| You’ve just pointed up an interesting
difference between the human eye and brain and the video camera
lens and electronics. You’re probably disappointed because
the video didn’t record the color as you saw it on your
dive. Video cameras have the ability to shift the color of
the recorded image toward what is programmed into the camera’s
computer as a more normal representative range, that is, to
"white balance." White balancing refers to electronically
shifting the color spectrum to make "clean" whites
without any tint. Underwater, the white balancing process
should operate towards minimizing if not eliminating the blue
tint. Your eye and brain do the same, and they do it a gosh
darn heck of a lot better. As you go deeper, and the color
shifts toward overall blue due to an absorption of light at
the red end of the visible spectrum, your mind makes continuous
corrections to your perceived color. You do this very quickly
and to a greater degree than the camera can.
Setting consideration of color, or chrominance as it is referred
to in video, aside for a moment, let’s take a look at
luminance, which is the other major component of the video
image. Luminance refers to the overall brightness of the recorded
image and is analogous to exposure or density in a photographic
image. Simply put, luminance is rarely a problem underwater.
Let’s see if we can turn this around a little and come
up with an acceptable way of stating this fact with appropriate
emphasis. Hmmmm—you could stuff a modern video camera
four feet down a cow’s throat and do video! Don’t
try this at home. Just take my word for it. Video is that
sensitive to light—much, much more sensitive than photographic
film—and video can adapt to lowering light levels much
faster than the human eye can. As a matter of fact, video
is so sensitive to low light levels that you can point the
camera under a ledge where it’s far too dark for you
to see any detail, press the record button. Go home and play
the tape, and be utterly amazed at the bright images you managed
to record. You’ll probably get very little inn the way
of color, but the recorded images will reveal virtually everything
that was going on in that dark environment. Had you stuck
your head under the ledge, it would have taken minutes to
dark adapt to the point that detail was discernible, whereas
the camera did it almost instantaneously.
So what’s the point of all this? Why, the point is
that you should use a filter, of course! Since chrominance
is a problem, and luminance simply abounds, you can make a
deal with the devil to trade off some luminance for some chrominance.
The filter you’ve heard about is almost undoubtedly
the U R PRO filter manufactured by Underwater Research Products
of Naperville, Illinois. The standard and by far the most
common of the three basic U R PRO types is the tropical filter.
This filter is sort of orangey in color and has been scrupulously
balanced to correct away the "blues" in tropical
waters between about ten and fifty to sixty feet. Use of this
filter will cost you one stop of light, but then you’ve
got stops to spare! The results are astounding. Video taken
at ten or twenty feet on a sunny day can look as if it were
shot in a studio! However, somewhere around sixty feet or
so, the gradual loss in effectiveness of the filter with increasing
depth reaches the pint at which the filter becomes more of
a liability than an asset. At just about the exact point that
the filter fails to do much to shift the color of the video
image, the specter of luminance-deficiency heads its ugly
rear.
Probably 99 percent of the filters in use thread directly
into the lens of the camera and can’t be removed during
the dive. You’d have to be awfully fast!
A couple of manufacturers provide a filter which can be moved
into and out of the image path by means of a control on the
housing. This is a nice feature that they acquired by making
a deal with you know who. Space must be provided between the
primary lens on the camera and the almost always desired secondary
wide-angle lens to allow for the filter to swing in and out.
The further you separate these two optics, the more degraded
the image—theoretically, at least.
You could mount the filter on the outside of the port. U
R PRO makes such a model, about four inches in diameter by
about two inches. It is, however, considered by most people
who have used it to be clumsy, unstable, and potentially disastrous
to videotaping should it slip out of alignment and become
part of the scene. And what can you do with this big thing
when it’s not in use? It could hang by a cord—and
get into all sorts of mischief on the reef, in front of the
lens, or with your gear. You could take your regulator out
and hold the damned thing in your teeth—probably not
an option for most of us. You could hold it between your knees
and swim using the "modified ruptured dolphin kick."
Of course, it’s possible to affix the filter to the
housing with a hook or Velcro when not in use, and if you’re
prepared to devote some serious attention toward its positioning
on the port, this filter is a viable option. In general, however,
you’re best off to belay using it.
If you expect to do your taping at over sixty feet for the
grater part off your dive, it’s better to leave the
filter off. Pick up color by using lights. If you’re
planning a shallow reef dive—mostly above fifty feet—the
filter is indispensable. Above ten feet, especially on upward
angle shots, the tropical filter will add an ugly reddish
cast. For a very shallow dive, such as a shark dive in a cage,
leave the filter off. If you’re greedy like the rest
of us and want both deep shots and shallow reef shots, consider
the approach most pros might take in addressing this problem:
make some of your dives with the primary objective of getting
the deeper shots, and some for the shallower, and set up appropriately.
This way you make no compromise in quality. It will also introduce
you to the discipline of planning your scenes, resulting in
more effective and more interesting videos, for you and your
audience.
U R PRO makes two other filter types. A tropical type with
only a half-stop density is made for use with lights in situations
where ambient and artificial light are in about equal intensities
when falling on the subject. Use of the normal tropical filter
with lights will virtually always result in overly red and
very displeasing video. A magenta-flavored "green water"
filter is offered for—you guessed it—green water!
This was supposed to include California water, but most divers
use the tropical type in California waters with excellent
results.
Keep in mind that the closer you are to your subject, the
better the filter works. Keep in mind, also, that leaving
the filter on in very low light conditions degrades the image
quality since the electronic image enhancement utilized by
the camera in its high sensitivity mode produces coarser detail
in a manner similar to that of high speed film in still photography.
Take all of this with a grain of salt, and so your own testing
and experimenting. You may wish to bend or break any of the
above general rules at any given time.
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