Canon A-1 - Manual (Page 30)

Memo Holder
The back cover of this camera is provided
with a memo holder. Once you have loaded
the film and set the ASA, it is very useful to
tear off the end of the film box and insert it
into this memo holder as a constant re-
minder of the type of film in use. Add other
information as you like.
The Basics of Exposure
This section contains some terms and
definitions which will be used throughout
this instruction booklet.
The amount of exposure is a matter not only
of the amount of light allowed to strike
the film but also of the amount of time
the light is allowed to strike the film. The
camera has two mechanisms to control
exposure, the diaphragm and the shutter.
The diaphragm consists of blades which
open and close to certain size openings
called apertures. The size of the aperture
determines the amount of light which will
fall on the film. The various size apertures
are indicated by a set series of numbers
called f/stops or f/numbers. Each f/stop
represents some amount of light that is
allowed to pass through the lens. The smaller
numbers are called large f/stops while the
larger numbers are called small f/stops.
This is because the larger numbers represent
smaller apertures and allow less light to pass
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