Half-frame 135 Lenses
24 x 18 mm image area · 2 interactive lens diagrams
Olympus Pen F and other half-frame 35 mm cameras | 24 x 18 mm half-frame 135 image area with a 30 mm diagonal
Half-frame 135 uses the same 35 mm film stock as full-frame 135 cameras, but each exposure occupies roughly half the usual area. The catalog reference is 24 x 18 mm, giving a 30 mm diagonal and a 4:3 frame shape. Cameras such as the Olympus Pen F made this into a serious interchangeable-lens format rather than just an economy mode, pairing small SLR bodies with lenses scaled to the smaller image circle.
The optical consequences sit between full-frame 135 and smaller digital formats. Lenses can be shorter and more compact than their full-frame equivalents, while still using film stock, processing, and camera mechanics familiar from 35 mm photography. Because the frame is half the size of standard 135, corner correction, vignetting, and field coverage are less demanding than full-frame, but grain and enlargement requirements become more noticeable for large prints.