Go for a walk. Shoot selectively with autofocus in AF-S mode set to AF-S priority selection = Focus.
Accurate autofocus with fast lenses in particular cannot be assumed with any camera, not Nikon, not Canon, and as this page will show, not the D800.
AF fine focus adjust
Many DSLRs from Canon and Nikon now have an “AF fine focus adjust” feature that can provide some benefits in centering the focus to be highly accurate on average.
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