I have been researching my next lens and I was going to go ultra-wide but now I am thinking that I will be happy with a 16 or 17 zoom lens for my D7000. I am looking at the 16-35 f4, 17-35 and 17-55 2.8 nikons. I am also considering the sigma 17-50 as that one receives high regards from what I've seen. Does anyone have any thought on these lenses?