| 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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