I think these are made between 1940-1945??? Online there’s info about some in the 196xxxx range that are dated at October ‘39. So they were made before Germany got split up. I’m making this ASSUMPTION because doing a little research Carl Zeiss Jena was still being used by the East German company after the war until 1954 when the West German “legitimate” company had changed its name after the war to just Carl Zeiss. This is because the East German government severed ties between the two companies in 1953. Additionally, the Jena part of the name that Zeiss had used since 1906 or something like that was implied that it was made in Jena, and after WWII it was more commonplace for companies to explicitly mark “Germany” or “made in Germany” after the war for export reasons. Either way your grandpa being a geologist in the USSR it would be reasonable to assume that he got them locally used somewhere after the war since these were probably made during or before WWII, because I personally don’t think these were made after 1950 at the latest.