Inscription on lens says "У.С.П. Металлозавод Москва", at first bought as an exotic camera (that's how it was listed on eBay), later by conclusion of experts it turned out to be some kind of toy film or "Diafilm" (Children stories on diapositive film) viewer.

The metal "lens cap" is used to close the second eye while viewing, since it is to be viewed vertically.

What signifcant about this unit is that it was not manufactured by an optical factory - it was made in a steel plant which makes it quite unique.

From collection of Vladislav Kern

whith your permission, i add the black one : these viewer is a part of film projector : you have to set it in a support whith lamp for projection on screen.may be use as is as a viewer.
from Alain Berry Collection