Canon AE-1 Manual page 14

Film Advance and Shutter Release Turn the film advance lever until it stops, so the film
will advance one frame all in one motion. The shutter will cock, and the diaphragm and mirror
will be ready for the next shutter release, while the frame counter advances simultaneously to
the next number. By pushing the film advance lever lightly with the tip of your thumb, it will
open to its 30 stand-off position away from the camera body for easy film advance. While the
film is advancing, the shutter will not be released.
Canon has developed the Power Winder A to be used with the AE-1 for automatic film
winding. It greatly increases the automation and mobility of the AE-1.
Shutter Button and Shutter Lock The shutter release button is designed to function as the
main switch of the camera to activate the AE meter and shutter operation. The shutter has a
magnetic release, so the meter can be read by pressing the shutter button halfway with light
pressure. By depressing it further, the shutter will be released.
When the shutter lock lever around the shutter release button is turned to the "L" position, the
shutter button will be locked to prevent unintentional shutter release. Keep the shutter release
button locked while carrying the camera to prevent film waste. Note: When the power level of
the battery is insufficient, a safety mechanism will keep the shutter from being released.
Film winding can also be accomplished by advancing the lever in short
strokes.
The magnetic release shutter button enables faster metering for shooting in
succession than the mechanical release method does. There is also less
chance for camera shake.