Canon A-1 - Manual (Page 81)

Automatic Diaphragm Control
When the A-1 is directly coupled with an FD
lens, diaphragm control is totally automatic.
Exposure metering is performed at full
aperture whether the lens aperture ring is at
the “A” mark or set to a specific aperture.
At shutter release, the diaphragm automati-
cally closes down to the aperture set by the
camera or by you with the AT dial or the
aperture ring. Following shutter release, the
lens automatically returns to maximum aper-
ture.
Manual Diaphragm Control
The insertion of manual accessories or a
macrophoto coupler between the camera
and an FD lens requires setting the lens for
manual diaphragm control before stopped-
down metering is possible. The instructions
for the various accessories involved will tell
you whether or not this is necessary.
All FD lenses which lack a Breech-
lock mount ring, with the exception
of the Macro lenses, are set for manual
diaphragm control as follows:
1. Before mounting the lens, insert the hole
of the accessory manual diaphragm adapt-
er over the tip of the automatic aperture
lever at the rear of the lens. Push the
lever to the right and lower the adapter
into the groove to lock the lever in that
position.
2. Mount the lens onto the accessory. The
diaphragm will now open and close as
the aperture ring is rotated.
When the manual diaphragm adapter is
attached on the rear of one of these lenses,
never mount the lens directly on the camera
or directly on accessories designed for
automatic diaphragm control, such as the
Auto Bellows or Bellows FL.
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