I would say Post-War. There is no code on it.
"Much that once was, is lost. For none now live who remember it."
Never seen marked only with "JENA".
East or West Germany?
These are East German Karl Zeiss post-war binoculars made for export. The Q1 logo stands for... 1st Quality. Apparently there was some wrangling over the trademark between East and West Germany. Binoculars meant for the West German market were marked 'Aus Jena.' Those meant for export were just marked 'Jena.'
Books published to date... 'Belfast Diaries: A Gunner In Northern Ireland'... 'A Tough Nut To Crack - Andersonstown'... 'An Accrington Pal: The Diaries of Pte Jack Smallshaw, September 1914 To March 1919'.