Thanks guys, may well go along to WEX and try a few S/H ones out...
How would one know the difference from the older Nikon 18-35 with the newer 18-35 as Paul suggested above..
Very different imo. The old one suffers with moustache distortion, very poor edge to edge sharpness, never gets sharp in the corners (and quite a way in too) as well as still vignetting at f8 ... add in fairly heavy CA (but not untypical for a wide angle ime) and it just plain stinks imo ... the new one is much better, it still has noticeable distortion but it is uniform, way better edge to edge and corner sharpness, much improved vignetting and better CA handling.How different are the 2 versions of the Nikkor 18-35 optically? I'm guessing that the older one might be screw driven rather than AF-S but IIRC all Nikon full frame bodies (so far) have in body motors (and IME, AF isn't that much slower using the screw compared to AF-S.)
FWIW, if you stand back in a corner of a rectangular room, the Sigma 12-24mm will get pretty much the whole room in. Little or no rectilinear distortion but the perspective is quite exaggerated!