Re: Quantify DOC Effects?

Wilba <usenet@xxxxxxxxxxxxxxxxxxx> wrote:
Chris Malcolm wrote:
Wilba wrote:
Chris Malcolm wrote:
Wilba wrote:
Chris Malcolm wrote:

For disks of confusion that are much further away from the camera
than the focal length of the lens you divide the size of the disk by
the
distance from camera and multiply by the focal length. That gives
you the size of the disk on the sensor.

Does that relationship hold for objects significantly beyond the plane
of focus?

Expand those by adding a fringe of width the radius of the CoC to
account for their blurring.

Excellent, thanks. That agrees with what I get working from first
principles - the image on the sensor of the DOC is twice the size of the
COC (for distant subjects).

The second part of my questions is, how does that affect the appearance
of things in the image? Merklinger says that objects smaller than the DOC
won't be adequately resolved ... can we say more about how that works?
Has this been written about by others?

Of course something smaller than the amount of blurring in your image
won't be adequately resolved! What more needs to be said about that?

You're very literal minded, aren't you? :- )

Let me put it another way. Saying, "Of course something smaller than the
amount of blurring in your image won't be adequately resolved!", is
perfectly valid. In this context it depends on the premise that the DOC
defines an area in a plane beyond the plane of focus that _is_ "blurred". So
far I only have Merklinger's word for it (and of course, his evidence, which
I trust and could replicate for myself if I didn't).

I'm interested if anyone else has theoretically validated Merklinger's
concept of the DOC in the object field. For instance, Igor Yefremov
(http://www.hobbymaker.narod.ru/English/Articles/sharpness_eng.htm) has a
good go at comparing focal sharpness and object resolution, but doesn't
explore the validity of the DOC concept itself.

That brings in subjective things like being able to recognise
things. I'm disinclined to pursue mathematical analyses which try to
pursue exact quantification of that because it's affected a lot by
training and experience. The expert eye, especially if long trained
from childhood in looking for certain very specific kinds of important
detail, can do surprisingly much better at making sense of poorly
resolved detail than the untrained eye. We don't just see with our
eyes. A very large proportion of our brains is devoted to analysing
visual data from the eyes, and the human brain is a very sophisticated
visual processor.

Finding numbers which can roughly quantify such things is certainly
useful, and is very helpful as a way of ranking images for general
clarity and detail when developing image processing algorithms. But
I'm sceptical about attempts to develop closer relationships between
anything as simple as a number and the much more complex issues
involved in recognition in conditions of poorly resolved detail.

That's my excuse for not pursuing such ideas of Merklinger's to the
depth that you're clearly interested in. It's an interestingly
different approach however, and thanks for drawing it to my attention.
Do you expect to get anything of photographic interest from finding
answers to your questions?

--
Chris Malcolm



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