The M4 started production in 1966 as the successor the M3 and M2 featuring framelines for 35 mm, 50mm, 90mm and 135mm lenses in a 0.72 magnification viewfinder. It has the frame counter of the M3, with automatic reset after reloading.
Three ergonomic modifications were introduced in the M4: •a different, angled film advance lever, as well as slightly different rewind, self-timer and frame selection levers •a crank for rewinding the film, that replaced the telescopic knob of the M3 •a faster loading system that does not need a removable spool.