| I love the performance of the SB26 with
its matrix metering and intelligent fill flash for my land
photos. The guide number of 138 on land indicates that there
should be plenty of power underwater.
Your SB26 is certainly a remarkable piece of equipment for
"land photography" as you point out. There are two
things going on with N90s/SB26 combo when you’re using
the system out of the water. The first is the much vaunted
"matrix metering," offered in most of the current
Nikon SLR cameras; and the second is the "D technology,"
available in the N90s when used with D-type lenses. This technology
is not offered in the F4, N90, or any of the 8008 models.
Let’s take D-tech first. Nikon gets points for observing
that when a lens has focused on a subject, it has, as the
same time, measured the distance between the camera and that
subject very accurately. The D lens passes this distance info
on to the camera’s computer. The SB26 sends out a series
of very small preflashes which are reflected back to the camera.
The computer now has reflected light data which it integrates
with its pre-programmed strobe guide numbers and information
from the matrix meter. The computer then determines how much
light to squirt on the scene by comparing distance-guide number
computations with TTL light meter data. This is accomplished
by a cooperative effort between lens, camera computer, and
strobe, and works great in air—as you already appreciate.
The rules are different underwater. You may recall from a
childhood game that "paper covers rock, scissors cut
paper, rock breaks scissors, and water eats light." The
fact that water is absorbing and dispersing light from both
the preflashes and the flash exposure blows all of the carefully
constructed guide number data in the computer out the window.
One might think that if the preflashes and exposure flash
are both reduced by passage through water, then it would follow
that errors should cancel out—like, that would be fair.
One should get real! When was anything about underwater photography
ever fair? The fact is that when the tiny preflashes go out,
the computer is left computing "wherred they go, where’d
they go-oooo?"
You’ve got not D-tech. Should you house the land strobe
to get matrix-metering? Trick Question! The matrix metering
is in the camera, not the strobe. Any—I say any—dedicated
strobe will give matrix metered TTL flash when properly connected
to a camera with matrix metering. Virtually all underwater
strobes, regardless of manufacturer, will "dedicate"
to the Nikon cameras with this metering system, since all
Nikon cameras which support TTL (thorough the lens) metering
use the same communications system between camera and strobe
that is used in the Nikonos cameras. All underwater strobes
work with Nikonos cameras—wouldn’t it be silly
if they didn’t? Well they do anyway!
So there appears to be no functional advantage to housing
a land strobe over using any one of the myriad of underwater
strobes on the market. Let’s evaluates SB26 on its merits
as an underwater unit. First the housings for this strobe
are up around $500. Underwater strobes putting out about the
same fifty or so Watt seconds of power start at or around
$250—about $325 with cord. Nikonos cords are used with
housed strobes and cost something over $100. You could buy
two basic UW strobes for about the price of one strobe housing--$650
versus $600. The housed strobe is huge compared to underwater
strobes in the same power range, about two and a fraction
times larger. The bulk of the housing for the strobe is parallel
to the arm as opposed to perpendicular, as in the case of
the UW strobes. This means that the bulk of the housed strobe
is right up close to the subject when shooting macro. The
bulk of the underwater strobes will protrude away from the
subject in macro. This makes them much easier to position,
with much less crowding. No difference in this respect when
shooting a subject a couple of feet, more or less, from the
camera—as with a fish portrait, for instance.
Now, to that humongous guide number—138, wasn’t
it? Your flash has a zoom feature which narrows and widens
the beam angle of the strobe to match the angle of acceptance
of the lens. Telephoto lenses have narrow angles of acceptance,
and therefore require less beam spread. When you use your
flash on land, it is mounted in a shoe on top of your camera,
and aim is very good. Aim is more problematic underwater.
Many photographers even prefer wide-angle strobes for fish
photography so they can’t miss with the light. The big
advertised guide number refers to the narrowest angle in the
zoom range—narrower than the lens you’re likely
to be using. When you widen the beam to a more practical angle,
the guide number is similar to that of other strobes in the
fifty or so Watt second range. It is possible to carefully
aim the SB26 strobe for a macro shot, then narrow the beam
to a point so that you produce way the hell more light than
you could ever need. The fact is that you can properly expose
even a slow film such as Velvia at 1:1 at an aperture of f22
(effectively f45 when shooting at 1:1) by properly placing
your AiN strobe or, for that matter, the smaller Ikelite 50.
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