I have both but I am unsure if I should keep both. I don't like to have too many similar lenses because I'm trying to fight the semi-collector within me. I recently got rid of three 50's and it felt good. The Sonnar is faster but the extra stop isn't that much more useful because the DOF is more narrow and the focus shift. I feel that if I were to have multiple 50's then a Summilux and/or a collapsible Summicron/Elmar would be more justifiable because the former is faster (without the shift) and the later is more portable.. I mean, I've shot maybe a dozen rolls from both lenses so not really enough to make a definite comparison and the lighting/scenes/films were not always the same. They both take good pictures. Anyone with both of these lenses feel that the drawing of one is different enough to keep both? Ofcourse your answer doesn't really dictate mine but I'm just trying to come up with the courage to get rid of one (the sonnar) or to be convinced by others that I really do need both. Maybe I'll appreciate the difference later down the road when I shoot more rolls. I just don't want to regret selling the Sonnar or keeping it when I think I can benefit from something else more photographically useful. I'd opt for the Summicron over the Sonnar because I prefer sticking with 39mm filter threads, it matches my M3, and I like the ergonomics better (clickly aperture).