M39 (lens mount)
M39 is a standardized, manufacturer-independent lens connection for interchangeable lenses using a screw thread in the field of photo technology .
The “M” in the name stands for a metric diameter, the dimension number for the diameter in millimeters. There are differences in this connection dimension in the pitch of the thread; the most important are the inch 1/26 ", as well as 0.75 and 1 (metric dimensions). The pitch dimensions 1/26 ″ (= around 0.977 mm) and 1 mm are very close to each other - special threads suitable for both are offered. M39 filter threads usually have a pitch of 0.5 or 0.75 mm.
Leica thread
The M39-Leica threads, including Leica L-mount or Leica Screw Mount - LSM called, has 1.26 "pitch and was from the 1930s, especially for small picture - Rangefinder Cameras used. Introduced at the screw Leica, it later developed into the general standard for rangefinder cameras , although it was replaced by the M bayonet by Leica itself in 1954 by numerous copies from other manufacturers. Even today, high quality lenses are still available for the thread.
In addition to the standardization of the thread, the flange focal length of the lenses is set at 28.8 mm.
The coupling of the distance setting of the lenses to the rangefinder of the camera is an inseparable part of the LSM standard. This is achieved by a ring or cam on the lens, which is moved out of the lens to different degrees depending on the setting range.
The movement or control distance corresponded to the adjustment movement distance of the normal lens used by Leica , whose “lens stroke” was transferred directly to the rangefinder. For lenses with different focal lengths, this control distance defined by the normal lens must then be generated inside the lens by an additional mechanism, since the adjustment movement distance (i.e. the "lens stroke") changes depending on the focal length.
The thread measure itself is also used for magnifying lenses and is still widely used. Although the lenses “fit”, they are not compatible with each other. There are also some other camera systems that also use an M39 thread, but are also incompatible due to a different flange focal length ( Braun Paxette , early Zenit mirror reflex cameras).
M39 × 1
Lenses with the very similar metric thread M39 / 1 were made in the USSR and Japan while copying the Leica thread; at least in the USSR this was corrected later. Experience has shown that both lens types are interchangeable. Threads that do not fit exactly in the pitch only touch a small part of the helix and are therefore less resilient as an odd pair and more prone to wear.
A thread was also used by the Braun Paxette system until it was converted to the SLK bayonet. Paxette lenses can be adapted with a spacer sleeve for the Leica and analogously to the Russian M39 SLR lenses using a threaded sleeve on M42 and thus on DSLR, with a small difference in flange focal length. This can be remedied by mechanical reworking of the camera adapter and thus allow the use of the respective lenses over the entire focus range up to infinity.
M39 x 0.75
Magnifying lenses, e.g. B. some focal lengths of the Schneider Kreuznach Componon S, were also equipped with the metric thread M39 × 0.75. Some shutters for large format or medium format lenses are also delivered with this size.
Web links
- Thread in the photo area thread standards
Individual evidence
- ↑ http://www.l-camera-forum.com/leica-wiki.de/index.php/Kategorie:Leica_Schraubgewinde Leica screw thread, Leica Wiki, February 4, 2009, accessed September 1, 2015.