Canon A-1 - Manual (Page 73)

This table does not necessarily apply when
using a lens of a different focal length. If
you are using a telephoto lens, for instance,
any subject movement and the least bit of
camera shake can have a magnified effect on
image sharpness. For a telephoto it is neces­
sary to use faster shutter speeds than with a
standard lens under the same lighting con­
ditions. It is generally said that, for sharp
image results in hand-held shooting, the
minimum shutter speed should be equal to
or faster than 1 divided by the focal length
of the lens. This means that for a 100mm
lens, the shutter speed should be at least
1/125 sec.; for a 200mm lens, it should be at
least 1/250 sec.
There are other considerations in the se­
lection of shutter speed. You can usually
freeze the action of relatively slowly moving
pedestrians or traffic at a shutter speed of
1/250 sec. The same is not necessarily true
of a rapidly moving bicycle. Instead of
freezing the action, you may want to empha­
size it by blurring some part of the picture.
For instance, you could blur a moving
subject with a relatively slow shutter speed.
Or, using a panning technique, turning the
upper part of your body to follow the
subject’s movement, at a relatively slow
shutter speed of perhaps 1/30 sec., you can
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