Circle of confusion general question

[Troy Ammons]

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.

 

[Dan Fromm]

Huh?

 

[rbarker]

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.

 

[rbarker]

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.

For clarity, let me add that the DOF scale on 35mm and MF lenses assume a certain CoC size for that format. Some DOF calculators allow you to adjust the CoC size to suit your own tastes.

 

[JBrunner]

For me, the circle of confusion is usually around the camera

 

[Ole]

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...

 

[Dan Fromm]

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.

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.

 

[Troy Ammons]

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...

Ah that might be part of it. I have noticed that Sigma lenses to focus shift.

Thanks for the help and for the constructive comment.

 

[Ole]

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.

 

[Troy Ammons]

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.

If you dont have something constructive to say, why even bother.

 

[Troy Ammons]

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.

Thanks

 

[df cardwell]

Everyone who uses 'depth of field' calculations, or uses the numbers on a lens, must adjust the numbers to give results they need. In other words, the value of C is assumed to be determined by the user.

In the early '50s, for instance, manufacturers inscribed lens scales for a small enlargement ( and a correspondingly generous C ). Today, the C is different, and the lenses should be inscribed differently.

In any case, Depth of Field is hardly an absolute, but an approximation. You have to work out what you like, or need, and go from there. You must determine C.

.