I found a polaroid back in a charity shop. It simply says polaroid land camera back on the inside. It had a cartridge of pack film (polacolor) inside, and the rollers are fine. It is clearly designed to go into a 4x5" camera, has the little ridge and everything, same size as my double film holders. The film gate is 80x106.5 mm (3.15"x4.2"). The former user has taped in a film mask in black card, the cropped area is 89x59.5 mm (3.5"x2.35"). Can this be used with fujiroids? What is it? Polaroid 405? EDIT: read the caliper wrong (at first 111.5, it turned out to be 106.5...), it seems now obvious that it's a 405, but any other opinions would be appreciated.