Industar-50 was a very successful Soviet made lens. It was a standard or optional lens on practically every Zorki camera, from Zorki-S in the mid 50's to Zorki-4K in the mid 70's. The lens was also made in a 39 and 42 mm SLR mount and was installed (standard or option) on every Zenit model as well, from Zenit-S to Zenit-E. It came in different shapes and finishes, from a chrome collapsible Elmar-style lens to a black "flat" Zenit lens. The optical formula was always the same, the lens produced sharp and contasty images.
This Industar-50 is the newer, rigid barrel black finished design used on the later Zorki-4 and Zorki-4K
The lens was made in 1970 by KMZ plant.
Focal length:50 mm
Aperture: 1:3.5, settings from 3.5 to 16
Focusing: 1 m - ¥
Optical registration (back focus) : 28.8± 0.02 mm
Mount: M39x1 mm (LTM). The lens mounts and RF couples with any Leica or Leica copy (FED, Zorki etc.)
The glass is coated; the barrel has a black finish.
(source: www.fedka.com)