I think Howard is pointing out that DOF is dependant on the circle of confusion (COC) which the larger you print the less in focus things appear in front of and behind the chosen focus distance. In other words, in a small print your COC is adequate to make things appear to be in focus. As you go larger and larger this is not so. Setting a lens to the hyperfocal distance does not perfectly focus everything. Only the selected focus distance is perfectly in focus. The rest falls off based on the COC which changes with the size of the sensor and print.
http://en.wikipedia.org/wiki/Circle_of_confusion
http://en.wikipedia.org/wiki/Circle_of_confusion
May I ask what sort of work you do? Because a reasonable number of people have not yet made this point (which would, now I come to think about it, would appear self-evident) and that might imply that it is more of a problem for certain sorts of work? I would have thought that for landscapes where the foreground interest is, say, ten metres away and the background is generally half a mile or so, mid-range glass should work?
I'll tootle off to a DOF calculator and try it out!
T
I just did so, at
http://www.panavision.co.nz/main/kbase/reference/calcFOVform.asp
coincidentally for a P45+ the first aperture which gives focus from 10 metres to infinity with an 80mm lens is F16... at which aperture you're in focus from 5.02 metres onwards