The M645J was manufactured from 1979 to 1982. This was a stripped-down version of the M645, with the mirror lockup knob and second shutter button removed, and finished off with a slower shutter speed at only 1/500th of a second. The standard lens was the Mamiya-Sekor C 80mm f/2.8. The prism viewfinder as seen in the image did not have a light meter built in either, the assumption was that you would use your ambient light light meter for portrait purposes.
Still an impressive backup camera for when the 645E or M645 breaks down while on the job. Most professional photographers have at least invested in some film cameras, however, medium format takes film to the next level. These cameras used to be reasonably priced, however, today you’d be lucky if you found one under $3,000.00 CAD. If you do, buy it, like land, they don’t make more of it.