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Leica M-series bayonet mount

Toronto. A camera’s lens mount does many things: keeps the film to lens distance unchanged in spite of 1,000s of lens changes so one can reliably focus to infinity at any aperture opening; keeps the lens firmly attached to the body (my first Exakta used metal with less ‘spring’ so in time the lens felt loose); the diameter is wide enough to accommodate any lens without vignetting; mounts were intended to allow quick lens changes in the field; the design of the mount limited the use of third party lenses to those that matched the camera; etc.

Until interchangeable lenses hit the market, lens mounts could vary the film to lens distance slightly. As long as the mount diameter accommodated available lenses, the diameter was of no consequence. The first Leicas used a screw mount made of hardened metal. To counteract publicity by competitors, Leitz emphasized that a screw-threaded mount was more precise than a bayonet – then in their post-war design, embraced a bayonet mount!

Earlier cameras used lens boards to join camera and lens, while a ground glass eliminated any need for precise distancing between film and lens. The zoom lens era allowed for a wide adjustment of focal length without changing the lens. Many modern cameras (especially the smaller digital cameras popular before smart phones and their fixed lenses) used a zoom lens instead of a removable lens/camera design.