Backscatter is the illumination of the particulate matter in the water between you and your subject. Underwater photography and backscatter are unfortunate bedfellows. While there are times that you will not be able to eliminate backscatter in your images, there are simple ways to minimize it, and in fact it is possible to prevent it altogether. Of course, when you are shooting in a situation with a lot of debris in the water, some backscatter is inevitable, but even with a moderate amount of particulate matter, you will eventually learn how to prevent it.
Minimizing Backscatter Comes Down To Strobe Positioning
(see strobe positioning)
Positioning your strobes out to the side of your housing will eliminate the illumination of the particles between your housing and the subject. Many compact point and shoot cameras have short strobe arms that do not adequately position the strobe away from the camera and therefore backscatter is harder to minimize. This is one of the primary reasons why the internal flash on a compact camera is usually not an option for underwater photography. The closer the strobe to the camera, and the more parallel the angle, the more backscatter will appear in your images.
Other Tips For Preventing Backscatter
Get closer! The less water between you and your subject, the less particulate matter.
Master buoyancy and only dive near other divers with good buoyancy who won’t stir up the bottom. Be careful of stirring up particulate matter yourself. Sometimes you may not realize that your fins are stirring up the bottom or the elbow or even finger that you use to brace yourself against the bottom is actually stirring up particulate matter from the sand. Note: be respectful of the environment and NEVER touch live coral or marine inhabitants. If you must brace yourself the best way is to use one single finger and positioning you body up in the water column, protecting both the environment and minimizing your chance of stirring up the bottom.
Even with perfect buoyancy skills, if possible, when a current is present, position yourself down-current of your subject so that you do not accidentally cause any additional backscatter.