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Complicated, but simply an incremental evolution of a very old solution. These complicated lens arrangements to counteract chromatic aberration got started in

Complicated, but simply an incremental evolution of a very old solution. These complicated lens arrangements to counteract chromatic aberration got started in the 18th century. The game is all about getting three distinct wavelengths to focus despite each reacting differently at each lens. The lens in the iPhone looks complex but it isn't any more complicated than others. The most complex I've ever read about was for a satellite which had to maintain focus despite temperature changes. Iirc that employed a stack of over a dozen lenses. https://en.wikipedia.org/wiki/Achromatic_lens https://en.wikipedia.org/wiki/Achromatic_lens https://www.dpreview.com/forums/post/61074908 https://www.dpreview.com/forums/post/61074908 https://photography.tutsplus.com/tutorials/here-is-what-to-look-for-when-you-buy-photography-lenses--cms-27047 https://photography.tutsplus.com/tutorials/here-is-what-to-l... https://www.spiedigitallibrary.org/journals/journal-of-applied-remote-sensing/volume-13/issue-03/032502/APIS--the-miniaturized-Earth-observation-camera-on-board-OPTOS/10.1117/1.JRS.13.032502.full?SSO=1 https://www.spiedigitallibrary.org/journals/journal-of-appli...

gmueckl 5y ago
The craziness in the iPhone design isn't exactly the number of elements, but their weird aspherical shapes. The traditional approaches for designing optics are have been developed for spherical lenses because they are much simpler to describe mathematically. Even then, optimizing them requires a lot of numerical computation. At first glance, optimizing these wavy, complex lens shapes seems to require much more involved methods.
- prvc 5y ago
  If only the designers at Apple had access to devices that could perform numerical computations...
  - gmueckl 5y ago
    You first have to know what to compute before you can compute it. A computer won't tell you that.
- fsh 5y ago
  I don't think the computational complexity has been a significant problem for at least half a century. Aspheric lenses are described by simple polynomials and ray tracing is just elementary geometry. You only need to analyze a hand full of rays to get the relevant parameters of an imaging system. Probably a few thousand floating point operations in total. The problem is that it is extremely difficult to manufacture surfaces with optical quality that are not spherical. Even today, aspheres tend to be more expensive than spherical lenses and have significantly worse surface quality. This is the price you have to pay if the objective has to fit inside a phone.

gmueckl 5y ago

The craziness in the iPhone design isn't exactly the number of elements, but their weird aspherical shapes. The traditional approaches for designing optics are have been developed for spherical lenses because they are much simpler to describe mathematically. Even then, optimizing them requires a lot of numerical computation. At first glance, optimizing these wavy, complex lens shapes seems to require much more involved methods.

prvc 5y ago
If only the designers at Apple had access to devices that could perform numerical computations...
- gmueckl 5y ago
  You first have to know what to compute before you can compute it. A computer won't tell you that.
fsh 5y ago
I don't think the computational complexity has been a significant problem for at least half a century. Aspheric lenses are described by simple polynomials and ray tracing is just elementary geometry. You only need to analyze a hand full of rays to get the relevant parameters of an imaging system. Probably a few thousand floating point operations in total. The problem is that it is extremely difficult to manufacture surfaces with optical quality that are not spherical. Even today, aspheres tend to be more expensive than spherical lenses and have significantly worse surface quality. This is the price you have to pay if the objective has to fit inside a phone.