Canon Model 7S - Manual (Page 23)

How to Set the Lens Aperture
The lens aperture adjusts the light volume that
reaches the film and also the depth-of-field. (See
page 35.)
The desired aperture stop can be obtained by
turning the lens aperture ring until the figures
align with the index mark.
Canon 7S, by using the built-in meter, can easily
determine the lens aperture which sets the shut­
ter speed.
• In the case of the aperture, as the numerical
value gets larger the amount of light reaching
the film becomes correspondingly less. For
each aperture, the light is reduced one-half.
Accordingly, when the aperture is increased
by one index point, the exposure is doubled,
and when it is increased by two index points
the exposure is quadrupled.
The lens aperture ring can also be set to
intermediate values.
The ratio between aperture and the amount
of exposure, using F 2 as the basis, is as
follows :
Lens Aperture
0.95 1.2 1.4 1.8 2 2.8(3.5)4 5.6 8 11 16 22
Exposure Ratio
1'4 1 3 1 2 1/1.2 1 2 (3) 4 8 16 32 64 128
a
11