Ok I am lusting for a wide zoom. I would like to have the Nikon 17-55 2.8 but I can't justify paying that much at this time. My other options are the Sigma 18-50 2.8, the Tamron 17-35 2.8-4 or the Tokina 12-24 f4. I am leaning toward the Sigma because of the 2.8, but I also like the idea of the wider Tokina. Are any of you familiar with these lenses. Would I see a lot of differences between the 2.8 and the 4. Any help that you can give will be greatly appreciated.