Canon AE-1 Manual page 28

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Film Plane Indicator

Scales on the Lens - Aperture Scale The aperture of the lens is the opening of the diaphragm

blades, 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 numerical 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 one

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 only

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 consideration when necessary.

Distance Scale The distance 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 photographing with infrared film. Read one-digit

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.

Depth-of-Field Scale You can determine the depth-of-field by checking the depth-of-field

EE Switch Pin

This pin protrudes when the aperture ring is locked at the "A" mark. In

this position, it transmits a signal for AE photography.

Reserved Pin

This pin is designed for use with accessories that may be developed in

the future.

This mark is engraved on the top of the camera between the film rewind crank and the

battery check button, just to the left of the pentaprism, to indicate the exact position of the

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

plane indicator. This mark is not used in general photography, but in close-ups and

macrophotography it is often used to obtain the exact subject distance.