Canon AV 1 - Manual (Page 17)

Operation with an FD lens which has a
chrome Breech-lock mount ring or with
an FL lens:
Removal from Lens
1. Turn the lens' mount ring clockwise until
it stops.
2. Pull the cap out.
Once the rear cap is removed, the Breech-lock
mount ring is locked so that it cannot be
turned. (The diaphragm blades are also locked
and will not move even if the aperture ring is
rotated.)
Reattachment
1. Make sure the mount ring is locked so
that it cannot be turned.
2. Align the arrow on the cap with the red
dot on the lens' mount ring.
3. In that position, push lightly down on
the cap and turn the mount ring counter­
clockwise until it is tight.
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