Yesterday, I went to the Boston Marathon to get some close-up shots of the runners with my X-T2 and the XF100-400 + 1.4 extender. I had the camera/lens on a tripod with a fluid head for smooth panning. I set the camera to CL and used AF-C mode with zone focusing in preset 1 (seemed most applicable here). OIS on the lens was left ON. After a bit of back and forth, I settled on fully manual exposure control with the apperture wide open (between 7.2 - 8 with the focal length kept between ~400 - 560mm most of the time), exposure time of 1/1000 and varying the ISO depending on light (usually around 1000 give or take a stop). With these settings, I would lock focus on to a runner at about 50ft away, pan and take shots in shorts bursts (3 images at a time, sometimes more) with the runner about 20 - 30ft away. But while the focus squares indicated a good lock on runners, the vast majority of my shots turned out not very sharp.There are only a handful that are ok in that regard. Here two examples of good and not so good focus at 100%: Given the above mentioned settings, I was expecting much better results and now I wonder where the culprit lies? Do I need better technique/settings? Am I asking too much of the system? Some advice would be greatly appreciated. P.S.: While most of the images are not tack sharp, the full images still look halfway ok on a monitor, especially when converted to a gritty B&W look. I might post a few later this week.