The M645 was manufactured from 1975 to 1987. This was the first model to offer a 6x4.5 cm frame, allowing 15 shots on a standard 120 roll film. The M645 was a true system camera, with interchangeable viewfinders and lenses. It used an electronically controlled cloth focal plane shutter offering speeds of 8 seconds to 1/500 second in one-stop increments. The camera featured a mirror lockup, as well as selectable multi-exposure. Film was carried in cartridges that could be pre-loaded, but no capability existed to allow changing of film magazines mid-roll. A waist-level non-metered finder was available, as well as a non-metered pentaprism and three varieties of through-the-lens (TTL) metered prisms (CdS, PD and AE). The metered prisms read the aperture dial through a mechanical coupling on the lens. The standard lens was the 80mm f/2.8 C or the 70mm f/2.8 C E or the 80mm f/1.9 C.