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Do scratches on my lens or port damage my photos? I've heard that water fills them in, and they aren't visible.


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Questions and Answers (Q & A's)

From Alan Broder (from Ocean Realm Magazine - April 1993)


Let’s define terms—what do you mean by scratches and what do you mean by damage? Scratches come in a great variety of sizes, shapes, and severities. I’m sure that you’ve been on a boat with a photographer who was cheerfully using a port covered with pretty much the entire range of types. I once owned such a port. Since I take the position that I really don’t need any more handicaps in my photography than I already have, I hadn’t used this port for some time. I had just been involved in an animated philosophical/scientific dialogue (big argument) with one of my esteemed fellow underwater photographers (knucklehead) on a dive boat as to whether scratches on the outside of the port disappear when in contact with water—the rationale being that water and the acrylic port have practically the same refractive index, the outside of the port and scratches should disappear when immersed. In the spirit of St. Thomas Aquinas, I decided to see for myself. I submerged the end of the port in some water in the kitchen sink and found that the smaller scratches did disappear, but most were still visible.

These scratches will definitely scatter light, and this will affects contrast and therefore sharpness and color saturation—theoretically, at least. Will they be visible in your image? If you’re using video, and shooting into the light, they will almost certainly be not only visible, but intolerable. The incredible depth of field inherent in a very small format system such as 8mm or even half-inch with a wide-angle lens will almost always include the port in the image. If you scratch your video port, you will either need to remove the scratch or replace the port. If you’re using a still system, you won’t record an image of the scratch on film since the larger 35mm format lacks the close focusing capability and, most especially, the depth of field required to bring anything as close to the lens as the port into focus.

I know of no standard way to measure the precise degree of scratchedness. For the purpose of discussion here, let’s arbitrarily place scratches on a "BP" scale. A score of, say, 20/20 on the BP scale would indicate a scratch which when first noticed on the port of a 28mm Nikonos lens, would raise the blood pressure of an owner of average anality twenty points for twenty seconds. We couldn’t use the 15mm lens because any scratch on a "15" has heart failure for at least twenty seconds, and all scratches get a score of 0/20, making the scale useless for comparison. Just to calibrate the scale, a 4/20m is a scratch that a normal person probably wouldn’t even notice, and a 100.20 is a gouge that would cause 50 percent of all underwater photographers to tear the lens off the camera and toss it overboard. The more sophisticated photographer, of course, knows that the $350 28mm lens can be fitted with a new port and repaired, even if flooded, for about a hundred bucks and will immediately jump overboard to retrieve it.

Let’s say you’ve taken a properly focused, well-exposed photo with a Nikonos or a housed normal or wide-angle lens with a 20/20 scratch somewhere on the port, and you took the shot to the world’s three most experience underwater photographers for a critique, "Yatatatatah, but I do see that you had a scratch on your port"? The answer is zip, zero, and nada damn one! If, however, you have a 42.5/20 to 79/20 or greater scratch in the center of a port with a 105 macro lens behind it, you will scatter a large percentage of the light entering the lens and will be entering the city limits of Fuzzyville.

So where do you draw the line? What do you call damage? Taken to the extreme, you obviously could scratch the port enough to totally obliterate the image. At the other end of the scale, you might have a scratch that would cause no measurable loss of image quality. Again, theoretically, any scratch scatters light, and light scattering degrades image quality (period). It may be reasonable to be almost as particular about the condition of your port as you are about the quality of your images. My personal attitude is simple: "When in doubt, get it out! If it ain’t there, it can’t hurt you."




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