I had more than a few vexing images today of this knot. Something about the position in the frame as my daughter crossed the wake made my AF briefly lock on. They can't all be keepers.
Don, I've thought that, and it does work when they are young and stay right behind the boat.The rope is a fixed length, perfect for one manual focus.
Yes, I think this is the "Blocked shot AF response". Mine is set to 3 (medium). Truthfully, this doesn't happen too often, but there was something odd about the lighting and that section of the rope yesterday that seemed to attract my AF.Don't you hate it when this happens. It is knot in focus.
It has been a couple of years since I shot with the d500, but isn't there a tracking lock on setting in focus? You can adjust it so the camera does not refocus when your subject is quickly obscured by something else. We used it a lot in bif, keeps the camera from locking onto branches, etc when the bird flies behind a branch- stays locked on the bird. Might be worth a try.