Threaded mount with 42mm diameter and 45.46mm flange distance, introduced by Pentax in 1957. Now widely used for vintage cinema lenses via adapters.
Technical Details
The M42 thread has an outer diameter of exactly 42mm with a pitch of 1.0mm. The flange focal distance is a standard 45.46mm for most manufacturers. The mount exclusively transmits mechanical connections – there are no electronic contacts for autofocus or aperture control. Variants include the original Pentax M42 system as well as adaptations from Zeiss, Schneider-Kreuznach, and Soviet manufacturers like Zenit. The maximum lens aperture is limited by the 42mm inner diameter of the thread.
History & Development
Pentax introduced the M42 mount in 1957 with the Asahi Pentax, establishing the first widely adopted standard for SLR cameras. Zeiss adopted the system in 1960 for the Contarex series, followed by numerous Eastern European manufacturers in the 1960s. The mount reached its peak between 1960 and 1975, when manufacturers like Takumar, Meyer-Optik Görlitz, and Helios produced high-quality M42 lenses. From 1975 onwards, bayonet-based systems like Canon FD and Nikon F successively displaced the M42 mount, as they enabled faster lens changes and electronic communication.
Practical Use in Film
M42 lenses are primarily used today on digital cinema cameras, adapted via special mount adapters. Cinematographers appreciate vintage M42 optics like the Helios 44-2 58mm f/2 for their characteristic bokeh properties and organic image aesthetics. The Takumar 55mm f/1.8 is often used for close-ups and portraits, while Soviet wide-angle lenses like the Mir-1 37mm provide distinctive distortions for stylistic effect. Manual focusing requires precise focus pulling and corresponding workflow adjustments on set.
Comparison & Alternatives
Unlike modern bayonet mounts such as Canon EF or Sony E-mount, M42 offers no electronic communication between lens and camera. Current cinema mounts like PL or LPL allow for larger sensors and shorter flange focal distances. M42 adapters exist for practically all modern camera systems, with the 45.46mm flange focal distance enabling adaptation to systems with shorter flange focal distances like MFT (19.25mm) or Sony E-mount (18mm) without issue. For longer flange focal distances like Canon EF (44mm), adaptation is only possible with corrective lenses.