Canon III-A User Manual
Page 14
Attention! The text in this document has been recognized automatically. To view the original document, you can use the "Original mode".
When the Lens Aperture is closed by one stop, the amount of light entering the lens is
decreased by one half; two stops, by one quarter and so on. Therefore you should adjust the
Lens
Aperture
in
conjunction
with
your
shutter
speed.
Suppose
your
exposure
meter
indi
cates a speed of 1/200 sec. at f:5.6. If you want to expose for a slower speed, say 1/100
sec., than you must close down the Lens Aperture to f:8. In other words, as you have
doubled the time of the shutter opening, you must reduce the amount of light entering the
lens by half to obtain the correct exposure.
The table below gives you the relation between the Lens Aperture and the relative time of
exposure for Canon Camera.
Lens Aperture
Relative Exposure Time
1.8
2.0
2.8
3.5
4.0
5.6
8.0
1 1
16
0.8
1
2
3
4
8
16
32
64
DISTANCE
SCALE
When
accurate
focus
(see
page
13)
has
been
made
on
any
object,
the actual distance from the plane of the film to the object is shown by the Distance Scale
(see next page) which is marked from 3.5 to infinity (os) in feet. Lenses with meter scales
are provided when specially ordered.
11