Canon F1-N Brochure & Specs page 74

29 SHOOTING WITH CLOSE-UP ACCESSORIES
automatic aperture lever fully counterclockwise, then push the lock lever to "L".
Be sure to reset the automatic aperture lever to its normal position before mounting
the lens directly on the camera. In the case of a lens with a lock lever, switch it
back to the position of the white dot.
Film Plane Indicator
This mark, engraved on top of,-the camera body, indicates the exact position of
the film plane. It is useful for measuring the exact shooting distance from film to
subject in closeup photography. Distances on the lens' distance scale are calibrated
from this mark. It is not used in general photography.
Note
The aperture ring of an FD lens must be removed from "A" before you mount the
lens on any of these close-up accessories except for FD-U Extension Tubes and Ex-
tenders FD 2x and FD 1.4x, which are designed for normal full-aperture metering.
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