I've been trying to shoot action shots of my little black dog running toward me chasing sticks tossed by my wife and not getting too many keepers. Conditions - either backlit or front, Av mode at f4 w 600 f/4 II, IS mode 3, shutter speed 1/1000 or higher, high-speed continuous, AF mode 4 (rapid accelerating subjects), central AF single point selection, shot from monopod. I get multiple images with the active AF sensor directly on the subject but they are completely out of focus. I have tried tracking well in advance of the shutter release but this lens/camera/photographer combo hasn't had much success to this point. Is this just too tough a subject? She is a very fast dog and a very black dog but I'd love to capture the joy on her face as she bounces along in pursuit. Would the 1DX do much better? Same AF system but better performance in the 1DX? My lens is not one of the firmware update versions that needed an AF adjustment and I have tuned it for focus microadjustment as described on the "birds are art" site - works fine for other subjects. Here's a sample that is OK, not great....Click image for larger version.  Name: 201A2177.JPG  Views: 219  Size: 76.6 KB  ID: 1578

Should I change the individual settings to create a custom AF for this subject? Advice welcomed.