I use single-point AF with AF-S for portrait work (think strobism), but have had difficulty.
Ultimately, I have to switch to manual focus in studio situations, but never had to with the D2X or D200.
>Good low-light AF performance may be near-useless if the >sensor cannot read the photons well enough (ISO performance), >and in that regard I'd say the D600 should run circles around >the older cameras mentioned. > >That said, I do recognize the need for low-light AF, without >the annoying assist light, sometimes even for speedlight work >(think strobism). > >I have found the D600 to focus accurately in every instance I >needed it to, with no complaints. For the record, I use >back-button, AF-C, most often on 9-point dynamic, center >point, focus and recompose.