It’s a long-standing “rule of thumb” that f/8 is the sharpest aperture. It’s important to remember, though, that there is exactly one distance from the focal plane that has “perfect sharpness” while distances near are simply “acceptably sharp”. There is no sharp boundary (if you’ll excuse the pun) between that is in focus and what is not but rather a gradual shift from one to the other.
With the D800′s exceptional resolution, however, the definition of “near” becomes rather small. The above image is a hedge in bloom and that was approximately 2 meters (1 meter is equal enough to 1 yard for this comparison) away at its closest and 6 meters away at its farthest. It was shot at f/8 at 68mm and is a full-resolution crop from the center of the image. As you can see from the full-size image, even at f/8, the range of “acceptable sharpness” covered a depth of probably about a ¼ meter (call it 1 foot). Down-scaling by a factor of X will of course increase that range by a factor of X.