Chapter 3 ✦Flash Photography Basics 73

In simpler terms this means you divide one
by the distance then square the result. So if
you double the distance, you get 1/2
squared, or 1/4 of the total light; if you
quadruple the distance, you get 1/4 squared
or 1/16 of the total light. This factor is impor-
tant because if you set your Speedlight to a
certain output, you can still accurately deter-
mine the exposure by moving the Speedlight
closer or further as needed.
GN ÷ Distance = Aperture
Here’s where it all comes together! You take
the GN of your flash, divide by the distance
of the subject, and you get the aperture at
which you need to shoot. Due to the com-
mutative properties of math, you can
change this equation to find out what you
want to know specifically.
✦Aperture ×Distance = GN
✦Aperture ÷ GN = Distance
✦GN ÷ Distance = Aperture
Sync Speed
The sync speed of your camera is the fastest
shutter speed you can shoot with and still
get the full exposure of the flash. The sync
speed is based on the limitations of the
shutter mechanism. The sync speed on dif-
ferent camera bodies differs with the type of
shutter mechanism used. The D70/D70s
uses a combination mechanical and elec-
tronically controlled shutter system that
enables it to sync up to 1/500 of a second,
much faster than the sync speed of the rest
of the Nikon camera bodies, all of which
sync up to 1/250 of a second.
When using Nikon Speedlights, the camera
body does not let you set the shutter speed
faster than the rated sync speed. When a
non-dedicated flash or an external strobe is
used via the PC sync, it is possible to set
your camera to a shutter speed higher than
the rated sync speed. The result is an incom-
pletely exposed image.
Fill flash
When shooting outdoors on a sunny day
using the sun as your main light source, you
usually get images that are very high in con-
trast. The shadows are invariably much
darker than they should be. In order to over-
come this, a technique called fill flash is
used. The SB-800 and SB-600 have a setting
for doing balanced fill flash (TTL BL) that
works very well. When using the Manual set-
ting on your Speedlight, you can also use fill
flash.
To do fill flash manually:
1. Position your subject so that the
sun is lighting your subject how
you like. When shooting a portrait
try not to have the sun shining
directly in their eyes, as this causes
them to squint.
2. Use your camera’s light meter to
determine the correct exposure.
A typical exposure for a sunny day
at ISO 100 is f/16 at 1/125 sec.
3. Determine the proper exposure
for your Speedlight. Use the GN
÷ Distance = Aperture formula.
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