Lens Signal Coupling - Canon A-1 Instructions Manual

Aperture Signal
Lever
Full Aperture
Signal Pin
AE Switch Pin
A 111omatic
Aperture
Lever
Reserved Pin
-78-
Lens Signal Coupling
There are several levers and pins at the rear
of an FD lens which transmit signals be-
tween the lens and the camera body. Usually
it is not necessary to know what t h ey arc,
but sometimes, when you must operate the
aperture manually for non-coupled acces-
sories for instance, it is. Just for your
information , we include explanations of
them here.
1. A p erture Signal Lever
With an
FD
lens, exposure metering is
performed t hrough the lens at
full aperture.
This is nice for you since you have a bright
viewfinder to focus and compose, but to
determine correct exposure , the camera
must know the effective aperture. For
most cameras, such as the Canon F-1,
this lever transmits the preset aperture on
the Jens aperture ring to the exposure meter.
It is coupled to the lens aperture ring and
moves in pr oportion to its rotation. In AE
photograph y, h owever, the exposure moter
receives
a
signal directly from the camera.
2.
Automatic Aperture Lever
T h is lever couples
Lo
the camera body to
stop the diaphragm down to the preset
aperture just before the shuLter releases. This
is the lever that must
uc
locked for manual
diaphragm control wi th a non-coupled acces-
sory.