Probably going to buy a nex-6 in the near future and am looking for a good zoom to go with it. The 16-50 and 18-55 kit zooms are not what I'm looking for, so I'd appreciate any recommendations on higher-quality alternatives. What I'm specifically looking for: Roughly 18-50mm range. Very low chromatic aberrations (axial, transverse, spherochromatism). Good corner sharpness, even to extreme edges. At least f/4.0 throughout range. Auto-focus on nex. No power zoom. No focus-by-wire if possible. Any manufacturer is fine, and adapters are fine as long as auto-focus is retained. If there are no auto-focus options, I'd be interested in suggestions for a lens fitting the other criteria. Thanks!