Short lens review: Sigma 30mm f/2.8 EX DN for Sony E mount & M 4/3 mount.
I've had this lens for just a few days. I'm using it on a Sony NEX -3. A fantastic, little lens for the price ($150 @ B&H, Adorama...). Image quality is excellent. Better than the Sony lenses I have. Looks really good in the corners even at f/2.8. Nice size: 1/2 way between the Sony 18-55 and the Sony 16mm. This will probably be the lens that stays on my NEX.
I was wary to read of "thunking" caused by a loose lens element in many of the reviews. Apparently this is how the lens was designed. A floating element moves slightly when the lens is un-powered. I read some griping about this, but with the lens in my hand it's not a big deal at all. Some reviews bitch about the plastic construction, but it seems quite soundly built to me.
My only gripe: I wish Sigma had skipped the fancy lens case, and included a lens hood instead. I never use these fancy cases.