I was out with Andreas last weekend and was having problems tracking focus with my D2X. I was troubled, because I have been able to track birds in flight in the past. I reviewed my technique during the week and decided I had been doing two things wrong: 1) I had setting A4 off (I had been experimenting and forgot to reset it) and 2) I was not tracking smoothly, keeping the target in the focus lenticle. I find it harder to smoothly track when the target is almost directly above. I am using a sidekick and swiss arca B1. This weekend, I set a4=on and concentrated on tracking more smoothly and had much better success. Capturing a Kingfisher in flight is not that easy, but I was able to make a number of shots, all in focus. My settings were continuous focus, dynamic area AF. I was shooting with the 500/4 + TC14EII.