Originally posted by Pål Jensen Of course APS has an advantage over D800. If you remove that advantage the D800 is not an FF camera any longer and hence the comparison becomes meaningless.
No, APS has no "reach" advantage. You can
crop your FF any time (i.e., rarely) that you actually "need" additional "reach" beyond your longest focal length lens. The only possible "advantage" is one of pixel density and the D800 has essentially made that a non-issue. Even though yet more pixel density (i.e., 24 MP sensors) is available in APS-C at this point, it won't matter, because what is now available is more than necessary for quality images.
The comparison is not meaningless, it simply reveals that FF encompasses all of the image possibilities of APS-C via a simple crop, while APS-C
does not encompass all of the image possibilities of FF, since the same shot will be at less magnification (i.e., less telephoto compression, for example) given the same field of view, whether by using a shorter focal length or by changing distance to subject (which also changes perspective).
Originally posted by Pål Jensen You buy the D800 to get the FF advantage not to make it equal to an APS camera.
Of course. With the exception of the rare circumstance of finding that you need more reach than that of your longest lens, that's exactly what you have.