The Industar-50 is one of the most successful Soviet made lenses. 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 optional) 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 (Leitz Elmar 50/3.5), the lens produced sharp and contrasty images.
This Industar-50 is the Elmar-type collapsible version. It was primarily used on the Zorki-5, but was also sold separately. The Industar-50 was also a popular enlarger lens.
Focal length:50 mm
Aperture: 1:3.5, settings from 3.5 to 16
Focusing: 1 m - ¥
Filter size: 36 mm slip-on type
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 polished chrome finish.
(Source: www.fedka.com)