I had the opportunity to test the Sony 24mm f/1.8 ZA Carl Zeiss Sonnar T* lens on a NEX-5n recently and despite the lack of a distance scale and depth-of-field markings the lens is a joy to use. It's also a world class performer optically*, and should perform equally well on the intriguing NEX-7. Apart from the attractive drawing style of Zeiss lenses, of particular merit for available light photography is the edge-to-edge performance at maximum aperture.
The above photograph taken at f/2.0 atop Primrose Hill, London on an overcast day, is cropped top and bottom but retains the original horizontal resolution.
This is a crop at 1:1 from the far left. Shooting cityscapes at f/2 is not recommended, this was purely for testing purposes but it reveals the imaging performance is of a very high order.
The lens has an unusually close 16cm minimum focus distance, which permits close-ups such as this small candle (it's about 3cm tall). Note the smooth differential focus (bokeh) and circular highlights (there's the slightest green tinge at the edge visible at 1:1).
*UPDATE: No lens is perfect, and this one has a propensity to produce purple fringing (common in fast primes shot at large apertures). It's also quite difficult to remove, even in Lightroom 4.1 RC2 with the new Lens Correction tools. In my estimation troublesome purple fringing was easier to remove in earlier versions of LR4 using a technique I have disclosed in a recent review of the software to be published in a forthcoming edition of the British Journal of Photography magazine.