Chromatic Aberration or just Aberration?

[MacGee]

Up till recently I'd only ever seen CA a couple of times, once through a pair of Nikon HG L (purple-fringed street sign) and once through a borrowed mid-range Japanese roof (coots with a triangular red patch on their faces). I've mostly used 8x32 Opticron SR.GA porros, which never show CA under any circumstances.

However, I'm thinking of getting some Leica/Zeiss/Swarovskis and last week I was trying out an Ultavid 8x42. It was great and I marginally preferred it to the 8.5x42 Swarovski EL I was also trying, but there was one problem. I was looking at some whooper swans, with their yellow beaks bright in the sun and the beak shapes seemed to be distorted. I remarked to the saleslady that they looked like flamingo beaks. It reminded me of the distortion I get when looking at an LED in the dark without glasses on, but I looked with and without glasses and it was just the same.

I don't really think this is CA, but if it's something else, is it an artefact of the binoculars, or my eyes, or a common phenomenon that I've previously not noticed? Do other people see similar things?

Michael.

[ThoLa]

Up till recently I'd only ever seen CA a couple of times, once through a pair of Nikon HG L (purple-fringed street sign) and once through a borrowed mid-range Japanese roof (coots with a triangular red patch on their faces). I've mostly used 8x32 Opticron SR.GA porros, which never show CA under any circumstances.

However, I'm thinking of getting some Leica/Zeiss/Swarovskis and last week I was trying out an Ultavid 8x42. It was great and I marginally preferred it to the 8.5x42 Swarovski EL I was also trying, but there was one problem. I was looking at some whooper swans, with their yellow beaks bright in the sun and the beak shapes seemed to be distorted. I remarked to the saleslady that they looked like flamingo beaks. It reminded me of the distortion I get when looking at an LED in the dark without glasses on, but I looked with and without glasses and it was just the same.

I don't really think this is CA, but if it's something else, is it an artefact of the binoculars, or my eyes, or a common phenomenon that I've previously not noticed? Do other people see similar things?

Michael.


Hello!

It's true. It was certainly not chromatic abberation but some sort of other abberation. All optical systems have them in various degrees. No engineer in the world has developed a lens without any such problems. They jump out of the physics.
Chromatic abberation is the colour-fringing you have described. The colour depends on in which way (for which wavelengths) and to which degree the optical system has been corrected.

The beak distorsion you describe could be due to distorsion (a physically distinct phenomenon), spherical abberation, field curvature (that some people mix up with distorsion), or astigmatism.

To make matters worse some of these abberations are reciprocal, i.e. if you push back one, another will be increased (and vice versa).

If it is in the binoculars or your eyes can only be determined by a ophthalmologist who examines and measures your eyes.


As far as distorsions are concerned, if you are sensitive to it (I happen to be) Zeiss is very good. There is a minimal degree of convex distorsion (bulging out).
Swarovski "bends is" the other way (concave distorsion). Things look slimmer in the middle.
The effect can easily be seen if you point the binoculars at a window-frame, for instance and watch out for how the straight lines on the sides look.

Maybe this helps?

Regards,
Thomas

[NWBirder]

Hello!

It's true. It was certainly not chromatic abberation but some sort of other abberations. All optical systems have them to various degrees. No engineer in the world has developed a lens without any such problems. They jump out of the physics.
Chromatic abberation is the colour-fringing you have described. The colour depends on in which way (for which wavelengths) and to which degree the optical system has been corrected.

The beak distorsion you describe could be due to distorsion (a physically distinct phenomenon), spherical abberation, field curvature (that some people mix up with distorsion), or astigmatism.

To make matters worse some of these abberations are reciprocal, i.e. if you push back one, another will be increased (and vice versa).

If it is in the binoculars or your eyes can only be determined by a ophthalmologist you examines and measures your eyes.


As far as distorsions are concerned, if you are sensitive to it (I happen to be) Zeiss is very good. There is a minimal degree of convex distorsion (bulging out).
Swarovski "bends is" the other way (concave distorsion). Things look slimmer in the middle.
The effect can easily be seen if you point the binoculars at a window-frame, for instance and watch out for how the straight lines on the sides look.

Maybe this helps?

Regards,
Thomas

Excellent post! Thank you

[ThoLa]

Excellent post! Thank you


Highly flattering indeed. Thank you!

If you are interested in the physical theory of aberrations, I can send a PDF of an in-depth treatment of the subject matter.

Cheers,
Thomas

[MacGee]

If you are interested in the physical theory of aberrations, I can send a PDF of an in-depth treatment of the subject matter.
Thomas, I'd be grateful if you could PM me that document.

Michael.

[ThoLa]

Thomas, I'd be grateful if you could PM me that document.

Michael.



It will be no problem if you drop me a line to my mail box

tlazar 'at' web.de

I don't know how to make an attachment here, and whether they would be limited in size, ....


Best regards, Thomas

[MacGee]

It will be no problem if you drop me a line to my mail box
I've now got the PDF. Thanks, Thomas.

Michael.