Leica's bayonet mount for rangefinder cameras, introduced in 1954. The 27.8mm flange distance allows adaptation onto many modern digital cameras.
Technical Details
The M Mount has an internal diameter of 44mm and features six sensors for lens recognition on digital M cameras. The flange focal distance of 27.8mm is significantly shorter than that of SLR cameras (Canon EF: 44mm, Nikon F: 46.5mm). Modern M Mount lenses transmit focal length and aperture data via electrical contacts to the camera body. The system supports focal lengths from 16mm to 280mm, with lenses from 28mm onwards usable without viewfinder issues.
History & Development
Leica introduced the M Mount in 1954 with the Leica M3, replacing the L39 screw mount used since 1930. The designer was Willy Kütter, who aimed to enable faster lens changes. In 1984, Leica expanded the system with 6-bit coding for automatic lens recognition. Electronic contacts were added with the digital Leica M8 (2006). Today, besides Leica, Zeiss, Voigtländer, and Cosina also produce lenses for the M Mount.
Practical Use in Film
Cinematographers appreciate M Mount lenses on mirrorless cameras for documentary work and Steadicam shots due to their compact design and low weight. The Leica Summicron-M 50mm f/2.0 weighs only 240g compared to comparable cine optics weighing 800-1200g. Filmmakers like Sean Baker used M Mount lenses on Sony cameras for "Tangerine" (2015). The continuous aperture ring mechanism allows for smooth aperture transitions during recording.
Comparison & Alternatives
Compared to cine mounts (PL, EF), the M Mount does not offer parfocality or focus gearing for follow focus systems. Sony E Mount (18mm flange focal distance) and Micro Four Thirds (19.25mm) allow the use of M Mount lenses with infinity focus via adapters. Canon RF Mount and Nikon Z Mount are modern alternatives with electronic communication and larger diameters. For high-end productions, specialized cine lenses remain the first choice, while M Mount optics excel in mobile setups and available light situations.