sentences:  The Pentax K-F mount added five electrical contact pins protruding through the lens mount flange at the 5 o'clock position (when viewing the ME F body from the front) to the original Pentax K mount (introduced 1975) to pass focus control information between the camera and the lens.The Pentax K-AF and K-AF2 autofocus lens mounts (introduced 1987 and 1991, respectively) have contacts of different number, position and function, and therefore the 35mm-70mm AF Zoom cannot autofocus on any other Pentax SLR.Almost all other Pentax K mount bayonet lenses will function properly under manual focusing, with the AF system providing focus indication – Asahi Optical called this TTL Electronic Focus.