Quote Originally Posted by eldarhau View Post
Agree. But from 70-200 it is in a different league and with the extender it is not that far behind, so overall, I still say that it is a better combo. If 400mm is the main objective I would seriously look at a used 400 f5.6L
Better...if affordable.

The 400/5.6 lacks IS, for me that was a deal-breaker. I find even the 2-stop IS of the 100-400mm useful.