Canon A-1 - Manual (Page 150)

aperture ring to the working apertures speci­
fied for an automatic electronic flash or be
determined through a guide number calcu­
lation using the following formula.
Aperture
Guide Number
Sho>oting Distance
When doing the math, make sure that the
guide number and shooting distance are both
in the same unit, whether meters or feet.
The fastest shutter speed for use with
electronic flash is 1/60 sec., for use with M
or FP bulbs, 1/30 sec.
It is recommended to use a Canon flash unit
on this camera. Using a flash or flash acces­
sory of another make may cause the camera
to work improperly or even possibly damage
the camera itself.
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