Canon AE-1 User Manual

Page 59

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Film Plane Indicator

Thi$ mark i$ engraved on the top of the

camera between the film rewind crank and

the battery check buttoc\, just to the (eft of
the pentaprism« to indicate the exact position

of the film plane. The distance scale on the
lens shows sublet distances measured from

the film plane indicator. This mark is not used

in general photography« but in close*up$ and
macrophotogtaphy it is often used to obtain
the exKt subject distance.

Scales on the Lens
Aperture Scale

The aperture of the lens is the opening of

the diaphragm Wades« like the iris of the
human eye. It controls the amount of light
passing through the lens to the film surface.

The f/number is a mimerical expression

of the effective aperture. It is obtained by

dividing the focal length of the lens by the
diameter of the effective aperture. When the

f/number is set orte scale gradation higher« the
lens allows in half the light it would at the
previous gradation. Intermediate settings of
the aperture scale can be used« too. In some
lenses« the f/number setting one gradation

higher than the first f/number setting does not

necessarily allow oofy half the amount of light

of the previous setting through the lens to

expose the film as Is the case at the other
settings. This should be taken into con­
sideration when necessary.

The aperture ring usually has gradations

marked as follows, taking f/2 as a basic

unit:

0

fw)

{

2

4 se a n le

n * u o

3

2

]

ir 'z

i/a i/e i/ia 1/121/64

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