>So, if AF-A always starts in AF-S, what happens to the area >mode if i have selected dynamic area AF? Is dynamic area >(where the camera considers info from the focus points >surrounding the selected focus point) disabled? Or does the >camera get confused?
When using AF-A, if the camera switches to AF-C mode, then the Area-AF mode will come into play and the selected mode should be used.
With Dynamic area-AF, the camera will determine the point of focus using the selected focus point only. Once a focus indicator is achieved, the camera will track your subject and adjust focus (in AF-C or AF-A in AF-C mode.) If your subject were to momentarily move away from the selected focus point, and the camera recognizes this, then the camera will use the surrounding focus point to pickup your subject and maintain focus. The purpose of this function is to prevent the AF system from focusing on the background, just because your subject got away from you momentarily.
ViewNX will indicate the active focus point if you happen to take the picture while your subject was under one of the surrounding focus points.
Note that this is not tracking. Exposure is still based on the primary focus point (your selected focus point.) The idea is to keep you from losing your focus while you get the subject back under the correct focus point.
I hear that the camera loses the subject more often when 21 and 39 points are selected...probably because there's a lot more processing going on with all those points. In any case, 9-point seems the most popular.
> Is it better to simply select AF-Area >mode = single point, when using the SB-600?
It doesn't make a difference. When the camera is in AF-S mode (either by having AF-S selected or the AF-S mode of AF-A) then all the Area-AF modes act like Single Point. So there's no need to switch.
Single point is useful with AF-C when you DO want the AF to adjust immediately to a new subject. This is useful when "hunting" through the viewfinder.