It's a mixed bag. My two Summiluxes (35 and 50) perform great optically on the Sony. The main issue is that I have to focus them wide open and then stop down before shooting. Overall I like it. Not quite as much as I do on a Leica, but there are some perks: simplicity of using one system, image stabilization, more accurate framing, easier to focus long teles, etc. And when I want to shoot a rangefinder and use the lenses as they were meant to be used, the MP is very satisfying.