The Zenit 3M is a 35mm SLR made in the USSR by KMZ between 1962 and 1970 as part of the long-running Zenit series. It has interchangeable lenses using a 39mm screw-thread mount (rangefinder lenses using the same thread will mount to the camera but will only focus at very short range). Some examples of the 3M sold in the UK are only marked 'Zenit' on the front of the prism (i.e. without the 3M, as pictured below left). The camera is very similar to the Kristall, which preceded it by about a year. The shutter release button is in the hub of the film advance lever (the button by the shutter speed dial is the rewind release); it is threaded for a cable release. The focal-plane shutter has speeds from 1/30 (synchronised for flash at this speed) to 1/500 second, plus 'B'. The flash synchronisation delay is adjustable with a selector under the shutter speed dial, marked for X- and M-synchronisation. Flash is connected via a PC socket on the front of the top housing. There is no shoe to mount a flash on the camera. The frame counter is also around the hub of the advance lever. Like earlier Zenit models, the mirror does not return instantly, so the viewfinder blacks out upon releasing the shutter; the mirror is reset when the film is advanced. The camera back opens on a hinge (like the Kristall; the other 39mm Zenits, including the Zenit 3 are bottom-loading). There is a self timer, with the lever on the front of the body; it is activated by the button just above it. The self-timer releases the mirror about half a second before the shutter, so that vibration from the mirror has time to finish before the exposure.
Che Guevara had a 3M with him in Bolivia when he was killed.