Format
The format uses a single, central perforation (sprocket hole) between each pair of frames, as opposed to 8 mm film, which has perforations along one edge, and most other film formats, which have perforations on each side of the image. The single hole allowed more of the film to be used for the actual image, and in fact the image area is almost the same size as 16 mm film. The perforation in the film is invisible to viewers, as the intermittent shutter blocks the light as the film is pulled through the gate to the next frame.
The width of 9.5 mm was chosen because three strips of film could be made from one strip of 35 mm film. This was useful when duplicating films, because only one strip of 35 mm had to be processed. Then the sides, which contained the special narrow 35 mm sprocket holes, were cut off, the remaining film was cut into 3 strips, and the central sprocket holes added to each new strip.
The projection system also incorporated a way to save film on non-moving titles. A notch in the film was recognised by the projector, which would then project the second frame after it for 10 seconds. By this method, 10 seconds of screen time was available for 1 frame of film, rather than the 140 frames required if the film was projected at the normal rate. The same principle was used by the 'Agfa Family' system of Super 8 camera and projector in 1981 though to provide still images rather than titles.
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