2 interactive lens diagrams
Pentax Auto 110 miniature SLR mount, late 1970s-1980s | 110 film
Pentax 110 is a specialized miniature SLR mount built for 110 cartridge film. The Auto 110 system used extremely small interchangeable lenses while keeping reflex viewing, making it an unusual mix of compact-camera format and true SLR architecture.
The camera body contains the aperture and shutter mechanism, so the lenses themselves are unusually simple and small compared with conventional SLR lenses. That system choice keeps the lens mount compact but also means the optical formulas live inside a tightly controlled camera body environment.
Because the image area is small, the lenses can be physically tiny. The optical compromises and possibilities are different from 35 mm systems: short focal lengths, small image circles, modest enlargement expectations, and compact groups dominate the designs.
Flange focal distance 27 mm, bayonet mount. 0° at 12 o'clock from the camera front; the lens-side view is the horizontal mirror. Dotted strokes mark photo-scaled or schematic (not-to-scale) dimensions.