i recently picked up a new lens for my M9, the 40mm Summicron-C, which is the lightest and most compact Leica lens to date. originally build for the Leica CL during the 1970s it features the M mount, therefore it's usable on all modern Leica cameras. the odd focus tab was changed to the current version by the previous owner, so it's easy to handle like the modern lenses. the only drawback is that the lens will show the 50mm frame lines in the viewfinder instead of the more suitable 35mm lines, but this can be changed with a bit of filing on one of the bayonet lugs (took me 5 minutes). a great and compact setup for street photography.