Today I got my hands on a Hawk's Factory Leica M to Sony NEX adapter. The key thing about these adapters is that they have a built in helicoid that enables much close focusing on rangefinder lens. So far I have just tried it out using the Leica 50mm Summicron and NEX 5n, but the improvement in close focusing is dramatic, enabling shots down to about 25cm instead of 70cm.
The Hawk's adapter seems reasonably well made, but probably not as nice as the non-helicoid ones from Voigtlander and Novoflex, though there are twice the price.
I get the feeling that as rangefinder lenses are not designed to be focused close, they will lose their edge in optical performance in this range, however I do look forward to trying it out.
|Sony NEX 5n with Sigma 30mm f2.8 Serena Gundy Park, Toronto|