This is the standard lens designed by Leica and manufactured by Panasonic. I tried it out on 3 different cameras. Olympus E-420, Leica/Panasonic Digilux3 and Panasonic GH1.
It performed well on all three, though the Olympus images were less sharp than the others. Probably the heavier AA filter on the E-420.
Its bulky but not that bad in use. I bought it mainly for Video on the GH1 to provide a fast lens for low light.
There are 3 full size samples, one from each camera, at:-
I enjoyed using it and used it exclusively for these tests, taking no other lens with me.
I have these attacks of "Photographic Purity" from time to time. The "I only need a camera and a standard lens, just like Cartier-Bresson" syndrome!!