3M-5A-MC 500 mm f/ 8 Lens

The ZМ-5А-MC 500 mm F/ 8is a catadioptric lens  for 35 mm SLR cameras with the M42 screw mount. The lens has constant, fixed aperture.

The lens came in two variants: with multilayer achromatic coating (MC) and with single-layer coating.

This lens was manufactured at the LZOS (Latyrkino Optical Glass Factory) in Latyrkino,  Moscow oblast. Later on it was replaced with  the ZМ-5САlens, which retaining the same dimensions weighs twice less (plastic elements, no tripod mounts).

With the M42 screw mount the ZM-5Аis compatible with modern Zenit cameras, including Zenit-11. Focal length - 500 mm, fixed aperture - 8 (presumably its actual aperture value is one step higher). The lens is equipped with a built-in hood, which is not only convenient, but also necessary (you cannot focus without retracting the hood).
 

Additional information:
The letter "А" in the lens name stands for "interchangeable rear part", i.e. you can replace one rear part with another. For example, with the Nikon. The ZM index stands for "mirror meniscus". Later on the same optical scheme came to be employed by Rubinar telephoto lenses. The Rubinar 8/500 Macro is an updated and revised version of the ZМ-5Аlens.

It has two tripod sockets for different screw mounts fit for modern and outdated tripods.