Canon A-1 - Manual (Page 39)

Film Advance and Shutter Release
At the base of the film advance lever is the
main switch of the camera. When it is at the
“L” (LOCK) setting, all active circuits are
turned off and the shutter button is locked
to prevent unintentional shutter release. This
switch should always be in the “L” position
to prevent battery consumption and film
wastage when the camera is not in use, such
as when it is in a camera case.
When the main switch is set at “A”, the
shutter button can be operated. The shutter
button serves to activate both the AE meter
and shutter operation. Since it is electro­
magnetic, it requires only gentle pressure for
both a very smooth shutter release as well as
immediate meter response when shooting in
quick succession. Pressing the shutter button
lightly only halfway gives a meter reading
preview inside the viewfinder. When you
press it gently all the way, the mirror flips
up, the diaphragm closes down and the