Contax RTS
In the 1970's, Contax cameras had ceased production but the desire to build a high-quality system using Zeiss lenses remained. Contax joined in a license agreement with Kyocera (Kyoto Ceramics) of Japan, who already manufactured the Yashica line of camera equipment. The result was a new line of 35mm SLR cameras using a lens mount shared by both Contax and Yashica camera bodies (known as "C/Y mount"). The body, manafactured in Japan, would accept lenses made and labelled by either Yashica or Zeiss, either in Germany or in Japan under Zeiss license. In theory, Zeiss lenses are for use on Contax bodies, while Yashica lenses are for Yashica bodies. In practice, both lenses can be freely intermixed.
The first camera of this line was the Contax RTS. The success of this line led to other later cameras, including the Contax 645 AF and the rangefinder Contax G1-G2.
Lenses for the RTS are manual-focus and come in two flavors: AE and MM. The later "MM" lenses permit the camera to automatically set the aperture, and are distinguished visually by the color of the f-stop markers -- the last, highest f-stop on such "MM" lenses will be marked in green. Earlier "AE" lenses ("automatic aperture" refers here to keeping the lens at wide aperture until the moment of exposure, not automated exposure) will be marked in white. Both lens series may be used on either new or old cameras.
While every brand has its adherents, optical testing has generally shown that the lenses made by Zeiss and Kyocera for the RTS series were generally the sharpest ever made for a production 35mm SLR. Adapters to use C/Y Zeiss lenses on other cameras, most notably Canon EOS, have proved popular.
The unique Contax AX camera allows autofocus using these lenses, by actually moving the film plane (rather than the lens) back and forth. The AX can actually be used with other lens mounts via adapters.
Later Contax SLR lenses for the auto-focus Contax N series use a different mount, aptly called "N mount."
