| You don’t mention which camera
you have so I’ll guess that it’s one of the Nikon
N8008 or N90 cameras. This puts the odds in my favor to the
tune of better than twenty to one, considering what’s
out there these days. The general principles will apply to
just about any camera.
I’ll assume that your whale shark photos will be of
the ambient lit variety, since possession by a civilian of
a strobe putting out the amount of power needed to light a
critter of that size would certainly be a capital crime in
virtually any country in the world. Your basic exposure can
be manual or automatic.
If you choose to use a manual exposure, you’d select
an aperture/shutter combination which would give you a "best
exposure" using your light meter to guide you. Generally,
when you’re doing wide-angle photography underwater,
ambient light exposure and background water color are interchangeable.
You’d select a light meter reading using aperture and
shutter speed controls which would yield the depth of blue
desired in the shot. Generally, this would be average (zero
on your light meter) to minus one-third or two-thirds of a
stop, although in some situations you might like a full stop
under. Underexposing water yields a deeper, richer blue. Overexposing
slide transparencies is generally no desirable, although there
are some situations when a slight foray in this direction
might be considered. So you make your decision as to the depth
of blue you want for the water. You select your shutter speed
and aperture. If the light is coming from behind your subject,
you’ll have a silhouette in some measure. Increasing
exposure will brighten the water and allow more detail to
show in your shark. If the light is coming from behind you,
separating the shark from the water becomes a major issue.
Without a bunch of experience, it’s hard to know exactly
what exposure will look best. Time to bracket!
You bracket in manual by moving either the f-stop or the
shutter speed. To bracket under, you’d either select
a faster shutter speed or a smaller aperture. If your original
exposure gave you enough depth of field and a shutter speed
fast enough to adequately stop movement—both yours and
the shark’s—you can’t screw this up. If
you’re bracketing to lighten the photograph, you’ll
either open the aperture or slow the shutter speed. Opening
the aperture decreases depth of field. Slowing the shutter
can allow movement to blur the image. This is especially true
when you’re hauling derriere, swimming like crazy trying
to keep up with this majestic, graceful, humongous, and seemingly
slow-moving object de photique. Concentrating on holding your
camera steady on your subject under these conditions is a
serious challenge at the very least. You’re generally
safer to open up the aperture to increase exposure, since
depth of field is generally less of an issue with a subject
of this size. Naturally, this depends on the angle you’re
shooting from.
It might, in fact, be easier to shoot on one of the automatic
settings. When shutter speed is the more critical variable,
shutter priority might be the best choice. You should be watching
the aperture that’s being selected by the camera for
the speed you set and be prepared to back off if the speed
selected causes the aperture to become unacceptable. You can
now bracket with the exposure compensation control. Remember
that it might be easier to bracket with the aperture control
since the exposure compensation method may require moving
two controls at once.
Macro is another story. Your subject will, almost certainly,
be entirely strobe-lit. I’d suggest that you use TTL
flash exposure control. Your shutter speed will be set to
a convenient sync speed—say 1/60 or 1/125 of a second.
Shutter speed has no effect on your photograph as long as
you select a speed slower than the maximum sync speed for
your camera and are not shooting into the sun, or nearly so.
Your aperture will be selected to yield the optimum depth
of desired for the shot, generally around f22 for most macro.
The strobe, or strobes, will be positioned at a distance from
the subject that is within the maximum distance as which the
power of the strobe is sufficient to provide a proper exposure
of the subject at the aperture selected (you paid for the
magazine; you’re allowed to read that twice, I did!).
When you use TTL, the resulting exposure will yield an "average"
exposure equal to 18 percent gray as measured and weighted
by the meter and computer. It’s generally dam close,
if not right on. To assure that you’ll get a proper
exposure of a specific part of the frame that’s darker
or lighter than its 18 percent gray surroundings, you can
bracket either by adjusting the exposure compensation control
or the ISO control. Since you’ve set you f-stop and
shutter speed manually, these won’t change when exposure
compensation is adjusted. If you have a light subject, such
as a flounder on sand or an albino eel with a cleaner shrimp
in its mouth, you might start with a base exposure of plus
two-thirds of a stop or so. TTL will yield 18 percent gray
at zero exposure compensations. You’d then do your bracketing
up and/or down from there.
You could expose manually with your strobes. In this case,
you can bracket by adjusting your aperture or by moving your
lights in or out. This requires practice, record keeping,
and disciplined systematizing in order to achieve predictable
results. If these things don’t bother you, then maybe
sacrificing ideal depth of field for exposure and/or arm-wrestling
with you strobes while your subject leaves the scene will.
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