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by Synaesthesia 477 days ago
Yeah I read that, and upon re-reading it I have some vague idea on how that might work, but I would still need to read the paper and see some illustrations to really get it.

Sounds like this may enable full-colour astrophotography (always wondered why it's all in B&W!) and/or make achromatic telescopes a lot lighter.
2 comments
Evidlo 477 days ago
I published a paper in this area a few years ago (but with a different lens design), so I think I can answer.

In conventional diffractive optics, the focal plane (where the sensor should be placed for a focused image) is wavelength-dependent. This means that you receive an in-focus image of the scene for a specific wavelength λ_i when your sensor is located a distance d_i from the lens [0]. By varying d_i you can scan the scene for all wavelengths even if your sensor is monochromatic. You get blurry versions of all other wavelengths as well, but the idea is to use computational techniques to separate these out.

Here, they've designed an optic which tries to eliminate the wavelength dependence of the lens focal plane. Instead of you place an RGB sensor at this one focal plane to get all the wavelengths.

0: https://ieeexplore.ieee.org/abstract/document/9191355?figure...

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jcims 476 days ago
Could these help with field curvature as well? To make the focal plane more, uh, planar?
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teamonkey 477 days ago
You can use a regular bayer-matrix colour camera (or colour film) for astrophotography, it’s very common in amateur circles.

However, mono cameras and filters are also often used because the interesting colours are often not R,G,B of the visible spectrum but certain emission frequencies of hydrogen, silicon, oxygen and others. These are often combined to make false-colour images.

Filters also help penetrate light pollution by keeping only the frequencies you’re interested in and rejecting much of the light reflected by the atmosphere.

In addition, getting lenses to focus all frequencies of light equally well at the same time is quite tricky. For a mono camera with narrowband filters, this is less of a problem: you can focus precisely on one colour at a time and you can get away with simpler optics or cheaper glass.

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