Rockwell's writeup on this particular issue actually isn't half bad. I landed on it many years ago when I got my mamiya 6, and found it useful. As I recall, his writeup is quite similar to a Popular Photography article that you can look up. So... try not to dismiss Rockwell's writeup on this just because he comes across as a complete ass on some other things; he probably can't help it

Quote Originally Posted by Michael R 1974 View Post
What I'm never sure about is whether to favour a smaller CoC with less depth of field or a larger CoC with more depth of field. Which will result in the higher perceived sharpness (all other factors remaining equal)?
The answer will depend on many things- not only pertaining to shooting but also to printing. E.g. the CoC becomes especially important at large print enlargement factors.

To me, it's important to remember something really fundamental about perception: we seldom miss what isn't there. If you have minor losses of fine detail here and there in a composition, in favour of more consistent focus throughout, I think you will find that the result is perceived favourably. But if you have regions of sharp detail near regions of blur, you will really notice that very quickly. So OOF transitions are an important thing. Think about a superfast lens in 35mm format- you can get disturbing bokeh lines where you least want them, if you're not careful.

But what you want of course depends on your composition and your intentions.

What I just wrote may sound vague so I will give a concrete example. Suppose you are taking a headshot of your dear uncle Bertie. He's got a pleasant, friendly face but (God bless 'im) he also has quite a lot of nose hair. Anyway, he won't be around much longer, so you want to take a nicely detailed shot for future generations to enjoy. You considered some petzvalish work with eyes in sharp focus and everything else creamy, but let's suppose you really want good detail throughout. Do you (a) give more value to critical sharpness and go for say f/8; or do you (b) go for consistent level of detail and go for f/11?

The answer, of course, is (c)... you do both, and you take multiples, because this is a valuable shot and you want to get it just right

The point is that you can debate this and come to many different but reasonable conclusions. And you can easily make a mistake (I think) of putting that plane of superduper sharpness right on the nose hair, and then what? At some almost subliminal level, the viewer will see that. Wouldn't you rather have consistent focus throughout?

I can't answer for you, you have to decide for yourself, maybe the nose hair is such a special thing about uncle Bertie...

It all depends on your subject and your intentions.

So I'd say the bottom line is not to forget that the familiar definition of CoC is based in perception. If you really want to get the largest net amount of detail, the answer won't necessarily be appealing.... it depends on your artistic intentions. And the fact that we photographers concern ourselves with perceptual issues is what makes us artists. If we just followed some formula for maximum detail then, well...