Originally posted by Marc Sabatella To put it as clearly as I can: there is *no doubt whatsoever* that a shot at 135mm and f/2.8 on APS-C is "equivalent" to one at 200mm and f/4 on FF - meaning same DOF and noise for the same shutter speed. Nothing crucial is being "missed" by this statement. But leaping from this to saying there is no benefit to FF is indeed missing something.
Anybody with time on his hands who goes back about, oh, 15 pages in this thread will find a number of posts from me in which I demonstrated, for a while, my inability to understand plain English. I had trouble with the equivalency idea because (a) I had not yet read the article on equivalency, which turned out to be quite and eye-opener, and (b) I was in the grip of the self-evident belief that full-frame cameras magically deliver pictures with lower noise, always and everywhere. Ignorant and wrong, I was, but ignorance and error are a potent combination. I'm still grateful to Marc and others for hanging in there while I banged my head against the wall until clarity arrived.
And it did. Eventually I came 'round and understood Marc (and others) to be saying just what Marc says here. He went on explicitly to explain one advantage of FF cameras by pointing out that there are plenty of f/2.8 lenses for FF but not very many equivalent lenses (f/2 and the appropriate focal length) for APS-C, so there is a real-world advantage to FF in that the available lenses make things possible that the lack of lenses makes impossible on APS-C. I think Marc or somebody also said that there might be other engineering advantages of FF cameras, arising simply from engineering tweaks provided in more expensive bodies.
It's been a great thread and I'm grateful for it.
Will