Circle of confusion general question

rbarker said:

While all lenses will have a CoC, they aren't really designed around that because CoC is really an externally applied metric, based on the enlargement factor of the print, viewing distance, etc. Thus, if you use a smaller CoC for a given format (negative size) to accommodate a greater enlargement factor (or, fussier viewers), DOF (which is really just an optical illusion based on the CoC) will be correspondingly reduced.

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Troy Ammons said:

Does a lens designed to higher standards according to the coc formula, have less general dof at the image plane than a lens with laxer standards.

That would assume the laxer standard lens would be slightly softer.

Anybody have a formula for the dof at the image plane according to the lens coc.

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Ole said:

Some lenses, designed with some residual spherical aberration, can display slightly more DoF (both -Field and -Focus). Said in another way they can be difficult to focus and may exhibit focus shift when stopping down. If you know exactly what you're doing and exactly what it's supposed to look like, and why, it's not difficult to focus accurately at full aperture and retain focus on stopping down.
That's the downside of Depth of Focus...

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Dan Fromm said:

Troy, when you asked this question on photo.net you were a little more forthcoming.

What you really wanted to know was why you couldn't get a sharp image from lenses in C/Y mount when you stuck them in the front of a Sigma SD9 body. The answer has nothing to do with circles of confusion or any of the other words you slung around. The two mounts' registers are different.

Ask what you want to know as directly as possible, don't play stupid guessing games.

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Ole said:

There would be NO Sigma lenses in that category. We're talking Imagon, converted Dagors, Landcape meniscus, Heliar, Verito and the like here.

Ask a too general question, get a too general answer.

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