Quote Originally Posted by Daniel Browning
So for macro, it's usually better to go with smaller pixels, because even when you are diffraction limited they offer improved detail, and that's very important, especially when cropping for magnification.

Daniel, do you mean that more pixels is better than fewer, or do you mean that, say, 15 million small pixels are better than 15 million larger pixels (ie, 15mp is better on a crop body than on full frame)? If you mean the former, I agree. If you mean the latter, I think I disagree. Even if you need a higher f/ number to get the same DOF on full frame (and thus have larger diffraction discs), the larger sensor exactly balances this, so you have the same amount of total resolution. As always, I hope you'll correct me if I'm wrong.


The reason I mention this is that if one is considering diffraction vs resolution in, say, a 5DII vs a 7D for macro work, I would give the nod to the 5DII because of its greater resolution (despite the larger pixels). Even though this is a tiny advantage, I think it would be a mistake to say the full frame with larger pixels is at a disadvantage due to diffraction.


Of course I'm only talking about diffraction here: there are other considerations back and forth (eg the 7D gives you more working distance on closeups because you need less magnification to reach the same framing, the 5DII will give you more dynamic range (I think) and better IQ from most lenses, 7D has leveling lines and better autofocus, 5D has a bigger viewfinder, etc etc)