In 1953, the Russians took one of the Leica copy cameras they were making, added a mirror box and prism, and made a single lens reflex camera, which they called the Zenit.
This is a second model Zenit - called an "S" ( C in cyrillic). The mirror cocking mechanism is different on this - it has a cord which runs around pulleys to bring the mirror down. I had to replace the cord, on this one.
The base plate of a 1930s Leica will fit this camera, and the film take up spool I fitted to it is from a Leica.
I do have other cameras!