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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.wikipe

by eps 6y ago

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

foxdev 6y ago
You can use the Fresnel lens in an old projection TV as a laser. https://www.youtube.com/watch?v=OmlXR2nsis4 https://www.youtube.com/watch?v=OmlXR2nsis4
- dvh 6y ago
  Laser is light amplification by stimulated emission of radiation. Fresnel lens doesn't amplify light it focuses it. It is not stimulated, it is just passive component.
  - foxdev 6y ago
    This is true, but I don't think many people think of laser as anything other than "dangerous light." That's how I used it. Colloquial meanings can be frustrating when they clash with the technical meaning, but trying to fight them is typically futile. https://www.merriam-webster.com/dictionary/laser https://www.merriam-webster.com/dictionary/laser >> "2 : something resembling a laser beam in accuracy, speed, or intensity " I gave up on fighting "CPU means the entire computer" a long time ago.
    - klyrs 6y ago
      > This is true, but I don't think many people think of laser as anything other than "dangerous light." "Many people" have taken first year physics, or at least read a wikipedia article, and understand that the defining feature of a laser is its coherence. But, sure. It's 2020. We live in a post-factual society, words have no meaning and it's impossible to know anything. Why resist?
      - deleted 6y ago
        [deleted]
userbinator 6y ago
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
- phkahler 6y ago
  >> this lens looks like a Fresnel lens taken to microscopic extremes: Except I don't think it is. It's probably more like a diffraction grating or a hologram. You can actually make a flat lens by creating a hologram of a real lens and it will be flat.
  - ben_w 6y ago
    That sounds like it would make it ridiculously easy to make VR headsets that are as thin as the prop glasses used in Westworld. What are the downsides?
    - dTal 6y ago
      Wavelength specificity. You only get the original focal depth at the wavelength you used to make the hologram, and it changes proportional to the wavelength. When you consider that blue light is 2/3 the wavelength of red light, you can see that this is chromatic aberrations big brother.
    - cycomanic 6y ago
      Diffractive elements are very wavelength dependent so while something like this would only work for monochromatic light (like a laser), but not for multiwavelength light. For that you would need to do some colordiversity.
- LolWolf 6y ago
  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.)
Learning2-2 6y ago
Here is a video explaining the difference between a Fresnel lens and a photon sieve: Photon sieves used to visualise optical wave front propagation https://www.youtube.com/watch?v=TshYfYIxR9E https://www.youtube.com/watch?v=TshYfYIxR9E

by eps 6y ago

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

foxdev 6y ago

You can use the Fresnel lens in an old projection TV as a laser. https://www.youtube.com/watch?v=OmlXR2nsis4 https://www.youtube.com/watch?v=OmlXR2nsis4

dvh 6y ago
Laser is light amplification by stimulated emission of radiation. Fresnel lens doesn't amplify light it focuses it. It is not stimulated, it is just passive component.
- foxdev 6y ago
  This is true, but I don't think many people think of laser as anything other than "dangerous light." That's how I used it. Colloquial meanings can be frustrating when they clash with the technical meaning, but trying to fight them is typically futile. https://www.merriam-webster.com/dictionary/laser https://www.merriam-webster.com/dictionary/laser >> "2 : something resembling a laser beam in accuracy, speed, or intensity " I gave up on fighting "CPU means the entire computer" a long time ago.
  - klyrs 6y ago
    > This is true, but I don't think many people think of laser as anything other than "dangerous light." "Many people" have taken first year physics, or at least read a wikipedia article, and understand that the defining feature of a laser is its coherence. But, sure. It's 2020. We live in a post-factual society, words have no meaning and it's impossible to know anything. Why resist?
    - deleted 6y ago
      [deleted]

userbinator 6y ago

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

phkahler 6y ago
>> this lens looks like a Fresnel lens taken to microscopic extremes: Except I don't think it is. It's probably more like a diffraction grating or a hologram. You can actually make a flat lens by creating a hologram of a real lens and it will be flat.
- ben_w 6y ago
  That sounds like it would make it ridiculously easy to make VR headsets that are as thin as the prop glasses used in Westworld. What are the downsides?
  - dTal 6y ago
    Wavelength specificity. You only get the original focal depth at the wavelength you used to make the hologram, and it changes proportional to the wavelength. When you consider that blue light is 2/3 the wavelength of red light, you can see that this is chromatic aberrations big brother.
  - cycomanic 6y ago
    Diffractive elements are very wavelength dependent so while something like this would only work for monochromatic light (like a laser), but not for multiwavelength light. For that you would need to do some colordiversity.
LolWolf 6y ago
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.)

Learning2-2 6y ago

Here is a video explaining the difference between a Fresnel lens and a photon sieve: Photon sieves used to visualise optical wave front propagation https://www.youtube.com/watch?v=TshYfYIxR9E https://www.youtube.com/watch?v=TshYfYIxR9E