Industar 50U
lens for enlarger, #6911
50 mm, 1:3.5, M39 mount
LZOS, USSR

Very good condition. Lens is clear, does not have any scratches or fungus. Inside there are microspecks of microdust. Body has signs of age. Aperture ring has a small backlash and rotates easily.

This is a lens for enlargers for frame size 24x36mm. Difference from previous "Industar-22u" - more precise registration of photo and visual layers. 

This lens was produced at three plants: LZOS (Lytkarino), KOMZ (Kazan), NPO Optica (Moscow) since 1954. Its variant I-50u-1 has much more resolving power that usual I-50u (60/20 lines/mm vs 45/20 lines/mm).

Note that lens is for enlarger so it does not have focusing ring. Focusing is achieved with moving of the enlarger body. If you want to use it on camera you need macro rings or extension bellows.

Thanks to its resolving power and sharpness it is now often used as macrolens.
This lens is very-very small and lightweight. You can easily put in your pocket.
Lens has one-layered antireflection coating.
Its price in USSR was only 4 Soviet Roubles (with average salary about 120 Soviet Roubles per month).

Characteristics:
Lens s/number - 6911
Number of lenses - 4 in three groups, Tessar.
Angle of view - 38o
Number of aperture blades - 6
Limit of aperturing - 1:3.5 (max), 1:11 (min)
Resolving power - (centre/edge) 45/20 lines/mm
Minimal distance of focusing - 0,3 m
Type of thread - M39
Type of thread for the nozzles -  cannot be mounted
Dimensions (mm): 42*43*43
Focal distance - 53,4 mm
Mass - 72 g
One-layered anti-reflection coating