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A
more sophisticated system is the dedicated unit
that connects to your camera's electronic control
system to provide automatic synchronization
and through-the-lens exposure automation.
Dedicated units come in two varieties. One is
made (or marketed) by the camera manufacturer
and is designed to work with its particular
brand of cameras. The other is equipment produced
by flash manufacturers using interchangeable
modules that adapt their units to work with
specific cameras. The SCA system is a prime
example of an interchangeable dedicated system. The
advantage of interchangeable flash systems is
that they can work with a wide range of cameras;
if you change brands, you can still use your
flash equipment.
We have not found any significant difference
in either quality or convenience between a flash
unit marketed by a major flash manufacturer
or one offered by the maker of your camera.
The most important variable in selecting a flash
unit is the amount of light produced. This information
is provided in technical data as the "Guide
Number" (GN) based on using an ISO 100 film.
A GN of 90 to 120 is commonly found in shoe-mounted
units and will provide ample light for working
distances up to 40 feet or so.
If you must work at longer distances or outdoors,
such as photographing sports events, you might
want to check out a handle-mounted unit. These
are readily identified by the large battery
case that serves as a carrying handle. Their
overriding advantage is sheer power with guide
numbers of 180 to 240. This will permit flash
photography at distances of at least 50 to 60
feet.
NO
NEED FOR A GUIDE
Guide
numbers were originally provided for non-automatic
flash equipment, going back to the days of flash
bulbs. By giving the user a measure of the light
produced by a specific flash unit, the correct
lens aperture could be calculated by dividing
the flash-to-camera distance by the guide number.
The quotient would be a fairly accurate aperture
setting. For example, if you are using a non-automatic
flash unit with a guide number of 80 and photographing
a subject 20 feet away, the simple computation—80
divided by 20—would give you an answer
of 4. If you set your lens aperture to f/4,
your exposure should be correct.
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