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ADVANCED OPERATIONS
Calculating the flash effective distance according to
the camera-to-subject distance.
Maximum flash distance = Guide Number ÷ Selected
aperture
Minimum flash distance = Maximum flash distance ÷ 5*
When the distance to the subject is less than 0.7m
(2.3ft), the flash cannot be used. If the flash is used with-
in that distance, it causes vignetting in the picture cor-
ners, light is distributed unevenly and the picture may be
overexposed.
• The value 5 used in the formula above was obtained
from the built-in flash.
The guide number (GN) depends upon the film speed
used as shown below.
Calculating the aperture according to the cam-
era-to-subject distance
Aperture = Guide Number ÷ Camera-to-subject distance
If the calculated aperture value is different than an indi-
cated f-stop on the aperture ring, for instance f/3, choose
the next smallest aperture ring number (f2.8 in this
case).
ISO25 → GN5.5
ISO50 → GN7.8
ISO100 → GN11
ISO200 → GN15.6
ISO400 → GN22
If an ISO100 film is used at an aperture of f/2.8, the flash
effective distance is obtained as follows:
Guide Number (11) ÷ f/2.8 = 3.9m
3.9 ÷ 5 = 0.8m
Thus, the flash effective distance is from approx. 0.8m to
3.9m.
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