9 x 12 format

The 9 x 12 cm format was already a common negative format in conventional photography. The format was also used by Steinheil in the early 1900s for its Alto-Stereo-Quart camera and the corresponding Altostereoskop.

The format became established through its adoption by Stereo-Indupor-Gesellschaft in the 1920s. The 3:4 aspect ratio made the format more suitable for portrait photography, one of the applications targeted by the company. The stereo format remained rare, and its use by Stereo-Indupor saw little wider adoption.