Tamron 150-600mm vs Sigma 150-500mm vs Nikon
I have been using the Nikon 55-300mm DX for the past two years, and would like a lens with more reach. I have considered the Nikon 300mm f/4.0 with a 1.4 teleconverter, as well as the new version of the Nikon 80-400mm (expensive but on sale).
It seems that the Sigma or Tamron lenses would be cheaper alternatives to the Nikon ones. Any feedback as to which one of these lenses may be a good choice would be greatly appreciated. I would like to spend as little as possible, but if the consensus view is that the Nikon 80-400 is significantly better than either the Tamron or the Sigma, I might go for it while it is on sale.