jackpi wrote:
Is the Sony 1.4TC compatible with the 20-400mm lens? Teleconverters work best on prime lenses. If you haven't bought the 70-400mm lens yet, you might want to consider renting a Sigma 150-600mm Sport lens with the Canon mount and the Sigma Canon-Sony adapter.
I think this is probably the better way to go rather than to fool around with the teleconverters. Tamron also has a 150-600. Do you know how they compare?