While the Sigma 150-500mm F5-6.3 gives excellent results it does need bright sunshine to get the best from it. In low light it struggles to focus, but that is the same for most lenses at the 6.3 end. I have the Tokina 28-70mm F2.8 ATX-Pro and it's a heavy but well made lens. Don't use it much now as I have the Nikon 24-70mm F2.8. The Sigma 105mm Macro is also a cracking lens and gives great results.
