Re: Vignetting due to pupil aberration

On Apr 14, 11:43 am, Helpful person <rrl...@xxxxxxxxx> wrote:
On Apr 13, 10:16 pm, Philli...@xxxxxxxxx wrote:

Hi folks

So I have a basic lens design question. I'm not sure if I fully
understand the connection between pupil aberration and vignetting. If
I'm using Code V, negative vignetting factors means I don't actually
have any real vignetting and its due to pupil aberration. Is this
correct? I mean is it possible to have pupil aberration that leads to
positive vignetting factors.

Thanks for any help you can provide.

There are several types of pupil aberration.  Usually the most
important is spherical aberration which is equivalent to geometrical
distortion of the image.  (Think about what happens to the principal
rays.)

Inward coma of the pupil can theoretically be used to get more light
through the system.  However, I have never seen a practical
application of this.

Vignetting is caused by apertures in the lens system (not at the
pupil) that cut off some of the light.  It's similar to looking
slightly obliquely down a long tube.  Vignetting is often added to a
lens to improve the off axis imagery at the expens of illumination.

I usually do not use the vignetting factors, although it's years since
I used Code V.  I prefer to see the full pupil aberrations and add
vignetting if necessary as the design progresses.

I think that makes sense. Vignetting isn't caused by the stop itself.
Otherwise it wouldn't be called vignetting.

I'm working a lens design assignment that requires vignetting to
improve my resolution. We gotta change a Cooke Triplet into plastic
and use vignetting and aspheres to obtain the same performance with
the regular glass design at a depth of field from 750mm to Infinity.
Wish me luck.
.

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