Leica screw (thread) mount has become defacto standard of interchangeable lens Rangefinder cameras, since so many manufacturers produced Leica copy cameras.
Along with lenses produced for both Leica and its copies are abandunt in used market, and on top of it some manufacturers like Avenon, Konica, Ricoh and recently Cosina (Voightlander) have been producing Leica screw mount lenses. Theselenses, can be used with Leica M models with ML ring.
New bodies are also produced or announced; Yasuhara T981 finaly started to appear in the market, Cosina's Bessa L was quite impressive hit, and models with coupled rangefinder are awaited, again expanding the market for screw mount lenses.
(Please click on the picture to enlarge)
Canon Lens 50mm/f1.8
Besides Nikon, Caonon was the chanpion of japanese copy Leica manufacturer. First Canon lens with Leica screw mount bore the name of Serenar, before switching to Canon Lens...roughly two versions exist; first in shiny chrome finish, the later models in black. With the speed range from 2.8 to 0.95 of the "dream lens", Canon offered the variety of selsction to choose from. Among which, 50mm/f1.4 was a remarkable performer, and gained high reputation for its sharp, crsip picture. (some even argue this as the sharpest screw mount lens!)
Economic version with the speed of f1.8, is also a good performer. But perhaps its so natural that it lacks "something" that you might expect from, say, russian jupiter lenses. Color balance and sharpness are both excellent, a bargain lens for Leica and Leica copies.
Jiyuugaoka, west-Tokyo, Canon 7 with 50mm/f1.8 at f4.0-5.6