A departure from the 35 mm format, the Contax 645 was an autofocus medium format SLR system introduced in 1999, featuring an array of Zeiss lenses and interchangeable film and digital backs. One of its unique features was a 220 film back equipped with the vacuum system originally developed for the 35 mm RTSIII SLR, which was claimed to increase sharpness by keeping the film perfectly flat in the plane of focus. By using the adaptor 'MAM-1' produced by Contax, Hasselblad V-series lenses including C, CF, CFE, CFI, F and FE can be mounted on Contax 645 as well.
In addition to 120 and 220 medium format backs with film inserts for quick loading, including the previously mentioned vacuum back, as well as a Polaroid/instant film back, many manufacturers offer a variety of interchangeable digital backs for the Contax 645 system:
- Imacon
- Leaf
- Kodak
- Jenoptik
- Sinar-Bron
- Megavision
- Phase One