Industar-50, collapsible lens for rangefinder camera
50 mm, f/3.5, M39 (LTM) mount, s/n 5951136
Krasnogorsky Mechanical Plant (KMZ), Krasnogorsk, USSR

Very good condition. Lens is clear and does not have any fungus. Front glass has cleaning microscratches. Inside there are microspecks of microdust. Aperture and focus rings rotate properly. Body has signs of age and use.

Camera "FED" is not included and shown as an example of mount.

This is a standard lens for Soviet rangefinder and SLR cameras: "Zorki", "Zenit", "Crystal" instead of "Industar-22" lens. It was designed in 1953 and produced in 1953-1986. This lens was made in 1959 at KMZ, also it was produced at LZOS (Lytkarino) and KOMZ (Kazan). The lens uses the "Tessar" lens scheme. The lens is anastigmatic and antireflected. 

Lens had foldable and unfoldable versions, variants for SLR, rangefinder and enlarger.
This lens is very-very small and lightweight. You can easily put in your pocket, and the hardest camera will seem lighter with this lens. But at the same time it has a perfect sharpness thanks to the "Tessar" scheme. Chromatic aberations are corrected. Bokeh is rather nice.
This lens is for rangefinder only, it can be mounted to SLR with M39 mount, but it will not work.

Lens s/number - 5951136
Number of lenses - 4 in three groups, Tessar.
Angle of view - 45o
Number of aperture blades - 7
Limit of aperturing - 1:3.5 (max), 1:16 (min)
Resolving power - (centre/edge) 38/22 lines/mm
Minimal distance of focusing - 1 m
Type of thread - M39x1/28.8 (LSM)
Type of thread for the nozzles -  22,5 mm 
Dimensions (mm): 58*58*44
Focal distance - 52,48 mm.
Mass - 107 g