BTW here are some shots from yesterday, of my son and his mother running towards me… Shot at f1.4 using a 6D, center focus point.
The first shot is back focused, and only the last one is okay sharp to me at least. So it seems the tracking can't keep up. I've got a few from indoors today that are really sharp, so I guess going back and forth with calibration is always a good thing.
The thing about the Sigma is that it is soo sharp that even slightly misfocused shots appear sharp enough.