M42 Lenses
20 interactive lens diagrams
42 mm screw-mount SLR standard, 1940s-1970s | 35 mm SLR
M42 became one of the most important open 35 mm SLR lens standards. It is mechanically simple, broadly compatible, and was used by many camera makers before proprietary bayonets became dominant, though aperture automation and metering details vary by brand and generation.
Because so many companies built for M42, the mount gathers a wide range of optical traditions: Takumars from Asahi Pentax, Carl Zeiss Jena Pancolars and Flektogons, Fujinon EBC lenses, Soviet Helios and Mir designs, and many third-party optics. The screw mount made cross-system adoption easier but also slower to use than later bayonet systems.
It is one of the best mount clusters for comparing common focal lengths across manufacturers. Similar 50 mm, 35 mm, and 135 mm designs can be viewed side by side without the mount itself forcing a single corporate design language.
Mount interface
Flange focal distance 45.46 mm, threaded 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.