6 ms·

A new, thin-lensed telescope design could far surpass James Webb

86 points by xoa 3y ago

tiffanyh 3y ago
Off topic: is this a reputable news source? It positions itself as "Academic rigor, journalistic flair" and appears to be sponsored by a number of US universities. But some of the articles on its site seem questionable.
- zoklet-enjoyer 3y ago
  Ars reprinted it https://arstechnica.com/space/2023/07/a-new-thin-lensed-telescope-design-could-far-surpass-james-webb/ https://arstechnica.com/space/2023/07/a-new-thin-lensed-tele...
  - tiffanyh 3y ago
    > "This article is republished from The Conversation under a Creative Commons license" This seem more like "free content" for Ars, than them fact checking the source / validity.
- SiempreViernes 3y ago
  Anything in particular you think of? After cursory look at the title nothing stands out.
- rmilejczz 3y ago
  Seems like it is yes https://adfontesmedia.com/conversation-bias-and-reliability/ https://adfontesmedia.com/conversation-bias-and-reliability/
- deleted 3y ago
  [deleted]
nayuki 3y ago
Is this technology really that new? Canon has been selling "Diffractive Optics (DO)" lenses for decades. For example, https://kenrockwell.com/canon/lenses/70-300mm-do-is.htm https://kenrockwell.com/canon/lenses/70-300mm-do-is.htm , https://en.canon-cna.com/pro/infobank/lenses-multi-layer-diffractive-optical-element/ https://en.canon-cna.com/pro/infobank/lenses-multi-layer-dif... .
- spywaregorilla 3y ago
  The article acknowledges this and even links to Canon products from 2004. https://global.canon/en/v-square/34.html https://global.canon/en/v-square/34.html They are not new. The issue is quality and scale.
  - Cthulhu_ 3y ago
    And launching them into space, of course.
    - malfist 3y ago
      Thing missing from all this, to see into the far infrared things have to be chilled near absolute zero. We do this with JWST. Can these thinner plates handle that cold? Do they still refract correctly? "far surpass" is interesting when the challenge of the JSWT isn't the lens technology, but everything else.
      - csours 3y ago
        Hmm. Can you image far infrared with lenses? Wouldn't the imager just "see" the lens? I don't see any mention of infrared in the article, so they may just be going for visible light
        malfist 3y ago
        Yes you can, but not from earth. The earth is too warm for that it has to be in space. Typically as long as the lens has a transmission for that wavelength it'll go through. A lot of your astrophography on the earth happens partially in the IR band. Hydrogen Alpha is a common emission spectrum to capture, and about 75% of it falls in the IR range. Your common cameras (DSLR, etc) have IR filters specifically to prevent IR from reaching the sensor after going through the lens. If they're only trying to capture in visible, then a better comparison would be the hubble, not the JWST. Source: am an astrophotographer, see: https://www.jeromehollon.com/ https://www.jeromehollon.com/
formerly_proven 3y ago
The main advantage of a reflective telescope is lack of chromatic aberrations, because light never disperses. The other, related advantage is that you don't need glass that's transparent over a large range of wavelengths. JWT ranges from the end of the visible spectrum to like 30 µm.
- delta_p_delta_x 3y ago
  Correct. Almost all large telescopes (read: ~50 cm aperture and wider) are reflectors. Glass is used almost exclusively on camera lenses only, and that's because a 'reflector camera' would be un-ergonomic and impractical. Not much of a concern for a bunch of mirrors stationary in a building or rocketed up to space.
  - dogsgobork 3y ago
    There are some reflector lenses available for SLR cameras, not everyone likes their different optical properties though.
    - dekhn 3y ago
      I have one of these- a 500mm "equivalent" (https://www.amazon.com/gp/product/B004WLEEHI https://www.amazon.com/gp/product/B004WLEEHI) and it's definitely got weird optical properties.
      - namibj 3y ago
        Sadly sensors are all bundled up with the rest of the camera, because a Schmidt camera (corrector plate like your objective, adjustable primary mirror, sensor directly in the primary focus with it's back facing the scene) can easily get a very wide aperture (e.g. nicely matching a CMV12000 with a fairly tame single glass up front and a tame mirror in the back, plus a slab and a plano-convex lens right at the sensor to flatten the field/focus, yielding 400mm f/2.0, though that's with the focal point dead center in the sightly over 800mm tube; still around f/2.4~f/2.8 brightness to the full f/2.0 sharpness (near center, but even at the corner you need a monochrome sensor to feel the mushiness)). Celeste's prosumer 8~14" (aperture) Schmidt-Cassagrain typically support replacing the secondary mirror with a camera mount to get that much shorter focal length (IIRC around f/5). Might be nice with one of those very narrow studio video camera bodies (e.g. Black magic has some); the catadioptric nature means you can carry even the very big ones on your shoulder (I'd highly recommend a gimbal if used for shooting from the shoulder).
danbruc 3y ago
They seem to be essentially talking about Fresnel lenses or am I misunderstanding something? Why are they calling them diffractive lenses, I always thought that Fresnel lenses are also refractive with some unwanted diffraction at the edges of the ridges? Or do those proposed lenses work differently, does diffraction contribute intentionally and significantly because of the finer structure?
- ycui1986 3y ago
  I am confused at the beginning, but it seems to me the author did not know the difference between diffractive optics and Fresnel lens. That significant reduce the credibility of the author. It is embarrassing for someone in academia to confuse these two different things.
  - zalo 3y ago
    Perhaps they should have started at the Wikipedia entry for “Zone Plate” instead
  - nimish 3y ago
    >It is embarrassing for someone in academia to confuse these two different things. I've been digging through the academic publications for a completely different field and it appears that they have very little or outdated knowledge of parallel fields, almost siloed.
- time0ut 3y ago
  I believe the author showed up in the comments on the Ars version of the article [0] and touched on some of these ambiguities. [0] https://arstechnica.com/space/2023/07/a-new-thin-lensed-telescope-design-could-far-surpass-james-webb/?comments=1&comments-page=1 https://arstechnica.com/space/2023/07/a-new-thin-lensed-tele...
  - kristianp 3y ago
    One of the comments (from user Wickwick) explains the difference concisely: > I was going to make a small adjustment to the post on this topic. The lenses Fresnel designed were refractive (and reflective) and not diffractive. In fact, it's the diffraction of the transitions that ruins the image quality of these sorts of lenses.
OldGuyInTheClub 3y ago
There's much more to a telescope than the primary mirror which the author conveniently neglects. As others point out below, making an IR observatory (JWST) requires keeping everything around the mirror cold so that the mirrors and instruments (not trivial, either) have a hope in heck of working. Livermore tested a multi-meter thin Fresnel optic back in 2002. They also worked with Robert Lang, physicist and origamist, to figure out how to pack the thing effectively. https://digital.library.unt.edu/ark:/67531/metadc1412512/m2/1/high_res_d/15005362.pdf https://digital.library.unt.edu/ark:/67531/metadc1412512/m2/... https://langorigami.com/article/eyeglass-telescope/ https://langorigami.com/article/eyeglass-telescope/
kristianp 3y ago
This is their paper from 2021: Design aspects of large-aperture MODE lenses https://opg.optica.org/osac/fulltext.cfm?uri=osac-4-1-171&id=446612 https://opg.optica.org/osac/fulltext.cfm?uri=osac-4-1-171&id...

86 points by xoa 3y ago

Off topic: is this a reputable news source? It positions itself as "Academic rigor, journalistic flair" and appears to be sponsored by a number of US universities. But some of the articles on its site seem questionable.

zoklet-enjoyer 3y ago
Ars reprinted it https://arstechnica.com/space/2023/07/a-new-thin-lensed-telescope-design-could-far-surpass-james-webb/ https://arstechnica.com/space/2023/07/a-new-thin-lensed-tele...
- tiffanyh 3y ago
  > "This article is republished from The Conversation under a Creative Commons license" This seem more like "free content" for Ars, than them fact checking the source / validity.
SiempreViernes 3y ago
Anything in particular you think of? After cursory look at the title nothing stands out.
rmilejczz 3y ago
Seems like it is yes https://adfontesmedia.com/conversation-bias-and-reliability/ https://adfontesmedia.com/conversation-bias-and-reliability/
deleted 3y ago
[deleted]

nayuki 3y ago

Is this technology really that new? Canon has been selling "Diffractive Optics (DO)" lenses for decades. For example, https://kenrockwell.com/canon/lenses/70-300mm-do-is.htm https://kenrockwell.com/canon/lenses/70-300mm-do-is.htm , https://en.canon-cna.com/pro/infobank/lenses-multi-layer-diffractive-optical-element/ https://en.canon-cna.com/pro/infobank/lenses-multi-layer-dif... .

spywaregorilla 3y ago
The article acknowledges this and even links to Canon products from 2004. https://global.canon/en/v-square/34.html https://global.canon/en/v-square/34.html They are not new. The issue is quality and scale.
- Cthulhu_ 3y ago
  And launching them into space, of course.
  - malfist 3y ago
    Thing missing from all this, to see into the far infrared things have to be chilled near absolute zero. We do this with JWST. Can these thinner plates handle that cold? Do they still refract correctly? "far surpass" is interesting when the challenge of the JSWT isn't the lens technology, but everything else.
    - csours 3y ago
      Hmm. Can you image far infrared with lenses? Wouldn't the imager just "see" the lens? I don't see any mention of infrared in the article, so they may just be going for visible light
      - malfist 3y ago
        Yes you can, but not from earth. The earth is too warm for that it has to be in space. Typically as long as the lens has a transmission for that wavelength it'll go through. A lot of your astrophography on the earth happens partially in the IR band. Hydrogen Alpha is a common emission spectrum to capture, and about 75% of it falls in the IR range. Your common cameras (DSLR, etc) have IR filters specifically to prevent IR from reaching the sensor after going through the lens. If they're only trying to capture in visible, then a better comparison would be the hubble, not the JWST. Source: am an astrophotographer, see: https://www.jeromehollon.com/ https://www.jeromehollon.com/

formerly_proven 3y ago

The main advantage of a reflective telescope is lack of chromatic aberrations, because light never disperses. The other, related advantage is that you don't need glass that's transparent over a large range of wavelengths. JWT ranges from the end of the visible spectrum to like 30 µm.

delta_p_delta_x 3y ago
Correct. Almost all large telescopes (read: ~50 cm aperture and wider) are reflectors. Glass is used almost exclusively on camera lenses only, and that's because a 'reflector camera' would be un-ergonomic and impractical. Not much of a concern for a bunch of mirrors stationary in a building or rocketed up to space.
- dogsgobork 3y ago
  There are some reflector lenses available for SLR cameras, not everyone likes their different optical properties though.
  - dekhn 3y ago
    I have one of these- a 500mm "equivalent" (https://www.amazon.com/gp/product/B004WLEEHI https://www.amazon.com/gp/product/B004WLEEHI) and it's definitely got weird optical properties.
    - namibj 3y ago
      Sadly sensors are all bundled up with the rest of the camera, because a Schmidt camera (corrector plate like your objective, adjustable primary mirror, sensor directly in the primary focus with it's back facing the scene) can easily get a very wide aperture (e.g. nicely matching a CMV12000 with a fairly tame single glass up front and a tame mirror in the back, plus a slab and a plano-convex lens right at the sensor to flatten the field/focus, yielding 400mm f/2.0, though that's with the focal point dead center in the sightly over 800mm tube; still around f/2.4~f/2.8 brightness to the full f/2.0 sharpness (near center, but even at the corner you need a monochrome sensor to feel the mushiness)). Celeste's prosumer 8~14" (aperture) Schmidt-Cassagrain typically support replacing the secondary mirror with a camera mount to get that much shorter focal length (IIRC around f/5). Might be nice with one of those very narrow studio video camera bodies (e.g. Black magic has some); the catadioptric nature means you can carry even the very big ones on your shoulder (I'd highly recommend a gimbal if used for shooting from the shoulder).

danbruc 3y ago

They seem to be essentially talking about Fresnel lenses or am I misunderstanding something? Why are they calling them diffractive lenses, I always thought that Fresnel lenses are also refractive with some unwanted diffraction at the edges of the ridges? Or do those proposed lenses work differently, does diffraction contribute intentionally and significantly because of the finer structure?

ycui1986 3y ago
I am confused at the beginning, but it seems to me the author did not know the difference between diffractive optics and Fresnel lens. That significant reduce the credibility of the author. It is embarrassing for someone in academia to confuse these two different things.
- zalo 3y ago
  Perhaps they should have started at the Wikipedia entry for “Zone Plate” instead
- nimish 3y ago
  >It is embarrassing for someone in academia to confuse these two different things. I've been digging through the academic publications for a completely different field and it appears that they have very little or outdated knowledge of parallel fields, almost siloed.
time0ut 3y ago
I believe the author showed up in the comments on the Ars version of the article [0] and touched on some of these ambiguities. [0] https://arstechnica.com/space/2023/07/a-new-thin-lensed-telescope-design-could-far-surpass-james-webb/?comments=1&comments-page=1 https://arstechnica.com/space/2023/07/a-new-thin-lensed-tele...
- kristianp 3y ago
  One of the comments (from user Wickwick) explains the difference concisely: > I was going to make a small adjustment to the post on this topic. The lenses Fresnel designed were refractive (and reflective) and not diffractive. In fact, it's the diffraction of the transitions that ruins the image quality of these sorts of lenses.

OldGuyInTheClub 3y ago

There's much more to a telescope than the primary mirror which the author conveniently neglects. As others point out below, making an IR observatory (JWST) requires keeping everything around the mirror cold so that the mirrors and instruments (not trivial, either) have a hope in heck of working. Livermore tested a multi-meter thin Fresnel optic back in 2002. They also worked with Robert Lang, physicist and origamist, to figure out how to pack the thing effectively. https://digital.library.unt.edu/ark:/67531/metadc1412512/m2/1/high_res_d/15005362.pdf https://digital.library.unt.edu/ark:/67531/metadc1412512/m2/... https://langorigami.com/article/eyeglass-telescope/ https://langorigami.com/article/eyeglass-telescope/

kristianp 3y ago

This is their paper from 2021: Design aspects of large-aperture MODE lenses https://opg.optica.org/osac/fulltext.cfm?uri=osac-4-1-171&id=446612 https://opg.optica.org/osac/fulltext.cfm?uri=osac-4-1-171&id...