Leica manufactured the Type 2 Summicron in two versions - the regular one as well as closed focus version (or dual range), which had an identical optical formula.
This is a six element version (3) with 10 blades, produced 1971 - 1979. Still with the same number of glass elements than Version 2, brought some improvement in overall contrast.
The smallest Leica 50mm lens. If mounted it makes even your Leica M small and light, perfect for traveling.
The Summitar 2/5cm is a fantastic high quality lens, made in holy Wetzlar. You can learn more about the history at Ken Rockwell. If you interested how this lens performs on a digital Leica, you can go to Steve Huff.
Leitz Summaron 2.8/35 is a small, high quality build lens. My version is from 1967, Leitz made it with the new rare earth glass.