Canon AT 1 - Manual (Page 69)

Releasing the Shutter
When you press the shutter button, try to
squeeze the shutter button gently with your
finger. Avoid hitting or pressing the shutter
button suddenly particularly when using slow
shutter speeds, otherwise blur may result.
At the moment of shooting, you should
exhale slowly while the shutter button is
being pressed.
Rewinding the Film
When the film advance lever cannot travel
all the way to the end of its stroke, the frame
counter tells you that you have reached the
end of the film. You have to rewind the film
in its protective cartridge, before you can
remove it from the camera. Since it is not
protected, any exposure to light will "fog"
the film and cause a drastic color shift and
loss of picture image.
To rewind the film, press in the small
rewind button on the bottom of the camera,