M39 lens mount
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The M39 lens mount is a screw thread mounting system for attaching lenses to 35 mm cameras, primarily rangefinder Leicas. It is also the most common mount for Photographic enlarger lenses.
The thread form is M39 x 26 tpi, meaning a major diameter of 39mm and a thread pitch of 1/26 inch (0.98mm). This unusual combination of metric and inch sizes likely arose from metalworking lathes first used for manufacture being equipped to cut only inch thread pitches.
The mount was developed by Leica who were in need of system that would allow for the exchange of lenses on their new small film cameras (Leica Type 1 and Leica Type 2). This would make them more versatile.
Until the 1970's the 39mm mount was the norm for exchangeable lenses in rangefinder cameras. The high cost of quality lenses led to the dual use camera/enlarger of the lenses, hence the fact that enlargers also accept 39mm lenses.
The last modern 35mm cameras to use the M39 norm are Voigtländer (Germany), FED (Russia), Lubitel(Russia) and Zorki(Russia) cameras. These give amateurs the rare chance of having a very professional camera by combining a used Leica lens with an M39 body at a price well below a real Leica combination. On the other hand one has to be careful as there are some issues with some bodies not using the same focusing system.
