Thanks for all that good advice, AaronT.Your camera+lens+TC might need an AF Micro-adjustment (AFMA). At say, 12 feet, 560mm at F8 your depth of field is about 3/4 inch. Not much room for error. Also, when using the 100-400+1.4 TC it might help to stop down a bit if you have enough light. It has been said that the 100-400+1.4TC combo is sharper when stopped down a bit. With mine I usually use F9.5 as a minimum. You were shooting at 1/1600 so you had room to trade some speed for aperture. The big whites are different, they are sharp wide open. But they are primes and cost 5 times as much. Just my opinion. The shot below was ISO800, F9.5 with 5DsR, 100-400L MKI, 1.4TC MKII at 560mm. About a 1/3 crop. I used center point, single shot AF. BTW, I got the same results when shooting with my 5D MKII.