
Engineers produce a fisheye lens that’s completely flat - chmaynard
https://news.mit.edu/2020/flat-fisheye-lens-0918
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eps
You'd expect at least a passing reference to Fresnel lens in a piece that
talks about flat lenses.

[https://en.wikipedia.org/wiki/Fresnel_lens](https://en.wikipedia.org/wiki/Fresnel_lens)

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userbinator
I agree, this lens looks like a Fresnel lens taken to microscopic extremes:

 _the new fisheye lens consists of a single flat, millimeter-thin piece of
glass covered on one side with tiny structures that precisely scatter incoming
light to produce panoramic images_

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LolWolf
It’s not. The mechanism by which it acts is quite different. The lens is a
metasurface lens, which has small structures that cause the phases of light to
constructively or destructively interfere. The result is caused by the fact
that, by carefully picking how light interferes, one can form an image on the
other side of the lens. This differs from a Fresnel lens (or other classical
lenses), which essentially form images by having rays of light which emerge
from one spot, on one side of the lens, converge to another spot on the other
side.

(In particular, wave theory is not needed to predict the behavior of classical
lenses.)

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LolWolf
> [...] which has small structures that cause the phases of light to
> constructively or destructively interfere

This is slightly unclear. I meant more specifically:

[...] which has small structures that change the phase of the light, which, in
turn, causes it to constructively or destructively interfere [...]

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andi999
Well, a fresnel lense (or any lense) also just changes the phase of which in
turn causes it...

But i will read the paper later.

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LolWolf
Yeah, I should have said "subwavelength" structures, since I really didn't
specify what "small" meant, but thought it was getting too technical.

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andreareina
I suspect "nanoscale structures" means that it's going to be highly sensitive
to the wavelength of light, I'm interested in seeing what kind of chromatic
aberration is going to come out from this.

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Lramseyer
I'm glad somebody pointed this out! Meta materials and diffractive structures
are not known for being low dispersion. This article mentions nothing about
bandwidth. However, I think the writer assumes that the indented reader knows
this already.

Also in the video you can see spatial ringing, which is highly indicative of
coherent light (single wavelength, like in a laser.)

This is still a cool discovery and could definitely have a lot of important
applications, but it's important to clarify what this is, and what it isn't.

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gus_massa
In the video and the top image, the caption says

> _3D artistic illustration of the wide-field-of-view metalens capturing a
> 180° panorama of MIT’s Killian Court and producing a high-resolution
> monochromatic flat image._

My guess is that it is only good for monochromatic light.

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xoa
> _My guess is that it is only good for monochromatic light._

Does anyone know how much of a limitation that'd be in practice though? CCDs
are monochromatic too, which we deal with using either Bayer filters (usually
RGGB IIRC) or (in fancier high end stuff) a splitter prism leading to 3
separate CCDs. Modern computational photography is also increasingly able to
do sensor fusion, even between different cameras. I can see how making use of
this would still be an extra challenge in a small form factor, because
normally the split/filter happens after the lens which simplifies things a
lot. Having to do 3x multisensor fusion with meta material fisheye only
definitely would be more effort and bulkier. Seems like it might still be
pretty useful though depending on final cost? Otherwise maybe it'll end up
niche, but it's really cool research anyway.

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andreareina
CCDs aren't monochromatic though: they detect a wide band of frequencies, they
just can't tell the difference. High dispersion in the lens is a problem
because a blue photon and a red photon originating from the same spot on the
same object, hitting the same spot on the lens, will be deflected to different
spots on the CCD. This causes fringing and fuzziness in the image.

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MichaelZuo
It looks impressive but given the standard exaggerated claims of university
press offices it’s hard to say if it’s really groundbreaking.

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em3rgent0rdr
Yeah. It currently works in infrared (though they say it can be modified to
visible light) and the video from the lab shows the images to look quite noisy
and blurry, honestly.

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MichaelZuo
Depending on the wavelength of the infrared even noisy and blurry may be
notable or it may be mediocre for their setup. All the important details are
in the paywalled paper so which type of infrared they calibrated for is
unknown.

Just too much stuff missing from the article to actually judge for technical
merit.

And plus making one for visible light is likely the main challenge as micro
machining precision optics is not subject to moore’s law type scaling. Though
I wouldn’t put it past Apple to sink billions into it if it helps making
camera modules a few mm thinner.

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alexchamberlain
> a few mm thinner

Isn't a typical consumer fish eye lens for an iPhone a couple of cm in depth?
Sounds like we're talking a more than a few mm here

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ashtonkem
At the claimed 180 degree field of view? Yes. Fisheyes that wide have lenses
that are not only incredibly thick, but also bulbous enough that protecting
the lens is quite difficult.

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ezconnect
There's a youtube channel doing experiment on this on his garage.
[https://www.youtube.com/user/huygensoptics](https://www.youtube.com/user/huygensoptics)

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Grimm1
Sounds like this solves a problem in VR too if the lens work for visible light
or at least contributes to solving it?

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interestica
360 cams currently use two back-to-back fisheye lenses... It would be great to
make them even smaller.

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tyingq
Does sound impressive. Even with UV-light-only, it would feel like military
uses abound.

If it works for visible light too, Apple seems like a ripe buyer. Supports a
thin enclosure and an obvious camera upgrade thus a win for them.

Will be interesting if it's a gross exaggeration.

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tantalor
> covered on one side with tiny structures

Click bait. Not "completely flat" at all.

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hombre_fatal
You should look at glass (something 99% of people would call "completely
flat") under a microscope.

The 3µm-wide structures in TFA deviate <1µm from the surface, so it's even
flatter than glass, and your objection sounds rather petty.

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noja
"The lens _appears_ completely flat" would be a much better description,
because the unflatness of the lens is the very thing that makes it work.

