Industar-90u
lens for enlarger, #830640
75 mm, 1:4, M39 mount, 
Lytkarinsky Plant of Optical Glass (LZOS), USSR

Very good condition. Lens is clear, does not have any fungus. Front and rear glasses have cleaning microscratches.  Inside there are microspecks of microdust. Body has very small signs of age. Aperture ring rotates properly. Aperture blades have a bit oil.

This is a lens for medium format enlargers for frame size 6x6 cm. 
It was produced by LZOS since 1978.
It is a lens for enlarger so it does not have a focusing ring. Focusing is done when moving the camera or enlarger with lens together.

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 28 Soviet Roubles (with average salary about 120 Soviet Roubles per month), so it was rather expensive.

Offered lens has a "USSR Quality Mark" meaning that this specific lens has higher quality than ordinary "Industar-90y".

Characteristics:
Lens s/number - 830640
Number of lenses - 4 in three groups, Tessar.
Number of aperture blades - 10
Limit of aperturing - 1:4 (max), 1:16 (min)
Resolving power - (centre/edge) 50/25 lines/mm
Type of thread - M39
Type of thread for the nozzles -  cannot be mounted. 
Dimensions (mm): 42*42*42
Mass - 83 g
One-layered anti-reflection coating