Auto vs Manual Strobes

skills º
+ IT’S ONE OF THE BIG CLASHES OF MODERN TIMES. HOLDEN VS FORD, RUSSIA VS AMERICA, AUTO VS MANUAL.
:
YES, THERE ARE PEOPLE WHO ARE PASSIONATE ABOUT SHOOTING EVERYTHING WITH THEIR STROBES ON AUTO
AND OTHERS WHO SWEAR BY MANUAL ADJUSTMENTS. WHICH IS RIGHT?
THE SIMPLE ANSWER IS: NEITHER. THERE ARE TIMES
WHEN AUTO IS FASTER IN CHANGING
CIRCUMSTANCES AND OTHERS WHERE IT FALLS FLAT
ON IT’S FACE. LIKE A GOOD POLITICIAN, YOU HAVE
TO KNOW WHEN TO EXCHANGE YOUR METHODS IN
THE FACE OF AN EVER-CHANGING ENVIRONMENT.
LETS LOOK AT HOW IT ALL WORKS.
M
anual is simple. The aperture, shutter speed and ISO
are set manually on the camera. Your external strobe
will have it’s own controls that are manually set.
Depending on the make and model, your strobe may have full,
half and quarter power. Some have more settings (the Inon Z240
has 13 settings), some have less. My old Sea & Sea strobes had
three manual settings, my new Ikelite DS 125’s have four plus
another four if you count the same settings with a diffuser
mounted on the front of the strobe. The most difficult part of
manual strobe use is working out the correct exposure.
Auto strobe settings are easy to set, just turn the dial to ‘Auto’
and shoot away. What could be simpler. But you will quickly find
out that life was not meant to be that easy. More on that in a
moment as well. There are two basic methods that are employed
to determine the ‘correct’ exposure using strobes on auto. They
employ either a sensor in, on, or outside the strobe which
measures the amount of light reflecting back from the subject, or
they use TTL (Through The Lens) technology where a sensor in
the camera measures the amount of light reflecting off either
your film during the process of exposure or your digital sensor. In
either case, when the sensor detects that the amount of light has
reached a level to provide a ‘correct’ exposure, it cuts off the light
emitted by the strobe tube. All this happens in a few
nanoseconds (billionths of a second).
Great in theory. In fact, in some situations it provides perfect,
pain-free, simple, easy, successful and consistent exposure. Then
there are all the other times when it’s success ranges from barely
adequate to total failure.
So why is it
inconsistent?
Strobe sensors, like
camera light meters,
cannot ‘see’ as we do.
They do not see colours,
contrast, hues, chroma,
saturation, details,
texture or any of those
things that make up an
image to us. What they
see is grey – 18% grey to
be specific – which is
about the tone of a
moderately overcast sky.
When enough light is
detected by the sensor
to make up 18% grey, it
kills the current to the
strobe tube, terminating
the exposure.
Technically, it is far more
complex than that but
this will give you the
basic idea.
This is where auto strobe exposure works very well, a subject that fills the frame with only small areas of pure black or bright whites which
otherwise would tend to sway the exposure.
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And as the Bard said,
“there's the rub”. If you
© KELVIN AITKEN 2006
are photographing a white cowry at night on a white piece of
coral surrounded by white sand and all sorts of bright, white bits
and pieces then the sensor is, in it’s mindless bureaucratic
manner, going to prematurely shut off the strobe leaving you
with a dull, underexposed photo. But it will average out to be a
perfect 18% grey. On the other hand, if the cowry is found at
daytime with it’s black mantle covering it and it is crawling
across a black sponge, the sensor is going to let the strobe grunt
away for all it’s little heart can give until the black pit becomes
18% grey, or in the real world, a washed out and over exposed
image.
In between those two extremes the auto function will perform
reasonably well, even perfectly, if the subject is within a tonal
Where Auto and TTL fails is with ‘High Key’ subjects like this one – a light coloured angel shark burying
itself in bright white sand. Instead of an underexposed shot, or fiddling with time-consuming ISO
compensation, manual exposure worked perfectly first time, capturing the fleeting action.
skills º
land, write it all out on a piece of white packing tape and stick it
on the back of your strobe. Sure, it will fall off after a few dives
but by then you will have it all set firmly in your mind. It takes a
bit of discipline, patience, fine tuning and effort, but after a few
dives it will all become second nature and your exposures will be
far more constant.
Ikelite DS125 Controls: Strobe controls show four manual
settings (Full to 1/8 power) plus Auto, here labelled as TTL.
Ikelite DS125: Manual exposure with a digital camera works perfectly.
Auto exposure has been a problem due to the camera triggering the
strobe too early with a pre flash. Recent models, such as this Ikelite
DS125, have new Auto or TTL circuitry which overcomes that
problem. This model is compact, light, powerful, recharges in 1 1/2
hours and has a fantastic built in modelling light bright enough to use
on night dives. The DS200 is one f-stop brighter, has a couple of extra
features at a slightly higher price and weight. Ikelite DS125: Manual
exposure with a digital camera works perfectly. Auto exposure has
been a problem due to the camera triggering the strobe too early
with a pre flash. Recent models, such as this Ikelite DS125, have new
Auto or TTL circuitry which overcomes that problem. This model is
compact, light, powerful, recharges in 1 1/2 hours and has a fantastic
built in modelling light bright enough to use on night dives. The
DS200 is one f-stop brighter, has a couple of extra features at a
slightly higher price and weight.
range that will translate to an 18% grey. Some images may look fine
but on close inspection the highlights may be blown out, in others
the blacks may clog up, but usually it will provide a very serviceable
exposure, especially if you are shooting in RAW format – which you
are, aren’t you?
The above example uses a small subject that would suit a macro or
close up camera set-up. This is where auto usually works very well
most of the time. Now imagine using a wide angle lens on a deep
shipwreck. You are down at 40 metres with your dive buddy who is
dressed in a black wetsuit with matching reg, BC, fins etc and a
flouro green mask. You know, the Ninja diver who buys everything
out of the reject bin. You line him/her up about two metres away
while they are sitting in the seat of a fighter plane down in the hold
of the SS Mistake. You raise your trusty camera and fire off a shot.
What does the strobe sensor see? Black, all except for the pasty
white narked face, a small strip of green flouro around the mask, a
pair of pink gloves (marked down to $8; bargain!) and a bright
specular highlight on that bit of chrome where the hose joins the
second stage of the reg.
All told, the sensor is going to take all your little strobe can give,
then maybe tell you to give it another go because the last exposure
was too dark, maybe only 5% grey. You then open the aperture,
crank up the ISO rating and hope for the best, eventually obtaining
a ‘correctly’ exposed image which translates to an 18% grey. But it is
hopelessly over exposed, the dark fuselage is light grey as is the
wetsuit and the pasty face has now disappeared into a glowing alien
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over exposed apparition, with two highly dilated pupils staring
out at you. No wonder they miss the deco line and end up in
upper Mongolia.
Auto strobe exposure is notoriously inconsistent when wide
angle lenses are used, even with brightly lit scenes. With large
areas of open water or subjects both close to and far from the
lens, the strobe sensor can only pick up on the amount of strobe
light reflecting back from the subject. An open water
background will reflect virtually no light so the strobe once
again works it’s little heart out trying to compensate for that
‘dark’ area, overexposing the foreground.
Over the years I’ve used manual strobe exposures for all subjects
and lenses, both wide angle and macro. It actually becomes easier
than auto exposure as you no longer have to fiddle with the plus
or minus compensation controls on your camera to get a correct
exposure. In fact, any sort of fiddling with auto exposure is more
complex and slower than manual exposure, at least after you’ve
done your initial tests. Give it a go, try it for a dozen dives and
see what works best for you and your equipment. What makes
all the above more difficult is a bad camera set-up where a single
strobe is set right over the lens, a lazy way to light your subject
and far more difficult to get good results.
COMING TO GRIPS WITH PRINTING
Like auto exposure, printing your images is supposed to be easy
and simple but it is not. As mentioned in previous articles, you
can just send off your card to a photo printer and hope for the
best or you can take control and get the best possible results
from your hard work in the water. The first step to successful
printing is to calibrate your monitor, a process which has been
covered previously. Second, calibrate your printer. Third, print
out and rejoice.
The simple solution is to shoot with your strobes set on manual.
If you read the last article, it explained how the inverse square
law works and why strobes offset from the camera on long arms
provide a fairly consistent exposure over a range up to three
metres or less. That makes it easier for you but those of you
stuck with a short strobe arm or, horror, a strobe built into the
camera, you can still sort out your manual exposures. You can
work it all out using the guide number of your strobe but there
are all sorts of problems that crop up, such as some rather
inventive guide numbers supplied by eager marketing
personnel.
TEST SHOTS ARE THE BEST WAY TO GO. THIS IS MUCH
EASIER WITH A DIGITAL CAMERA AS YOU CAN CHECK
YOUR SHOTS AS YOU TAKE THEM, SORTING IT ALL OUT IN
THE FIRST 10 MINUTES OF YOUR DIVE. HERE’S HOW.
Select a mid toned subject one metre from your camera/strobe.
Set your strobe to manual and full power. Set your aperture to
f11. Take a shot. In previous articles we spoke about using the
histogram to check exposure. If it is not right, change your
aperture and take another, in fact take as many as you like until
you get a correct exposure. Write down the aperture that gives
you the correct exposure at that distance. Open up one f-stop,
set the strobe on half power and take another photo. The
exposure should be correct. Open up another f-stop and take
another photo at 1/4 power. Again it should be correct. If not,
note down the f-stops needed for each setting. Move to half a
metre and do it all over again. If you are using long strobe arms
you will find that the exposure will be the same or almost the
same. Do it again at two metres from your subject. Back on
Modern inkjet printers are capable of excellent image quality,
with the latest generation of inks also going a long way to solve
the fading problems that plagued the first printers. To get
consistent accurate results you will need to install and use
printer profiles for the particular paper you are using.
When printing your images, you need to select the right profile
for the paper you are using. Here a paper profile is selected
when printing from Photoshop. Profiles for most common
papers recommended by your printer manufacturer will either
be included with the software provided or can be downloaded
from their web site.
For home printing, there are inkjet printers and dye sublimation
printers. Inkjets are cheaper to run and it’s easier to control their
output, so we will deal with those. Inkjet printers come with
software that enables you to create a profile or assign a provided
profile. Your printer takes the information from the image created
on your computer and uses a profile to translate that information
in such a way as to print out an image as close as possible to what
you see on your monitor. Not only are all printers different, but the
type of paper you use will affect the appearance of your image, so
paper and printer specific profiles are necessary to control the
entire printing process. Its all part of what’s called Colour
Management, controlling the appearance of your images from the
camera through to the final output.
This is a good example of a test image for printing and testing
your printer profiles that shows a range of objects and colours
that the human eye is familiar with along with neutral mid tones.
It is beyond the scope of these brief articles to delve fully into this
subject. However, there are some excellent online resources and
books that deal with printing in detail. To get the best results from
your printer requires some research, patience and testing. The first
step is to choose an image that can be used as a reference.
Photoshop includes images that can be used for testing as does
Kodak and a number of other companies. Or you can create your
SPORTDIVING MAGAZINE
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own. What is needed is a subject that has a wide range of
colours as well as neutral tones. A portrait of someone in
colourful clothing against a grey background would work just
fine, something with skin tones, primary colours and neutral
blacks and whites.
With your image looking spiffy on your calibrated monitor, use
your printers software to assign the correct profile for the paper
you are using. If it works fine first time, then great. You have
won the lottery. But don’t be disappointed if it is lacking in
some areas or looks downright ghastly. As long as the printer is
working properly, with no blocked jets or missing inks, then the
profile needs adjusting. See the side bar for links to more
information about wrangling your printer into submission.
Kelvin Aitken is a
Melbourne-based
professional photographer
and diver passionate about
the big blue and the big
sea creatures to be found
out there. He’s dived from
the Arctic to the extremes
of the South Pacific and if
there’s a new marine dive adventure to be experienced or
invented, he’s always the first to put up his hand. He’s also
dived the southeastern Australian continental shelf and
photographed shark species nobody knew would be found
out there. Kelvin is a BBC Wildlife Photographer of the Year
marine category winner and his unique work is on
www.marinethemes.com
USEFUL LINKS
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http://homepage.mac.com/billatkinson/FileSharing2.html – Free sample profiles, printing targets and other goodies.
http://www.luminous-landscape.com/tutorials/understanding-series/und-print-mgmt.shtml – Profile basics
http://www.ddisoftware.com/printerprofiles/ – Printer profiles explained
http://en.wikipedia.org/wiki/Inkjet_printer – How inkjets work plus links to other printer types
http://www.pcworld.idg.com.au/index.php/id;1950419218;pp;1 Printer buyers guide
http://www.large-format-printers.org/ColorGateRIPlargeformatprinters/RIPsfor_largeformatprinters.htm RIP printing
http://www.bairarteditions.com/pages/tutorials/epsonprinting/index.html
How to use an Epson printer. Includes links to profile use and some good basic printing tutorials.
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