Caution ! Dynamic AF versus single point AF... !

That's how the D800 behaves in my experience. The camera makes a decision of its own about the part of the image on which to focus only in the auto area mode. Otherwise it uses the selected AF point to start the focus operation when the shutter is half pushed regardless of AFS AFC and the various 9/21 etc 3d settings.

However I do agree with Peter in the sense that in AF-C 9/21/51 the camera has the freedom to switch from one AF point to the other as soon as the initial shutter half press is one, and sometimes it does it right away after the very first instant of acquisition. So one cannot be sure which focus point will ultimately be used in these modes.

I don't feel that the principles have changed between the D300 and D800. It's just a machine with a relatively simple algorithm tracking a feature it can detect. Depending on the type of scene the user may have to limit the camera freedom in its selection of surrounding AF points to less than all the 51 AF points. I think the right choice depends not just on the scene but on how easy it is to keep the subject under the focus point (or how skilled one is at it). So to me the fundamentals are the same. One thing though: the 51 points / 3D tracking works quite a bit better with the D800 than with the D300 in my hands.

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Thierry - posted as regular forum member