Re: Quantify DOC Effects?

Wilba <usenet@xxxxxxxxxxxxxxxxxxx> 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?

If what you're interested in is what the effects of various amounts of
blurring are on the appearance of things, then just simulate it using
a blurring operator in one of the many image editors which have
blurring operators. Or for CoC problems look at the world through
various strengths of reading glasses, and for DoC problems look
through binoculars at the unfocussed bits of the view.

--
Chris Malcolm



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Relevant Pages

  • Re: Quantify DOC Effects?
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