17 x 13 mm image area · 2 interactive lens diagrams
Pocket film cameras and miniature interchangeable-lens systems | 17 x 13 mm frame with a 21.4 mm diagonal
The 110 format was introduced for pocket cameras, using cartridge film to make loading simple and camera bodies extremely compact. The exposed image is only 17 x 13 mm in this catalog's reference geometry, so even a lens that covers the whole frame can use a much smaller image circle than a 35 mm still-camera lens. That is why 110 cameras and systems such as Pentax Auto 110 could put interchangeable optics into bodies that feel closer to compact cameras than conventional SLRs.
Optically, 110 designs operate in a very different scale from 35 mm systems. Focal lengths are short, entrance pupils are small for a given f-number, and depth of field is naturally deep at equivalent angles of view. Designers can keep lenses physically tiny, but the small negative also asks a lot from film grain, manufacturing tolerances, and alignment. In this catalog, 110-format lenses are useful for seeing how familiar optical formulas shrink when the capture area becomes much smaller than full-frame.