Nikon S is the name for the Nikon rangefinder camera system, but it's essentially a modified Contax/Kiev mount. After World War II, both Contax and Leica's designs became available to the public, and many Japanese countries attempted to produce their own rangefinders. Most, like Canon or Leotax, chose to follow Leica's footsteps and use the Leica M39 mount, but Nikon followed Contax. Nikon produced 8 different Contax-pattern rangefinders between 1948 and 1960. 

Despite being extremely similar, Nikon S cameras cannot use all Contax lenses. Wide-angle lenses work normally, but slight differences in flange distance make lenses of 50mm and above incompatible.

In the 2000s Nikon released some limited edition fully working replicas of Nikon S3 and SP cameras with lenses. In 2002 Cosina released the Bessa R2S camera and a series of lenses with the Nikon S bayonet mount.