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I looked for a simple explanation of why dispersion matters, and this seems helpful: https://www.targettamers.com/guides/apochromatic-lenses/ https://www.targe

by k310 3y ago

I looked for a simple explanation of why dispersion matters, and this seems helpful: https://www.targettamers.com/guides/apochromatic-lenses/ https://www.targettamers.com/guides/apochromatic-lenses/ in the context of apochromatic lenses: those that are optimized for three different wavelengths of light, not just two, which an achromatic lens does. In the old days, calculations were done by hand, not that this is a big deal, but the big deal is that some really outstanding lens designs were made this way. Computers make the optimization extremely fast these days, but the calculations rely on the properties of the elements, which also vary in cost, durability and so on. So the computer can’t optimize for a continuous range of refractive indices and dispersions, only discrete real-world ones that the glass makers list, and which are specified (or not) to the program by the designer. Fluorine also has special properties as a coating. https://www.digitalcameraworld.com/features/this-is-why-your-camera-lens-needs-a-fluorine-coating https://www.digitalcameraworld.com/features/this-is-why-your...

lobochrome 3y ago
The linked article perfectly explains it though no?
- readyplayernull 3y ago
  Never bother someone who has just came out of a rabbit hole.
  - drittich 3y ago
    I laughed at the fact that you seem so familiar with this state and are sympathetic to it.
Sharlin 3y ago
I mean, dispersion matters simply because people generally don't want colored fringing and general haziness in their photos? There are two types of chromatic aberration (CA), both caused by dispersion. * Axial: perfect focusing is impossible because different wavelengths focus at different distances. If green light is focused correctly, then red and blue light is out of focus. This affects the entire image and is very difficult to fix in post-processing. * Transverse: there's no unique image because magnification depends on wavelength. Blue light forms a slightly larger image than green, and green larger than red. This manifests as color fringing, most apparent near the edges and corners of the image, far from the optical axis. This can be alleviated algorithmically, by resizing the red and blue sub-images to match the green one.
foobar1962 3y ago
> in the context of apochromatic lenses: those that are optimized for three different wavelengths of light, not just two, which an achromatic lens does. Achromatic lenses (corrected for blue and green) was acceptable for black and white orthochromatic film and plates which are only sensitive to blue and green. Even with panchromatic b+w film, achromatic lenses are usually satisfactory, but the chromatic aberration becomes visible with colour film. Aprochromatic lenses are corrected for blue, green and red. Lenses can also be corrected for broader spectrums that include UV and IR: Nikon made such a lens – the UV 105mm f4.5 – for technical/scientific applications.
- nimish 3y ago
  Zeiss and Hasselblad sold some superachromat lenses as well.
  - buildbot 3y ago
    Mamiya did as well, for the RZ67. Or at least, their charts claim they are corrected well into 700nm+: https://ianbfoto.com/downloads/Mamiya%20RZ67/Mamiya%20RZ67%20Apo%20Lenses.pdf https://ianbfoto.com/downloads/Mamiya%20RZ67/Mamiya%20RZ67%2... They say no focus adjust is necessary for the APO lenses for IR, B&W, and color film.
- mnw21cam 3y ago
  Telescopes for astronomy are often corrected well into the infrared regime due to some of the fairly interesting emission lines that can be imaged using an appropriate camera.
wegfawefgawefg 3y ago
Future improvements in simulations and manufacturing will probably enable micromanaging light in 3 dimensions. Ive seen some very strange fractal and composite lenses.
foobar1962 3y ago
> Computers make the optimization extremely fast these days... A lot of computer design is now aimed at optimising for tolerances in lens elements and mechanical housings to reduce precision necessary when assembling them: they can drop elements into the tube and ship them off with little or no calibration: this is done particularly with kit lenses which are price sensitive.
- k310 3y ago
  I did error budgeting for environmental effects on optical systems at Itek. Glad to see so many optics folks here. I wonder who they are, but won't ask. ;-)
  - foobar1962 3y ago
    I'm not a lens designer, but want to play one on TV.
  - verditelabs 3y ago
    I assume that's the same Itek that made lenses for the Corona Spy Satellite program? That's cool as heck. I am just a photographer, but I collect aerial lenses and own 2 Pacific Optical 18" f/3 lenses in 70mm format, serial numbers 6 and 13. I'll keep my eyes peeled for a surplus Itek 24" f/3.5 though :)
    - k310 3y ago
      Yes, same one. I find de-classified articles and books now, and share them with former colleagues. All the designs I worked on were meant for space. And I have no idea if any were actually deployed. As I noted in the “handle” post, k310 is the office number I had at Itek, as well as a nifty sonata by Mozart. I later worked for Lockheed. More space optics and other cool stuff. I was in the R&D division. I hope you can make good use of those lenses. I stuck with commercial optics (Nikon and Hasselblad). My optical hacking never exceeded making some adapters with a Unimat SL that I got. Surprise, computers got my attention, and my first “real” computer was an IMSAI that I built. I read a lot. Kingslake, Smith and so on. A nice book, if you can find it is “Photographic Optics” by Neblette. It goes over all the classic designs, including all the familiar camera lenses from the 70’s and 80’s. Nowadays, computers do all the designing, and you can’t recognize “classic” designs like the tessar, Sonnar and so on, in them. But TBH, I finally got a new 105 macro lens with unrecognizable (to me) design from Nikon to augment the old 55mm macro that I started out with in 1970 or so. A simple double-gauss design. Did you know what those “P” and “H” and other suffixes meant on Nikon lenses? They are the number of elements, in Optics Latin. H for hex, or 6 elements, P for penta or 5, and so on. The old lenses, without the “AI” aperture index gizmo, fit the new mirrorless body with the FTZ adapter. I gather that they were no-go on the DSLR’s. I skipped the DSLR generation entirely, since I used a Coolpix with 24-1000mm effective focal length for many, many years. Heck, it worked and got me great photos.

by k310 3y ago

lobochrome 3y ago

The linked article perfectly explains it though no?

readyplayernull 3y ago
Never bother someone who has just came out of a rabbit hole.
- drittich 3y ago
  I laughed at the fact that you seem so familiar with this state and are sympathetic to it.

Sharlin 3y ago

I mean, dispersion matters simply because people generally don't want colored fringing and general haziness in their photos? There are two types of chromatic aberration (CA), both caused by dispersion. * Axial: perfect focusing is impossible because different wavelengths focus at different distances. If green light is focused correctly, then red and blue light is out of focus. This affects the entire image and is very difficult to fix in post-processing. * Transverse: there's no unique image because magnification depends on wavelength. Blue light forms a slightly larger image than green, and green larger than red. This manifests as color fringing, most apparent near the edges and corners of the image, far from the optical axis. This can be alleviated algorithmically, by resizing the red and blue sub-images to match the green one.

foobar1962 3y ago

> in the context of apochromatic lenses: those that are optimized for three different wavelengths of light, not just two, which an achromatic lens does. Achromatic lenses (corrected for blue and green) was acceptable for black and white orthochromatic film and plates which are only sensitive to blue and green. Even with panchromatic b+w film, achromatic lenses are usually satisfactory, but the chromatic aberration becomes visible with colour film. Aprochromatic lenses are corrected for blue, green and red. Lenses can also be corrected for broader spectrums that include UV and IR: Nikon made such a lens – the UV 105mm f4.5 – for technical/scientific applications.

nimish 3y ago
Zeiss and Hasselblad sold some superachromat lenses as well.
- buildbot 3y ago
  Mamiya did as well, for the RZ67. Or at least, their charts claim they are corrected well into 700nm+: https://ianbfoto.com/downloads/Mamiya%20RZ67/Mamiya%20RZ67%20Apo%20Lenses.pdf https://ianbfoto.com/downloads/Mamiya%20RZ67/Mamiya%20RZ67%2... They say no focus adjust is necessary for the APO lenses for IR, B&W, and color film.
mnw21cam 3y ago
Telescopes for astronomy are often corrected well into the infrared regime due to some of the fairly interesting emission lines that can be imaged using an appropriate camera.

wegfawefgawefg 3y ago

Future improvements in simulations and manufacturing will probably enable micromanaging light in 3 dimensions. Ive seen some very strange fractal and composite lenses.

foobar1962 3y ago

> Computers make the optimization extremely fast these days... A lot of computer design is now aimed at optimising for tolerances in lens elements and mechanical housings to reduce precision necessary when assembling them: they can drop elements into the tube and ship them off with little or no calibration: this is done particularly with kit lenses which are price sensitive.

k310 3y ago
I did error budgeting for environmental effects on optical systems at Itek. Glad to see so many optics folks here. I wonder who they are, but won't ask. ;-)
- foobar1962 3y ago
  I'm not a lens designer, but want to play one on TV.
- verditelabs 3y ago
  I assume that's the same Itek that made lenses for the Corona Spy Satellite program? That's cool as heck. I am just a photographer, but I collect aerial lenses and own 2 Pacific Optical 18" f/3 lenses in 70mm format, serial numbers 6 and 13. I'll keep my eyes peeled for a surplus Itek 24" f/3.5 though :)
  - k310 3y ago
    Yes, same one. I find de-classified articles and books now, and share them with former colleagues. All the designs I worked on were meant for space. And I have no idea if any were actually deployed. As I noted in the “handle” post, k310 is the office number I had at Itek, as well as a nifty sonata by Mozart. I later worked for Lockheed. More space optics and other cool stuff. I was in the R&D division. I hope you can make good use of those lenses. I stuck with commercial optics (Nikon and Hasselblad). My optical hacking never exceeded making some adapters with a Unimat SL that I got. Surprise, computers got my attention, and my first “real” computer was an IMSAI that I built. I read a lot. Kingslake, Smith and so on. A nice book, if you can find it is “Photographic Optics” by Neblette. It goes over all the classic designs, including all the familiar camera lenses from the 70’s and 80’s. Nowadays, computers do all the designing, and you can’t recognize “classic” designs like the tessar, Sonnar and so on, in them. But TBH, I finally got a new 105 macro lens with unrecognizable (to me) design from Nikon to augment the old 55mm macro that I started out with in 1970 or so. A simple double-gauss design. Did you know what those “P” and “H” and other suffixes meant on Nikon lenses? They are the number of elements, in Optics Latin. H for hex, or 6 elements, P for penta or 5, and so on. The old lenses, without the “AI” aperture index gizmo, fit the new mirrorless body with the FTZ adapter. I gather that they were no-go on the DSLR’s. I skipped the DSLR generation entirely, since I used a Coolpix with 24-1000mm effective focal length for many, many years. Heck, it worked and got me great photos.