Canon A-1 Instructions Manual page 72

~hang:ing
th e ASA Setting
1
h ~re
is ano ther way to correct exposure
whic h can be used whe ther you arc in the
manual o r th e AE mode. That is to change .
the ASA film speed setti ng on the camera. A
fil m with
an ASA rating tw
ice that of
an other film requires onJy half the amount
o~
light for correct exp osure as compared
wi th the other f ilm. For instance, if you
h ave an ASA 2 00 film lo aded, yo u can make
an exposure correcti on equal to closing the
ap er ture one f/stop or raising the sh ut ter
speed o ne s tep by cha nging the ASA setting
on the ca mera to ASA 4 00.
Other useful tricks CCln be p e1f orm ed by
changin~ tl~e
A SA
~etting.
Y?u may be
stuck, fo r instance, indoors without f lash.
Even w1:th A SA 400 film loaded in your
camera., you may be fo rced to use undesira-
bly slow shutter speeds. You may solve
this by "pushing" t he ASA setting on the
- 72-
cam era to a higher VCllue. Usually t his
is done by multiplying the normal ASA
rating by some multiple of two, say by two
o~
four. In this case, the whole roll of
film must be shot at the "pushed" ASA
or you will have to sacnfice one or the other
of a whole series of frames. Also, do not
fo rget to inform your develop ing lab of the
change or t he whole film will be incorrectly
develop ed. This is only an introduction t o
this technique.
N ot
all f ilm s can be
"p1 ;,shed"
and
not all developing labs w
ill
handle then'!. R ead more about "p ushing"
the A SA
m
photographic literature and
k now what you 're doing before you try it.
This trick sho uld not be confused with t he
above w hic h involves in ten tional exposure
correction for only one frame after which
the ASA d ial should be reset to its origin al
value.