Not interested in your semantic discussions Ray. The point is that at f/16 the D800 cannot reach its maximum effective resolution, and that means you cannot enjoy its full 36Mpx because of diffraction (among other possible factors).
Then you will likely be more confused than you otherwise would be, Guillermo. Semantic issues are to help clarify concepts and help us say exactly what we mean. This thread seems to be full of confusion about the significance of driffaction on cameras which have a high pixel-count such as the D800. I see this confusion resulting, in part, from the sloppy concept that a camera's sensor can be diffraction limited. It can't.
The sensor is there to record whatever the lens throws at it.
The point is that at f/16 the D800 cannot reach its maximum effective resolution, and that means you cannot enjoy its full 36Mpx because of diffraction (among other possible factors)
simply reinforces the confusion. The facts are, the D800 cannot
reach its maximum resolution at any aperture
, whether F16, F8 or F5.6, unless you think we have reached the stage of producing the perfect lens. People sometimes spend thousands of additional dollars to get a lens which is noticeably sharper, at its sharpest aperture, than another cheaper lens of the same focal length. Such additional sharpness from the more expensive lens can be seen when the image is recorded on sensors with a much lower pixel-count than the D800 has.
With any camera, whatever its pixel count, there is a trade-off in resolution at the plane of focus, when attempting to increase the DoF of the scene by using a narrower aperture than the aperture at which a particular lens is sharpest. That sharpest aperture is usually around F4 to F5.6, but can range from F2.8 to F11, depending on the quality of the lens.
Those who are a bit obsessed with resolution, as I am, and many others on this forum it would seem, naturally try to avoid using a narrower aperture than is necessary to achieve the desired DoF because we all know that stopping down reduces resolution at the plane of focus, whatever the camera we are using and however slight such loss may be.
The high pixel-count of the D800 doesn't change that broad principle. However, it is useful to know, and also comforting for those who have moved up to the D800 from a camera with fewer pixels, such as the D3X, that such lucky owners of a D800 can now use F16 with their D800 and expect to get at least
the same resolution at the plane of focus that they would have got using F11 with the D3X, or other equivalent camera, but also get the advantge of that increase in DoF that F16 provides.
I only believe in charts and graphs that can be confirmed with real-world testing. When DXOMark make a claim that camera A has, for example, 2EV more dynamic range than camera B, I'll test that for myself, if possible, if I own the cameras in question, or can at least get access to them without too much trouble. Whenever I've done this (the Canon 5D versus the Nikon D3, the Canon 50D versus the Nikon D7000, the Nikon D700 versus the D7000 etc), I've always found that the DXOMark results very closely match mine, with respect to DR differences.
My advice to some of you guys is, instead of waffling on, ad nauseum, about imaginary concerns, go out and take the shots for comparison purposes, using your best technique. Or stay in and photograph a newspaper taped to the wall. The comparative legibility of fine text is always a very meaningful result regards image resolution.