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Question:

Backscatter has ruined some of my best shots. What can I do to minimize or, better yet, to prevent this problem.

 

 

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Questions and Answers (Q & A's)

From Alan Broder (from Ocean Realm Magazine - June 1994)

Answer:

For the purpose of discussion, let’s suppose that there are three main factors determining how much backscatter will be in your photographs. First to be considered is how much particulate matter (crap) is suspended in the water. The "visibility" factor varies from place to place, from season to season, from day to day, even from hour to hour, so that a little planning can go a long way towards eliminating, or at least reducing the handicap of dirty water. Plankton blooms and silt from rain runoff are generally seasonal. If you can choose where you travel, you might inquire as to the months which will offer the highest probability of clear water. Once you have arrived on the dive site and an assessment of conditions determines that the visibility is poor, you could ask if conditions might be better at another site.

Now that you’ve done the best that you can to get the odds in your favor, you swim down through the "nutrient-rich" (dirty) water toward the reef which lies ahead in a haze. You may be able to find a sort of oasis of clearer, if not downright clear water somewhere around the reef. A tunnel would be an excellent prospect, especially if you’re the first to find it. Look in nooks and crannies, especially on the side of the reef that’s on the lee of the current. Close to this side of the reef there may be some relatively still water and much of the particulate matter may have settled out.

Now that you’ve done your best to find the clearest water you can, the next step is to eliminate as much of it as possible. You’ll have fewer suspended particles to light up between camera and subject if there’s less water between camera and subject. This means macro or shorter focal length lenses. If you’re using a standard Nikonos camera, select you shorter focal length lens (a twenty-eight instead of a thirty-five) or an extension tube on the boat. If you’re using a Nikonos SLR or a housed SLR, a fifty or sixty macro will give you a great deal of flexibility to choose between fish portraits and macro, so that if conditions don’t favor longer shots, you can switch to macro during the dive.

Lighting technique is your third line of defense against backscatter. Since the largest-appearing particles are the most disagreeable, and since the closer a particle is to the lens, the larger it appears on film, the best lighting techniques are those that don’t direct light between the lens and the subject. It’s natural to want to light the subject with the middle of the strobe beam since there’s less chance of missing with the light. In gin-clear water, this works fine, but in dirty water bigtime backscatter is the result. Try to light the subject with the inside edge of the beam. Learning to do this takes a little study and practice, but the results will be worth the effort. You can make it easier to judge the edge of the beam if you secure a piece of ten mil plastic about ninety to about 120 degrees around the inside front edge of the strobe, forming a deflector. The deflector needs to protrude about an inch or so.

Backscatter will become less noticeable as you move the strobe light off the axis of the lens. It’s generally best to avoid front lighting in anything less than very clear water. At around forty-five degrees, scatter becomes less obvious, and as you move further around toward side lighting, you see less and less scatter. Of course you get harsher and harsher shadows. However, this type of dramatic lighting may be very pleasing. If it doesn’t please you, using two strobes, each at forty-five degrees, and using the inside edges of the beams to light the subject results in even, shadowless lighting with a minimum of backscatter.

An observation: In underwater photography, as in life itself, we seem to create most of our own backscatter. Be certain that you’ve achieved total buoyancy control before you settle to the reef. It’s important to arrive at camera position as if you were gently descending by parachute and not mask over teakettle as if you were shot out of a cannon. Any kicking of fins will bring up murk and may be damaging to pictures and the reef. If there’s a reef above you, be aware that your bubbles will dislodge debris, and what doesn’t become reef dandruff may become backscatter. If you’re using extension tubes, do so with great care. When adjusting the framer around the subject while maintaining a stable body position in the water, it’s easy to inadvertently grind up the reef with a framer, resulting in a cloud of scatter around the subject.

 

 

 

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