Pentax K

The Pentax K was the third SLR with a pentaprism made by the Asahi Optical Company.  It was released in May 1958 just a year after the AP, and only a month after the S.  It was the first Pentax to have a semi-automatic diaphragm.  The new Auto-Takumar lenses (here shown is the Auto-Takumar 55mm f/2.2 lens) have a lever around the base of the lens barrel.  Cocking this lever opens the aperture. When you fire the shutter a plate in the body strikes a pin which protrudes from the back of the lens and closes the aperture to the value set on the aperture ring at the front of the lens.  You then have to manually cock the aperture for the next exposure.

As with the AP and the S, the K has a slow speed dial on the front of the body.  This example is the more unusual black model.  It was working, but broke during a service...!  I have now picked-up a "spares or repair" body and have my fingers crossed this one can be made functional again.