Chromatic Aberration: Calculating the Axial Color of a Lens
Ғылым және технология
This info-packed video will explain the theory of axial chromatic aberration and how to compute it using paraxial ray tracing. Two examples are presented. The chromatic aberration of a singlet lens is computed and the calculation is benchmarked against Zemax. The chromatic aberration of an achromatic doublet is computed and the calculation is benchmarked against the expectation of zero aberration. The doublet lenses will be modified, and the YNU spreadsheet is then used to find new radii that give zero chromatic aberration.
A paper predesign of a cemented achromatic doublet is demonstrated.
Dispersion of real glass is reviewed. Abbe number is discussed.
The primary color spectrum and secondary color spectrum that arise during achromatization are briefly explained.
Textbook references are to Joseph M. Geary, Introduction to Lens Design: with Practical Zemax® Examples, (Willmann-Bell. Inc., 2015). The American Astronomical Society has assumed ownership of Willmann-Bell inventory.
Introduction to the paraxial ray trace equations • Paraxial Ray Trace Equ...
Spherical aberration theory • Video
Here is an excellent 5-minute description of chromatic aberration: • What is Chromatic Aber... Pay attention to how chr. ab. is minimized in color film, but not in digital detectors. Fascinating explanation of things.
A very thorough guide for YNU spreadsheeting, and an important resource to help you work through your own spreadsheet, is the "Pencil of Rays" website www.pencilofrays.com/lens-des...
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Пікірлер: 7
Hi Stephen, I was going through the derivation around 6:15. I think the exiting ray angle u'=tan(y/f)= (y/f) for paraxial approximation. That might be a typo from the slide. Then the expression for LAXC where you have 1/(u')^2 makes sense. Cheers. Its a great reference for a rough estimation of the achromat design. Thanks.
@stephenremillard1
Жыл бұрын
You are correct. A typo on the slide. Clearly the tangent is y/f. Thanks for noticing it.
Thank you sir.
Hi Stephen, First really thank you for putting all the things together. Following your tutorial really makes me understand the thought process step by step. I just have one question wants to verify. For the Achromat YNU spreadsheet, the CLA you quote -0.00047 mm. I recall the CLA = LAXC*(u')^2 where the u' is -0.3125 in this case. My calculation gives -0.000104 mm for the CLA. Maybe I missed some thing here? Thank you.
@stephenremillard1
Жыл бұрын
Yadong, You are correct. It is -0.000104 mm. This question is concerning cell C27 in the spreadsheet beginning at 19:25. I checked the spreadsheet that I used in the video, which miraculously I still have. The formula for CLA should be "=C26*(G21*G21)" . I had "=C26*(E21*E21)". Probably when I added the third and forth columns I didn't update that cell. Thank you for bringing this up.
@stephenremillard1
Жыл бұрын
By the way, this cell wasn't used for any purpose. It was just there. So, fortunately there are no "domino-effect" errors to be concerned about.
What if the object is placed in some distance from the lens (not infinity). Will it influence the axial shift? And is there a way to calculate this dependency knowing the object angle?