Opinions on how this combo would work. Looking to use it for birding. Looking for reach and this should do it. Wide open at 400 would the sharpness be up to par? Thought about the Sigma 150-500 but keep reading it is soft. That's the last thing I need.
If you primarily shoot birds then the 400mm prime might be better, (slightly sharper, takes a teleconverter, cheaper,) I use the 100-400 because it's more versatile than a prime for sports, zoo, and of course birds.