both came from KMZ factory museum and was given to a friend by the museum leader ( I don't remember name , only I'm be sure she was a lady)
This museum leader told to my friend , glass came from lenses (may be defect ?) normally fitted in zenit objectives (helios and so on....)
back side is made in aluminium, both the same , whithout inscription.
My be at this time, the factory try to make some business for some institution ?

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About glass, I think it is the truth as far as I remember me , JL Princelle told me in the past : when visiting KMZ factory, he saw on the ceiling, in main entrance , a big chandelier made from zenit prism...!