I have two Zeiss Ikon Box-Tengors (54/2 & 56/2). The one thing I miss is a way to attach filters. I found this video on Youtube and it seemed like what I was looking for.
I tried it and this holder works on both of my Box-Tengors. I tested a roll of film in the 54/2 and there was no vignetting. Still need to test the 56/2. Plus I need to remake the holder from a black film can or paint the white ring with some black chalk paint. I used a 30.5mm to 49mm step up filter adapter because the 49mm is the smallest filter size I have that includes an IR 720nm filter.
IIRC (and that's a big leading "I" - memories are 60+ years old) a 32mm slip-on filter or Series V adapter would fit into the lens recess on the post WWII Tengor.
IIRC (and that's a big leading "I" - memories are 60+ years old) a 32mm slip-on filter or Series V adapter would fit into the lens recess on the post WWII Tengor.