Lens Mounts: Leica M

Pekka Buttler, February 2023

Basic Information on the Leica M mount:

The German camera company Ernst Leitz of Wetzlar pioneered the use of 35 mm motion picture film in still cameras with the 1925 mass-market introduction of the Leica (LEItz CAmera). In 1932 an upgraded Leica was introduced to enable interchangeable lenses using a 39 mm diameter 28 tpi thread mount (what we today know as the Leica thread mount/LTM/L39 mount).

In 1954 Leitz introduced the Leica M3 – a new, post-war design that (beside other improvements) introduced a new bayonet type mount to replace the thread mount. The Leica M Bayonet mount was seen to offer both more rapid changing of lenses and a more secure, precision fit.

Judging by the fact that Leitz/Leica¹ still manufactures film cameras using a fundamentally unchanged Leica M mount, it is easy to deem the Leica M a successful mount. Also, when Leica decided to launch a digital rangefinder camera (the M8) in 2006, they felt the Leica M mount to be fundamentally suitable, even though some minor extensions² were added.

As of this writing, the Leica M mount remains one of the oldest, still current lens mounts, and nothing indicates that the Leica M mount would not continue to stick around.

Leica M mount specifications

Mount type: Bayonet mount (lens release on camera)
Flange focal distance: 27,8 / 27,95 mm ³
Film format: 36mm x 24mm (‘Full frame’)
Mount communication:
• focusing distance for rangefinder and parallax correction (lens-to-camera)
• lens 6-bit code (lens-to-camera, on some recent lenses)

Adapting Leica M lenses

First, why would you want to adapt Leica M lenses? In the simplest terms, because some of the finest lenses ever have been manufactured for the Leica M mount. This is not only limited to Leica lenses, but also Carl Zeiss rangefinder lenses and Voigtländer lenses, but also (more recently) an increasing number of Japanese and Chinese enthusiast lens manufacturers.

But, for most of the Leica M mount’s 70-year history, it has been impossible to adapt Leica M lenses to anything but the odd small-frame motion picture camera, because of the Leica M mount’s short flange focal distance. Instead, the traffic has rather been the other way around, with a plethora of adapters being offered to adapt not only Leica Thread mount lenses but also rangefinder and SLR lenses to Leica M cameras.

However, since the introduction of mirrorless interchangeable lens cameras with their inherently short flange focal distances, It has suddenly become not only possible but tempting to adapt Leica M lenses. Hence, in short:

Leica M lenses can be used natively on any analog or digital Leica M camera.

Leica M lenses can be adapted to any digital, mirrorless interchangeable lens cameras (including, explicitly: Canon EF-M; Canon RF; Fujifilm G; Fujifilm X; (Leica) L-mount; Micro Four Thirds, Nikon 1; Nikon Z, Samsung NX; Sony FE ) using a simple dumb adapter. Moreover, some specialised, autofocus adapters allow autofocusing Leica M mount lenses on some of the mirrorless systems. However, depending on the combination of sensor and lens, some Leica M lenses may produce partial colour casts when adapted.

Leica M lenses cannot be used on any SLR/dSLR cameras

Footnotes:

¹ Leitz (company) changed its name to Leica in 1986.

² That ‘extension’ is what is referred to as 6-bit coding a strip of 6 white/back dots on the lens’ flange that can be read by a digital Leica M body to determine the lens in question. The digital Leica M body then uses that information to a) activate the correct built-in correction profile, and b) bring up the correct viewfinder frame lines.

³ There is some confusion regarding the Flange focal distance of the Leica M, as two alternative numbers: 27,80 mm and 27,95 mm are both regularly mentioned. Given that the difference between those numbers is 0,15 mm, which is very close to the thickness of regular photographic film, these may be values to the film surface and to the pressure plate respectively. Should someone have hard facts, you’re welcome to point be to definitive source I have this far missed.