Sun 17-Feb-13 08:02 PM | edited Sun 17-Feb-13 08:06 PM by richardd300
My Nikon 80-400mm worked well enough on my D300 and D90, but was very poor on my D7000. In all cases the old technology lacked the fast focusing response of Nikon AF-S lenses. I found this particularly poor in low light and focus hunting in high contrast areas. In short the images on my D300/D90 were good enough allowing for the slow focus.
In the end I bought a Sigma 50-500mm OS and the difference between this lens and the Nikon was immediately apparent. I have a friend who has the Sigma 150-500mm OS and I tried it on my D7000 and D800 and found it as good as my 50-500mm.
In fairness the Nikon 80-400mm VR is still a very capable lens in terms of IQ, but lacks the response and slickness of Sigma's offerings. In my opinion Sigma offers equal image quality.
You may find the comparisons between both lenses in thom hogan's reviews. See: