Canon A-1 - Manual (Page 31)

through the lens. Each time you move from
one f/stop to the next smaller f/stop (larger
number), the amount of light allowed
through is exactly halved. In effect, the
amount of exposure itself is also halved.
Using f/2 as a standard, the amount of light
reaching the film will change according to
f/stop as indicated below.
On the A-1, aperture can be controlled
either by turning the AT dial or the lens
aperture ring to the desired f/stop. Other-
wise the camera controls the aperture.
The largest f/stop on the lens is called the
lens maximum aperture. The smallest f/stop
on the lens is called the lens minimum
aperture. The maximum and minimum
apertures differ according to the lens.
The maximum lens aperture is important
because it indicates the largest amount of
light that the lens will transmit.
f/stop
1.2
1.4
1.8
2 2.8
3.5
4 5.6 8 11 16 22
Brightness ratio
3
2
1¼
1 ½ P ¼ Q 1 /
16
1 /
32
1 /
64
1 /
128
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