Effects of Lens Element Aberrations on a Fully Corrected Lens Image

[Mustafa Umut]

Leitz Summicron 50 is one of the extremelly well corrected lens in the world. Legend says about this lenses internal elements and their spherical aberrations was responsible of lot of beatiful effects on image.

For highly corrected lens image , does high internal aberration really effects the image or is it a legend ?

Thank you,

Mustafa Umut Sarac
Istanbul

 

[Drakkith]

Forgive me, I partially completed an optics degree but I don't think I ever got far enough to learn about 'internal' aberrations. What are those?

Leitz Summicron 50 is one of the extremelly well corrected lens in the world. Legend says about this lenses internal elements and their spherical aberrations was responsible of lot of beatiful effects on image.

If the lens was extremely well corrected, then I presume it has negligible spherical aberration, which wouldn't have any effect on the image other than reducing image blur.

 

[Mustafa Umut]

Drakkith, Thank you very much for your answer.

There are two things.

First , glass lens elements
And second , completed camera lens made up with these above glass lens elements.

Two ways to design first ,each glass lens elements.

A - Fully correct each of glass lens element
B - Allow some aberrations for glass elements - first- and than correct everything to second completed lens .

Why Leitz lens designer Mandler used extremelly high spherical aberration for the two lens glass elements , one is in front of aperture , second in behind of aperture.

What are their effects to image. COMPLETED camera lens was extremelly lowest aberrations , even no aberration.

 

[Drakkith]

Okay, so internal aberrations are just the aberrations from a single element, or from the combination of some of the elements that makes of the optical system.

Two ways to design first ,each glass lens elements.

A - Fully correct each of glass lens element

This isn't possible. No single element can be completely corrected for all possible aberrations. Only the combination of multiple elements of different shapes and different materials can correct for all aberrations.

What are their effects to image. COMPLETED camera lens was extremelly lowest aberrations , even no aberration.

There are many, many different ways to design a well-corrected lens, so it's difficult to say that high internal aberrations result in low overall aberrations. Because it's not strictly true. It all depends on the exact number, shape, size, composition, and placement of the different elements. All that can really be said is that the lens was designed to be extremely well corrected and the designers used many different techniques to do this, one of which was using elements with high individual spherical aberration that was corrected for once the elements were put together into a compound lens.

 

[Mustafa Umut]

Drakkith , Thank you very much for your answer.

Do internal spherical aberration have a targeted image quality ? Does spherical internal aberration effect the image or all goes finally corrected for compound lens and have no effect on image quality ? We talk about leitz summicron r 50mm

 

[Drakkith]

Do internal spherical aberration have a targeted image quality ?

Only in the sense that you have an overall 'acceptable limit' that you choose when you first start designing the lens, and you have to choose how much spherical aberration each element has so that the final result is less than your acceptable limit.

Does spherical internal aberration effect the image or all goes finally corrected for compound lens and have no effect on image quality ?

The spherical aberration of one element can be corrected by another element with opposite spherical aberration, or by a combination of different amounts of spherical aberration from multiple elements. This is true in general for other aberrations as well.

We talk about leitz summicron r 50mm

It's true regardless of the exact optical system. These are general properties and techniques of optical system design.

 

[sophiecentaur]

Summary: Internal Aberations and Image Formation of Fully Corrected Lens

For highly corrected lens image , does high internal aberration really effects the image or is it a legend ?

It isn't clear what your question is about. You seem to be suggesting that it may be better to start with a first element that is not as good as possible and to use other elements, also with only 'fair' performance to correct the aberration of the first one. You need to consider the Chromatic Aberration as well - which can only be corrected by using multiple elements, afaik.
There is an analogy with RF band pass filters which can have extra group delay correcting networks added to the frequency selecting stage. In that sort of design, achieving an overall good band pass characteristic with good group delay performance can involve an imperfect band pass stage in order to allow a good group delay correcting stage. The overall band pass characteristic will be good.
PS what is your overall level of understanding of lens design?

 

[Drakkith]

You seem to be suggesting that it may be better to start with a first element that is not as good as possible and to use other elements, also with only 'fair' performance to correct the aberration of the first one.

That's actually a valid design method since the 'best' optical elements are typically very expensive and made out of 'exotic' materials and in shapes that are difficult to fabricate. You can still achieve perfectly acceptable results using relatively inexpensive materials and shapes for the elements.

 

[Mustafa Umut]

Sophiecentaur,

I think delay correcting relates to transfer function ?

Let me try to explain why I asked my first question,

Legend says high spherical aberrations at some elements of summicron - its highly corrected lens at final - makes some beatiful images at the photography.

I think Sophiecentaur , you accept this , I think you relate above errors in design to delay correcting and finally to transfer function where transfer function dictates the frequency and time relation completely.

Lets talk about high spherical aberration and other aberrations.

Do they act to transfer function differently or the same ?

How can I learn which aberration how effect the transfer function ?

 

[sophiecentaur]

That's actually a valid design method since the 'best' optical elements are typically very expensive and made out of 'exotic' materials and in shapes that are difficult to fabricate. You can still achieve perfectly acceptable results using relatively inexpensive materials and shapes for the elements.

That's introducing a new variable, though. I thought we were assuming a given glass quality. "Perfectly acceptable" is not a well defined description, I think. Leitz lenses will have been made to a spec that's somewhat higher than acceptable and material costs could be anything. You're dead right about the situation with semi-pro lenses though. I just though about wall building in which a good 'bricky' can use rough bricks but still keep the wall as level as needed. Otoh, I can make a sloping wall out of even the best bricks available.
I think the OP needs to be considering CA as well as SA for an explanation of what's done in lens design.

 

[Andy Resnick]

Legend says high spherical aberrations at some elements of summicron - its highly corrected lens at final - makes some beatiful images at the photography.

Lets talk about high spherical aberration and other aberrations.

Do they act to transfer function differently or the same ?

How can I learn which aberration how effect the transfer function ?

I found this well-written discussion about Leica photography lenses:

https://www.overgaard.dk/pdf/Leica-M-Lenses-Their-Soul-and-Secrets_en.pdf
In it is a lot of detailed description about specific design trade-offs for nearly every single lens Leica makes, and I recommend that you carefully read as much of this as you can.

As has been pointed out, the whole concept of aberration balancing is to combine contributions from individual elements to result in much lower lens aberrations. But, some lenses allow user-control of lens aberration (Nikon calls it 'defocus control'), specifically control of spherical aberration:

https://kenrockwell.com/nikon/images1/135mm-dc/patent-5841590.pdf?vid=USPAT5841590https://photo.stackexchange.com/questions/7044/how-do-soft-focus-or-defocus-control-rings-work
The PSF images in the stackexchange site are particularly helpful to understand your specific question about control of spherical aberration.