G'day guys and girls, just would like to know if anyone has one of these, or has used on of these lenses on a Nikon dx camera? I've got a d7100 and currently have a sigma 70-200. I'd like more reach and had looked at the nikon 300mm f4 for a bit, but would still like the flexibility of a zoom (i think). Probably looking at using my current 1.4tele and possibly purchasing a 2.0 x tele. Mostly using the lens for trips to zoo's, and would like to get into birding (preferably birds of prey). After reading a number of reviews, it looks like the sigma 120-300 has just about the best sharpness available from a lens, on the d7100, though i'd love it if soeone was to chime in and share their own experience from using one of these combinations.