Canon A-1 - Manual (Page 24)

Rear Dust Cap
The rear dust cap must be removed before
moimting the lens.
Operation with ah FD lens which lacks
a chrome Breech-lock mount ring:
The rear dust cap for this type of lens has
serrated edges. Do not mount a rear dust
cap which lacks the serrated edges.
Removal from lens
1. Turn the cap coimterclockwise until it
stops.
2. Pull the cap out.
Reattachment
1. Align the arrow on the cap with the
red dot at the rear of the lens.
2. In that position, apply slight pressure to
the cap and turn it clockwise until it is
tight.
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