Breechlock

Glossary Terms

Canon used the term breechlock to describe the fastening element of the original FD lens mount. The lens is presented to the camera aligned correctly for use, and bayonet apertures in a ring at the rear of the lens engage with lugs on the camera. The ring is then twisted to fasten the lens to the camera. The later New-FD lens mount is a true bayonet fitting, in which the lens is presented to the camera body aligned about 60 degrees from correct alignment, and the whole lens then twisted into the correct alignment to fasten the mount.