This page contains descriptions of the five major lens mounting systems for still cameras:
Lens board mount systems
This is a mounting system that was popular on press and view cameras. The lens is mounted to a board that is fastened to the camera's front standard via a spring mounted clip or sliding metal tabs.
Screw thread lens mount systems.
This is a very basic mounting system. The lens is screwed into the mount by turning the lens clockwise. Two popular examples of this are the M42 and M39 systems.
Breech-Lock lens mount systems.
A breech-lock lens is placed against the camera's mount and a ring is turned to lock the lens in place. This minimizes wear on the mounting surfaces. Examples include Canon F mount cameras and Mamiya press cameras.
Bayonet lens mount systems.
This is the most common lens mount system for still cameras. Examples include Canon EF, Nikon F, Pentax K, Olympus OM, Four-thirds mount and many others.
Slide-Lock lens mount systems.
This is a new system introducted with the Ricoh GXR camera. The lens unit includes the image sensor and slides into an electrical connector with a spring lock.