Canon AT 1 - Manual (Page 81)

Generally, the depth-of-field will become
deeper as the aperture becomes smaller, and
shallower as the aperture becomes larger. A
shorter focal length as well as a greater
camera-to-subject distance will also deepen
the depth-of-field.
Comparing a 28mm lens with a standard
50mm lens set at the same f/stop, the 28mm
lens's depth-of-field will be greater. And when
the photographic distance changes, the depth-
of-field changes, too. For example, if the same
subject is photographed from three and then
from seven meters away, the sharp foreground
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