[chrismiller]

point iii) has a few assumption that doesn't hold out - its like saying my vw golf with 100hp can do 140mph so a Ferrari with 500hp will be able to do 700mph.

 

Interestingly the pixel density of old tests done on an 10Mpix APC sensor are similar to the density on the 24Mpix full frame sensor (24/1.5/1.5 = 10.6), so if you were feeling brave and ready to ignore lots of factors such as photodiode geometry, sensor glass thickness & and other unknowns and dodge the wrath of the rest of photozone you could maybe do a comparison of center values (ignore borders as the APC edge is a different part of the lens to FF). The 17-35 center number is 2200, so scaling for a large sensor gives 3300lp/ph. So way worst than the 20mm 1.8 at 3900lp/ph, and the center is usually the good bit. Frame corners are always worse.

 

I think the adage of marry your lenses and date the bodies rings true here. If the Tamron is resolving 3300lp/ph over the whole of the D810 sensor (unlikely) you are only getting 14.5Mpix of information, hardly worth having a 36MPix body I would say.