The mount was a mechanical copy of the Zeiss Ikon Contax rangefinder mount, however, small differences between the two mean that although Zeiss wide-angle lenses can be used on the Nikon cameras and vice versa, the longer lenses (50 mm and above), if used, will not be able to focus at both close range and infinity.

[1] [2] Nikon made a small number of longer focal length lenses specifically designed to focus properly when mounted on a Contax.

The external bayonet is used to mount longer and heavier lenses where the built-in helicoid would not be strong enough to rotate the lens barrel.

Such lenses are focused using a focusing ring and distance scale on the lens just like typical interchangeable lenses; the distance scale on the camera body is covered by the lens flange and thus is not visible when the external bayonet is in use.

In general, wide-angle Nikkor lenses with S-mount will mount directly to Contax bodies.