Mechanical (non-electronic connection) film magazines: 12, 16, 16S, 24: (no letter prefix). Original backs made for the initial 500 series and SW cameras. This style (non-automatic) back has a chrome winding key for advancing the film, some models have the key covered by a black accessory crank which is not foldable. Wind film to first frame using the rear viewing window to see the "1" on the paper roll film backing. Then twist the film advance lever back to reset the frame counter to "1". Useable on all cameras. When used on 203FE and 205FCC/TCC cameras the film ISO speed must be set manually in the camera's Pr-mode. VARIATIONS: Magazine 12: 6cm x 6cm image size, 12 exposures per 120 roll film. Magazine 16: 6cm x 4.5cm image size, horizontal format, 16 exposures per 120 roll film. Magazine 16S: 4cm x 4cm image size, 16 exposures per 120 roll film. Also called "super slide" format, suitable for mounting and showing in standard 35mm slide projector. Magazine 24: 6cm x 6cm image size, 24 exposures per 220 roll film.