Thanks Arash .As usual extremely helpful to us mad enthusiasts on this site. As you say once you get on the the bird the d5 just hangs on, even when the likes of a Peregrine is coming straight at you. The 500 pf lens by itself is great on this camera, but I have found that with the 1.4 on in my hands it tends to wander off the fastest moving subjects..But with the 500 f4 plus 1.4 combination the d5 hangs on as well as one could possibly hope for. Thanks again for all the work you put into this review.