This shows the type of good,fast autofocusing performance the D2x and 70-200 AF-S VR-G lens can achieve. The runner has come up on my shooting position very rapidly,and in this type of situation FRAME RATE being higher boosts the ability of the autofocus system to collect,analyze,and act upon information. The D2-series has exceedingly rapid mirror action,and that means that when shooting in HSC mode at approximately 8 frames per second, the autofocusing system has many more tries,as well as much more RAPIDLY-delivered information than when a very "slow" camera is used.Slow frame rates like 2.5 FPS versus fast frame rates of 4.5 to 5.0 frames per second, and then FPS rates in the 8 to 8.2 FPS range all equate to very "different" types of autofocusing systems. A D-SLR's AF system can not work when the mirror is "up"...information can be sent to the AF sensors only with the mirror down,in viewing position, and this is why a rapid per-second frame rate, as well as rapid mirror actuation times,both work in concert to help an AF system deliver more in-focus images. It's not the frame rate per se which is advantageous with an ultra-responsive camera, it is the rapidity and the frequency with which the AF system can "try" to get focus lock-ons. It's not the machine-gun we are after, but the ability to drive a long,wide-aperture lens to _precise_ focus,with split-second timing.The more times-per-second the AutoFocus System is evaluating,and acting upon target information, the BETTER the AF tends to be in fast-acquistion shooting,as well as in tracking targets.