Re: Quantify DOC Effects?

Chris Malcolm wrote:
Wilba wrote:
Chris Malcolm wrote:
Wilba wrote:
Chris Malcolm wrote:
Wilba wrote:
Chris Malcolm wrote:
Wilba wrote:

I wonder if there is a way to quantify the loss of resolution due
to the "disk of confusion" (DOC) in the object field (as in Harold
Merklinger's writing, e.g.
http://www.trenholm.org/hmmerk/TIAOOFe.pdf).

It's easy to quantify the _circle_ of confusion (COC) due to
focus error, since the circle appears at the sensor, but the DOC
is out there beyond the plane of focus. How can I mathematically
estimate its effect at the sensor?

Since Merklinger explains in great detail with lots of examples
how to do this in the document you refer to, you need to explain
what it is that you don't understand.

Sure.

A specific size of disc of confusion at a specific distance in the
world ends up on the sensor at a size proportional to the relative
distances from the centre of focus of sensor and disc.

I see the equations for determining the size of the disk, but not for
relating that to the size of an effect on the sensor. That's my
question - how do I calculate the size of a DOC effect on the
sensor?

The same way as calculating what size on the sensor anything you
photograph ends up as.

Right, that's precisely the first part of my question.

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.


.

Relevant Pages

  • Re: Quantify DOC Effects?
    ... "disk of confusion" in the object field (as in Harold Merklinger's ... It's easy to quantify the _circle_ of confusion due to focus error, ... since the circle appears at the sensor, but the DOC is out there beyond ...
    (rec.photo.digital.slr-systems)
  • Re: Quantify DOC Effects?
    ... to the "disk of confusion" in the object field (as in Harold ... focus error, since the circle appears at the sensor, but the DOC ... I'm not sure I'm remembering correctly but it was something to do with limits of resolving point sources, however if you are looking at linear detail, that limit can be exceeded. ...
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  • Re: Quantify DOC Effects?
    ... to the "disk of confusion" in the object field (as in Harold ... It's easy to quantify the _circle_ of confusion (COC) due to focus ... error, since the circle appears at the sensor, but the DOC is out ... Of course something smaller than the amount of blurring in your image ...
    (rec.photo.digital.slr-systems)
  • Re: Quantify DOC Effects?
    ... to the "disk of confusion" in the object field (as in Harold ... It's easy to quantify the _circle_ of confusion due to focus ... error, since the circle appears at the sensor, but the DOC is out ...
    (rec.photo.digital.slr-systems)