The Pentax K-mount, sometimes referred to as the "PK-mount", is a bayonet lens mount standard for mounting interchangeable photographic lenses to 35 mm single-lens reflex (SLR) cameras. It was created by Pentax in 1975, and has since been used by all Pentax 35 mm and digital SLRs and also the MILC Pentax K-01. A number of other manufacturers have also produced many K-mount lenses and K-mount cameras. Mounts The Pentax K-mount has undergone a number of evolutions over the years as new functionality has been added. In general, the term K-mount may refer to the original K-mount, or to all its variations. Originally designed by Zeiss for an alliance with Pentax, it was intended to be a common lens mount for a proposed series of cameras and lenses. However, the plan failed to work out and the two firms parted company amicably, but Pentax retained the lens mount and at least one Zeiss lens design for its own use. K-mount The original K-mount is a simple bayonet connection with three tabs. It was introduced with the K series of cameras. The lens is locked into the camera with an approx. 70° clockwise turn (when looking at the front of the camera). The only linkage with the camera is mechanical and involves the aperture. A slot between two of the bayonet tabs on the lens allows the stop-down coupler from the camera to sense the aperture setting on the lens and adjust the light meter display accordingly. Opposite this is the diaphragm release from the lens which extends into the camera body and holds open the spring-loaded diaphragm of the lens. When setting up a shot this keeps the diaphragm fully open. When the shutter is released, so is this lever. It allows the diaphragm to close to the desired setting while the film is being exposed, and opens it again after the shutter closes. Both of these linkages are arranged so that they are aligned and spring-loaded by the act of inserting the lens and turning it until it locks. Bodies equipped with the original K-mount include the K series, the M series except the ME F, and the LX. Lenses that support it include those labelled 'SMC Pentax', 'SMC Pentax-M' and 'SMC Pentax-A'. These K-mount bodies cannot use lenses that lack an aperture ring, such as FAJ or DA. K-mount lenses can be used on all Pentax bodies, but