Franke & Heideck were a well-known producer of stereo cameras. In 1928 the idea came up to develop a twin lens reflex camera based on the stereo camera. It looked quite simple: cut one third of the stereo camera off and you are nearly done. This is exactly what Mr Heidecke did, but he soon found out that things were more complicated and a lot more work had to be done. At the end of the day he used his cut-up stereo camera to convince his commercial partner Mr Franke that more funds were needed to develop the TLR.
From the beginning it was clear that the camera had to be small. Not as small as the Leica but as small as roll-film allowed. That determined the choice for a roll-film with a small diameter spool. The B 1-6. It allowed only 6 exposures of 56 by 56 mm. A few clever ideas were realised in the design. The basic design consists of two camera parts: on one hand the viewing camera with the focusing screen, reflex mirror and viewing lens and on the other hand the taking camera with the taking lens and film aperture. The reflex mirror was sunk into the taking camera as far as possible and the film chambers were located in unused space. The un-exposed film resides in the bottom of the taking camera near the lens, while the exposed film is stored behind the reflex mirror in the viewing camera.