Canon AE-1 Manual page 26

switch and adjust the aperture ring and/or shutter speed dial until the meter needle inside the
viewfinder is aligned with the stopped-down metering index mark. Press the shutter button
and the photograph will be perfectly exposed. If the lens should be mounted on the camera
with the stopped-down lever locked, correct exposure will not be obtained. In this case, a red
warning mark by the stopped-down coupling lever inside the camera body is visible. After
removing the lens, on the lower part of the camera body, just below the mirror, this stopped-
down coupling lever becomes visible, as does the red mark in the case described above.
Manual Aperture Control
When accessories requiring manual aperture control are used between the camera body and a
lens, lock the automatic aperture lever in the manual position before mounting the lens.
A) Lock for Manual Aperture Control (1) For manual aperture control, push the automatic
aperture lever counterclockwise until it stops and locks. When accessories such as extension
tubes are attached to a lens that has been set for manual control, the diaphragm blades of the
lens open or close as the aperture ring is turned. To revert from manual control, reset the
automatic aperture lever in its original position.
With these particular lenses, the automatic aperture lever must be turned fully
counterclockwise while the manual lock lever is brought to the "L" position. Once this has
been done, when the lens is mounted on the camera, the diaphragm blades will open or close
by turning the aperture ring. To revert from manual aperture control, reset the manual lock
lever at the position of the white dot.
C) Lock for Manual Aperture Control When Using the Macrophoto Coupler (3) In
close-up photography of high magnification with a lens reversed on the Macrophoto Coupler,
the automatic diaphragm mechanism is not coupled. You must, therefore, remember to close
down the diaphragm manually after having locked the automatic aperture lever in the manual
position as explained above in (1) and (2). Then, fix the Macrophoto Hood on the lens mount
by turning the bayonet ring.
B) Lock for Manual Aperture Control (2)
There are some FD lenses with the manual lock lever requiring a different
procedure for manual control setting.