Page 103 - AlertDiver_Winter2013
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what shutter speed I used for a model holding a flashlight
who is relatively close to the strobes. But, returning to
the example of 1/250 versus 1/15, there is a four-stop
difference in the amount of perceived illumination
coming from the dive light. Brighter is definitely better in
a product illustration.
Making hand-held light appear brighter is just one
of several reasons to embrace slow shutter speeds in
underwater photography. Two of the most important uses
are bringing more light into backgrounds (specifically, the
areas beyond that which can be illuminated by strobes)
and creating intentional blur to enhance the perception of
motion in a photograph.
Increasing Background Light
The physical characteristic that guides all underwater
photography is the density of the medium. Water is
800 times denser than air, and light transmission is
correspondingly reduced. That big fill-light in the sky,
the sun, is very powerful, but transmission is variable
according to where on the planet you are, the time of day,
depth, water clarity, cloud cover and surface conditions (a
choppy surface transmits less light than a slick calm one).
Down to about 50 feet deep, light is absorbed at a degree
equal to about one stop for every 10 feet of depth. Deeper
than 50 feet, that relationship begins to fall apart. Light
from strobes is not nearly as bright as the sun, of course,
and illumination is reduced at a degree equal to about one
stop for every foot of distance from the strobe head. Based
on these approximations, I like to think of light in terms of
“vertical” (that which comes from the sun and penetrates
down into the water column) and “horizontal” (that which
comes from the strobes and strikes the subject).
Note the wide-angle shipwreck photograph; this
image exemplifies the way both forms of light should be
considered when calculating an exposure.
The wreck photo is an anniversary shot, too. I was hired
to document the decade of growth on the wreck of the
Spiegel Grove off Key Largo, Fla., on the occasion of the
10th year since it was intentionally sunk as an artificial
reef. It’s now a riot of color, thanks to encrusting sponges
and deep-water gorgonians, so I knew I would use the light
from my strobes in the foreground to restore the color
lost at the 90-foot depth. I used an 8-15mm zoom lens (at
13mm) so I could work very close to the gun emplacement
and bring ample artificial light to the foreground. The
diver in the photo is a compositional element, providing
a bit of human interest as well as scale to the immense,
510-foot ship. Given the strobe-to-subject distance and the
reflectance of the foreground I chose an aperture of f/8, an
ISO of 320 and a strobe power setting of 50 percent. That
was all pretty well revealed on the camera’s LCD screen in
my first test shots, but the real experimentation came with
the shutter speed.
If I had taken the shot at 1/125 (a pretty standard
shutter speed for underwater photography), the
background would have been quite dark, and there would
have been no differentiation of the superstructure in the
far distance. Not only that, the inevitable particles in
suspension in the water column (backscatter) would have
been very obviously illuminated as white spots against
an indigo backdrop. Instead, I chose to shoot at 1/30. A
slower shutter speed meant a lighter-colored background
and the backscatter less obvious.
This was still fast enough to allow me to hand-hold
the camera. There is a dampening effect of the water
that makes steadying the housing at slower shutter speed
practical; more significantly, the speed of the strobe light
in the foreground (approximately 1/4,000th of a second in
duration) would preclude any evidence of minor camera
shake. Slow shutter speeds like this, or even slower, are my
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