Pentax K-mount

The Pentax K mount was a lens mount standard for mounting interchangeable photographic lenses to 35 mm single-lens reflex (SLR) cameras. It was created by Pentax in 1976, and has been used by all 35 mm and digital Pentax SLRs since. A number of other manufacturers have also produced K mount lenses, and in a few cases, K mount cameras.

Mounts

The K mount has undergone a number of evolutions over the years as new functionality has been added.

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 of course 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' and 'SMC Pentax-M'. The bodies cannot use FAJ lenses since these lack an aperture ring. The lenses can be used on all Pentax bodies but can only be used in stopped down mode with "crippled" K_AF mount bodies.

K_F mount

The K_F mount was Pentax's first attempt at an autofocus system. It was used by only the Pentax ME F and its accompanying SMC Pentax-AF 35-70/2.8 lens. This autofocus system used sensors in the camera body and a motor in the lens. The two were connected via five new electrical contacts on the bayonet mount itself. One permitted the lens to turn on the camera's metering and focus sensors, two focussed the lens (towards and away from infinity) and two appear to have been unused and may have been reserved for future functionality.

The ME F can use all Pentax K-mount lenses except for FAJ lenses, which lack an aperture ring. The 35-70 mm lens can be used on all other Pentax K-mount bodies in manual focus mode, but it must be used stopped down on "crippled" K_AF bodies.

K_A2 mount

The K_A2 is identical to K_AF, but lacks the autofocus drive shaft. Thus it supports the same lens features, except autofocus.

"Crippled" K_AF mount

The "crippled" K_AF mount is used on the MZ-30/ZX-30, MZ-50/ZX-50, MZ-60/ZX-60, and *ist cameras. The only difference between the regular K_AF mount and the crippled version is the removal of the stop-down coupler/indicator.

More information

Bojidar Dimitrov's Pentax K-Mount Page

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