So I modded my Industar 69 lens (28mm f/2.8 Leica thread mount) this morning -- thought I'd do a brief writeup and post a couple samples since I haven't seen anything anywhere yet that showed what it can do on a G1 when it's been modified for infinity focus.
These are just sitting outside my neighborhood cafe. Laziest photography ever: Wait for the subjects to come to you, then point and click
Construction is really cheap and flimsy!
I found that you need to grind the infinity stops down to the same height as the lip of the mount piece they're a part of. This is the only note I'd add to Hamish Gill's tutorial.
When it's modified for infinity focus, the aperture scale no longer lines up with the dot. So you're just guessing the whole time. This is fun f/2.8 is really soft. Definitely lomo snapshot sort of look. It sharpens up real nicely around the f/5.6ish region. Covers the full sensor no problem. Color is distinctly pastel-ful, though I'll point out that today the sky is a bit overcast. In general, IQ wise I'm sure any color skopar would blow it away at just about any aperture, and if you're looking for the extra stop of speed I doubt f/2.8 on this lens is preferrable to f/4 and a stop higher ISO on a skopar.
In use, this becomes a fun lens to use on the G1, turning it into perhaps the most hi-tech snapshot camera ever. Much more fun than the IQ would indicate. At infinity, anything over 15 feet away is in focus, so I set it around f/5.6 and start snapping. Framing is optional, but the swivel screen makes it fun. Using the VF often feels like a waste of time and effort. It's just compact enough to fit the G1 into a large coat pocket, and the lens is recessed enough that a lenscap is entirely optional. It seems silly, but aesthetically it's such a good match I find I just want to leave it on
All in all, for the money, it's fun to have a compact normal prime that reduces the process to point-and-click operation without the AF lag of a compact digital. It's refreshing to let go and concentrate solely on what's going on around you. It's also really fun to have a pancake on the G1, and I'm sure the 20/1.7 will live on mine.