Canon 199 A - Manual (Page 23)

This is an exclusive switch for A-1 and New
F-1 uses. When this switch is set at AUTO,
the shutter speed is automatically set to
1/60 sec. (A-1) or 1/90 sec. (New F-1) no
matter where it may have been set (except
B).
When switched to MANU (to the right), all
fast shutter speed settings on the camera
of 1/60 sec. (1/90 sec, in the case of the New
F-1) or faster are automatically set to 1/60 sec.
(1/90 sec, in the case of the New F-1). When
the shutter speed setting on the camera is
1/30 sec. (1/60 sec. in the case of the New
F-1) or slower, shooting is performed at the
shutter speed of your choice. In other words,
use of slow shutter speeds is possible for
getting lighter background. In choosing slow
shutter speed, the A-1 camera is to be, of
course, set to Tv mode.
Shutter Speed Selector
23