I should have clarified my earlier comment. Corner smearing and other optical artifacts are only "bad" in the eye of the beholder. It's a subjective issue more than optical, since the subject matter of the image itself trumps any technical consideration.
Of course, given that there're lots of legacy, MF lenses out there from which to choose from, one can get nearly the same quality of images for a lot less dollars. In my case, I already have a Minolta MD kit of lenses, which I enjoy adapting to my G1. These lenses aren't as sharp as the Lumix 20-1.7, but they're fun to use and do give good results.
The issue with corner smearing using M-mount lenses I understand affects mainly the wide angle lenses; the examples of images I've seen posted using longer focal lengths have the typical Leitz sharpness one would expect.
Some of this also has to do with optical design; I've seen some example images posted taken using Zeiss M-mount glass, in wider focal lengths, that don't show the typical corner smearing; perhaps these designs include a bit more telecentricity.
I need to keep reminding myself that the technical merits of a lens has little to do with the aesthetic merits of the resulting image. This was reinforced upon me yesterday when I was on my back porch, composing still-life images using my homemade 8"x10" nested box camera, using a 150mm binocular lens and paper negatives. I'd say there's a bit of corner smearing here, what? Yet the image seems to hold together. Again, beauty can't be measured by an MTF curve.
~Joe
