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Crazy question: Combining light from multiple telescopes for high brightness at low power?

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#1 smiller

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Posted 06 December 2018 - 11:45 AM

Just a crazy thought,

 

Given the limits of optical systems to present a brighter image to the pupil than what we can see unaided (other than for point sources like stars), our only options today are:

 

1) Magnify an image with, at best, the same surface brightness.

2) Do this with a binocular telescope so that at least each eye gets its own fully bright light path.

3) Use electronically assisted astronomy.

 

What if we were able to bring the image from several small refractors (say four 80mm refractors) to focus together.  Would this allow (relatively) low magnification views with 4x the surface brightness we can get with one scope?

 

I’m not talking about bringing the scopes into coherent focus as in optical intereferometry systems as I’m not attempting to increase angular resolution.  I’m only talking incoherent focus like in the Very Large Telescope:

 

https://www.eso.org/...a/news/eso1806/

 

if you add enough scopes, you could call the system “bug eye”!

 

I’m ignoring practical cost, size concerns right now.  In the end, I expect a more practical solution is to rely on continued advancements in EEA: Use ever larger advanced CMOS sensors and high resolution microprojectors to present an enhanced virtual eyepiece view.   But I thought I’d ask...

 

Cheers,

 

Steven

 


Edited by smiller, 06 December 2018 - 01:47 PM.


#2 Jon Isaacs

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Posted 06 December 2018 - 12:56 PM

Your link seems to be broken.

One thing to keep in mind:  The ESO is a camera system so it is not limited in surface brightness by exit pupil considerations. 

Jon



#3 TOMDEY

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Posted 06 December 2018 - 01:49 PM

Hi, Steven... the short answer is "No". That is to say, IF the individual scopes are already optimized for speed and field... that's it. I could go into all sorts of gyrations to justify that blithe conclusion... but the Occam's Razor to this one is Emmy Noether's Theorem. No more to be gained.

 

On the other hand... if the individual scopes are slow, like unnecessarily slow, then YES, you can combine them, like the six-shooter that used to be up there on Mt. Hopkins. These were six 72-inch F/2.7 PMs (from surplus stock) with relay optics that further slowed them down (to F/31.6). That DID (of course) get all the light to the detector, but over a miniscule field.

 

PS Emmy's Theorem is essentially "No Free Lunch", as dictated by Mother Nature.  Tom



#4 smiller

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Posted 06 December 2018 - 01:54 PM

Your link seems to be broken.

One thing to keep in mind:  The ESO is a camera system so it is not limited in surface brightness by exit pupil considerations. 

Jon

 

Hopefully fixed.

 

Yes, ESO uses cameras and has a huge instrument, hence I referenced using small scopes for direct viewing with the proper magnification and exit pupil (ex about ~12x-16x with ~5-7mm exit pupil for 80mm refractors) .  Not sure if possible in a non-prime focus system.  

 

Steven



#5 havasman

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Posted 06 December 2018 - 03:48 PM

Are you talking about something like this, the Dragonfly multi-lens array?

 

http://www.dunlap.ut...ion/dragonfly/ 



#6 mashirts

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Posted 06 December 2018 - 06:57 PM

Maybe the wording you are looking for is augmented reality.  

 

https://www.newscien...niverse-closer/



#7 smiller

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Posted 06 December 2018 - 07:07 PM

Are you talking about something like this, the Dragonfly multi-lens array?

 

http://www.dunlap.ut...ion/dragonfly/ 

I certainly like the name!.  This is similar but this appears to have a camera on each scope so it is adding the light electronically.  So it’s very close and is capitalizing on the same concept of i depressing the surface brightness at a given image area by adding multiple together, although I was wondering if the light could be added optically.

 

- Steven



#8 smiller

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Posted 06 December 2018 - 07:09 PM

Maybe the wording you are looking for is augmented reality.  

 

https://www.newscien...niverse-closer/

Ha!  Ok, now that’s just cheating!  



#9 TOMDEY

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Posted 06 December 2018 - 09:50 PM

I certainly like the name!.  This is similar but this appears to have a camera on each scope so it is adding the light electronically.  So it’s very close and is capitalizing on the same concept of i depressing the surface brightness at a given image area by adding multiple together, although I was wondering if the light could be added optically.

 

- Steven

Emmy's Theorem places an upper bound on (theoretically possible) optically-additive to 4 pi combined telescopes' exit pupil solid-angular subtent.

For myriad practical reasons, the limit is closer to 2 pi. (assumes flat, black-body, one-sided detector!)

And for Really Practical reasons, it's more like 1 pi... which would be an extremely-aggressive F/0.287 feed!

 

You can see where this is going... most detector arrays that comprise lenticules, cannot even accept an F/2 feed gracefully, let alone a 1 pi feed!

A max realistic F/2 feed is a rather pathetic 0.1995 solid-angular subtent.

 

As always... No Free Lunch!  And THAT's why the Mt. Hopkins six-shooter was decommissioned. Cool idea, fundamental limitations, even more severe Practical Limitations!

 

Virtually ALL of these attempts are Miniscule Field, adaptive optics. Granted, they are arbitrarily large entrance pupil (your original posit) and you even propose forgoing phasing to gain resolution... which doesn't leave one with much to show for all the effort.

  

On the other hand, combining signals Electronically is sensible... the addition would, of course, be incoherent, but still interesting, as you propose!

 

PS: Combining signals coherently is the Gold Standard, and is not precluded by Emmy's Theorem... indeed, would be Encouraged by it! That's what we do with radio telescope arrays, but essentially impractical at optical wavelengths, except in highly-restrictive special cases... aka interferometry.

 

Anyway, those are some of the restrictions that Mother Nature and practical technologies put on what we can pull-off.  Tom



#10 smiller

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Posted 07 December 2018 - 09:56 AM

Emmy's Theorem places an upper bound on (theoretically possible) optically-additive to 4 pi combined telescopes' exit pupil solid-angular subtent.

For myriad practical reasons, the limit is closer to 2 pi. (assumes flat, black-body, one-sided detector!)

And for Really Practical reasons, it's more like 1 pi... which would be an extremely-aggressive F/0.287 feed!

 

You can see where this is going... most detector arrays that comprise lenticules, cannot even accept an F/2 feed gracefully, let alone a 1 pi feed!

A max realistic F/2 feed is a rather pathetic 0.1995 solid-angular subtent.

 

As always... No Free Lunch!  And THAT's why the Mt. Hopkins six-shooter was decommissioned. Cool idea, fundamental limitations, even more severe Practical Limitations!

 

Virtually ALL of these attempts are Miniscule Field, adaptive optics. Granted, they are arbitrarily large entrance pupil (your original posit) and you even propose forgoing phasing to gain resolution... which doesn't leave one with much to show for all the effort.

  

On the other hand, combining signals Electronically is sensible... the addition would, of course, be incoherent, but still interesting, as you propose!

 

PS: Combining signals coherently is the Gold Standard, and is not precluded by Emmy's Theorem... indeed, would be Encouraged by it! That's what we do with radio telescope arrays, but essentially impractical at optical wavelengths, except in highly-restrictive special cases... aka interferometry.

 

Anyway, those are some of the restrictions that Mother Nature and practical technologies put on what we can pull-off.  Tom

I’m afraid your explanation is a bit above my pay grade, but your reference to the original University of Arizona Multiple Mirror Telescope (MMT) is spot on.  Here is one old article on it, which also lists other similar concepts:

 

https://www.mmto.org/node/442

 

Cheers,

 

Steven



#11 quazy4quasars

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Posted 07 December 2018 - 05:46 PM

I like to think of my 30" as the combined light of 25 6" scopes.

(It's really a bit more because the secondary is smaller in proportion.)


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