Industar-69, 
lens for scale-focus camera "Chayka"
28 mm, f/2.8, M39x1/27.5 mount lens, 
BelOMO, USSR

Good condition. Lens has cleaning microscratches on the front glass and dirt at the edges. Inside there is microdust. Aperture ring rotates properly, focus rings rotates very tightly. Body has strong signs of age (see the photo). 

This is default lens for half-frame scale-focus film cameras from "Chayka" family which were produced at BelOMO in 1965-73. First "Chayka" had a stationary (non-removable) "Industar-69", and "Chayka-2","Chayka-3", "Chayka-2m" got it in removable variant, like the lens offered.

As the cameras are half-frame (with frame size 18x24 mm), "Industar-69" is a normal (not wide-angle) lens for that frame.

Although the default lens became removable, there are no other lenses for "Chayka" family known. Probably, there were plans about producing option lenses, but "Industar-69" is the only lens for that mount.

Please, note that "Industar-69" has mount M39x1/27.5, so it is not interchangeable nor with Leica thread mount (it is M39x1/28.8), nor with Soviet M39 for SLR cameras (it is M39x1/45.2). "Industar-69" can be set, but it will not work. It is a mystery why engineers from BelOMO created a new mount with unique flange focal distance. 

It can be used with adapters at modern DSLR, but with cropped matrix. When set at full-frame camera, it will give a great vignetting. The best usage is to set this lens at mirrorless camera via adapter.
It is very often used as a perfect macrolens.

haracteristics: 
Lens s/number - none
Number of lenses - 4 in three groups, Tessar
Number of aperture blades - 5
Limit of aperturing - 1:2.8 (max), 1:16 (min)
Minimal distance of focusing - 0.8 m
Type of thread -M39х1/27,5
Type of filter thread - 22.5x0.5 mm
Dimensions (mm): 48*48*21
Focal distance - 28 mm.
Mass - 52 g