I highly recommend anyone using the NEX-7 to check out both the Sigma 19 and Sigma 30 that are available. They are lightweight, small, and very sharp. The Sigma 30, in particular, is astoundingly sharp at all apertures across the frame. I've owned and used several ZM and Contax G lenses on NEX, and the Sigma 30 is as good or better than all of them, including the venerable Contax G 45. Sigma really pulled a rabbit out of their hats for $199 each. In fact, I like the Sigma 30 so much that I sold all of my ZMs, and I sold my Zeiss 24/1.8 as well. Go figure!
The lenses are plasticky and lightweight, but do yourself a favor and spend the $199 on the Sigma 30 and Sigma 19.
p.s. the Sigma 30 is so sharp that, according to the mtf tests over at lensrentals.com, combining it with the NEX-7 actually resolves similarly to the D800 with some Zeiss and Nikkors (but not all of them, obviously.)