Leica M lens mount
Leica introduced the M mount in 1954 with Leica M3 camera, a full frame sensor one. There are no electrical contacts so no information is transmitted to the camera, though since 2006 an engraved six-bit code on the mount has been introduced to allow the camera to know which lens is attached - this system is quite limited supporting maximum 64 lens models and not including other shooting data (e.g. focus distance, aperture).
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