Is anyone have info about this lens? I have it since some month, but can't find a lot of infos. Princelle says it's KMZ prototype from 1960. I have many doubt about this (I would date it from the end of 60's or 70's), and nothing shows that KMZ could have made it.
Photohistory doesn't help.
Mount is M42, but focal flange is not 45.5mm, it's a bit shorter.
I have disassembled it, didn't found any special things that could lead me to any soviet factories...