By Marty Snyderman
Backscatter-the word that collectively describes those horrible, strobe-lit, out-of-focus blobs in the foreground of an underwater photo-has ruined more potentially wonderful photographs than all the flooded gear, bad weather and strobes that wouldn't fire put together. That is the bad news. The good news is, backscatter is avoidable. So when Bob G. of Albuquerque e-mailed me asking how he could avoid backscatter, I thought the answer would help many underwater photographers.
Bob told me that he had recently been on a three-day trip in Southern California. At the after-trip party everyone noticed that one photographer had almost no backscatter in her photographs. His own pictures, however, were disappointing by comparison because of backscatter. Bob wanted to know if his friend had gotten rid of the scatter in her shots with a computer.
I can't say with 100 percent certainty what Bob's friend did, but my guess is that she knows something very valuable about positioning her strobes. Backscatter is caused when strobe light illuminates out-of-focus particles that are between your subject and your film. Placing a strobe directly over your lens or too close to the area the lens "sees" are the primary causes of backscatter. Poor water conditions contribute, but the main culprit is poor strobe placement. It is easier to get away with poor technique in clear water, but you can do much to avoid backscatter in any conditions by using good techniques.
Whether hand holding or using a strobe arm, the key to minimizing backscatter is to position your strobe to the side of your lens. Placing your strobe slightly above your subject will also help create a more natural look as well, with any shadows created by your strobe light falling below your subject. This positioning will help, but you can help yourself even more if you do not point the head of your strobe directly at your subject. Instead, aim your strobe slightly to the outside, so you light your subject only with the inside portion of the beam. This will help you avoid lighting too many backscatter-causing particles. This technique is called edge lighting, because you light your subject with the inside edge of the beam of light emitted from your strobe.
Edge lighting takes practice, but once you gain confidence in the technique, it will go a long way toward helping you minimize backscatter. Soon those pictures that were once headed for the nearest trash can will be ones that you can proudly display.