Canon A-1 - Manual (Page 56)

The length of time that the light is allowed
to strike the film is determined by the
shutter
speed. The relationship between
shutter speeds is like that between f/stops.
As you move from one shutter speed to the
next
higher shutter speed, exposure is
halved. Your image is actually exposed by
the opening of the shutter. Shutter speed
can he controlled on the A-1 by turning the
AT dial. Otherwise the camera controls it.
Now suppose that you have the camera set
for a certain exposure value (EV), say the
exposure you get with f/4 at 1 /60 sec. There
are certain other combinations of aperture
and shutter speed which will give you the
same amount of exposure as that above.
Some of these combinations in this example
include f/5.6 at 1/30 sec. and f/2.8 at 1/125
sec. You simply move up and down the
f/number and shutter speed scales. It is not
important to know this relationship when
you use the A-1 in an AE mode. The camera
will do the figuring for you. But it is an im­
portant
photographic fact which you may
find useful when you use the camera
manually or in correcting exposure.
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