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Old Jan 17, 2018, 7:04 PM   #21
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I'm trying to understand this "metal" lens.

https://www.dpreview.com/news/465712...s-we-know-them

Is that glass with metal pillars on it? Or is it completely metal?

Either way, I think its the metal "fins" that are bending the light, not any substrate, even if the substrate is clear.

I'm not really sure how that works.
Titanium dioxide nanoparticles are transparent, in which case, they can be used to make lenses.
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Old Jan 17, 2018, 8:19 PM   #22
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A lens is something which can bend the path of light.
Re- Pin Hole Camera.
The lens is a hole.
A hole is made up of nothing.
Therefore it doesn't exist.
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Old Jan 17, 2018, 9:34 PM   #23
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Re- Pin Hole Camera.
The lens is a hole.
A hole is made up of nothing.
Therefore it doesn't exist.
So is it a lens? Or an aperture / stop?

LOL.

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Old Jan 17, 2018, 10:23 PM   #24
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It isn't the hole itself which bends light in a pinhole lens, it is the boundary condition of the edges of the hole, relative to the wavelength. My guess, though I haven't really studied the metalens, is that it is acting as an array of waveguides which are subtly altering the light path. Cool stuff. I suspect that at this point, the transmittance is not very high, so using the material as lens elements would result in an equivalent high f stop.
Fun to speculate about, though.
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Old Jan 18, 2018, 12:09 AM   #25
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I wonder if this image applies. It is an image of a person who was exposed to intense thermonuclear heat/ light in Hiroshima. The resulting image is on a wall. Does a photograph have to be exposed on a sensitized medium in order to be called a photograph? In this case, neither a camera nor a lens was used.
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Old Jan 18, 2018, 7:23 AM   #26
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I wonder if this image applies. It is an image of a person who was exposed to intense thermonuclear heat/ light in Hiroshima. The resulting image is on a wall. Does a photograph have to be exposed on a sensitized medium in order to be called a photograph? In this case, neither a camera nor a lens was used.
Although a sad case, I believe it is based on Merriam-Webster.

https://www.merriam-webster.com/dictionary/photography

MW's definition of photography does not mention a lens, camera or the absolute need of a photosensitive medium.

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Old Jan 18, 2018, 8:14 AM   #27
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MW's definition of photography does not mention a lens, camera or the absolute need of a photosensitive medium.
Definition of photography

: the art or process of producing images by the action of radiant energy and especially light on a sensitive surface (such as film or an optical sensor)
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Old Jan 18, 2018, 9:32 AM   #28
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Definition of photography

: the art or process of producing images by the action of radiant energy and especially light on a sensitive surface (such as film or an optical sensor)
This is the way I read it.
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Old Jan 18, 2018, 9:51 AM   #29
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... A lens is something which can bend the path of light. ...
No. A lens is something that can focus light. A pinhole can focus light, and thus, is a lens. If you increase the size of the pinhole, it lets in more light but the focus blurs.
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Old Jan 18, 2018, 10:02 AM   #30
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I wonder if this image applies. It is an image of a person who was exposed to intense thermonuclear heat/ light in Hiroshima. The resulting image is on a wall. Does a photograph have to be exposed on a sensitized medium in order to be called a photograph? In this case, neither a camera nor a lens was used.
Clearly, that's a durable image, it was caused by electromagnetic radiation, and therefore, it's a photograph.

Since the image is durable, and presuming that the electromagnetic radiation was intense, in that situation, I think it's safe to say that the wood was, to some degree, a light sensitive (if not sensitized) medium. The same can be said for this, though of course, not in the same context:

https://www.youtube.com/watch?v=nkfFmKsmyWo
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