Ricoh's 35mm SLR system based on the original Pentax K mount. The most advanced cameras of the system - XR-2, XR-2S, KR-10, KR-10SE, XR6, XR-S, XR7, XR500 auto, XR-2000, XR-F - featured an electronically controlled shutter and aperture-priority auto exposure mode, while conventional models - XR-1, XR-1S, XR500, XR5 - had a mechanical shutter and offered manual exposure mode only. The XR-8, XR-8 Super, XR Solar, and KR-5SV, conventional models introduced in the 1990s, were designed and manufactured by Cosina.
In order to implement shutter priority and programmed auto exposure modes, Ricoh modified the original Pentax K mount and introduced a separate line of cameras and Rikenon P lenses in 1984.
An unusual feature of the Ricoh K system was a large selection of standard lenses: from several versions of budget models with moderate speeds of F/2.2, F/2 and F/1.7 to professional models with speeds of F/1.4 and even F/1.2. As for the accessory lenses, they were produced in collaboration with companies such as Asahi, Sigma, and others.