A half-frame camera exposes only half of the usual format on conventional 35mm film. Instead of the classic 24x36 mm, the image size is only 18x24 mm. This doubles the number of available shots on a film roll: a standard 36-shot film thus provides 72 shots.
Due to the smaller format, the cameras could be built extremely compact, as impressively demonstrated by the Olympus Pen series. A side effect of the smaller negative is a slightly more pronounced film grain in large enlargements, which often gives the images a very distinctive, characteristic look.
