To freeze a moment in time and create an image with mood and feeling is any photographer's greatest challenge, and underwater photography is one of the most demanding of all the photographic specialties. It occurs in an alien environment that can prove detrimental to both the photographer and his or her equipment. Underwater photography is a labor of love.

Underwater photographers must have excellent dive skills and remain fully cognizant of both dive plan and dive buddy, while still concentrating on the photographic subject. To be successful, extensive knowledge of the marine environment-- both the flora and fauna-- is essential. Subjects must be approached cautiously with little or no disturbance to the reef. And, the photographer must locate an intimate angle to make the most dramatic photograph possible. The objective is to light, expose, and retreat- leaving only a memory of human contact.

Exposing Film Underwater

Factors unique to the underwater environment cause most land photography techniques to fail. Water is 800 times denser than air, with both organic and inorganic materials suspended in the photographic path. These materials can reflect, absorb, refract, and diffuse light, making the "correct" exposure a kind of search for the truth.

Light absorption causes more color to be filtered out as depth increases. Wave action and time of day influence the angle of light reflection, as well as the intensity of the light penetrating below the surface of the water. Light refraction also causes objects underwater to appear 33 percent closer than they really are. Therefore, objects must be measured in apparent rather than actual distance.

To create aesthetically pleasing images underwater, you should start by identifying and isolating the main subject. This can be done by choice of background (open water or habitat), differential focus (such as an out of focus background), flash position, and picture format (horizontal or vertical to suggest depth). Frames within frames, such as portholes or cave entrances, are good compositional elements to lend depth and perspective. Other elements that add to the central theme of an image are color, pattern, and modeling. Try to make the body posture appear fluid and natural, attentive or interactive.

Available light photography is best taken in shallow water during peak daylight hours (10 a.m. to 2 p.m.), when higher light levels are present. The shortest camera-to-subject is best, and you should always try to photograph your subject level, or upward to include some surface area in the photograph. Although most available light images are monochromatic, silhouettes of easily recognizable subjects can have terrific visual impact.

Almost every image requires some form of additional light due to the shortening of light wavelengths and the filtering of color and light intensity. Underwater flash units play an integral role in uncovering the kaleidoscope of colors hidden in the ocean depths. Every processed roll reveals colors previously obscured by the inherent monochromatic blue-green cast of the sea. Underwater flash is used either as the primary source of illumination to restore natural color, or as a means to augment colors, or fill in shadows. Single flash is generally used from the top left at a 45-degree angle. However, side lighting is very effective for translucent subjects. Back lighting, with a rim light positioned behind the subject and directed back at the camera, works great for outlining hairy, feathery edges, or tentacles. Holding the flash by hand allows variable positioning of the flash relative to the subject.

Multiple flash units are beneficial, especially for close-up photography, because the short camera-to- subject distance requires a second flash unit to fill or remove the shadow created by the primary flash. A built-in photocell allows wireless triggering of a slave flash if there is sufficient light reflected from the subject. A dual sync cord, or T-connector, usually provides a more reliable means of triggering a second flash. In general, if two flashes are of the same intensity, positioned in the same plane, and covering the same area, a 1-f/stop reduction in exposure will be needed. As this is rarely the case, a 1/2-f/stop reduction is more realistic. If the second is of a lesser intensity, base your exposure on the main flash.

Just like land photography, flash guide numbers (GN) express the power output of a strobe. To determine your working aperture, divide the GN by the subject distance to find the desired f/stop. However, remember that guide numbers are only the starting point. You must also know the ISO, measured or apparent distance, and the changing water clarity when working in an underwater environment.

When focusing the camera on a distant object, be sure to angle the light and calculate flash exposure on the total light path or the actual flash-to-subject-to-camera distance. Flash angle and placement is critical, because lighting the suspended material between the camera and subject will result in backscatter, making the subjects appear as if they were photographed in a blizzard.

Mastering the ability to balance ambient light and flash in the underwater environment is paramount to good underwater photography. For successful use of fill light, use the flash to merely lighten and add color to foreground. This is accomplished by closely matching the flash intensity with that of the natural light. Remember, that natural light is based on both f/stop and shutter speed, while flash is determined by only f/stop.

Through-the-lens metering (TTL) works well in situations that require balancing of flash and natural light. When using a TTL flash, the exposure is determined solely by the amount of light reflected off the film. You will obtain a correct exposure if your subject fills most of your frame, and is of average reflectance. Be aware that some cameras, such as the Nikonos V, use two different meter cells to read available light and flash. If light is allowed to enter the lens at a shutter speed slower than 1/90 second, the image will be overexposed. Always meter the natural light first. An aperture of 1/2 to 1-f/stop below the ambient light reading achieves the best results.

Wide-angle lenses should be used to eliminate as much water as possible between the camera and subject, ensuring better color, detail, and contrast in your images. Close-up underwater images can be taken with SLR cameras enclosed in underwater housings with macro lenses. Alternatively, supplementary close-up lenses or extension tubes may be employed on any camera, although they are most frequently used on Nikonos cameras.

On assignment I use two Nikon F4s camera bodies with a wide array of lenses, including the 16mm, 18mm, 20mm and 24mm for wide-angle, with the 60mm, and 105mm used for macro and close-up images. I house my SLRs in two Aquatica 4n units.

I also use two Nikonos V 35mm underwater camera bodies with 15mm, and 20mm for wide-angle work. Artificial illumination is provided by Sea and Sea YS 300, and Sonic Research SR2000 strobes. I use the Seconic Marine meter II to meter the ambient light underwater. Don't forget to use effective apertures when calculating macro exposures.

Underwater photography is directly related to Murphy's Law: Whatever can go wrong eventually will. H2O, the very medium that provides us with a unique photographic environment, is continually wreaking havoc on our equipment and bodies. Sync cords that worked perfectly on land begin to malfunction as air comes out and water goes in. Improperly greased O-rings, a stray hair, or a grain of sand easily causes problems.

All metal parts will eventually corrode or seize without proper maintenance. Particular attention must be given to nuts, bolts, camera and flash controls, screw-in plugs, and brackets. After use, all equipment must be carefully washed in fresh water and dried to remove salt and moisture. O-rings must be cleaned and greased. The Oceans treasure chest is not easily opened, but with patience and diligence, one may reveal jewels of exquisite, priceless beauty.

No image is worth your Life; always dive within your abilities.

Safe diving!

CG-NPN