Canon AE-1 - Manual (Page 60)

Distance Scale
The disieoce scale is for distances
measured from the film plane. This scale is
not generally used except for confirming the
depth*of*field. performing guide number
calculations in flash photography« or photo­
graphing with infrared film.
Read i^enjigit distances in the middle of
the number marked on the scale. Two-digit
distances should be read at the point in the
middle of the two digits.
DoptfK)f-Field Scale
You can determirw the depth*of*field by
checking the depth*of*lield scale and the
distance scale on the lens barrel. Both are
closely interrelated.
Infrared Irsdex Mark
The red dot infrared index mark engraved
on the lens barrel is a focusing correction
index mark for infrared film. Because infrared
light rays have longer wavelengths, they focus
on a plane slightly behind that of ordinary
visible l»ght rays. Therefore, it is necessary to
slightly modify the normal method of focus­
ing the lerH. After focusing the same as usual«
note the tiny red dot engraved on the lem
barrel fo % % to the right of the distance index
and turn the focusing ring slightly to align the
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