Pentax K mount
Pentax introduced the K-mount in 1975 for full frame (35 mm) sized film cameras, then evolved in a lot of variations essentially for electonic communications between camera and lens (KF, KA, KA2, KAF, KAF2, KAF3, KAF4) - details in this article.
The K-mount is used in lenses for both full frame and APS-C sensor cameras.
An interesting article on K-mount evolution is at this link.
Sigma stopped production of K-mount lenses in September 2019.
|Name||Sensor format||Sensor crop||AF support||Year||Notes|
the first K mount with electronic contacts
|APS-C||1.52||motor in camera||1989|
|Full frame||1.00||motor in camera||1989|
|APS-C||1.52||motor in camera, motor in lens||1991|
power contacts added for power zoom or AF
|Full frame||1.00||motor in lens||2007|
|APS-C||1.52||motor in lens||2007|
|Full frame||1.00||motor in lens||2016|
like KAF3 but with electromagnetic aperture control