The Pentax K-mount was introduced 50 years ago:
“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. 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.” (Wikipedia)
“The Pentax K-mount, a bayonet-style lens mount, was introduced by Asahi Optical Co. on June 1, 1975, replacing the M42 screw mount. This new design, reportedly developed in conjunction with Zeiss, offered a more secure and quicker lens changing experience, crucial for professional use and accommodating more advanced lens designs. The original K-mount featured a simple bayonet connection with three tabs and mechanical linkages for aperture control and open-aperture metering. Over the decades, the K-mount has seen significant evolution, with Pentax adding functionalities such as autofocus (initially with the short-lived KF-mount and then refined with KAF, KAF2, KAF3, and KAF4 variants) and digital information exchange, all while striving to maintain a high degree of backward compatibility with older lenses. This commitment has allowed a vast catalog of K-mount lenses produced over nearly half a century to be used, with varying levels of functionality, on subsequent Pentax film and digital SLR cameras.” (AI generated)
Ricoh also has a very nice page on the history of Pentax.
