Sorry if this is the wrong place to post this but I can't find any info about this lens - Carl Zeiss Planar 1:4.5 75mm, seems to have a 34mm screw thread. Does anyone know what 34mm thread lenses might have been originally used for? Thanks!
That focal length is within the "normal" range for 6x6 or 6x4.5. There were a number of 6x4.5 format plate cameras, IIRC at least one with focal plane shutter. There are resources for dating Zeiss lenses by serial number, though I don't know how well they work as far back as the 1920s.
Just looked through this list, and the only thing I found that were close were the Argus screw mount at 33 mm, and the X-Pan bayonet (34 mm, but obviously not a thread mount).
OP, if you're lucky someone who has a copy of Thiele on Zeiss lenses should be able to give you more and good information. Go over to LFPF and try to attract David Linquist's attention.