I'm thinking about an ultra-wide for my M and this lens looks like it might fit the bill. I have had 21mm's and somehow don't find them quite wide enough (compared to the 28mm which I have) when I want to go wide, 15mm might be too much of a good thing though. The Zeiss looks very attractive, although it is clearly, despite being only f4, a big lens. Has anyone tried it out or used it? On paper it looks to be an excellent performer. Can anyone give me any feedback on it? Thanks.