Industar-26M 2.8/52 silver lens for rangefinder M39 LTM mount USSR FED

Industar-26m, 
silver lens for rangefinder, #1853771
50 mm, f/2.8, M39 (LTM) mount lens, 
"FED" plant, Kharkiv, USSR

Very good condition. Glass is clean and clear, without any fungus. Front glass has tiny, almost invisible cleaning microscratches. Inside there are microspecks of microdust. Aperture ring rotates properly and has a backlash. Focus ring rotates properly. Body has signs of age.

Camera "Zorki-4" is not included and shown as an example of mount.

This is a normal lens with anti-reflection coating for rangefinders. Lens was default for camera "FED". It is the only version of this lens (with the letter "M"). Simple "Industar-26" remained experimental.
Lens was produced since 1954 for M39 mount at "FED" plant in Kharkiv. Also a small lot of this lens for SLR camera was made at KMZ (Krasnogorsk). Variant for enlarger was known as "Industar-26M-U". 

Characteristics: 
Lens s/number - 1853771
Number of lenses - 4 in three groups, Tessar
Angle of view - 45o 
Number of aperture blades - 10
Limit of aperturing - 1:2.8 (max), 1:22 (min)
Resolving power - (centre/edge) 27/18 lines/mm
Minimal distance of focusing - 1 m
Type of thread -M39х1/28,8 (Leica screw mount)
Type of filter thread - 40.5x0.5 mm
Dimensions (mm): 55*57*44
Focal distance - 52,49 mm.
Mass - 114 g
One-layered anti-reflection coating