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Backscatter in Underwater Photography
Backscatter in Underwater Photography
Nemesis of all underwater photographers: backscatter, and how to minimize it with strobe placement. We have all seen images with small white specks in them, most noticeably with a blue or black background. Some photographers call this the starry night effect. In fact, these white specks are backscatter and they are tiny particles in the water column that have been lit up by the strobe. Even the clearest of tropical waters have suspended particles that can ruin your images. Can you eliminate backscatter? Not always. Can you minimize it? Absolutely. When the light from the strobe strikes particles in the water column, the particles reflect the light back. When the reflected light hits the lens, it produces backscatter in the image. Essentially the particles are being lit as if they were a subject. Backscatter is worse when the strobe is aligned with the lens to subject axis. In other words, the strobe is pointing straight at the subject, just like the lens. In order to minimize backscatter, you must move the strobe away from this position. By moving the strobe to the left of the lens and up about 45degrees, you will reduce backscatter. The particles will still be hit by light from the strobe, but instead of the light reflecting back into the lens, it will reflect off to the side where they will be less visible. The degree to which this strobe position will work depends on how many particles are present. If there are not too many, they will probably disappear. If, however, there are many particles in the water column, this strobe position will reduce them, but not entirely eliminate them. If your camera has a built-in strobe, it is better to disable or misdirect it and use an auxiliary strobe for lighting your subjects. You can cover the front of the camera’s strobe and deflect the light upward where it could trigger a slave strobe set at the appropriate angle. Particles are not always the natural state of things. Many times the particles you see are the result of poor buoyancy control by you and/or your dive buddies. Excessive or forceful finning or putting your hand or camera on the bottom too aggressively can stir up the substrate and add to the number of particle in the water. If you wait a few minutes, these particles will often settle down. Remember the basic rule – to be a good photographer you must first be a good diver. Shadows
As you move your strobe away from the lens to subject axis, you may reduce the backscatter, but you will start to create shadows in your image. Some shadows are good because they add contrast and dimensionality to a subject. Sometimes they are too harsh and detract from the subject. What’s the solution? If you have ever had your picture taken by a studio portrait photographer, you know they used more than one light source: one main light and a second one to fill the shadow caused by the first. The same principle works for underwater photography. You can improve your images by adding a second strobe to reduce the shadows caused by the main strobe. The idea is not to completely eliminate the shadows, but to reduce them to produce a more pleasing effect. Adding a second strobe adds expense and complexity, but it generally improves your images. It makes your subjects pop out. You can create perfectly acceptable images with only one strobe and many people never make the move to a second one. You will have to decide if a second strobe makes sense for you and the images you want to create. Be warned though, if you add a second strobe, you probably would not go back to using one.
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The copyright for this content entitled "Backscatter in Underwater Photography" has been specified by the contributor as:
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This content may not be copied, distributed or adapted by anyone under any circumstances.
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This intel was contributed by Mike Chua
Mike Chua
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February, 2012
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