Zenit-S, one of the original Soviet designs and the first mass produced Soviet SLR camera.
The Zenit-S replaced the original Zenit in the mid-50's. It added a flash synchronization mechanism and a new mirror drive - the mirror was lowered with a string (this feature was mentioned by McKeown in his price guide).
The camera is essentially a Zorki-S (Leica II (D) copy) with a rangefinder replaced with a reflex housing. The film loads from the bottom, as in screwmount Leicas. It has all the Zorki-S specifications. The camera is very compact and handles nicely. Early cameras had a folding foot under the lens mount.
The camera has a flash synch mechanism with the adjustable synch timing advance (from 0 to 25 ms). Also, the shutter speed can be selected before of after the film is wound and the shutter is cocked.
* Shutter speeds - B, 1/25, 1/50, 1/100, 1/250, 1/500.
* Lens - Industar-50, F=5 cm, 1:3.5, coated, still 39 mm mount, but the optical registration is different from the Leica type lenses. Leica lenses will mount, but can only be used for close-ups.
The original Zenit evolved into some nice SLRs - Zenit-S, Zenit-3, Kristall, Zenit-3M. After that, in the late 60's the Zenit-E came and with millions and millions copies produced, it made the Zenit name a symbol of mediocrity. (fedka.com}
As well as the Cyrillic version of Zenit-S on the front of the prism, there were two Roman versions, Zenit-S and Zenith-C. The last photo shows the Zenith-C version. (David Tomlinson)