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Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

dunlap.utoronto.ca

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Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#51

Post by itishappy »

dekhn wrote: post #35
itishappy wrote: post #34

Earlier quoted context omitted.

> 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!

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...

Wow, thanks! That first image is really something else.

I wonder if Dr. Pilipp Seidel has any relation to Philipp Ludwig von Seidel.

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#52

Post by Aspos »

EnigmaFlare wrote: post #49
Aspos wrote: post #43

Earlier quoted context omitted.

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?

Took me a while to understand what you meant. A phone camera already is millions of smaller detectors .... But I think you mean coordinating millions of people to all take photos of the same direction in the sky and then combining all the photos? I'm sure it can be done with an app and a way to build that crowd of users! But the field of view will still be huge because they're not telescopes/telephoto lenses.

Yeah, modern phones use multiple cameras to produce a single image. Would it be possible to produce a higher resolution photo using millions of images taken from millions of locations?

I have no clue what I am talking about, but would love to hear somebody knowledgeable speculate on this.

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#53

Post by DarkSucker »

Can someone provide/link-to a principle of operation? I looked at references (https://www.dragonflytelescope.org/publications.html) but they point to publications that look to be behind pay walls.

In particular, I don't see how N co-aligned cameras is any different than N images taken in sequence with one camera (averaging over noise), other than a reduction in time required to take N images with one camera.

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#54

Post by gelstudios »

smaddox wrote: post #44

> 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.

From the various links in the comments, the telescope uses special filters in front of the lenses to capture the faint glow in specific wavelengths emitted by the circumgalactic medium (a new word for me!) aka "gas" around galaxies.

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#55

Post by dekhn »

dylan604 wrote: post #33
buescher wrote: post #10

Earlier quoted context omitted.

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…

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…

From what I understand, reconstructing images from virtual telescopes requires extremely accurate timing so all the wavefronts are in phase: https://en.wikipedia.org/wiki/Aperture_synthesis

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#56

Post by buescher »

dylan604 wrote: post #46
buescher wrote: post #41

Earlier quoted context omitted.

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 f…

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 t…

That's almost certainly an achromat unless you got a screaming deal I want to know about. It's not in the same league optically as the Canon lens, which is more like an apochromat, even though you'd probably be disappointed using the Canon lens as a visual telescope - it will be tough getting and keeping sharp focus on stars with the Canon. They had to use a feedback control system on the focuser in the early paper. They also use a lot of image processing.

Also they're not so much using the speed of the lens for shorter exposure times but for field of view and for high sensitivity.

In general photographic lenses make mediocre telescopes and telescopes make mediocre photographic lenses - try using one of your tubes for some terrestrial photography to see. So it's pretty amazing that the Canon lens performs so well to begin with, that they're able to use it like a fast apochromat, and even more so that they're able to build it out to be roughly equivalent to a really large apochromat. With eight lenses, the early paper claims the instrument is equivalent to a 40cm f/1 refractor. How would you build such a thing? Well, this is how.

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#57

Post by jcims »

perihelions wrote: post #21
jcims wrote: post #17

Earlier quoted context omitted.

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?

This is an extremely long (18 hour) exposure in specialized narrowband spectral filters that have no usefulness for anything other than these particular targets.

Oh nice!!! I looked at a couple sky surveys in different, and it was nowhere to be found in their data, that’s so cool!

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#58

Post by gammarator »

DarkSucker wrote: post #53

Can someone provide/link-to a principle of operation? I looked at references ( https://www.dragonflytelescope.org/publications.html ) but they point to publications that look to be behind pay walls. In particular, I don't see how N co-aligned cameras is any different than N images taken in sequence with one camera (averaging over noise), other than a reduction in time required to take N images with one camera.

> they point to publications that look to be behind pay walls.

If you click the “ADS” link you will find most will have links to a free preprint on arXiv.

> other than a reduction in time required to take N images with one camera.

Life is short!

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#59

Post by gammarator »

tupilaq wrote: post #8

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/

Different science goals, though.

Re: Dragonfly: An optical telescope built from an array of off-the-shelf Canon lens

#60

Post by gammarator »

smaddox wrote: post #44

> 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.

That’s exactly why they are using commercial lenses! Canon’s modern AR coatings are so good that the performance for low-surface brightness imaging beats larger-aperture telescopes which can gather more light but scatter it around the image. See the third page of https://arxiv.org/abs/1401.5473
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