[HN Gopher] Dragonfly: An optical telescope built from an array ...
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Dragonfly: An optical telescope built from an array of off-the-
shelf Canon lens
Author : fanf2
Score : 117 points
Date : 2024-05-15 16:24 UTC (6 hours ago)
(HTM) web link (www.dunlap.utoronto.ca)
(TXT) w3m dump (www.dunlap.utoronto.ca)
| tocs3 wrote:
| Here are some pictures.
| https://www.dragonflytelescope.org/gallery.html
|
| It uses a raspberry pi for each
| lens(https://www.raspberrypi.com/news/dragonfly-spectral-line-
| map...)
|
| Early paper about the telescope.
| https://ui.adsabs.harvard.edu/abs/2014PASP..126...55A/abstra...
| perihelions wrote:
| Unfortunately their website is not built from a large, redundant
| array of off-the-shelf server parts.
|
| Here's a mirror,
|
| https://web.archive.org/web/20240507234024/https://www.dunla...
| araes wrote:
| This article talks about the upgrades they recently (2022) made
| to the telescope array and has a few example images.
|
| https://www.dunlap.utoronto.ca/new-dragonfly/
|
| The publication resulting from the work, "Giant Shell of
| Ionized Gas Discovered near M82", can be found:
|
| https://iopscience.iop.org/article/10.3847/1538-4357/ac50b6/...
|
| The companion publication from Yale, "Nascent Tidal Dwarf
| Galaxy Forming", can be found:
|
| https://iopscience.iop.org/article/10.3847/2041-8213/ac3ca6/...
|
| Edit: And, actually from the post below, full publications
| related at:
|
| https://www.dragonflytelescope.org/publications.html
| Iulioh wrote:
| >Here's a mirror,
|
| Ah!
|
| So there's a large mirror involved?
|
| (sorry)
| 1024core wrote:
| RAIT (Redundant Array of Inexpensive Telephoto lenses)?
| buescher wrote:
| Not that inexpensive - that's a $12000 lens with a nearly 6"
| aperture. The telescope itself is a fairly specialized
| instrument. It's more like a redundant array of very fast (for
| a telescope) lenses. From the paper: "Our primary goal is to
| test predictions that at very low surface brightness levels
| galaxies display a wealth of structures that are not seen at
| higher surface brightness levels." (But yes, the lenses are
| going to be cheaper from Canon than the tubes would be from a
| specialized telescope maker).
| dekhn wrote:
| The thing to appreciate is that in academic science, $12000
| lens _is_ inexpensive; the scale is different from consumer
| and prosumer pricing. A typical project like this would get
| at least a million dollaras in funding (see
| https://www.artsci.utoronto.ca/news/astronomer-roberto-
| abrah... which shows they got $2M to buy lenses; 120 lenses *
| 12K = $1.5M.
|
| I work with microscopes that cost $1M and just sit in a lab.
| That's not atypical for an academic or industrial microscope.
|
| One of the biggest issues in modern science is that to make
| many discoveries you need to pay very high prices to get the
| latest and greatest hardware. I've been exploring how to make
| lower cost telescopes and microscopes (and definitely love
| this project), that are "good enough" to open up new areas of
| research/discovery for people with budgets in the $1K-10K
| range. But it's hard! So far I have mostly been relearning
| what people already knew in the 1800s and early 1900s, that
| is easily obtained off-the-shelf tech today.
| itishappy wrote:
| > I work with microscopes that cost $1M and just sit in a
| lab. That's not atypical for an academic or industrial
| microscope.
|
| Ooo, what for!? I always love hearing what people do with
| optical equipment I can't afford. :)
|
| I'm sure I'd be interested in your pet project as well!
| dekhn wrote:
| The scopes I work near are typically for applying cutting
| edge imaging techniques to cellular or organoid growth.
| Like this:
| https://www.zeiss.com/microscopy/en/resources/insights-
| hub/l...
| buescher wrote:
| The point is it's not _that_ inexpensive for the optics. I
| 've worked in an interferometry lab where we used high-
| volume photographic lenses where we could, and yeah, they
| were probably an order of magnitude less expensive than
| something made for the purpose, and real exotic optics were
| more than two orders of magnitude more expensive.
|
| But talking apples to apples, a $12000 professional camera
| lens is closer to something like a $12000 research
| microscope than you think in terms of the build-or-buy
| decision. There's also a whole industry of telescopes for
| amateurs that are made in low volumes to much higher
| optical standards than photographic lenses that are mostly
| not that expensive. A top tier 6" refractor might be $15K
| and blow the camera lens away as a general purpose
| astronomical instrument, but it would not be nearly as
| fast, which is important for this application, and if you
| placed an order for 120 of them, you might get them in five
| years. Maybe. I'd guess that made-for-the-purpose tubes
| would come in within a factor of two or three of the off-
| the-shelf lens if you could find a supplier. They might
| even be cheaper. The project risk would be larger, and that
| might be determining also.
| dylan604 wrote:
| There are plenty of much cheaper telescopes in that 6"
| aperture range. My 152mm was only $1k. My polar mount was
| $1500. Even adding in a tracking scope/camera to attach is
| still a fraction of the price of single lens. Tack on a
| similar SBIG dedicated astro camera and cheap laptop to run
| the guiding and imaging would still come in under that price
| tag.
|
| So, is there an advantage of having all of the lenses on the
| same tracking platform to justify the expense of the single
| mount? If you place individual 6" scopes in an area where
| humans could comfortably move between them all pointed at the
| same object or even slightly different areas to get the wider
| image, would that not be the same/similar result?
| Essentially, building the VLA but with commodity off-the-
| shelf visible scopes.
| buescher wrote:
| It's more of a "that they could do it at all" sort of feat.
| They're coming in somewhat cheaper (probably) and at lower
| project risk by using off the shelf professional camera
| lenses than by having tubes made for the purpose.
|
| Your 6" scope is slower, probably much slower, than the
| telephoto lens they used. There really aren't any amateur
| telescope tubes I know of that you could directly compare
| to the 143mm aperture f2.8 Canon lens. The right comparison
| would be to a 6" apo, which would run $8K-$16K and still be
| slower.
| dylan604 wrote:
| You of course are correct regarding f-value. My specific
| scope maths out to an unusual f/4.8 at 731mm focal
| length. However, I'm not trying to take 1/100th images.
| I'm doing 30s exposures, so a f/2.8 vs f/4.8 isn't that
| bad of a trade off.
|
| Even if this isn't doing the same "science", it would be
| an interesting thing to play with for sciene. Instead of
| stacking images from the same camera, just stack each
| image from the array. Or capturing an entire mosaic in
| one "snap" which is essentially what WASP is doing
| (mentioned in a post from yesterday).
| buildbot wrote:
| Anyone know what sensor they are using behind all that nice Canon
| glass?
| perihelions wrote:
| - _" Each of the eight lenses in the array is connected to a
| Santa Barbara Imaging Group (SBIG) STF-8300M CCD camera. These
| cameras have Kodak KAF-8300 CCD detectors, which have a 3326 x
| 2504 pixel format."_
|
| https://arxiv.org/abs/1401.5473 ( _" Ultra Low Surface
| Brightness Imaging with the Dragonfly Telephoto Array"_)
| buildbot wrote:
| Thank you!
| 0cf8612b2e1e wrote:
| That write up could have used significantly more details. Is this
| competitive with a traditional telescope? 1/1000 the cost? Just
| the benefit of not having to share instrument time? Being able to
| incrementally expand the array?
|
| Some kind of technical measurement for me to better appreciate
| the work.
| tupilaq wrote:
| Cool.. a more up-to-dateish version of Wide Angle Search for
| Planets (WASP[1] and SuperWASP[2])
|
| [1]https://warwick.ac.uk/fac/sci/physics/research/astro/researc..
| . [2]https://www.superwasp.org/about/
| antognini wrote:
| This kind of a setup of a large number of small, cheap detectors
| works well for observing diffuse objects with low surface
| brightness. Generally speaking telescopes improve with size
| because larger telescopes can resolve smaller objects, so you can
| concentrate the light from your source into a smaller patch and
| increase the signal-to-noise with respect to the background. But
| once you have resolved the object (which doesn't require a very
| large diameter for a diffuse object) you no longer get any
| benefit from a larger telescope except for the greater light
| collecting power. So there's no benefit to having a single large
| mirror vs a large number of smaller detectors. Since it's a lot
| easier and cheaper to just buy a bunch of off the shelf
| components rather than build a large mirror from scratch that is
| what they did here.
|
| A friend of mine in grad school worked on a project that is
| similar in spirit called ASAS-SN. It also used off the shelf
| cameras but distributed them around the world so that they could
| detect supernovae and other transients. Because everything was
| off the shelf they could build out their network on a shoestring
| budget. I think they're the first to discover the vast majority
| of all bright supernovae these days.
| perihelions wrote:
| - _" diffuse objects with low surface brightness"_
|
| Are things amateur photographers with small telescopes (and
| lots of patience) sometimes discover,
|
| https://old.reddit.com/r/space/comments/13uco46/i_discovered...
| ( _" I discovered this planetary nebula using a $500 camera
| lens, now it carries my name"_)
|
| https://www.astrobin.com/i9yy6f/ (18 hours!)
| gnatman wrote:
| I was struggling to see the planetary nebula inside that blue
| circle before I realized that _is_ the planetary nebula.
| cool!
| perihelions wrote:
| Somewhere there's a large, bright nebula in the shape of a
| red arrow no astronomer's _ever_ noticed.
| llm_trw wrote:
| https://en.wikipedia.org/wiki/Redshift-space_distortions
| jcims wrote:
| I still don't understand how objects in space of that angular
| diameter are still being discovered. I would have to imagine
| lots of people have seen it, but just never chose to document
| or catalog it?
| perihelions wrote:
| This is an extremely long (18 hour) exposure in specialized
| narrowband spectral filters that have no usefulness for
| anything other than these particular targets.
| Aspos wrote:
| Can one use millions of smaller detectors if one finds a way to
| point them in one direction and synchronize them to take
| pictures at the same exact moment?
|
| I mean, can millions of phone cameras make one giant virtual
| telescope?
| diracs_stache wrote:
| Not too much to add from what others have mentioned but this
| looks like a good (low cost wide fov) photon bucket with low
| complexity (important for reducing stray/scattered light).
| shiftpgdn wrote:
| Can someone smarter than me explain why astronmers can't stick
| something like this on the back of an existing geostationary
| platform (like what is used for the XM radio sattelites) and get
| amazing data out of them? Surely sticking something like this
| array 100km into space will yield better results without the
| overhead of a 20 year mission plan like James Webb or Hubble.
| VohuMana wrote:
| Not a professional so take this with a grain of salt but my
| guess would be weight first and foremost. From what I
| understand geostationary orbit isn't cheap to get to and each
| added kilogram increases cost significantly. These lenses while
| not incredibly heavy are heavy enough to add a fair amount of
| cost.
| consp wrote:
| I also doubt these lenses will hold up in a very cold or very
| hot near-vacuum.
| sgt101 wrote:
| I am no expert, but the things I would worry about:
|
| - cost to get into geostationary orbit might dominate the
| value/saving of the cheap instrument, so it might be smart to
| spend more on that - managing and controlling it might be very
| challenging - need to get the data down from it - might create
| difficulties and costs that kill the value - heating and
| cooling in space might kill it - radiation in space might kill
| the hardware - acceleration during launch might kill the
| hardware - the payload needs to be stable during launch or
| there will be an accident - scientific value might be lower
| than other missions for similar spend
| gridspy wrote:
| The lenses are made of materials that will not resist the
| conditions in space (high temperature gradients, oxidizing
| environment, radiation).
|
| Once in space they cannot tweak the array.
|
| Launch weight and stresses would damage this array.
| dekhn wrote:
| Projects like this have been done; see for example
| https://www.jpl.nasa.gov/missions/arcsecond-space-telescope-...
| lvspiff wrote:
| I've always wondered that myself - If the Russians could build
| and launch sputnik in 1957 and get it around the earth a few
| times why aren't we seeing a huge number of backyard dad+son
| duos building rockets to launch their own telescope array. Its
| amazing that its a 60 year old feat that is still only in the
| hands of governments and massive corps
| dylan604 wrote:
| Rocket science ain't easy. Just because you can build a great
| telescope does not mean you can build a rocket. Also, I could
| only imagine the NIMBY revolt when you file your permit plans
| to build launchpad-38A in your backyard. I hope you don't
| spend too much time wondering before coming to obvious
| answers
| FredPret wrote:
| 1) You need more than just getting to space, you need to go
| really fast when you get there. So, lots of propellant and a
| big rocket is needed. So, it's really expensive.
|
| 2) Because you're setting fire to a big tube of propellant
| that then goes crazy fast, you need all sorts of permits and
| safety reviews to do it
|
| 3) Space is hard, so your rocket will almost certainly blow
| up / fail a couple of times.
|
| All of this means: big budgets and state-level patience and
| persistence is needed
| eichin wrote:
| The problem is the lack of a "backyard" ICBM program to
| piggyback off of... the R-7 that the sputnik launcher was
| based on "was designed with excess thrust since they were
| unsure how heavy the hydrogen bomb payload would be"
| (wikipedia.)
| Aspos wrote:
| But there are actually so so many startups and garage
| enthusiasts at various stages of readiness to put payloads
| into orbit
|
| https://www.youtube.com/watch?v=SH3lR2GLgT0
| perihelions wrote:
| I don't think there's that big of an advantage for space-based
| astronomy here, for visible-wavelength light with large pixel
| scales, and relatively bright (total luminosity) objects.
| Because it's done in narrowband filters, it's particularly good
| at erasing sky noise.
|
| /not an astrophotographer
| ianburrell wrote:
| Cause it wouldn't give better results. The big advantage of
| putting telescope in space is that don't have to deal with the
| movement of the air distorting the image. That doesn't matter
| when taking pictures of diffuse objects.
|
| The disadvantage is that it is in space, you have to spend 10x
| or 100x as much making something that can work in space, and
| you can't maintain it. I bet it would be much better to spend
| that money making dozens of these around the world, or
| iterating on the design.
|
| The other advantage is that atmosphere is opaque for some
| wavelengths. The infrared wavelength that JWST looks in are
| absorbed. It also helps to be able to cool down the detectors
| to lower temps. One reason we aren't seeing direct replacement
| for Hubble is that the big ground telescopes with active optics
| are as good.
| sandworm101 wrote:
| Forget this telescope. I'm more intrigued by the location: New
| Mexico Skies, a campground for telescopes. I'd rather visit such
| a place than most any museum.
|
| https://nmskies.com/
| dylan604 wrote:
| This is "when I grow up" type of wish to have my gear at this
| type of location for my remote sessions. Otherwise, I'd just
| really like for my retirement plot to be remote like this.
| rhelz wrote:
| Question: why is, saying having 100 different lenses
| simultaneously take images, rather than just a single one taking
| 100 sequential images, and then using something like registax to
| combine them?
| MeteorMarc wrote:
| How can multi-element lenses have less scattering than a large
| mirror telescope? Do they mean smaller diffraction patterns
| instead?
| smaddox wrote:
| > with unprecedented nano-fabricated coatings with sub-wavelength
| structure on optical glasses.
|
| Also known as an anti-reflection coating. Definitely not
| unprecedented.
|
| Cool project, though.
| somethingsome wrote:
| Is it possible to download somewhere in full quality a raw image
| captured with it?
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