[Oakland Rob]

One thing Tony Northrup did say - which I found surprising, and disagree with - is, why FF from Pentax now? His argument was that with the right glass (read: *fast* equivalent-focal-length glass) on APS-C, you can re-create anything on FF. The reason I disagree is, the lenses would have to be large, heavy and much more expensive. Just imagine... 18-50mm f/1.8... 50-135mm f/1.8... I don't think my pockets are that deep, and the K3 / K3II would be dwarfed by such glass!!!

He kinda expands on this line of reasoning better in other videos. Essentially he compares the best made for APS-C fast lenses against some very good FF stuff, each on their respective bodies, both visually and using DxOMark data. And prices. And the result is that you get just as sharp pictures. I don't think he'd go so far as to say that in every case; obviously an exceptional lens on the FF would best the APS-C in resolution, but certainly not value-wise.

And he points out that sharpness isn't everything. Because as you go to a smaller sensor you also go to less DOF per focal length/aperture the background may not be as nice, even with super sharp lenses. He had some good examples of that in one of the other videos, plus some stuff on the dynamic range. Probably the fact he does wildlife shots and outdoors stuff as opposed to being a portrait photographer influences that.

And yeah, that Sigma art lens is heavy. And big. Big apertures are big by definition. But he compares a Nikon FF with a Nikon APS-C using that Sigma and another very nice FF lens, and you come out way ahead price wise on the APS-C. Not to mention another factor, that the Sigma is one of those "stack of primes" lenses so you get as good quality as maybe three decent primes for the price. But it's pretty hard to fast, light, and cheap. Once you use PS, if you do, the failings of lenses becomes a bit more apparent, unfortunately....