Ricoh's 35mm SLR system based on modified Pentax K mount with support of shutter-priority and program auto exposure modes. The only difference from the original mount is the addition of a small pin to signal that the aperture ring is set to the "P" position (automatic diaphragm control). However, mechanical compatibility was lost due to this additional pin: when a "P" lens is mounted on a Pentax camera, the pin enters the screw drive autofocus shaft and the lens becomes jammed on the camera.
NOTE: we removed Rikenon P zoom lenses from the database, as most of them were rebranded lenses from such third-party manufacturers as Cosina, Sigma and Tokina. Some of the Rikenon P prime lenses were also Cosina rebrands.