Had the 2xTC III for use with the 70-200 II, but felt I just ended up with a cumbersome heavy combo. Probably should have chosen the 1.4 EX instead also giving me f4 and not 5.6. Had to send the lens to Canon as the lens new out of the box had a defect rubber gasket at the lens mount (part missing). Also I am not that impressed on the sharpness. It is great but not great as in fantastic.