Canon A-1 - Manual (Page 77)

make a focusing correction. Follow the
detailed instructions of the film manu-
facturer.
The position of the infrared index mark has
been computed for the use of infrared film
with peak sensitivity at 800nm (such as
Kodak IR 135) and a red filter such as
Wratten 87.
Checking the Depth of Field
There are two ways to find out what the
depth of field is. One is by using the depth
of field scale which is a series of f/stops
repeated on each side of the distance index
mark on the lens barrel. The scale differs
according to the lens. First focus your
subject. Find the two f/stops on the depth
of field scale which correspond to the
aperture you or the camera have set for the
exposure. Draw imaginary lines from these
two f/stops to the distance scale. The
effective depth of field extends between
those two distances. For example, using a
standard 50mm lens focused at 3m with the
aperture set at f/8, depth of field extends
from 2.4m to 4.5m. Any subject from
2.4m to 4.5m away will be in reasonably
sharp focus in the image.
You can also visually check the depth of
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