Hi, I guess I've been AWOL from this thread, but in my defense I
don't have anything directly useful to add. Although I've worked
in photography my entire adult life, I've never had occasion nor
need to study acutance. Not that it wouldn't have been fun, just
no way to justify it from a business standpoint.  Regarding
information from Michael Kriss, he authored the chapter on image
structure in Theory of the Photographic Process, 4th edition
(James). If you can find a copy, there are about 40 pages of
dense reading. I don't see it as directly practical info, mostly
it applies fairly advanced mathematical treatments to things
such as spread funtions. If you're familiar with the convolution
theorem and Fourier analysis, then you might breeze right
through this, but it's mostly beyond me.