Water is the enemy of underwater photographers. It suspends backscatter-causing particles, removes warm colors, and degrades image sharpness. Photographers try to get as little water as possible between their lenses and their subjects. This is done with specialized equipment—macro lenses and wide-angle lenses.
A common technique for producing stunning underwater images is called close focus wide-angle (CFWA) photography. CFWA photographs have a characteristic photographers call depth; they have a definite foreground, middle ground, and background. The middle ground is often a diver, although a coral head, fish or another object may be employed. The middle ground may be far enough from the strobe to be a silhouette or can be close enough to be illuminated by strobe light. The background can be a black, but often better images have either a blue water background or a sun burst. California photographers may select a background of kelp. Getting all of these elements into one photograph requires a bit of planning and a lot of control over lighting. The key here is not to just find an interesting foreground subject, but to find one with an interesting background.
CFWA photographers need a wide-angle lens with a minimum focus distance of 12 inches or less. Nikonos fans should choose the 20 mm or, preferably, the 15 mm lens. These are optically very sharp and can focus very close without the need to add supplementary close-up (diopter) lenses. Those who prefer housed cameras should pick a lens of 24 mm to 16 mm. These offer an optimum viewing angle along with a large depth of field. If your lens does not focus to 8 to 10 inches you will need to add a diopter lens.
A single strobe may be used in CFWA shots. However, this is one case where I almost always use two strobes. The subject is often so close to the lens that the camera prevents placement of the strobe where it may illuminate the entire subject completely. Two strobes will evenly light both sides of the subject, regardless how close you get. At times a third strobe is nice as well for illuminating the diver in the middle ground, or a slave strobe for the diver to hold. This diver-held strobe may be used to illuminate a secondary point of interest or to produce the illusion that the diver is holding a flashlight.
The first step in CFWA photo is selection of an appropriate subject. Choose something colorful that you can shoot from below. Focus and a small aperture (f22 or 16) are set to achieve maximal depth of field. Due to the extreme aperture and attenuation of light by water, the camera is normally aimed upward and often directly at the sun. The proper background exposure is determined with your light meter, and strobe light is balanced by relying on TTL metering.
With the camera settings and strobes in the proper position you can then compose the shot. If you are using a model have them swim into position. There is often no one best lighting setup or exposure, so try several with each subject. I often spend half a dive searching for the “right” subject and shoot half a roll of film to get the image my mind “sees.”