Chapter 9- Underwater Photography
Underwater Photography
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FIGURE 9-2. Without artificial light, pictures appear predominantly blue and with minimal contrast.
SOME FUNDAMENTALS
It helps to compare a camera to your eye to understand
photography. Both are self-contained and have
lenses, irises (called an aperture in a camera), light
recording surfaces or sensors, and shutters (the eye uses
the eyelid as the shutter). If you open your eye momentarily,
light passes through the iris and is focused by the
lens of your eye onto the retina, the light-sensitive surface
in the rear of the eye. When less light is available, the iris
opens wider to allow more light to enter and record the
image. If it is dark, a source of light is needed in order to
supply enough light for vision. The same principles apply
to a camera. The shutter is opened to allow light to pass
through the aperture and be focused by the lens onto the
light-sensitive surface (digital image sensor or film). The
less light present, the wider the aperture must be opened
or the longer the shutter must stay open. At times, a
flash must be used to provide enough light to register an
image.
The principle of photography is to register
the refracted light rays in a controlled and predictable
manner, and the less light there is, the more challenging
the task becomes. As a diver descends into the water and
depth increases, the amount of light decreases. The light
from the surface is absorbed and diffused and is often
insufficient for natural light photography. The lack of
adequate available light often requires light to be supplied
artificially with lights or strobes.
Another important reason for using artificial light
is to add color to photographs. You are aware that white
light is comprised of various colors. As you learned
in your entry-level scuba course, different colors are
absorbed at different depths as the light passes through
the water. Bright colors such as red and orange will not
be recorded in your photograph unless the water is very
shallow because these colors of the natural light spectrum
are absorbed by the water and cannot be reflected from
a red or orange object at depth. By illuminating objects
at close range with artificial light, their colors become
visible. Without artificial light, pictures appear predominantly
blue and with minimal contrast.
You now know two good reasons for using an artificial
light source underwater, but the use of the light
source requires certain light-handling techniques for
good results. There are almost always particles suspended
in water, and if light from your flash unit strikes these
particles straight-on and is reflected from them back
into your camera, the result will be “backscatter,” or a
picture that looks like it was taken in a snowstorm. The
more turbid the water, the greater the problem. Not stirring
up silt is an absolute requirement in order to obtain
acceptable photos, and you will learn how to minimize
backscatter through proper light positioning techniques
such as side-lighting.
When light rays pass from air into water or from
water into air, they bend or “refract.” The refraction,
which occurs underwater at the face mask/water interface
or the camera lens/water interface, causes the
familiar magnification of objects. It also causes them to