Comments about Off Brand Sigma 50-500 4/6.3 Apo Ex F/nik Afd Hd:

This lens will best serve those who will use a tripod. A mono pod is not enough at the long end of this lens. I bought one, sold it and had to have another after reviewing the images this lens made. I got tired of using the 80-400 VR Nikon lens as it focused very slowly, but did not require a tripod to make acceptable images.
This Sigma requires the use of a tripod but focuses very quickly. It is also sharper at the long end over the Nikon lens. I've decided quick focusing trumps VR in most situations for me. I wish I could afford the Nikon 200-400 VR, but that is not to be for me, so its the 'Bigma' for me.
It is very heavy and gets tiresome to carry around, but is no worse than the 300mm f2.8 I was considering.
Anyone considering the 80-400 VR should take this lens into consideration if they do not mind the tripod 'ball & chain'.
Too bad Nikon and Sigma can't get together with a 50-500 VR with HSM focusing.
I use the long end of this lens, the 200 and beyond as I have an 18-200 VR AF-S lens already. The extra 300mm of reach is really nice for small birds and animals that don't like humans getting close.
Forget the Nikon 80-400 VR, I owned one for 5 years and am glad its gone, but forget this Sigma too if you won't use a tripod.