# Dragonfly, Powered by Canon Lenses



## Canon Rumors Guy (Jul 12, 2014)

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<p><span style="color: #676767;">Dragonfly is an innovative, multi-lens array designed for ultra-low surface brightness astronomy at visible wavelengths. Commissioned in 2013, the array is proving capable of detecting extremely faint, complex structure around galaxies.</span></p>
<p style="color: #676767;">According to Cold Dark Matter (CDM) cosmology, structure in the Universe grows from the “bottom up”, with small galaxies merging to form larger ones. Evidence of such mergers can be seen in faint streams and filaments visible around the Milky Way Galaxy and the nearby M31 galaxy.</p>
<div id="attachment_16863" style="width: 310px" class="wp-caption alignnone"><a href="http://www.canonrumors.com/wp-content/uploads/2014/07/dragonfly.jpg"><img class="size-full wp-image-16863" src="http://www.canonrumors.com/wp-content/uploads/2014/07/dragonfly.jpg" alt="Image Copyright University of Toronto" width="300" height="450" /></a><p class="wp-caption-text">Image Copyright University of Toronto</p></div>
<p style="color: #676767;">But the CDM model predicts that we should see more of this structure than is currently observed. However, images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure.</p>
<p style="color: #676767;">Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using ten, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.</p>
<p style="color: #676767;"><strong><a href="http://dunlap.utoronto.ca/instrumentation/dragonfly/" target="_blank">Read More at the University of Toronto</a></strong></p>
<p style="color: #676767;"><strong><span style="color: rgb(255, 0, 0);">c</span>r</strong></p>
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## Hesbehindyou (Jul 12, 2014)

Canon Rumors said:


> images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure [...] Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using ten, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.



?!

Is this using commercially available lenses with non-commercially available coatings?


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## Vossie (Jul 12, 2014)

Canon Rumors said:


> It achieves this using *ten*, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.



I only count 8.


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## lintoni (Jul 12, 2014)

Vossie said:


> Canon Rumors said:
> 
> 
> > It achieves this using *ten*, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.
> ...


The complete article describing the Dragonfly Array is available at arxiv.org/pdf/1401.573. The article states that it is an array of 8 lenses, but may be modified easily to hold up to 15!


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## lintoni (Jul 12, 2014)

Hesbehindyou said:


> Canon Rumors said:
> 
> 
> > images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure [...] Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using ten, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.
> ...


No, from the article I linked to


> ...the latest generation of Canon lenses features the first commercialized availability of nano-fabricated coatings...


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## wtlloyd (Jul 12, 2014)

Far from unique application.
SuperWasp.

https://www.google.com/search?q=SUPERWASP+IMAGES&rlz=1C1CKMB_enUS568US568&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ei=bkfBU723HdPfoASQ_YKQBQ&ved=0CBwQsAQ&biw=1390&bih=872#q=SUPERWASP+astronomy+IMAGES&tbm=isch


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## David Hull (Jul 12, 2014)

Vossie said:


> Canon Rumors said:
> 
> 
> > It achieves this using *ten*, commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.
> ...


It looks like it could hold 10. Maybe the other two are back-ordered at B&H or had to go back to Irvine for adjustment ;-)


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## jrista (Jul 12, 2014)

I chatted with one of the guys on this project over on the CloudyNights forums a couple months back. Back then, he said the current version of DragonFly had 8 commercially available Canon EF 400mm f/2.8 L II lenses, however that they were in the process of adding four more for a total of 12. Their ultimate goal was to get up somewhere round 20-24. To achieve that, they had to redesign the mount that holds the lenses. The original version was a squareish contraption, and I think the new approach uses something more modular, some kind of hexagonal or circular cells that can be attached to each other.

Anyway, it's a pretty cool setup, incredibly sensitive for an earth-based telescope.


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## LetTheRightLensIn (Jul 12, 2014)

pretty cool

hope it brings some good results


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## tolusina (Jul 12, 2014)

A couple questions come to mind;
Are Canon engineers going like "whoa, I had no idea our stuff could do that!!"

Are any astronomers building similar arrays using Zeiss, Nikon, Sony, Pentax or any other off the shelf glass?



jrista said:


> I chatted with one of the guys on this project ....


What do such arrays use for image recording?


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## emko (Jul 13, 2014)

it said they have used it in 2013 is there any pictures that we can see?


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## Pieter (Jul 13, 2014)

I'm one of the astronomers who put the thing together - thanks for the interest!
We use standard SBIG off the shelf astronomical cameras as detectors. The lenses are fast enough, and the integration times long enough, that read noise is negligible even with only modest cooling of the detectors.

We've published a paper that describes the thing; this is the publicly available version, for those who are interested:
http://arxiv.org/abs/1401.5473
As you may notice we're mostly concerned with scattered light; we measured the point spread function out to ~1 degree (Fig 6) and found that it is amazingly well controlled (this was recently confirmed by another group, who compared our results to a wide range of other telescopes).

We've had some science results out this year, too - and we just put out a press release on the discovery of seven very faint galaxies (which might be why CR posted it today!). The reason why we went with Canon is that I'm a Canon shooter (with a special interest in dragonflies..) and I was aware of the quality of the updated lenses. I know lenses and Bob knows telescopes, so it all worked really well.

Other groups have used Canon lenses for astronomical purposes, but typically just to cover a wide area of sky - not to detect very low surface brightness emission, beyond the reach of reflecting telescopes.
Anyway, sorry for rambling on - it's a fun project!


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## epsiloneri (Jul 13, 2014)

Thanks Pieter! I read your paper with interest. Dragonfly is a very cool project from an astronomical perspective, but there are also several points that could be of interest for the more general Canon shooter / astrophotographer:


 The optics are found to be essentially diffraction limited, at least <1 degr of the center, which is quite amazing. This means that the image sensor will give increasingly sharp images all the way to a pixel pitch of about 0.63 µm before out resolving the lens. This is 6.8 times smaller than the effective pixel size of a 7D and would imply a 839 MP APS-C or 2.18 GP FF sensor! The lens resolution is likely decreasing from diffraction limited away from the central regions, but this sets the upper usable limit for sensor resolution. In practice, there will be other things limiting the resolution, like turbulence in the atmosphere (for anything shot at a distance).

 Strehl ratios between 0.2-0.8 (where 1.0 is 'perfect') indicates that the lens provides a very high contrast (which we knew). I wonder if the Canon designers have deliberately tried to keep the effective point-spread function constant with wavelength (reducing colour mis-matches in images), deacreasing the Strehl at short wavelengths.

 The precise focus of the lens is strongly temperature dependent: a temperature difference as small as 1C gives a significant shift in focus. This is mostly relevant for exposing an extended period, like in astrophotographical applications.

 The foot of the 400/2.8L IS II provided by Canon shows significant flexure so that care must be taken during tracked exposures.

 For those wanting more images, I found two papers accepted by ApJL providing such for M101:

http://arxiv.org/abs/1401.5467
http://arxiv.org/abs/1406.2315

The project seems to have left the start-up phase only recently (they are apparently still extending the array), so I'm sure we can expect more results soon. Note, however, that they are targeting the faint structures around galaxies, and with only two broad-band filters ('r' and 'g'), meaning the images will probably not be as spectacular aesthetically as narrow-band imaging of more photogenic nebulae. But when they're done with the galaxies perhaps they can put in some nebular filters instead, and give us the most surface-brightness sensitive images of nearby nebulae 

Actually, surveying for nearby supernova remnants in H-alpha might be a pretty interesting project scientifically in itself for this Dragonfly.

And then we have the transiting exoplanets, of course, but that has probably been covered pretty well by the already mentioned super-WASP projects and the upcoming NASA TESS mission.


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## scyrene (Jul 13, 2014)

What I wouldn't give to have just one of those lenses... With all those, they couldn't miss one, right?


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## dolina (Jul 13, 2014)

A financial question. Did Canon USA, their distributor or dealer give you guys a discount on the purchase? You guys did buy 15 400s and are looking to almost double it? ;D

And many thanks for the academic paper and epsilloneri's highlights. It is awesome to know that my lens wont get outresolved any time soon.


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## capcoast (Jul 13, 2014)

I won't pretend to understand all of what you guys do, Pieter, but the paper you linked to certainly provides a good layman's overview. Also good to see you have my kind of sense of humour - footnote 13 on page 9 gave me a long chuckle


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## Pieter (Jul 14, 2014)

epsiloneri said:


> Actually, surveying for nearby supernova remnants in H-alpha might be a pretty interesting project scientifically in itself for this Dragonfly.



Yes - the problem is that we'd have to get different detectors, with much lower read noise. With narrow band filters the read noise is no longer smaller than the noise from the sky background, and the setup is no longer competitive. We are considering other projects to augment what we're doing now - particularly when the moon is up and our main science is on hold. We're also hoping to build a bigger array at some point in the future - with 50 lenses we'd effectively have a 400 mm f/0.4 lens, with a 1m aperture.


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## jrista (Jul 14, 2014)

Pieter said:


> epsiloneri said:
> 
> 
> > Actually, surveying for nearby supernova remnants in H-alpha might be a pretty interesting project scientifically in itself for this Dragonfly.
> ...



Any chance you guys have some forward knowledge of larger ultra-low-noise sensors coming out? Sony's newer ICX line are pretty nice, with very low dark current, and pretty low read noise (~5e-?). But the sensors are tiny. Really tiny, as in 1/3" or maybe 1/2", which is about half the size of a KAF-8300 and about 1/5th the size of a full-frame/KAF-11002 sized sensor. Would be really nice to know that Sony has some larger sensors based on their new low-noise technology coming out... 



Pieter said:


> We are considering other projects to augment what we're doing now - particularly when the moon is up and our main science is on hold. We're also hoping to build a bigger array at some point in the future - with 50 lenses we'd effectively have a 400 mm f/0.4 lens, with a 1m aperture.



f/0.4 @ 1m...now that would *really *start to surpass, just in specs, some of the really large earth-based telescopes for sensitivity.


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## tolusina (Apr 4, 2016)

Don't know if this is new or old news.
The Dragonfly Array is up to 24 lenses, anticipating 50!
http://nautil.us/issue/32/space/how-to-discover-a-galaxy-with-a-telephoto-lens





.


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## Bdube (Apr 4, 2016)

jrista said:


> Pieter said:
> 
> 
> > epsiloneri said:
> ...



The gains from lens arrays are not so perfect; for example, the large binocular telescope uses 2 large telescopes and achieved only about a 40% gain.


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## Bdube (Apr 4, 2016)

Pieter said:


> I'm one of the astronomers who put the thing together - thanks for the interest!
> We use standard SBIG off the shelf astronomical cameras as detectors. The lenses are fast enough, and the integration times long enough, that read noise is negligible even with only modest cooling of the detectors.
> 
> We've published a paper that describes the thing; this is the publicly available version, for those who are interested:
> ...



Your results evaluating the lenses are quite interesting. I am not sure they are correct, however. I have measured 6 of these lenses under photopic light at an aperture of f/4, and even then they are nowhere near the diffraction limit. I have little to no doubt they are designed this well - but realizing such a performance in large scale manufacture, when I have measured to the contrary, leaves me skeptical.

I am not familiar with the technique you have used to measure the wavefront error, but judging by the use of defocused images, it seems to measure only wavefront curvature, not tip/tilt, yes? I am then confused how your synthesized interferogram is dominated by tilt, if the test would be unable to see tilt. 

Further, your defocus is quite enormous, and I would suspect that the very large defocus term you have added to the zernike polynomial may be masking other aberrations. However, I am not familiar with the method, and perhaps it is robust with respect to that parameter. It seems that by increasing the size of the defocused spot, you will increase the spatial resolution of the reconstructed wavefront, but decrease the sensitivity of the test.

Are you able to describe in more detail the workings of this method? It intrigues me, but I have my doubts as to its accuracy.


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## jrista (Apr 4, 2016)

Bdube said:


> jrista said:
> 
> 
> > Pieter said:
> ...



That is because the gain is relative to the square root of the number of lenses used. With 2 telescopes, you gain SQRT(2) or ~1.4x...or ~40%. With 50 lenses, the gain would be ~7.1x, or 610%. Even at full retail cost, arraying 50 400mm f/2.8 L II lenses is _*significantly *_cheaper than building a gigantic telescope on top of a mountain. With over a seven fold gain in final SNR for the cost of around $500,000, I'd say that's a steal.


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