Zeiss Ikon part numbers, and fabricating a GG back
I don't have enough quixotic projects already, so I'm thinking about trying to build a ground-glass back for my Kodak Recomar 18 (a 6.5x9 plate camera made by the Nagel factory). It takes Normalfalz holders (equiv. Millionenfalz? I can never remember), like a Voigtlaender or most of the house-brand German cameras of the same era.
I haven't been able to find an intact GG back to fit, but there are some 6.5x9 film-pack holders floating around. Most of the ones I'm finding are Zeiss Ikon products, and as we all know, ZI used a bunch of different holder/back standards. I'm trying to decode their part numbers.
So far I've found alleged 6.5x9 pack-film backs numbered 728/2, 668/2, and 688/2, as well as unnumbered (and a few associated with cameras, but I don't really want to spend the extra money for a camera carcass). First off, I'm a little worried because I had thought that "/2" was always 6x9, but leaving that aside, which number corresponds to which back standard?
I think 728 is the "fat lip" version that fits the Maximar. The others both look like they *could* be Normalfalz, but surely with different numbers, at most one of them is right...Any insight?