Having taught underwater photo seminars for the past 20 years, I find a high percentage of mistakes are repeated from student to student, year to year, regardless if the tool is an amphibious camera like the Sea & Sea Motormarine II or the Nikonos V, or a more sophisticated housed SLR or Nikonos RS.

Much of what I know about underwater photography has come from critical analysis of my shots that didn't work. Helping to illustrate this article are some examples of photo-buffoonery from my files, mistakes I've made and saved only for their value in illustrating what not to do in underwater photography.

Blind Reliance on Technology

In 1984, a new acronym entered the underwater photo lexicon: TTL. That's the year the Nikonos V was introduced, complete with two built-in auto-exposure controls. One was for metering sunlight and the other for controlling the companion TTL strobe. Both sensors were located very near the film plane and measured the light that passed through the lens. This was a powerful improvement. Prior to TTL, choosing an f-stop meant distance estimating and guessing subject reflectivity. Now, virtually all cameras and housings employ TTL automation for exposure control. Generally, this works quite well. But there are limitations that result in one of the most common student bloopers: blind reliance on TTL.

Out of TTL Coupling Range

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There are f-stops that simply won't deliver a proper TTL exposure. At a certain point, the strobe will have dumped full power, and at that given strobe-to-subject distance, a smaller f-stop can't work. For example, with a Motormarine IIEX and YS-60 strobe, using ISO 100 film, a full power dump might yield f-16 at three feet. TTL can't save the shot from underexposure if the camera is set at f-22. Conversely, at f-3.5 there is a strong possibility that the shot might be overexposed due to excessive ambient light or the inability of the strobe to quench quickly enough. Trial and error may suggest that f-8 to f-16 is the best TTL coupling range and provides the highest percentage of keepers.

Blind reliance on TTL can result in underexposure (top) or overexposure (bottom). TTL shooters must select an optimum f-stop for strobe-to-subject distance. F-stops of f-8 to f-16 usually provide proper TTL coupling range.

Not Accounting for Subject Reflectance

For TTL to work, light must bounce back to the sensor. A small subject in a field of blue water doesn't have much area to reflect light back to the camera, and consequently TTL rarely works. Macro subjects and fish are examples of subjects with a reasonably high percentage of primary subjects filling the frame. TTL works pretty well for these. However, when shooting wide-angle, there is often a fair amount of blue water that will not reflect back to the camera, and TTL is typically erratic. Rule of thumb: If 75 percent of the frame is not filled by the subject, don't count on TTL.

Failure To Confirm Electronics

Because there are so many little things that can go wrong with camera and strobe electronics, the prudent shooter should make a habit of checking these things daily:

• Make sure the battery is working properly and that the strobe cord is transmitting all electronic data to the camera.

• Topside, before putting film in the camera, before going out on the boat, make it a daily ritual to test fire the strobe.

• If you intend to trust TTL exposure automation, advance the camera to frame #1 (to engage the electronics) and fire the strobe once with the lens cap on. Theoretically, no light should get to the TTL sensor, and the strobe should dump full power, as indicated by a slow recycle and a blinking ready light.

• Aim the strobe directly into the lens at maximum aperture. The strobe output should be minimal and the recycle almost instantaneous.

If either of these tests is unsuccessful, analyze your gear piece by piece. Try a new camera battery first, then try a different strobe cord. Of course, it could be a more complex (and expensive) problem with either the camera or strobe head, but those are harder to fix in the field. That's why we carry redundant gear.

Improper Distance Estimation

Viewfinder cameras like the Motormarine IIEX and Nikonos require the shooter to estimate the distance to the subject and then manually adjust it on the lens. Wrong distance estimates result in out-of-focus pictures. Even autofocus cameras require accurate distance estimation to determine exposure. All of this is complicated by the fact that we see the world in "apparent distance" under water. Water magnifies; so something that looks like it is three feet away is truly four feet away. This isn't a huge problem because water-contact lenses are calibrated in apparent feet, but without good spatial estimates it is impossible to choose the optimal f-stop or aim the strobe correctly. Some students find it helpful to take a four-foot length of PVC pipe under water for a while. Using it as a gauge will accurately peg three apparent feet.

Failure To Get Close

The classic pro advice to novice underwater shooters, to the point of cliche is "Get close. And when you feel you are close enough, get closer." Reason? Water is 800 times denser than air and introduces strong cyan filtration. In order to get sharp pictures and vibrant colors, you have to shrink the water column. To shoot big subjects, get close with wide-angle lenses. To shoot small subjects, get close with macro lenses.

Right Subject, Wrong Lens

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This is a corollary of the advice to get close. Given the distance limitations and the need to get close, there is only a small universe of subjects appropriate for any lens. A zoom lens might have a bit larger universe, and the Sea & Sea Motormarine cameras allow the addition of supplementary optics while under water, thereby creating more viable subject choices per dive. But no matter what lens is in place, you must restrict your vision to the appropriate subject. If you see a pygmy seahorse while cruising the reef with your 15mm wide-angle--tough. And if the whale shark swims by while you have an extension tube mounted--double tough. Find the subjects that are right for your optic and don't waste shots on those that aren't.A classic example of "right subject, wrong lens." Although the shot is well-exposed, this fish is far too small for medium- and wide-angle lenses.Ah, that's much better: A macro lens or macro set-up lets this peppermint goby fill the frame. Right subject, right lens.

Improper Strobe Placement

If you can't estimate the distance properly, you can't aim the strobe properly. Remember the difference between real and apparent feet under water: If it looks three feet away, is it really four feet? The strobe needs to find the subject where it really is, so in this example it should be aimed to four feet. Typically, aim a little above and behind your perception of where the subject appears to be. Strobe placement also affects backscatter to a great extent.

Hello, Backscatter

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Backscatter is those ugly, annoying white specks that inevitably show up in your otherwise stunning photographs. You can digitize your photo and retouch to get rid of the particles, or you can shoot it right to begin with. On some days, the water is so miserably dirty that no amount of imaging skill can return a shot free of backscatter. But there are tricks that put the odds of a backscatter-free photo in your favor.

• Aim the strobe properly. Avoid lighting the particles held in suspension between the lens and the subject. Use articulated strobe arms to move the strobe above and away from the lens. With this technique, most of the particles are not illuminated, and those that are lighted get rim light instead of being blasted with full-frontal light.

• Control the ambient light. Your shutter speed/aperture combination determines how much ambient light records in the background. White particles of backscatter are less obvious against a light blue background than a dark blue background. For this same reason, it is hard to shoot wide-angle at night unless the visibility is extraordinary. Otherwise the white particles are disturbingly obvious against the black background.

• Shoot against a busy background. Some-times no level of creative lighting or tweaking ambient light will eliminate backscatter. In this case, your only option may be to find visually confusing backgrounds to hide the particles. Shoot against the hull of a wreck instead of the open crow's nest. Find a colorfully encrusted reef overhang instead of shooting angelfish in midwater.

Shooting Before the Strobe Recycles

If you want to avoid backscatter entirely, just shoot before your strobe recycles, because it's your strobe light that illuminates those pesky particles. Of course, your pictures will instead be monochromatic blue, and probably underexposed and boring. With the exception of blue, we have to accept that most color in underwater photography occurs as a function of artificial light. Once fired, your strobe needs time to recharge the capacitor to be ready for the next shot. A ready light indicates the recharge, but be aware that usually the ready light comes on when the strobe is only at about 80 percent of its full capacity. Shooting too quickly can mean the obvious--the strobe simply doesn't fire. Or it can mean the insidious--the strobe will fire, but isn't able to dump sufficient quantity of light. Underexposure is a common consequence of an itchy trigger finger.

Ambient Ignorance

Even when TTL is working at its optimum, it accounts only for the strobe light hitting the foreground. The ambient light in the background records as a function of the aperture and the shutter speed. With a Nikonos V and strobe, for example, there are three choices of synch speed: "A" (1/90th second), 1/60th and 1/30th. Within this range there is a full stop-and-a-half difference in ambient light level in the background at the same identical aperture. The creative shooter will be concerned not only about the aperture that correctly renders the foreground, but also the shutter speed ideally suited for the background.

Tail-Shot Syndrome

This is my lump-all category for lame composition. With fish photographs, it is the classic fish-swimming-away-in-panic view we call the tail-shot. But it could be failure of any of the numerous admonitions found in the excellent photo reference, Jim Church's Essential Guide to Composition. You can learn the rules, but at the end of the dive, composition is instinctive rather than learned. You have to know what looks right, and then use your tools and skills to translate the image from your mind's eye to film.

To contact Stephen Frink with photo questions or topics for future Viewfinder columns, call (305) 451-3737.