4 ms·

I still haven't come across a summary I liked so I'll try: Refractive index of a material, typically ~1.5, is not a fixed single number for material. Rather it

I still haven't come across a summary I liked so I'll try: Refractive index of a material, typically ~1.5, is not a fixed single number for material. Rather it is wavelength dependent, because diffraction is of course quantum interference thing strengthening at new directions and canceling out elsewhere. Wavelength-index plot shows some sort of exponential or asymptotic, monotonically decreasing curve from UV towards IR. This means any convex lens always has a higher than intended magnification at blue, higher still at green, okay at red, and only technically right at Sodium vapor yellow, creating "aberrated(NOT after Ernst Abbe)" color-shifted image at its focal point. To counter this, convex and concave lenses built from different chemical compositions that show different rates of decreasing indices are used, such as Schott BK7 and F2, so that extra positive magnification for blue at first convex lens cancels out with extra negative power for blue at following concave lens, and so on. The chain of lenses can be continued to cancel out effects at as many additional wavelengths, as well as side effects and other types of imperfections, as desired. Significance of Fluorite or CaF2 crystals in this context is, this material shows a completely flat curve on that wavelength-refractive index plot, referred to as "abnormal dispersion". It naturally focuses all colors across visible spectrum to a same point, skipping over a lot of lens and lens canceling out. Challenge is scaling out camera-sized crystals of Calcium and Fluoride with optical clarity is hard, which Canon has been trying for a few decades.

gregschlom 3y ago
> aberrated(after Ernst Abbe) Are you saying the word aberration comes from Ernst Abbe's last name? Because it doesn't, it comes from latin. https://www.etymonline.com/word/aberration https://www.etymonline.com/word/aberration
- numpad0 3y ago
  My mistakes. I stand corrected.
kpozin 3y ago
> creating "aberrated(after Ernst Abbe)" color-shifted image at its focal point This is a clever bit of folk etymology [1], but aberrate is derived from the Latin verb aberro, meaning to wander or stray [2]. [1]: https://en.wikipedia.org/wiki/Folk_etymology https://en.wikipedia.org/wiki/Folk_etymology [2]: https://en.wiktionary.org/wiki/aberro#Latin https://en.wiktionary.org/wiki/aberro#Latin
- saalweachter 3y ago
  It would be interesting to know if the term was or wasn't related. I've been around enough brainstorming sessions to see people come up with sneaky ways to name things after themselves; someone named Abbe deciding to use "aberration" to describe the particular distortion of an image because it sounds like Abbe is totally plausible. On the other hand, if the term predated Abbe's work and the creation of the Abbe number, it's also possible Abbe decided to work on the problem -- or his mentor assigned him the topic -- because Abbe sounds like aberration. (It doesn't mean there is a connection, I'm just saying that just because the etymology of the word is independent doesn't mean the use of the word is also.)
  - dotancohen 3y ago
    I've seen clever ways of sneaking loved ones' names into projects as well. I'm a habitual offender. You might be interested in the series of inventions that led to the modern flush toilet. There are at least two funny names in that history, which may or may not be related to colloquialisms used when discussing toilet matters.
    - taneq 3y ago
      Prince John: Such an unusual name, "Latrine." How did your family come by it? Latrine: We changed it in the 9th century. Prince John: You mean you changed it TO "Latrine"? Latrine: Yeah. Used to be "????house."
      - spockz 3y ago
        FYI. This comes from Robin Hood: Men in Tights” by Mel Brooks.
  - eesmith 3y ago
    Here's an 1825 use of "chromatic aberration" in "An elementary treatise on optics" by Henry Coddington: https://archive.org/details/elementarytreati00codd/page/94/mode/2up?q=%22chromatic+aberration%22 https://archive.org/details/elementarytreati00codd/page/94/m... Ernst Abbe was born in 1840, says https://en.wikipedia.org/wiki/Ernst_Abbe https://en.wikipedia.org/wiki/Ernst_Abbe . There are many uses of chromatic aberration in archive.org which predate Abbe's research in optics. The Wikipedia adds "Already a professor in Jena, he was hired by Carl Zeiss to improve the manufacturing process of optical instruments, which back then was largely based on trial and error." which seems like it had nothing to do with his surname.
kragen 3y ago
some of this is correct 'naturally focuses all colors across visible spectrum to a same point' would be no dispersion, not 'abnormal dispersion'. abnormal dispersion (usually called anomalous dispersion) is when the refractive index increases with increasing wavelength, instead of decreasing as in normal dispersion https://en.wikipedia.org/wiki/Dispersion_(optics)#Material_dispersion_in_optics https://en.wikipedia.org/wiki/Dispersion_(optics)#Material_d... if you had a material with no dispersion you could just make a lens out of it and avoid chromatic aberration, but since you don't, you need to use the dispersions of different materials to cancel it out in the way you describe fluorite doesn't have anomalous dispersion in the visible spectrum, it just has low dispersion canon has evidently successfully been scaling out camera-sized crystals of calcium fluoride since the 01960s. other companies have too actually; https://en.wikipedia.org/wiki/Fluorite https://en.wikipedia.org/wiki/Fluorite says > In the laboratory, calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 µm to 9 µm) and exhibits an extremely low change in refractive index with wavelength. Furthermore, the material is attacked by few reagents. At wavelengths as short as 157 nm, a common wavelength used for semiconductor stepper manufacture for integrated circuit lithography, the refractive index of calcium fluoride shows some non-linearity at high power densities, which has inhibited its use for this purpose. In the early years of the 21st century, the stepper market for calcium fluoride collapsed, and many large manufacturing facilities have been closed. Canon and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid apochromatic design, and to reduce light dispersion. This use has largely been superseded by newer glasses and computer-aided design. As an infrared optical material, calcium fluoride is widely available and was sometimes known by the Eastman Kodak trademarked name "Irtran-3", although this designation is obsolete. sodium, fluorite, calcium, and fluoride are not brand names or other proper nouns and thus should not be capitalized in english as they are in german
- jjgreen 3y ago
  But English and German should :-)
  - kragen 3y ago
riperoni 3y ago
Yeah thank you, that summary is better than the article. The definition of refracitve index in the article is also just wrong, since it is simply not an angle. It can be calculated from incidence and refraction angles of the light beam - very different. See https://en.m.wikipedia.org/wiki/Snell%27s_law https://en.m.wikipedia.org/wiki/Snell%27s_law To add to your answer, the refractive index is not just wavelength dependent, but can also be depending on the polarization of light, leading to birefringence: https://en.m.wikipedia.org/wiki/Birefringence https://en.m.wikipedia.org/wiki/Birefringence
- Balgair 3y ago
  For HNers and CompSci people, optics is a notoriously difficult field and much more frustrating. If you break up the Nobel Prizes a bit differently, then the filed of Optics becomes the most dominant. So very many breakthroughs in science are because of some new optics method. Mostly in the bio/chem fields, it's about gaining a new form of 'contrast' (very broadly defined). People have spent decades trying to align some little crystal just the right way. Or they did it in their living room with cardboard in a weekend. It's a frustrating field. One fun thing to remember about lenses are that they aren't really light bending thingys, but more accurately a lens is a Fourier transformer. Of a sort. Again, optics s frustrating. One fun thing for the more matrix-ly minded are Mueller Matrices. Most modern optics SW is based on this calculus, though it goes a lot further nowadays. Also, most developments in optics are all about the little exceptions that Mueller matrices have. Still, a good little thing to read about, if interested: https://en.wikipedia.org/wiki/Mueller_calculus https://en.wikipedia.org/wiki/Mueller_calculus
  - kridsdale1 3y ago
    I have been way in to Nikon and Canon lenses as well as DSP for like 20 years now, and have a degree in EE and did a ton of quantum, and I never had the insight that a lens is a physical EM Fourier transformer. Cheers for that.
    - aj7 3y ago
      “A lens creates the spatial Fourier transform from the front focal plane to the rear focal plane.”
IshKebab 3y ago
Diffraction isn't a quantum effect. Classical waves diffract.
ricardobeat 3y ago
> Challenge is scaling out camera-sized crystals of Calcium and Fluoride with optical clarity is hard, which Canon has been trying for a few decades Not really an informative summary on that. They’ve been succeeding, not trying, for decades. The problem of growing the crystals was solved in the 60s and this is commonplace now. Fluorite is also used in Fuji lenses, and Nikon/Sony have their own special glass to deal with the same problems.
- ubercore 3y ago
  Yeah, according to the article, their first commercial lens with flourite was delivered in 1969.
  - throwaway81523 3y ago
    I thought there was at one time an issue with the fluorite elements in those huge many-kilobuck lenses absorbing moisture from the air and cracking or having other sorts of failures. Canon for a while stayed with fluorite while Nikon worked out ED glass that avoided the problem. I don't know if today's Canon L lenses use fluorite.
hammock 3y ago
Good explanation (assuming it’s accurate) thank you
dekhn 3y ago
Abbe was amazing. He worked with Zeiss and a couple other glass manufacturers to systematize optics. One of his greatest accomplishments, beyond levelling up glass quality, was developing an actual "theory of optics" which explained optical phenomena in terms of diffraction. He defined diffraction limited imaging, which meant that people were able to resolve details as fine as opticals can possibly allow (this has only recently been surpassed using Nobel-prize-winning technology). Abbe illumination, which is a way to set up your microscope's light paths to get optimal quality. He is also known for introducing the eight hour workday(!) and all sorts of employee/company innovations. My friend from grad school shows how to set up abbe illumination and talks/shows a bit about how to set up optical fourier transforms. https://www.youtube.com/watch?v=d8Tqoo0S6gc https://www.youtube.com/watch?v=d8Tqoo0S6gc If you want to draw a straight line of technology development that led to industrialization and an incredible increase in life quality, it goes right through Abbe (and Newton, Pasteur, Maudsley, and Rutherford). All of these people were absolute giants who saw far past the limitations of their day and continue to inspire new generations of geniuses who can take advantage of the amazing resources we have available today (thorlabs.com is a good example).

gregschlom 3y ago

> aberrated(after Ernst Abbe) Are you saying the word aberration comes from Ernst Abbe's last name? Because it doesn't, it comes from latin. https://www.etymonline.com/word/aberration https://www.etymonline.com/word/aberration

numpad0 3y ago
My mistakes. I stand corrected.

kpozin 3y ago

> creating "aberrated(after Ernst Abbe)" color-shifted image at its focal point This is a clever bit of folk etymology [1], but aberrate is derived from the Latin verb aberro, meaning to wander or stray [2]. [1]: https://en.wikipedia.org/wiki/Folk_etymology https://en.wikipedia.org/wiki/Folk_etymology [2]: https://en.wiktionary.org/wiki/aberro#Latin https://en.wiktionary.org/wiki/aberro#Latin

saalweachter 3y ago
It would be interesting to know if the term was or wasn't related. I've been around enough brainstorming sessions to see people come up with sneaky ways to name things after themselves; someone named Abbe deciding to use "aberration" to describe the particular distortion of an image because it sounds like Abbe is totally plausible. On the other hand, if the term predated Abbe's work and the creation of the Abbe number, it's also possible Abbe decided to work on the problem -- or his mentor assigned him the topic -- because Abbe sounds like aberration. (It doesn't mean there is a connection, I'm just saying that just because the etymology of the word is independent doesn't mean the use of the word is also.)
- dotancohen 3y ago
  I've seen clever ways of sneaking loved ones' names into projects as well. I'm a habitual offender. You might be interested in the series of inventions that led to the modern flush toilet. There are at least two funny names in that history, which may or may not be related to colloquialisms used when discussing toilet matters.
  - taneq 3y ago
    Prince John: Such an unusual name, "Latrine." How did your family come by it? Latrine: We changed it in the 9th century. Prince John: You mean you changed it TO "Latrine"? Latrine: Yeah. Used to be "????house."
    - spockz 3y ago
      FYI. This comes from Robin Hood: Men in Tights” by Mel Brooks.
- eesmith 3y ago
  Here's an 1825 use of "chromatic aberration" in "An elementary treatise on optics" by Henry Coddington: https://archive.org/details/elementarytreati00codd/page/94/mode/2up?q=%22chromatic+aberration%22 https://archive.org/details/elementarytreati00codd/page/94/m... Ernst Abbe was born in 1840, says https://en.wikipedia.org/wiki/Ernst_Abbe https://en.wikipedia.org/wiki/Ernst_Abbe . There are many uses of chromatic aberration in archive.org which predate Abbe's research in optics. The Wikipedia adds "Already a professor in Jena, he was hired by Carl Zeiss to improve the manufacturing process of optical instruments, which back then was largely based on trial and error." which seems like it had nothing to do with his surname.

kragen 3y ago

some of this is correct 'naturally focuses all colors across visible spectrum to a same point' would be no dispersion, not 'abnormal dispersion'. abnormal dispersion (usually called anomalous dispersion) is when the refractive index increases with increasing wavelength, instead of decreasing as in normal dispersion https://en.wikipedia.org/wiki/Dispersion_(optics)#Material_dispersion_in_optics https://en.wikipedia.org/wiki/Dispersion_(optics)#Material_d... if you had a material with no dispersion you could just make a lens out of it and avoid chromatic aberration, but since you don't, you need to use the dispersions of different materials to cancel it out in the way you describe fluorite doesn't have anomalous dispersion in the visible spectrum, it just has low dispersion canon has evidently successfully been scaling out camera-sized crystals of calcium fluoride since the 01960s. other companies have too actually; https://en.wikipedia.org/wiki/Fluorite https://en.wikipedia.org/wiki/Fluorite says > In the laboratory, calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 µm to 9 µm) and exhibits an extremely low change in refractive index with wavelength. Furthermore, the material is attacked by few reagents. At wavelengths as short as 157 nm, a common wavelength used for semiconductor stepper manufacture for integrated circuit lithography, the refractive index of calcium fluoride shows some non-linearity at high power densities, which has inhibited its use for this purpose. In the early years of the 21st century, the stepper market for calcium fluoride collapsed, and many large manufacturing facilities have been closed. Canon and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid apochromatic design, and to reduce light dispersion. This use has largely been superseded by newer glasses and computer-aided design. As an infrared optical material, calcium fluoride is widely available and was sometimes known by the Eastman Kodak trademarked name "Irtran-3", although this designation is obsolete. sodium, fluorite, calcium, and fluoride are not brand names or other proper nouns and thus should not be capitalized in english as they are in german

jjgreen 3y ago
But English and German should :-)
- kragen 3y ago

riperoni 3y ago

Yeah thank you, that summary is better than the article. The definition of refracitve index in the article is also just wrong, since it is simply not an angle. It can be calculated from incidence and refraction angles of the light beam - very different. See https://en.m.wikipedia.org/wiki/Snell%27s_law https://en.m.wikipedia.org/wiki/Snell%27s_law To add to your answer, the refractive index is not just wavelength dependent, but can also be depending on the polarization of light, leading to birefringence: https://en.m.wikipedia.org/wiki/Birefringence https://en.m.wikipedia.org/wiki/Birefringence

Balgair 3y ago
For HNers and CompSci people, optics is a notoriously difficult field and much more frustrating. If you break up the Nobel Prizes a bit differently, then the filed of Optics becomes the most dominant. So very many breakthroughs in science are because of some new optics method. Mostly in the bio/chem fields, it's about gaining a new form of 'contrast' (very broadly defined). People have spent decades trying to align some little crystal just the right way. Or they did it in their living room with cardboard in a weekend. It's a frustrating field. One fun thing to remember about lenses are that they aren't really light bending thingys, but more accurately a lens is a Fourier transformer. Of a sort. Again, optics s frustrating. One fun thing for the more matrix-ly minded are Mueller Matrices. Most modern optics SW is based on this calculus, though it goes a lot further nowadays. Also, most developments in optics are all about the little exceptions that Mueller matrices have. Still, a good little thing to read about, if interested: https://en.wikipedia.org/wiki/Mueller_calculus https://en.wikipedia.org/wiki/Mueller_calculus
- kridsdale1 3y ago
  I have been way in to Nikon and Canon lenses as well as DSP for like 20 years now, and have a degree in EE and did a ton of quantum, and I never had the insight that a lens is a physical EM Fourier transformer. Cheers for that.
  - aj7 3y ago
    “A lens creates the spatial Fourier transform from the front focal plane to the rear focal plane.”

IshKebab 3y ago

Diffraction isn't a quantum effect. Classical waves diffract.

ricardobeat 3y ago

> Challenge is scaling out camera-sized crystals of Calcium and Fluoride with optical clarity is hard, which Canon has been trying for a few decades Not really an informative summary on that. They’ve been succeeding, not trying, for decades. The problem of growing the crystals was solved in the 60s and this is commonplace now. Fluorite is also used in Fuji lenses, and Nikon/Sony have their own special glass to deal with the same problems.

ubercore 3y ago
Yeah, according to the article, their first commercial lens with flourite was delivered in 1969.
- throwaway81523 3y ago
  I thought there was at one time an issue with the fluorite elements in those huge many-kilobuck lenses absorbing moisture from the air and cracking or having other sorts of failures. Canon for a while stayed with fluorite while Nikon worked out ED glass that avoided the problem. I don't know if today's Canon L lenses use fluorite.

hammock 3y ago

Good explanation (assuming it’s accurate) thank you

dekhn 3y ago

Abbe was amazing. He worked with Zeiss and a couple other glass manufacturers to systematize optics. One of his greatest accomplishments, beyond levelling up glass quality, was developing an actual "theory of optics" which explained optical phenomena in terms of diffraction. He defined diffraction limited imaging, which meant that people were able to resolve details as fine as opticals can possibly allow (this has only recently been surpassed using Nobel-prize-winning technology). Abbe illumination, which is a way to set up your microscope's light paths to get optimal quality. He is also known for introducing the eight hour workday(!) and all sorts of employee/company innovations. My friend from grad school shows how to set up abbe illumination and talks/shows a bit about how to set up optical fourier transforms. https://www.youtube.com/watch?v=d8Tqoo0S6gc https://www.youtube.com/watch?v=d8Tqoo0S6gc If you want to draw a straight line of technology development that led to industrialization and an incredible increase in life quality, it goes right through Abbe (and Newton, Pasteur, Maudsley, and Rutherford). All of these people were absolute giants who saw far past the limitations of their day and continue to inspire new generations of geniuses who can take advantage of the amazing resources we have available today (thorlabs.com is a good example).