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Comment by kragen | Hacker News Reader

The abstract: https://www.osapublishing.org/optica/abstract.cfm?uri=optica...

The paper: https://www.osapublishing.org/optica/viewmedia.cfm?uri=optic...

I've only skimmed it, but it looks super interesting.

I was expecting some kind of computational holography wizardry, but no, it's just a multilayer diffractive lens with circular symmetry which produces a beam with a really stretched-out waist.

Usually diffractive lenses are limited to a single wavelength — they're using 850 nm. Is there a way something like this can work over the whole visible spectrum? If not, this might be more like a lightsaber than a camera.

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> Conventional cameras also use multiple lenses to keep different colors of light in focus simultaneously. Since our design is very general, we can also use it to create a single flat lens that focuses all colors of light, drastically simplifying cameras even further.

Not sure if they already have a full-spectrum version working though.

Can't you correct for the abberation in software?

I don't understand it well enough to say.

Even if it doesn't work over the whole visible spectrum, is there any way that this could be used in some way that is sort of like an inverse ink jet printer where half-toning is used with a couple basis wavelengths to simulate the whole color spectrum? Am I basically just describing something similar to an LED screen but in lens form?

Maybe! You'd be sacrificing most of the light, though.

> I was expecting some kind of computational holography wizardry

Is this the type of tech the Lytro camera was based on? I thought that was an interesting concept. Imagine you'd be able to do something similar with this type of lens.

No, that was a microlens array. This one is just a lens, it just focuses the light (within the near-field zone!) in a way that I wouldn't have imagined was possible.

If they can get it to work well with one wavelength, can't you just use 3 of them positioned in a triangle for RGB

I thought 'Nah that'd never work' because I was thinking of the lenses stacked. But you're talking iPhone 11 Pro style. Depending on the properties of the glass that could actually work quite well -- though It may require a standard 4th lens for other optical properties these aren't suited to. White balance for instance, may be hard in this case, I'm not sure.

Up until a few years ago I would have said 'No way. The software isn't there yet, and it'd be prohibitive from a cost/processing power standpoint in mobile form factor.' But... see previous comment on iPhone 11 Pro.

The problem is that 3 narrowband wavelengths doesn't add up to very much light. If we call visible range 400-700 nanometers, and bandwidth is 1nm, then you are throwing away 99% of visible light.

Also, if the incoming light is banded you might end up throwing away 100% if the sensors happen to fall into the gaps.

might be good enough for machine vision applications with a narrow bandwidth LED or something like that. I'm guessing light that's not exactly at that wavelength will cause additional blurring.

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