Canon R lens mount

The mount employed a "breech lock" system to attach the lens to the camera body.

The semi-automatic diaphragm works in the same way, with a small exception: the aperture does not return to fully open until after the photographer winds the film on following the exposure.

[4]: 5–7 To mount the lens, the breech-lock ring must be turned so the red dot is aligned with the positioning pin.

For Super-Canomatic R lenses, if the charging lever is not pre-charged before mounting the lens on the body, the automatic diaphragm mechanism will not operate for the first exposure.

[4]: 21–22 Since the mechanism for controlling the aperture is different from both the later FL and FD mount, using R lenses on later bodies requires stopped-down metering mode and a manually-set aperture; however, the lugs, flange focal distance, and breech-lock ring are mutually compatible, so most R, FL, and FD lenses can use the same mount adaptors.

R 35mm f /2.5 , the only wide angle lens Canon made with the R mount
Super-Canomatic R lens on right and FL lens on left, illustrating similar parts and features. Compared to "Super-Canomatic R" lenses, "Canomatic R" lenses omit the charging lever, while "Canon Lens R" lenses omit both aperture and charging levers.