Canon A-1 - Manual (Page 128)

camera to a higher value. Usually this
is done by multiplying the normal ASA
rating by some multiple of two, say by two
or four. In this case, the whole roll of
film must be shot at the “pushed" ASA
or you will have to sacrifice one or the other
of a whole series of frames. Also, do not
forget to inform your developing lab of the
change or the whole film will be incorrectly
developed. This is only an introduction to
this technique. Not all films can be
"pushed" and not ail developing labs will
handle them. Read more about "pushing"
the ASA in photographic literature and
know what you 're doing before you try it.
This trick should not be confused with the
above which involves intentional exposure
correction for only one frame after which
the ASA dial should be reset to its original
value.
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