Pentax's ultraminiature 110-film SLR system — interchangeable f/2.8 lenses, TTL metering, programmed exposure, 1978-85.
The Pentax Auto 110 was a fully automatic interchangeable-lens SLR for 110 film cartridges, introduced by Asahi Pentax in 1978 and sold until 1985. Officially the Pentax System 10 — though advertising mostly said Pentax-110 — it was the only complete ultraminiature SLR system built for the 110 format, and claims to be the smallest interchangeable-lens SLR system ever made. A brown-and-tan Safari edition was also offered, and the improved Auto 110 Super arrived in late 1982.
Exposure is fully programmed with TTL centre-weighted metering and no user adjustments, running from 1s at f/2.8 to 1/750 at f/13.5. Uniquely, the aperture lives in the body, doubling as the shutter, so every lens is an f/2.8 design: 18mm, 24mm (normal, equivalent to 50mm on 135) and 50mm at launch, joined in 1981 by an 18mm pan-focus, a 70mm and a 20-40mm zoom. Film speed is sensed from the cartridge ridge, which Pentax mapped to ISO 80 and 320. Accessories included two motor winders, AF130P and AF100P flashes, close-up lenses and filters.
As a genuinely pocketable SLR system with proper TTL metering and a six-lens line-up, the Auto 110 remains a favourite with collectors and experimenters. Its lenses have found a second life adapted to Pentax Q and Micro Four Thirds bodies. The two-stroke film advance and complete lack of exposure override are the main handling quirks; the split-image finder makes focusing the f/2.8 lenses manageable.
110 film is a niche today: Lomography still produces fresh cartridges, but choice is limited and modern ISO 400 film ridged as 'low speed' fools the camera unless the ridge is filed off. Check the battery door — a known weak point — and confirm the body-mounted iris/shutter fires cleanly through the mirror cycle. Winder battery covers are fragile, and the flash-sync socket covers are commonly missing.