and
must be multiplied by the normal
rate at a particular latitude.
Degs:
0
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
10
20
30
40
50
60
70
80
11.1
11.3
11.8
12.8
14.5
17.3
22.2
32.5
64
10.9
11.1
11.7
12.6
14.3
17
21.9
32
63
10.4
10.6
11.1
12.1
13.6
16.3
20.9
30.5
60.2
9.6
9.8
10.2
11.1
12.6
15
19.3
28.1
55.4
8.5
8.6
9.1
9.8
11.1
13.2
17
24.9
49
7.1
7.3
7.6
8.3
9.3
11.1
14.3
20.9
41.1
5.6
5.6
5.9
6.4
7.3
8.6
11.1
16.3
32
3.8
3.9
4
4.4
5
5.9
7.6
11.1
21.9
1.9
2
2.1
2.2
2.5
3
3.9
5.6
11.1
0
0
0
0
0
0
0
0
0
-1.9
-2
-2.1
-2.2
-2.5
-3
-3.9
-5.6
-11.1
-3.8
-3.9
-4
-4.4
-5
-5.9
-7.6
-11.1
-21.9
-5.6
-5.6
-5.9
-6.4
-7.3
-8.6
-11.1
-16.3
-32
-7.1
-7.3
-7.6
-8.3
-9.3
-11.1
-14.3
-20.9
-41.1
-8.5
-8.6
-9.1
-9.8
-11.1
-13.2
-17
-24.9
-49
-9.6
-9.8
-10.2
-11.1
-12.6
-15
-19.3
-28.1
-55.4
-10.4
-10.6
-11.1
-12.1
-13.6
-16.3
-20.9
-30.5
-60.2
170
180
190
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
-10.9
-11.1
-11.7
-12.6
-14.3
-17
-21.9
-32
-63
-11.1
-11.3
-11.8
-12.8
-14.5
-17.3
-22.2
-32.5
-64
-10.9
-11.1
-11.7
-12.6
-14.3
-17
-21.9
-32
-63
-10.4
-10.6
-11.1
-12.1
-13.6
-16.3
-20.9
-30.5
-60.2
-9.6
-9.8
-10.2
-11.1
-12.6
-15
-19.3
-28.1
-55.4
-8.5
-8.6
-9.1
-9.8
-11.1
-13.2
-17
-24.9
-49
-7.1
-7.3
-7.6
-8.3
-9.3
-11.1
-14.3
-20.9
-41.1
-5.6
-5.6
-5.9
-6.4
-7.3
-8.6
-11.1
-16.3
-32
-3.8
-3.9
-4
-4.4
-5
-5.9
-7.6
-11.1
-21.9
-1.9
-2
-2.1
-2.2
-2.5
-3
-3.9
-5.6
-11.1
0
0
0
0
0
0
0
0
0
1.9
2
2.1
2.2
2.5
3
3.9
5.6
11.1
3.8
3.9
4
4.4
5
5.9
7.6
11.1
21.9
5.6
5.6
5.9
6.4
7.3
8.6
11.1
16.3
32
7.1
7.3
7.6
8.3
9.3
11.1
14.3
20.9
41.1
8.5
8.6
9.1
9.8
11.1
13.2
17
24.9
49
9.6
9.8
10.2
11.1
12.6
15
19.3
28.1
55.4
10.4
10.6
11.1
12.1
13.6
16.3
20.9
30.5
60.2
10.9
11.1
11.7
12.6
14.3
17
21.9
32
63
11.1
11.3
11.8
12.8
14.5
17.3
22.2
32.5
64
ƒƒ
The following table gives values above 80 degrees.
As can be seen,they get very large near the zenith.
Degs:
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
81
82
83
84
85
86
87
88
71.1
79.9
91.2
106.3
127.5
159.4
212.4
318.5
70
78.7
89.8
104.7
125.6
156.9
209.2
313.7
66.8
75.1
85.7
99.9
119.9
149.8
199.6
299.3
61.5
69.2
79
92.1
110.5
138
184
275.9
54.4
61.2
69.9
81.5
97.7
122.1
162.7
244
45.7
51.3
58.6
68.4
82
102.4
136.5
204.7
35.5
39.9
45.6
53.2
63.8
79.7
106.2
159.3
24.3
27.3
31.2
36.4
43.6
54.5
72.6
108.9
12.3
13.9
15.8
18.5
22.1
27.7
36.9
55.3
0
0
0
0
0
0
0
0
-12.3
-13.9
-15.8
-18.5
-22.1
-27.7
-36.9
-55.3
-24.3
-27.3
-31.2
-36.4
-43.6
-54.5
-72.6
-108.9
-35.5
-39.9
-45.6
-53.2
-63.8
-79.7
-106.2
-159.3
-45.7
-51.3
-58.6
-68.4
-82
-102.4
-136.5
-204.7
-54.4
-61.2
-69.9
-81.5
-97.7
-122.1
-162.7
-244
-61.5
-69.2
-79
-92.1
-110.5
-138
-184
-275.9
-66.8
-75.1
-85.7
-99.9
-119.9
-149.8
-199.6
-299.3
-70
-78.7
-89.8
-104.7
-125.6
-156.9
-209.2
-313.7
-71.1
-79.9
-91.2
-106.3
-127.5
-159.4
-212.4
-318.5
-70
-78.7
-89.8
-104.7
-125.6
-156.9
-209.2
-313.7
-66.8
-75.1
-85.7
-99.9
-119.9
-149.8
-199.6
-299.3
-61.5
-69.2
-79
-92.1
-110.5
-138
-184
-275.9
-54.4
-61.2
-69.9
-81.5
-97.7
-122.1
-162.7
-244
230
240
250
260
270
280
290
300
310
320
330
340
350
360
-45.7
-51.3
-58.6
-68.4
-82
-102.4
-136.5
-204.7
-35.5
-39.9
-45.6
-53.2
-63.8
-79.7
-106.2
-159.3
-24.3
-27.3
-31.2
-36.4
-43.6
-54.5
-72.6
-108.9
-12.3
-13.9
-15.8
-18.5
-22.1
-27.7
-36.9
-55.3
0
0
0
0
0
0
0
0
12.3
13.9
15.8
18.5
22.1
27.7
36.9
55.3
24.3
27.3
31.2
36.4
43.6
54.5
72.6
108.9
35.5
39.9
45.6
53.2
63.8
79.7
106.2
159.3
45.7
51.3
58.6
68.4
82
102.4
136.5
204.7
54.4
61.2
69.9
81.5
97.7
122.1
162.7
244
61.5
69.2
79
92.1
110.5
138
184
275.9
66.8
75.1
85.7
99.9
119.9
149.8
199.6
299.3
70
78.7
89.8
104.7
125.6
156.9
209.2
313.7
71.1
79.9
91.2
106.3
127.5
159.4
212.4
318.5
Field Rotation Plot
I hope this information and my ideas about pointing your telescope have been of some value. Sincerely -- Doc G
-----------------------------------------------------------------Subject: Derotator Advise (more)
From: Doc G, Date: March 2005
Believe me when I say that I wish the de-rotator had been more of a success. A decade ago I got my first 12" LX200 classic with
a de-rotator and a Pictor 1616. I worked diligently for 12 to 18 months with this equipment and never got it to work well. The
litany of problems was overwhelming. The equipment never worked all at the same time. I lost over a year of imaging with this
equipment. Perhaps that is why I warn people to proceed with great caution when trying to get this equipment to all work
together. There are significant disadvantages to the de-rotator when used with a fork mount.
After a year of struggle I got a wedge and an SBIG ST-7. Within one week I had dozens of fairly nice images even though in
monochrome. This was the period, a decade ago, in which I worked very hard to tune up the LX classic to the point where it was
suitable for imaging. I came to the conclusion that for small scopes, like a 12", the wedge was the way to go. I certainly hope
that the new GPS and RCX scopes have improved mechanics and will be able to be more easily tuned up for imaging. I will not be
trying this newer equipment since I have moved on to different equipment which better suits my needs. (Paramount, SBIG
Canon, Takahashi and the like)
Tentative reports indicate that the newer scopes optics are excellent, mechanics have greatly improved and the software has also
improved significantly. I really hope this is the case since Meade, with its pricing, opens the joys of astrophotography to a much
larger group. The SBIG group is the premier astro imaging group in my opinion. But they also for the most part have significantly
more costly setups. Paramounts, Takahashi, RC and big SBIG cameras. All big bucks. I one time did a survey of the SBIG group
and found that only about 5 % of them use Meade scopes.
I think you will find an interesting and challenging experiment when you go to a de-rotator. I wish you the best of luck. I rather
this you will find the need for mother luck to be on your side.
By the way, I do not really understand the problem with wedges at lower latitudes. I have seen Meade scopes used on wedges in
Aruba which is at 12 degrees and I have a friend using one on a wedge in Singapore which is at 1 degree. I was just to the
Winter Star Party and saw hundreds of scopes on wedges and that is at 24 degrees. Wedges work well at any latitude. They just
look funny at very low latitudes.
Subject: De-Rotator Mod to Use with NGF-S
From: Dave Dixon
The Meade 1220 de-rotator does a very nice job of solving the problem of field rotation for an ALT-AZ mounted LX200. At the
same time it introduces problems in backfocus and flexure especially when heavily loaded with an OAG, CCD camera and
autoguider and trying to use a JMI NGF-S zero shift focuser. However with one modification the de-rotator and NGF-S can be
utilized together in a combination that reduces back focus by 30 mm and almost completely eliminates flexure. Figure 1 shows
the de-rotator with the SCT mount replaced by a 2" barrel that slides into the NGF-S as if it were a 2" eyepiece. Figure 2 shows
the assembly mounted on an LX200. The only negative is that the weight of the de-rotator becomes added to the other
accessories that the NGF-S has to move when focusing. A combination of the de-rotator, a Van Slyke Slider II, Meade 416xt, and
208xt are right at the limit of my NGF-S to lift when at an altitude of about 55 degrees.
Figure 1
Subject: Field Derotator Experiences
From: Radu Corlan <rcorlan
profis.ro> Date: Sept., 2000
In case any of the list readers wondered if they really can avoid carrying a 15kg wedge and still make photographs -- well, you
can (that is, the de-rotator works). But "there may be dragons".
Made the first test with the de-rotator (#1120) on a 12'' LX200 yesterday. I used the following setup: LX200->de-rotator->offaxis guider->35mm camera. The scope was leveled carefully an daligned with a 12mm reticle eyepiece.
First, the good parts:
1. The up-swing limit is not as bad as it would seem. Although (for some unknown reason) the scope sets the limit to 40
degrees from zenith, in practice it is below 20 degrees. I can imagine having to have a tighter limit when using a camera
that extends a lot towards the mount. But you get within 20 degrees from zenith even when a 35mm camera is positioned
vertically.
2. The camera/guider doesn;t rotate that much. You can make 1 hour exposures without the guiding being much more
difficult than without rotation.
3. This is the really pleasant surprise: guiding in dec is as smooth as the r.a. The dec drive doesn;t reverse any more (it just
accelerates/stops), so the corrections are smooth and instantaneous. Although i didn;t use an autoguider (yet) i can tell
the thing is "autoguider-friendly".
I tool some 20-min unguided shots, and the result is that star images make nice arcs, about 15'' in diameter. This is to be
expected, and at the normal level of the drive gears. The circular pattern comes from combining the dec and ra drives' periodic
tracking errors.
I also took some manually guided shots (10 and 20-mins). When guiding yu go for example w for a minute or two, then w and
south, then south, then e and south etc - as expected to cancel the circles. I took the shots in the Pleiades region, so i have
enough bright stars in the field to check the tracking. All came out nice and round, and without signs of firld rotation.
>From the above, you can see i'm sold to the de-rotation process. But now comes the unpleasant part: the de-rotator unit itself.
When i got the telescope, i was a little disappointed. The construction and finish weren;t what i expected in a quality optical
instrument (look at a real microscope or similar piece of gear, and you will know what i mean). But it really is "a lot of telescope
for the money" and the overall design is optimised, (at least for cost ;-> )
But the de-rotator is another matter. First it's unnecessary bulky. It has a heavy steel cover, and eats way too much back focus
unnecessarily. On the 12'' it could have been mounted directly on the 3'' thread, flush with it's baseplate, and still clear the
scope. That alone would decrease it's backfocus by nearly 4cm.
Second, when i first unpacked it, it had about 0.5mm free play in the rotating bearing - imagine your camera flipping up and
down 0.5mm! And it had play in the rotation direction.
I opened it up (at least it's easy to assemble/disassemble).
The unit is built on a backplate. On the telescope side, there is an SCT thread coupler (way too tall IMO). On the other side,
there's a circa 4'' dia worm gear rotating on a bearing. The "output" coupler is bolted on the gear. The gear is turned by a worm,
which is driven via a totthed belt by a gearbox reduced stepper. The stepper and gearbox are a single unit (and look mighty
strong - way larger than the LX drive motors).
The rotation-wise play was easy enough to fix - the worm's position was maladjusted (or should i say unadjusted?) Pushing it a
little against the worm gear did the trick. But when i took the worm off to check the worm gear play in the bearing - surprise! Not
only was the play in the bearing _huge_, but the wheel felt rough when turning.
I suspected that the wheel had some sort of nylon bearing, and they forgot to put the bearing element in altogether. So, off come
the many screws that hold the thing together. It turns out that thegear is rotating on a ball bearing. But not a preassembled
bearing, but rather one built from the gear itself and the hub. The gear has a semi-circular race machined on the inside, and the
hub is made of two beveled parts which screw together. When fitted, they form a "v" shaped track. A lot of loose bearing balls
complete the bearing.
The rough rotation's cause was pretty evident: all the beaaring area was full of aluminium shavings. Fortunately, the races
themselves were smooth and even - the shavings must have come from the many threads that are around. But the play was just
grossly imprecise machining! Not having the required gages around, i couldnt determine if the play came from the semicircular
race in the worm, or just wrong diameters. In the latter case, it can be cured by machining the hub halves, making the "v"
narrower, and thus pushing the balls towards the gear. If the race itself is the problem, the thing can still be fixed by using larger
balls.
Until i get to do one of the above, i mounted some Teflon pads underneath the gear, and the play is gone. Still, this is obviously
not a final solution.
Does anybody have better experience with the de-rotators? I may "just" have had a bad unit.
MAPUG is hosted by
Dew Zapping and Grounding Danger
Dew Zapping --3 parts
Dew Controller Schematic
Dew Zapping & LX200 Grounding Danger --2 parts
Dew Formation & Its Prevention --4 parts
Dew Prevention Inside Corrector Plate --3 parts
Homemade LX200 Dew Zappers --7 parts
Dew Shield Construction & Proper Color
The DewBuster & Placement of Heating Element
Subject: Dew Zapping --part 1 of 3
From: Mike Hamann <mikehamann
jps.net>
I have used both a Kendrick dew shield and an Orion Dew Zapping in this area, and if I had to cast a vote for either (or both),
the Dew Zapping wins hands down.
First, I suspect I live in one of the wettest, but darkest places in the US -- the Northern California coast, right next to the Pacific
Ocean, halfway between 'Frisco and the Oregon border. Both myself and another observing buddy have used C-8 and Ultima
2000 alt-az mounted scopes here. The dew shield is sometimes good for 60 - 120 minutes from setup to dew-down (literally!),
and so we both went to the Orion 20 watt, 12 v.d.c. Dew Zapper because the dew shield could only keep the corrector plate dewfree for a limited time.
It seemed like when things got interesting, the dew would start its buildup. The time it took for the dew was dependent upon
the relative humidity, which is almost always 90% plus. The Dew Zapper never failed either one of us. The only question in my
mind is, "Does the 20 watts of heat applied to the corrector plate periphery degrade the image?" The answer hasn't concerned
me yet -- it was either get rid of the water (dew) or don't observe. I never noticed any obvious degradation, but I was only using
the scope visually -- no astrophotography/imaging involved. After the Dew Zapping is applied to the periphery of the corrector
plate, the Zapper barely feels warm to the touch; on the other hand, the Zapper on its own (not attached to anything else) is
quite hot to the touch.
-------------------------------------------------------------------Subject: Dew Zapping --part 2
From: Bill Arnett <billa
nineplanets.org>
..I have seen plans for a homemade zapper somewhere on the web...
Mine is at: <http://obs.nineplanets.org/dp/dewpower.html> Note: a new browser window should open over this one.
And at the bottom are links to a few others. Let me know if you find any more I should add to the list.
--------------------------------------------------------------------Subject: Dew Zapping --part 3 of 3
From: Don Holcombe
After reading Philips Blanda's account of wrapping his AP 130 in foil, I coerced the wife into fabricating a Mylar wrap for my 10"
LX200. The material was purchased to make a 'Desert Storm' cover, but I had enough extra Mylar for this project. I've attached a
pic much like his description.
Subject: Dew Controller Schematic
From: Michael Sangster
My dew controller schematic is on my web site: http://members.aol.com/lx10user/astro/images/dewc.jpg
See the section on Dew. Note: should open a new browser window over this one.
Subject: Dew Zapping & LX200 Grounding Danger --part 1 of 2
From: Michael Gregory
If you are going to work outside with any device connected to the power grid, I would strongly recommend using a ground-faultinterrupter. These devices (which are not all that expensive anymore) disconnect the power source if more than 1 thousandth
(typically) of an Ampere leaves the positive phase of the source and does not return to the negative side of the source. This is
really a life-saver if your dew zapper were to develop a fault allowing a current from the OTA through you to the earth (ground).
The 0.001 Ampere current would not kill you, and the GFI would disconnect the circuit when the fault was sensed.
------------------------------------------------------------------Subject: Dew Zapping & LX200 Grounding Danger --part 2 of 2
From: Chris Frye <cfrye
ix.netcom.com> Date: Oct., 1998
For those of you unfamiliar with the Orion Dew Zapper, it is a rubberized band that is wrapped around the OTA near the corrector
plate. The AC model has a green ground wire coming out of the orange rubberized band. This wire must be connected to one of
your OTA accessory screws to prevent possible electrical shock. It has a 10 foot heavy duty line cord attached to it. The last thing
I want to do in the dark is to loosen one of my OTA's accessory screws and attach that green ground wire. I thought, why not
attach it permanently and make a provision whereby I can detach the 10 foot long AC line chord. Here is what I did:
I attached the Dew Zapper around the OTA and grounded the green wire to one of the OTA's accessory screws (don't use the
anodized one Meade supplies, it's an insulator, use a 6-32 x 1/4" stainless steel screw form the hardware store. I cut the AC line
cord about 5 inches from the "Dew Zapper" and used a male and female 3 pin microphone connector to be able to detach the 10
foot line cord for OTA storage. The Radio-Shack numbers are: 274-010 & 274-011.
Additional notes:
Orion supplies a fabric wrapped AWG-18 cable capable of carrying 15A. This cable is very heavy and I don't think it will do
tracking any good. The "Dew Zapper" is rated at 25W (about .2A at 110V), this means we can use very thin and lighter wire. On
the other side of the 274-011 connector I used 10 feet of 2 strand speaker wire, to which I adjoined another strand using micro
wire ties. Speaker wire insulation is good for 250V for some reason, so it's safe. I only wish the microphone connectors were
smaller, together they weigh about 8 ounces.
Subject: : Dew Formation & Its Prevention --part 1 of 4
From: John Hopper <JohnLX200
michael
aol.com>
schwarz.org writes:
>I have heard and read this in a couple of places and the statement confuses me. It says that dew forms on a scope
when the scope cools off faster the air.
>How does this happen? What causes the scope to cool off faster than the air. I thought the air surrounding the
scope is what determines the temperature of the scope. If it cools off faster than the air, how does the scope know
when to stop cooling off?
It's from radiational cooling. The clear night sky has an equivalent "black-body" temperature near absolute zero, sucking heat out
of you and your telescope in the same way that the high black-body temperature of the sun pumps heat into you: directly
through (mostly infrared, but really a distribution of wavelengths including visible in the case of the sun) radiation rather than
contact with air or anything else.
This is why frost can form on blades of grass when the air temperature and ground temperature are both above freezing. It is
also why the surface of the moon heats up and cools off, in the absence of air. Of course in that case, there's also conduction
through the soil too.
The good news is, it's also why a dewcap helps. It provides an air-temperature body rather than sky-temperature body for your
optics to look at over the majority of the scope's 180 degree "view" of the sky, cutting down the section of sky with a direct look
at your optics. By heating the dewcap just the right amount, it's also possible to have it radiating the same amount of heat to the
optics that the optics are radiating to space, hence leaving the optics at air temperature.
I won't get into all the equations, but the amount of radiational heat transfer between two objects is proportional to the difference
between the fourth power of each of their absolute temperatures, all other things being equal such as distance, geometry,
orientation, surface properties, etc. The three surface properties which also heavily determine the amount of heat transferred
are: reflectivity, absorption, and emissivity.
-------------------------------------------------------------------------------Subject: : Dew Formation & Its Prevention --part 2
From: Michael Sparks <sparksmd
zoomnet.net>
John Hopper's explanation is very good. I would like to add an additional comment to his.
Dew formation occurs on any object which has a temperature lower than the current dew point of the surrounding air. In other
words air can only absorb so much water (humidity). The amount of water it can absorb per unit of air varies by temperature
(relative humidity). The dew point is the temperature at which the air can no longer hold the water it has absorbed due to cooling
of the air. As a result you get dew, fog and frost. As the night air cools to its dew point objects in the night air also cool to that
temperature. As the air moves around the object the water condenses on the object. The water in the air likes a solid surface or
particle to condense on. That is why you see the dew on your scope before you see fog in the air.
-------------------------------------------------------------------------------Subject: : Dew Formation & Its Prevention --part 3
From: Peter Dietrich
Every material has a special property called specific warmth capacity (direct translation of German expression) when theory of
heat is considered, which is defined by J/(G*K) Where is joule, is gram and is Kelvin.
In other words: joule per gram and Kelvin, e.g.: 1 J/(G*K) means you need the energy of one joule to heat up one gram of
material for one degree centigrade or for one Kelvin.
You certainly have made the experience that temperatures in areas near the coast are higher than in inland areas of the same
country and in the same season. The different warmth capacities (dwc) of water and soil are the reason.
Water has a higher dwc than soil, so water heats up slower than soil does, but that also means that water loses warmth much
slower than soil. In fact, the water of the sea warms the coast during night.
And now back to the scope. Metal has a much lower dwc than gas. From what was mentoined above, we can tell that metal heats
up very fast (good heat conductor) but also cools down very fast (faster as air).
-------------------------------------------------------------------------------Subject: : Dew Formation & Its Prevention --part 4 of 4
From: Philip Freeman
I know this is getting beat to death, but I'll interject a few ideas (maybe it will help, maybe not). The corrector plate will reach a
steady state temperature when the heat flowing into the plate = heat flowing out of the plate (Qi = Qo). Heat flow is Q = heat
flow by conduction + heat flow by convection + heat flow by radiation.
Heat flow by conduction is done from the plates direct contact with the OTA. This is proportional to the difference in temperature
between the plate and the OTA. Heat flow by convection is done between the plate and the air. This is also proportional to the
difference in temperature between the air and the plate.
Heat flow by radiation is done between the plate, the air, the ground, and outer space. This however is proportional to the
difference in the fourth power of temperature, so the heat transfer between the plate and outer space DOMINATES this term.
You can set up the equations (found in a basic heat transfer text book) and solve for the temperature of the corrector plate.
Because of the radiation term, it is not only possible, but likely, that the equilibrium temperature of the telescope will be below
that of the air. Yes, the air is _still_ putting heat into the plate, but that heat is just being radiated out to space. Heat hasn't
stopped flowing, it's just reached equilibrium. If this equilibrium telescope temperature is below the dew point, dew will form,
even if the air temperature is still above the dew point.
So, what can be done to increase this equilibrium temperature is two fold, and well known. 1) increase one of the other terms in
the heat equation. A dew heater will raise the conduction term. A gentle breeze will raise the convection term. 2) Reduce the
radiation term. Use a dew shield. The dew shield now blocks the telescope optics from radiating out to space. It can be as simple
as a piece of cardboard. Now the radiation term becomes radiation with air, ground, space, and dewshield, with space still
dominating, but having less impact because there is less "view angle" now between space and the telescope. Trace rays from the
telescope's corrector plate to space without intersecting anything, before the dew shield you could trace rays all the way around.
This is a full hemisphere of view angle. Now with the dew shield you have only a tiny patch of space that is part of the view angle.
The corollary to this is: when not at the eyepiece, point the telescope at the ground. Now radiation with space is zero (no view
angle to space) and you can prolong the onset of dew.
Subject: Dew Prevention Inside Corrector Plate --part 1 of 3
From: Gene Horr <genehorr
texas.net> Date: Dec 2002
Alan Voetsch wrote:
> Occasionally this time of the year I get a layer of dew on the inside
> surface of the corrector. Using a hair dryer takes forever and causes such
> a heat increase that star images go crazy.
Try a blast through the rear opening with no heat. Just getting the corrector to ambient will dry it out.
> I would like suggestions on how
> to permanently remove this problem. I use a dew-zapper on the outside and
> for the most part that solves that problem.
A dewshield will help a lot. The less exposure to the open sky the lower the radiation. That plus a heat strip on a low setting
should work fine. I work at close to 100% humidity almost year round and this works for me.
> What about inside the OTA? A couple 'Dri-Z-Air' packets?
The OTA is far from air tight. If you want to get really fancy a fan blowing air into the OTA would keep the corrector warmer. But
IMO the best solution is a long enough dewshield along with your heat strip.
---------------------------------Subject: Dew Prevention Inside Corrector Plate --part 2
From: Kevin Wigell <kwemail
twcny.rr.com>
I've never had problems with moisture build-up inside my OTA, even when other LX200's right next to me have. Here's what I
do:
When I have the OTA inside (where the relative humidity is presumably low), I often leave the cover off the rear cell, with the cell
pointed down (so that dust is less likely to find its way inside). A few hours of this should allow dry air to permeate the inside of
the tube. Then, before I take it outside, I either put the plastic cover on or put the glass "UV" filter on. Then, once I'm outside, I
minimize the time that the OTA is open to the atmosphere. If I'm changing eyepieces or putting on a camera or whatever, I don't
leave the OTA open to the outside air any longer than necessary. I figure this keeps the dew point of the air inside the tube below
the ambient temperature.
Doing this, I've never had a hint of moisture inside the OTA, even while other LX200 users right next to me are complaining
about the same. Not only is the moisture build-up annoying, but over time it could promote mold. However, it will likely work only
if the telescope is in an air conditioned room.
If your scope is permanently mounted outside, I don't see anything wrong with putting some desiccant (see part 3 below) inside
with the tube all closed up. Just remember to take it out, or it may end up somewhere where you don't want it!
The reason my method works is that I do most of my observing in the spring through fall (due to near-constant clouds in the
winter where I live - central New York State), and my house has central air conditioning. So, with the A/C on, the absolute
humidity (i.e., dewpoint) inside would lower than outside. You are soooo right that the method I described would probably not
work well in the winter, when the absolute humidity indoors is almost certainly higher than outdoors.
---------------------------------Subject: Dew Prevention Inside Corrector Plate --part 3 of 3
From: Gregg Ruppel <ruppelgl
SLU.EDU>
I use a method similar to what you have described. Use a standard 35 mm film canister; this fits snugly into a 1.25 inch eyepiece
holder. Punch or drill some small holes in the bottom of the canister. Go to a craft store and get some Drierite (anhydrous
calcium sulfate). This stuff is blue and turns pink when saturated with water vapor; it's sometimes used to dry flowers etc. You
might also search for it online. Put a piece of coffee filter or similar porous material in the canister and then fill with Drierite:
<http://www.drierite.com/>, they have online ordering.
Drierite is supplied as granules but contains some dust. The filter material helps prevent any dust from getting into the OTA. Put
the cap on the canister and insert into the 1.25 inch adapter whenever the scope is not in use. When the Drierite turns pink you
can put it in the oven to drive the water off, but it is not terribly expensive so I just refill the film canister with fresh Drierite. If
you can't find Drierite you could try to put some small packs of silica gel in the canister but it doesn't seem to be as effective.
Note: another source is: <http://www.sigmaaldrich.com/>
In either case, be sure to order "indicating" which is pink when dry, blue when wet.
Editor's note: for sources of heat tape, see Miscellaneous Topics-->Telescope Storage.
Subject: Homemade LX200 Dew Zappers --part 1 of 7
From: Scott Baker <scottb80
cts.com> Date: Feb., 2001
I don't like the idea of the resistors so I built my own dew zapper using NiChrome wire, for my 10" LX200. I've been meaning to
put this up on a web page, but just haven't gotten around to it yet. Anyway, here's how I did it.
I first decided that 20 - 25 Watts was about the maximum wattage I'd need on the worst night. I also decided that simplicity is
better, and that a simple On/Off switch was all I needed to turn it on, no rheostats or electronic drive circuits. I also decided that
running it at 12 Volts was good if I ever wanted to power it from the car. I next measured the circumference of my scope (about
36"). I then calculated the resistance needed to achieve 20 - 25 Watts at 12 Volts (Ohms law) R = Voltage squared (12*12)
divided by 22 Watts = abut 6.5 Ohms.
I then went shopping for NiChrome wire. I need a wire that would give 6.5 Ohms in three feet of length. NiChrome wire is rated
in Ohms per foot, so I was looking for approximately 2 ohms per foot. What I found was 4 ohm per foot wire, which is fine, I just
needed twice as much. This worked out very well, since now I could use two pieces of wire in parallel and two separate switches
to turn them on. One switch on = 11 watts, two on = 22 watts. I then connected an insulated wire to one end of each of the two
NiChrome wires (three wires in one connection). I then took some tubular nylon strap and had my wife sew up the center of it,
creating two insulated tubes. I then fed one piece of the NiChrome wire down one tube and the other NiChrome and the insulated
wire down the other tube.
I then sewed some Velcro to the tube end where the three wires come together, thus sealing that end. I then took the other end,
where the wires exit the tube and put them into a small plastic box that holds the switches. This box also has a wire coming out
the other end for my 12 volt input. Velcro on the box allows me to strap it onto the scope. I know this sounds a little confusing
and a picture is worth a thousand words, so If you'll email me, I'll take some shots of the dew zapper, and email them to you.
This is not a difficult job and can be done by anyone that can use a soldering iron. The toughest part is finding small quantities of
the wire without spending a fortune. I got 50' roll of 26 gauge (4 ohms per foot) from <http://www.omega.com/> for $10.00
plus shipping and handling.
Now before anyone jumps on me for having heating elements in a meltable tube, let me say this, at 22 watts, maximum output,
the two pieces of wire never get hot enough that you can't hold them in your hand. It gets real warm, but not even close to the
melting point of nylon. This zapper works great, was cheap and fun to build. I even put two red LED's on the box to show which
element is on, not necessary, but looks cool.
--------------------------------------Subject: Homemade LX200 Dew Zappers --part 2
From: Bruce Johnson
Since dew removers with NiChrome is being talked about, I might as well throw in something as well. Now, this is strictly for
permanent mounted scopes with AC available.
I took a broken toaster and used the wire from that, (NiChrome) and made a strip that would develop 20 watts off of 12.6 volts.
Then, I bought a dimmer switch that is used for dimming house lights for $3.00, and I also took an old Radio Shack 12.6 volt, 3
amp transformer. I just wired the dimmer switch in series with the transformer primary (wouldn't work at 12.6v). I laid the strip
of heat wire along a stretch of duct tape and covered it with another strip of duct tape. The duct tape goes around my 10" LX200
(OT) and I now have a dew zapper that can give continuously variable heat from 0 to 20 watts.
Before I decided to try the dimmer, I had made a small box with two switches in it. The switches were the kind with the 'center
off' type of toggle switch. By using the five combinations of the two switches, I had a setup that could give me five different heat
settings, from 7W to 20W. I just used the switches to short out more and more of the NiChrome wire, which then developed more
and more power.
--------------------------------------Subject: Homemade LX200 Dew Zappers --part 3
From: David Sanders
American Science & Surplus (http://www.sciplus.com/) has heat rope for sale. Their part number is 1490 and cost $1.95 each for
a 27" long piece 3/16" in dia.
---------------------------------------
Subject: Homemade LX200 Dew Zappers --part 4
From: Robert Cadloff <bomo
sympatico.ca>
There's also Watlow (watlow.com), who make a huge range of heaters of various types. Their silicone flexible heaters are perfect
for the job. I managed to get a 1" x 30" sample. Here is the direct link to a pdf brochure:
<http://www.watlow.com/literature/specsheets/files/heaters/colflx0202.pdf>
Note: should open a new browser window over this one.
--------------------------------------Subject: Home-Made Dew Zapper --part 5
From: Wendel Burkhardt, Date: Feb 2001
Here is an update on a dew heater, that I have now completed, that is made from NiChrome wire from an old heating blanket. I
have tried building one several ways including using a potentiometer to allow variable resistance and have found an approach
that what seems to work best. Here it is:
For my dew heater I wanted several power settings. The levels that I eventually selected were 6.5W, 9W, 13W, 18W, and 28W.
The NiChrome wire from the dead heating blanket that I used had a resistance of 0.33 ohms/ft. In the heating blanket, each
heating "wire" contains 2 separate NiChrome wires imbedded in insulation. the insulation is flat and about 1/8 inch wide and 1/16
inch thick. The two wires are insulated from each other, similar to what the old flat TV antenna cable was like. To get the lowest
setting, I needed a 75 ft. length of NiChrome wire. Higher power settings required shorter lengths of NiChrome. Since, the wire is
doubled, I used about 37 feet of cable, enough to do 14 wraps of my 10" OTA and then used a crimp connector to join both wires
at one end giving me a total length of 75 feet. For the other power settings, I spliced into one side of the heating blanket cable,
at the appropriate lengths, to get shorter lengths of NiChrome wire. At each splice, I used crimp connectors to slice in a supply
wire.
Prior to wrapping the OTA, I put a wrap of duct tape around the OTA, adhesive side out. I wrapped 2 layers of the heater cable on
this, 7 wraps to a layer. I used the duct tape to cover the wrapped heater elements. With a few more layers of duct tape on it, it
is pretty strong and holds its shape well.
To supply the power to heater cable, I used some extra CAT 5 Ethernet cable that I had available. This cable had 8 24 gauge
wires in it, which are thick enough to handle the 2.3-2.5 amps that the heater would draw at maximum power. I ran the Ethernet
cable back to a control box where I connected the wires to a 6 position rotary switch I purchased at an electronics store. For a
power cord, I used a cigarette lighter connector that I purchased at Radio Shack.
I find it works very well, is easily removed from my scope, and the control box doesn't heat up, which is the problem I found
when I tried to use a potentiometer to vary resistance. The duct tape protects the OTA very well and provides a very good
enclosure for the heating elements.
I plan to write this up in a bit more detail, with pictures, and put it on my web site when I have a few spare minutes.
--------------------------------------Subject: Home-Made Dew Zapper --part 6
Dew Controller information and Instructions on Making a Dew Strip
From: David Moody <blckbelt
bellsouth.net> Date: Feb 2002
Previously, some of you had expressed interest in a dew controller that Ron Keating, a member of the Pontchartrain Astronomy
Society, had designed and built. This dew controller can maintain a user adjustable temperature above ambient, has 8 total
outputs - 4 temperature controlled and 4 set to 40% activation (this can be adjusted internally). It is compatible with Kendrick
heating strips (Or you can make your own like I have been doing. If any of you are curious, see my postscript).
Here is a link to a picture of the controller:
<http://personal.atl.bellsouth.net/b/l/blckbelt/interest.htmimages/DewBuster.jpg>
Ron calls this the "DewBuster". He told me to let you know about his web site: <http://personal.atl.bellsouth.net/b/l/blckbelt/
interest.htm>, you may contact him at <ron_keating
yahoo.com> if you are interested in ordering one of these units. He said
that the price, fully assembled, is $150. This is an excellent controller that can reduce your battery drain, carry a higher load than
a Kendrick, and will easily work with the more complex dew control requirements (say for example, if you want to control dew on
your Schmidt/Cass corrector plate, Telrad, eyepiece, diagonal, finder lens and finder eyepiece).
Ron has put a great deal effort over the past year designing and refining this controller, testing it on several different types of
telescopes. Several members of the club now have these controllers and are actively using them in the field with solid results.
I have no financial interest in this, but Ron is a terrific guy with a great deal of enthusiasm for this hobby. I have been constantly
frustrated with the dew problems down here in southern Louisiana and he has, with something that started out as a small project,
made a product that works really well. If this is something in which you are interested, drop him a line.
So you want to make a dew heating strip? It is very easy to do as long as you have a soldering iron and associated tools,
and a little patience. Ron showed me how to make these, and I learned a few other things in the process. I know there are
several other ways of doing this, but this way just turned out to be the most convenient for me.
The basic design for this homemade dew strip is a parallel circuit of 330 ohm 1/2 watt resistors (I would try to buy these in bulk
instead of from a place like Radio Shack, because you will need several. Radio Shack charges $.79 for 5 whereas I can buy them
in bulk for about $4-5 per 200). The general rule that seems to work best is to have one resistor every 1/2". So, the first thing
you need to do is determine how many you will need. Measure the outside diameter of whatever you are planning on heating,
say, a corrector plate. If you have a 10" SCT, the outside of the rim is a little over 37". That means you will need 74 resistors for
that strip. The connecting wires on either side should be 16 gauge copper wire or better (that also goes for your connecting cable
that goes from the dew strip to the controller, otherwise the cable will heat up, which is not what you want to do.). On a smaller
dew strip for an eyepiece, 18 gauge should be sufficient.
I made separate connecting cables, using RCA plugs on either end, that hook the dew strips into the controller. You could just
have a long extension going from the dew strip to the controller, but I wanted a little more modular design since I alternately
change from a 80mm f/5 to a 90mm ETX on top of my 10" SCT (an LX50).
Once you have everything laid out, wrap the ends of the resistors once around the wires. Your wires should be pretty close, say 2
or 3mm to the body of the resistor, but not any closer so it is touching the body of the resistor since you will be soldering those
wrap points. I would wrap all of the resistor leads and then commence soldering, checking the distance interval between each
resistor before soldering. When you are done and everything looks neat and satisfactory, clip the excess leads and use a fine file
or emery board to smooth the solder joints.
Put a long strip of non-flammable, heat-resistant foam on what will be the back of the strip. This will help keep the heat directed
inwards towards the corrector plate. If you are from the Tool Time School of assembly, now is the time for Duct Tape! Actually,
however you end up covering your dew heater, applying a strip of duct tape over either side of the length of the heater and then
trimming to edge will help keep your heater together with the insulation and will provide a protecting layer from or for the outer
covering. If you want to put an outer covering (a light but high wear fabric, for instance) on, this would be the time to do it. You
will then want to attach a strip of fuzzy side Velcro to the back of the dew strip towards the connection side. Then attach the hook
side Velcro to the far end of the dew strip so when you wrap the strip around the corrector plate, the hook side will lay face down
on the fuzzy side and secure the strip.
Subject: Home-Made Dew Zapper --Part 7 of 7
From: Jim Talbot, Date: Sep 2002
I have a home-made dew heater for the corrector plate of my LX200 that may be of interest:
<http://frontpage.wave.co.nz/~jtalbot/dew_heater.htm>
Subject: Dew Shield Construction & Proper Color
From: John Mahony <jmmahony
hotmail.com>
A dew shield should be your first line of defense against dew. Using a heater without a dew shield requires lots of heat, more than
enough to create your own bad seeing.
Astrozap makes lighter flexible shields, but they have a black exterior, which is the last color you want on the outside of a dew
shield. Dark shields radiate heat rapidly at night and loose their effectiveness. See <http://www.dewshields.com/> for a very
effective, very lightweight dew shield. This is the only commercially available dew shield I know of that's made with any
consideration of the basic thermal issues involved. These are made of Reflectix™ insulation, available at most hardware stores,
with a layer of black felt on the inside, so you can make one yourself if you want. A reflective car windshield sunblocker with a
layer of black felt added also works well. Ever notice how many other radiative insulators are shiny? There's a reason!!! At least
in this case since the 16" is white you probably got a white dewshield, but I can't believe other dewshields are almost always dark
color.
BTW make sure you get the above url dewshields.com correct. If you go to www.dewshield.com (note: not plural) it will just take
you to Astrozap again.
I learned in freshman physics that just as dark objects absorb light/heat fast in the daytime, they emit it fast at night and cool
rapidly, so the typically dark colored flexible dew shields are not as effective as they could be. A reflective exterior makes a big
difference. As an alternative you can also use a reflective car windshield sunblocker. These are also extremely light, made of
insulating material, with reflective foil on the outside, and just the right size to roll into a dewshield. About $5.
Subject: DewBuster & Dew Formation --part 1 of 3
From: Mark de Regt <deregt
earthlink.net> Jun 2003
David Moody observed:
> You noticed that Rod and I have mentioned the DewBuster. That is an example
> of something a lot of folks use down here for dew heating. It applies a
> very tightly controlled amount of heat to the optics so they are only
> whatever number degrees above ambient that it takes to keep the dew from
> forming. This has two benefits: 1) It minimizes the heat being applied to
> the optics, thus minimizing its possible deforming effects, 2) It maximizes
> the efficiency of the system in terms of battery use.
David, I agree completely with your entire post, especially this part. During much of our year, on those rare occasions when we
are not clouded over, the dew is so heavy, I could not be dew-free for more than 1/2 hour, even with a very good, insulated dew
shield. Adding the DewBuster has made a great deal of difference. I have to apply very little heat, but it is the difference between
being able to stay out all night, and having to either blow-dry my corrector plate every half hour, or pack it in.
Unlike other products, the DewBuster actually has a thermostat, and carefully regulates the amount of heat applied. One cannot
feel any heat; it just keeps the corrector plate however many degrees warmer than ambient you tell it to. My scope was pointed
almost straight up all night last night; dew was collecting in pools on my observing table, but my optics stayed clean all night.
Check the product out at: <http://www.dewbuster.com/>
-------------------------------------------------------Subject: DewBuster & Dew Formation --part 2
From: Bill Dougherty <bd5572
yahoo.com>
The issue of where to place the corrector heater caused a heated debate on the LX200GPS list a while back. What Bill describes
below is exactly the position recommended by Ron Keating on his Dewbuster web site. He and Bill both reason that heating the
upper end of the tube will actually discourage thermal currents inside the tube and heat the corrector evenly over its entire inside
surface, not just around the edge.
I have my heater just behind the front mounting blocks of my upper and lower Losmandy rails. Even here in the soggy
Northwest, I set my Dewbuster on low and forget it. I have no dew problems on the optics and have not noticed any tube
currents either. I suggest trying out different placements of the heaters until you find the best arrangement for your scope and
conditions.
Bill wrote:
Not sure I agree with you on heating the corrector from the edge or center. I apply my heating strip to the OTA of
my LX200GPS about an inch behind the corrector. As best I can tell, it warms up the air in the tube which helps
keep the corrector evenly heated. Sometimes I will have temp temperature differential on my DewBuster set too low
and dew will form. When this happens and I turn up the temperature differential, the dew goes away uniformly
across the corrector plate, not from the outer edge of the corrector first. At least that is my impression.
I know that those far wiser than I can explain the problems with heating the corrector plate, but it seems that by putting the
strap on the OTA, vice the edge of the corrector, and setting it to the minimum required temp differential you should not distort
images. By putting the strap in the metal tube it warms up the tube, the air inside it, and the corrector evenly as far as I can tell.
Not sure about air currents in the tube. Guess I always assumed that they were minimal and would not impact the image. Am I
wrong on that?
As for power consumption, this is where the DewBuster shines. You tell it how many degrees you want it to keep the OTA over
ambient and it adjusts power accordingly. For my 8" LX200GPS I usually only have to set a 5 degree temperature differential to
keep dew away--and that is here in the swamps of Louisiana. The DewBuster comes with a sensor that detects the ambient air
temp and the temp of your OTA. It measures the difference then applies enough juice to maintain the temp differential you want.
The jump start battery I use can easily power both my scope and the DewBuster for over two nights without a recharge. When I
ran my Kendrick and scope I had to recharge the battery after one night's use. That may not be scientific, but it convinced me
that I was using less power.
--------------------------------------------------------Subject: DewBuster & Dew Formation --part 3 of 3
From: Bill <gatorchaser
atvci.net>
Sounds like you have it as bad in Ireland as we "dew" in Louisiana. I am wondering if you don't have a problem with your heating
strap since it's not keeping your corrector clear. I have heard that the internal connections to the straps can sometimes come
loose and interrupt current flow. Might want to check that out. Otherwise, your Kendrick should work. The one I had worked great
down here in the swamps. Except for the amount of power it consumed I liked it. That's why I got the Dew Buster instead.
MAPUG is hosted by
LX200 Astrophotography --Page 2
(Guiding Issues)
For Pictor Camera & CCD topics, return to Archive main page, right column.
ETX as Guidescope --2 parts
ETX and Autoguider
When Autoguiding, Does the Guidescope Have to be Pointing in same Area as Main Scope?
Guidscope Scope Focal Length Calculations
Guidescope for LX200 URLs
Guidescope vs. Off-Axis Choice Revisited
Guidescope vs. Off-Axis Guiding
SCT Guidescope Issues
Guidescope Mounting and C-5 Mirror Operation URL
Guiding w/Guidescope
Pros & Cons: Flip mirror, OAG, Guidescope, Parfocal Tube
Economical Classic Autoguiding?
Meade Off-Axis Guider Adjustments
Finding Stars for Off-Axis Guiding
Lumicon Giant Easy Guider Experiences and Report
Go to Astrophotography Misc Issues:
or
Subject: ETX as Guidescope --part 1 of 2
From: Donald Tabbutt <don
tabbutt.com>
Steve, The ETX works very well as a guide scope. The focal length makes it no dimmer than any other 90mm scope (central
obstruction notwithstanding). It only makes the field of view smaller (than a scope with a shorter focal length) on a given CCD.
And 90mm should be adequate aperture for guide stars down to mag 10 or 11 under dark skies.
I have an ETX piggybacked using the Losmandy "D" system on an 8" LX200.
Also, see the quoted mail message where I explained via private e-mail to a questioner how to better center the image in the
guider. Quoted message follows:
I think maybe your guide star isn't really in the guider's field of view. Use the Pictor as an imager and flip between
the images from the Pictor and the view through the 9mm Reticle eyepiece using the flip mirror. When the Pictor
image is centered, move the eyepiece's reticle screws to center it on the star. Note the orientation of the eyepiece...
always use that orientation in the future. Remember to switch back to the 26mm eyepiece that was parfocused per
my previous post to focus the camera for imaging or guiding. Also remember to flip the mirror... this'll bite ya!
One last thing...cover the eyepiece after flipping the mirror. Extraneous light can enter the ETX through the eyepiece port even
when the mirror is flipped to the rear port (the mirror flips down to the "floor").
I just photographed M13 this past weekend while guiding on mag 7.2 SAO 65481 with no guiding problems for a one hour
exposure.
--------------------------------------------------
Subject: ETX as Guidescope --part 2 of 2
From: Emery Hildebrand <emeryh
earthlink.net>
> I would appreciate anyone who is currently using the ETX with an LX200 to
>share some knowledge and help.... I would be mounting the ETX on a 10" LX200.
>Some pictures I have seen have the ETX mounted on the LX200 with 6.5" rings.
>The outside diameter of the ETX is only about 4", why are such large rings used?
>Can you use smaller 5" rings?<
I don't have an ETX, but I do use a 2045 SCT as a guider for my 8" and 12" LX200s. I use the 6.5" Milburn rings. The extra
diameter allows you to point far enough away from the object you are photographing to locate a suitably bright guide star. You
can use smaller rings with an ETX, but the larger the rings, the more range you'll have. The larger rings will also come in handy if
you upsize to a C5 guider, which would be a more suitable guide scope for a 10" working at f/10. With either, you should guide
with at least a 2x barlow but a 3x would be better.
> From my estimation, once mounted the ETX would be about 10" off center
>from the center of the LX200 as compared to an OAG which is only about 1"
>offcenter. Is there any difference in a photograph taken at prime focus
>between the two setups given the large variance in the offcenter distance?<
The off center distance won't make any difference. You can accurately guide on stars at least 5 degrees away from the object you
are photographing. Both Losmandy and Milburn rings will be stable enough so that flexure will not be a problem - as long as you
tighten the alignment screws very tight. I use rubber caps made for wire shelving tips to keep the screws from marring the guide
scope.
> I have read a lot about guidescopes having flexure problems. The ETX
>seems fairly light and the dovetail mounting looks fairly snug. Does the
>ETX flex at all or is this setup snug enough to eliminate this problem?<
If they are badly mounted they can be a nightmare, but the rings you're considering won't allow flexure. Some people worry about
mirror shift during exposures, but I've never seen this happen in 30 years of astrophotography with SCTs. What I have seen
people blame on flexure has always been caused by not using enough magnification in guiding.
>My 4" SCT has a 1,000mm focal length. Using a 9mm eyepiece and 2x barlow
>is barely adequate for guiding my 8" f/6.3.
>It isn't nearly enough magnification for guiding the 12" scope.<
The ETX has a 1,250mm f/l which with a 9mm and barlow just might be enough to guide your 10", but it will be close. The C5 has
about the same focal length as the ETX, but it would be a better guide scope since the guide stars will be much brighter and easier
to track.
Subject: ETX and Autoguider
From: Don Tabbutt <don
tabbutt.com>
I use an ETX as a guidescope on my 8" LX200, along with a 208XT, and I have been experimenting to find a solution to two issues:
1. Mount the autoguider rigidly to the rear of the ETX.
2. Find an eyepiece that is parfocal to the autoguider using the ETX's built-in flip mirror.
The answer to (1) is fairly straightforward, and may apply to owners of 201XT and 216XT cameras as well. When you remove all
screw-in adapters from the front of the camera, the threads that are left are T-threads. Into these screw in the front half only of
the ETX T-adapter (model #64), then mount the camera/T-adapter to the rear of the ETX. This forms a very rigid mount with no
flexure like that caused with the slip-in eyepiece adapter.
Once mounted this way, a means of focusing the autoguider and finding a guide star must be found. My experiments have found
that using the ETX's right angle eyepiece holder with its 26mm eyepiece works pretty well. The locking eyepiece spacer ring that
comes with the camera should be installed on the eyepiece such that it is about 3mm (1/8") from the eyepiece's stop (i.e. you can
see 3mm of shiny metal between the spacer and the black part of the eyepiece barrel). This makes the eyepiece very nearly
parfocal with the guider. If you can, image a star to fine tune the focus and readjust the spacer on the eyepiece. This combination
also gives a one degree field of view, which is important when you can't see through the main telescope due to a camera being
attached there (you can, of course see through a film camera's viewfinder, but that's bad at best).
That's it...works fine and lasts a long time. The only caveat is to remember to flip the mirror down after finding a guide star. That
can (and will) bite you from time to time.
Subject: When Autoguiding, Does the Guidescope Have to be Pointing in same Area as Main Scope?
From: John Mahony, Date: March 2005
>When using a separate guide scope and SBIG's STV unit as an autoguider,
> does it HAVE to be pointing in the same direction as the imaging scope?
One of the main reasons for using a guidescope rather than an off-axis guider is that you can aim it slightly different for a better
choice of guide stars. But you don't want to go too far from the imaging frame, or errors from polar misalignment are not
corrected as well. In the long run the image will rotate around the guide star. Actually, the rotation from polar misalignment will
always be there, but the effect on individual star images depends on how far they are from the center of rotation, which will be at
the guide star. So you want the guide star to be in or near the imaging frame. A guide scope also has an advantage here if there
happens to be a good guide star in the middle of the imaging target, where you couldn't guide on it with an OAG (off-axix guider).
>I've noticed that tracking circumpolar stars is steadier than tracking the more equatorial stars.
That's only because the scope itself is not moving as much, so the tracking errors that need to be guided out are smaller (the RA
motor is still running as fast, but the angular motion on the sky is less).
>The tracking is a lot better if tracking a star bright enough to average 3 or more exposures per second.
I don't think you get much advantage from such fast corrections, since the mount itself has a hard time reacting this fast. But if
the guide star is reasonably bright, guiding is better because the guiding camera "reads" it more accurately. If you push for short
exposures (for fast corrections) on a dim star, the noise in the image will cause larger errors in the guide star centroid location
algorithm in the autoguiding software.
>I can imagine that pointing a guidescope at all odd angles
> would confuse the tracking software, (?) but perhaps orienting
> the guidescope at 90 deg. angles from the photo-scope would work?
No, you want to stay close to the imaging frame.
Subject: Guide Scope Focal Length Calculations
From: Greg Hartke <ghartke
clark.net>
Rich Michaels wrote:
> Maybe that's the way to go. But the problem is that I would need a
> hell of a focal length since I prefer to shoot at f10 (3048mm) and
> f/6.3 (over 2000mm) on the LX200 12" My 500mm scope is too small and
> my ETX might work (if I tear it apart)
I do have one germane comment that may help you with your guidescope ruminations. No matter what the focal length of your
scope, the seeing (particularly when considering long exposure photos) will prevent you from getting star images smaller than a
couple of arcseconds or so. Hence any guider resolution greater than this is actually wasted because you won't be able to see finer
detail than this in your photos anyway. We can certainly calculate the shortest focal length required for a guidescope to have an
accuracy of at least 1 arcsecond per pixel:
To a good approximation, the image scale at prime focus is:
I = 1/F
in units of radians per unit length where F is the focal length of the scope. (The length units here are whatever units you use to
express F.) In degrees per unit length, this is:
I = (180 degrees)/(pi*F) ,
and in arcseconds per unit length, it's:
I = (2.063 x 10**5 arcsecond)/F .
The pixel size (S) of the 201XT is 10 microns or:
S = 10**-5 m = 10**-2 mm.
We then want an image scale of:
I = (1 arcsecond) / S
= (1 arcsecond) / (10**-2 mm)
= 100 arcsecond/mm.
Thus:
100 arcsecond/mm = (2.063 x 10**5 arcsecond)/F .
Solving for F:
F = 2.063 * 10**3 mm.
So any guide scope with a focal length of around 2000 mm will give you a resolution of very close to 1 arcsecond per pixel on the
201XT. As I said, I would expect you could do handily with a resolution of 1.5 to 2 arcseconds/pixel which would reduce you're
requirements to, say, 1000 to 1500 mm focal length. My 80 mm guidescope has F = 912 mm which gives a resolution of 2.26
arseconds/pixel for the 201XT. I don't think I'd want to go with resolution any worse than that with my 10" f/6.3. (I have some
nice round stars on 90 minute exposures that indicate that the focal length of my guidescope is adequate.) What's the focal length
of the 90 mm ETX? I seem to recall that it's 1250 mm. That would seem to be spot on your requirements so it might be the way to
go.
Thus any guide scope with a focal length of around 2000 mm yields a resolution of very close to 1 arcsecond per pixel on the
201XT. As previously mentioned, I expect we could do handily with a resolution of 1.5 to 2 arcseconds/pixel which would reduce
the focal length requirements to, say, 1000 to 1500 mm focal length. My 80 mm guidescope has F = 912 mm which gives a
resolution of 2.26 arseconds/pixel for the 201XT. I don't think I'd want to go with resolution any worse than this with my 10"
f/6.3. (I have some nice round stars on 90 minute exposures that indicate that the focal length of my guidescope is adequate.)
So now we know the minimum focal length necessary for adequate guiding. I would suggest the user choose nothing less than an
80 mm aperture for a guidescope. The 201XT will be able to guide on any star you can see in the guidescope and larger apertures
will, of course, equate to more stars from which to choose. I use an 80 mm guidescope and wish I had more aperture. Then again,
I *don't* wish I had more weight to put on the mount!
After mounting the guidescope above the main OTA, it will be obvious that it must be counterbalanced. I (and most others)
recommend the flexibility of a 2-D counterweight set for the Meade SCTs. Scott Losmandy (of Hollywood General Machining)
makes a version that works very well and is used by many of us.
Focusing the 201XT is not the easiest task in the world and of course it's imperative to have good focus to insure the guider
properly locks onto the guide star. My 201XT locks onto and guides on stars very easily; I've successfully guided on stars that
would really be too faint for me to guide on manually. (BTW, I use an 80 mm f/11.4 Celestron refractor as a guidescope and never
use an exposure time of greater than 10 seconds on the 201XT and that only for the absolutely faintest stars under rather dewy
conditions. Without dew, the longest exposure time I ever need is 5 seconds for the faintest star I can see in the guidescope.)
Note that a guide star that's too bright can't be used - it saturates the CCD. For my guidescope, any star brighter than about
magnitude 2 is too bright to use for guiding. With my equipment, stars of approximately magnitude 2 to 3 or so can be easily used
for guiding with an exposure time of 0.1 seconds and I always use a star of approximately this brightness to calibrate the 201XT.
(More on calibration below.) Anyway, I focus by cheating: I have a Meade 9 mm illuminated reticle EP that is well known to be
very close to parfocal with the 201XT. I've never been able to consistently improve the focus I obtain using the autoguider at the
same focal position as the 9 mm reticle EP. Since I seem to be able to guide on stars which are quite faint (and for exposures in
excess of an hour), I would suggest that my focus seems to be perfectly adequate. I understand the 201XT does not have the
most complex algorithms on the market so I would expect that it requires star images that are well focused.
As mentioned above, I always calibrate the 201XT motion using a moderately bright star. Experience has shown that the
calibration procedure works best this way: I found it fails with alarming regularity on faint stars and succeeds with virtually
uniform success with stars bright enough to use a 0.1 sec exposure with a brightness reading in the 60 to 90 range. Because of
this, I index the 201XT in the guidescope so that I rarely have to recalibrate - I can calibrate and go through an entire roll of film
over many nights without having to recalibrate. Again, I cheat. <G> Against the advice of others, I mount the 201XT in a diagonal
on the guidescope. (I find this makes it much easier to find and center guide stars when the guider is swapped out with the reticle
EP. This can, however, increase the likelihood of differential flexure. I'll discuss this below.) Whenever I place the 201XT in the
diagonal, I always make sure that the 201XT is aligned parallel to a portion of the backplate of the diagonal. In this way, the
guider is effectively indexed so that I can always replace it in exactly the same orientation obviating the need to continuously
recalibrate. This is very sneaky and works great.
A serious problem for any astrophotographer using a guidescope is differential flexure. I have several techniques to maintain
rigidity. First, I have the guidescope focuser locked for rigidity. Secondly, I've drilled and tapped the diagonal *and* the mounting
ring on the guidescope for 2 extra 6-32 knurled screws (that I got from mcmaster.com) at each coupling so that I don't have a
single set screw holding any tube in the optical path in place. Instead, all tubes are tightly held in place by a trio of set screws set
120 degrees apart to effectively eliminate any chance of flexure in the system. I do the same thing for all couplings in the camera
optical path on the main scope. It was traumatic to drill and tap my 2" TV diagonal, but necessary if I wanted good results! I
would expect this to be unnecessary with the 2" AP diagonal which uses a brass locking ring.
Another source of potential flexure in the guiding system comes from stresses induced by the power and signal cables running to
the guider. I capture the cables and run them from the control panel, along the mount, down the side of the guidescope, and to
the guider using ratcheting adjustable quick clips that I found in the electrical section of the hardware store. These clips have
adhesive pads on the bottom allowing me to stick them where I need them. I used duct tape before I found these but of course
the clips are much neater.
In addition, much consideration must be given to the mounting of the guidescope to insure there is no flexure there. Many
recommend (as do I) Losmandy components here. The dovetail and rings attach very rigidly on the main scope OTA. When I'm
shooting, I make darn sure I tighten the rings very smartly on the guidescope without worrying about marring the finish on the
OTA. The proper mantra for using a guidescope is tight, tighter, tightest! Don't use rings that are very large compared to the size
of your guide scope OTA. I use 108 mm rings for my 80 mm guidescope.
For mass-market SCT drivers, the major source of potential differential flexure comes from the moving primary mirror. Meade
SCTs of 10" and greater aperture actually have provision for locking the main mirror in place which can, with care, eliminate this
major source of flexure in the optical path. You literally cannot use a guidescope for exposures over 15 or 20 minutes with an SCT
(at least a Meade SCT) without the ability to lock the primary rigidly in place.
If you go to Chris Vedeler's web site at
<http://www.isomedia.com/homes/cvedeler/space.htm>,
you'll find that he has a nice discussion with accompanying pictures that should easily allow you to properly put together the bits
you need to lock the mirror down. The basic parts are a 6" long 1/4"x20 bolt with some nylon spacers and a wing nut. Chris also
details how to spring load the focuser for a better feel. This isn't suitable for astrophotography but works nicely for casual
observing. For my own use while photographing without an aftermarket focuser, I found it very clumsy to use the wing nut etc.
when trying to tweak the focus with a Spectra SureSharp. (Check focus, loosen wing nut, change focus a tiny amount, retighten
wing nut while trying to hold the head of the bold with fingers. Check focus, find it still isn't right, repeat ad nauseum.) I bought a
couple of 1/4"x20 knurled nuts from McMaster-Carr. (mcmaster.com, part no. 91833A134, $3.27 each, although maybe you can
find them locally. I tried but couldn't.) One I permanently attached to the top of the 6" long 1/4"x20 bolt using JB Weld and the
other takes the place of the wing nut I once used that is tightened against the nylon spacers and locks the mirror in place. This
makes it *much* easier to lock the mirror consistently.
All of this allows me to take prime focus exposures up to 90 minutes with a pretty reasonable probability of success. I'd guess I
get approx. 60-70% (say, 2 out of 3) success rate at the moment with exposures this long. That's actually pretty good with this
equipment - SCTs are notorious for making guidescope operation extremely difficult with long exposures. BTW, the likelihood of a
good exposure does indeed improve with shorter durations. I'm still refining my techniques and equipment and expect to get my
success rate still higher: I have reason to expect it to be at least 80% or so for these long exposures by the time I'm done.
I actually find the 201XT to be very easy to use. I had no real trouble right out of the box - my only real challenge has been to
systematically refine my techniques to eliminate sources of flexure now that longer exposures are very practical. Once done, the
above techniques (locking the primary mirror in place, triply locking in place all connections between tubes in the optical paths,
and capturing cables to remove strain) will serve to eliminate most of the rest.
If you have trouble remembering the mode tree for the 201XT, I would suggest that there are at least a couple of mode diagrams
on the web that are easier to use than that in the 201XT instruction manual.
I printed this out and placed it in a clear plastic vinyl slip cover for protection. With a little experience you'll probably never need it
again (I didn't after about 2 sessions) but it's still handy to have around. Guido also has some other interesting info on the 201XT
on his website that you might like to read. It's worth noting that he's working with an OAG (not a Lumicon GEG, either) on his
LX200 and is doing very well with his 201XT. Go figure.
Using a guidescope with an SCT is definitely a challenge but it can be done. If the weather ever improves here, I'm going to try
some shots using an AP Barlow in the optical path to increase the image scale when shooting certain galaxies. I'll probably add a
Barlow to the guidescope, too, to effectively get guider resolution of around 1 arc second per pixel. I'm curious to see if this can be
made to work becau