http://www.nikonchat.com/nikon-f2-8-300mm/

Nikon and Sigma glass?
I have reduced my search for a telephoto lens to the Nikon D 80-200mm f2.8 and Sigma 70-200mm f2.8 HSM. I use a Nikon D50. Anyway, the Nikon is only $ 20 more than the Sigma, so I'm sort of caught between the two. My main concern now is that one is faster for focus. That was my main problem with my old lens, Tamron 70-300mm. It was a good job but I need something faster approach. Therefore, the focus Nikkor fast lens? Or will I be better off with the Sigma HSM? Is it better optical quality with the Nikon, or is it two lenses on it? Thank you.
$ 20 plus lens for Nikon? I think I know the answer to this. Stay with the Nikon lenses for Nikon. You should try in a store to see how they "feel"
Sigma 70-200mm F2.8 EX MACRO Lens 70-200mm Microglobe.co.uk