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What is the biggest true apo?

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#51 StarHugger

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Posted 31 July 2020 - 12:20 AM


At some point mankind will learn how to bend and shape light by force field where there are no lenses just empty spaces where the objective would be, a sensor has already replaced a film camera and for the most part they have replaced the eyepiece in mostly all but amateur astronomy so this is not so far fetched. An electromagnetic lens or maglens could create any f ratio at any focal length any moment apochromatically and instantly making the refractor telescope objective size limitless. This is something that might be already a twinkle in the eye of some optical designer but I have never read about anyone preceiving such a device but I did so maybe the tech will at some point make it possible and I will be totally vindicated for my extreme forthought. But until then I'll just enjoy what I can carry round the yard without getting hernia and continue on with my fanciful daydreaming and semi apo hugging.

#52 Astrojensen

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Posted 31 July 2020 - 02:25 AM

At some point mankind will learn how to bend and shape light by force field where there are no lenses just empty spaces where the objective would be,

This can already be done, by using the gravity of large objects, such as planets, stars, galaxies, etc. 

 

There's a mission planned, where a spacecraft will use the Earth's gravity as a giant lens, some 12.742km in diameter, to observe exoplanets directly. The resolution will be an astounding 0.00000000895"! 

 

This "telescope" could show the same amount of details on Mars that our 127mm telescopes can, if Mars was a hundred MILLION times further away. That's 585 light years, if Mars is at a close opposition..! 

 

On a planet close by, such as one around Barnard's Star, for example, the resolution would be the same as observing Mars through a 12 METER telescope! I think you can imagine the possibilities by now.

 

 

Clear skies!

Thomas, Denmark


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#53 fate187

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Posted 31 July 2020 - 08:25 AM

There are chromatic abberations with electron beams in SEMs. Is the deflection of light in a gravity field also dependent on the wavelength? There surely is some effect due to the distance of the center of gravity (or lens center) the ray passes, mimicking something like spherical abberation. hmm.gif



#54 drprovi57

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Posted 31 July 2020 - 01:41 PM

Interesting thought regarding Gravity to bend light - another area of research is "quantum light" - "field of research that uses semi-classical and quantum-mechanical physics to investigate phenomena involving light and its interactions with matter at submicroscopic levels. In other words, it is quantum mechanics applied to photons or light"... stay tuned for some exciting new optical systems...

 

Jason


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#55 gnowellsct

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Posted 02 August 2020 - 03:02 PM

Really?  Is that it?  Is there a scientific need for such a scope or is it just an expensive toy?

Well it used to be common wisdom that there really was no scientific need for a refractor once the coatings on the mirrored designs reached a high level of reflectivity.

 

As it turns out light scatter off a mirrored surface does cap the limiting magnitude of large instruments.  You can increase the aperture but not get more gains in faintness because light scatter creates noise in the images.  This happens around mag 28 or so.  

 

Ultra precise refractors with ultra good coatings however can do better.  But you don't make one big humongo refractor, as the Dragonfly array shows.  So for ultra faint extended object detection you'd want to go with something like the Dragonfly.  But that's very different from building a 40 inch refractor.

 

Refractors can do scientific work, any small aperture instrument can these days, hooked up to watch exoplanet transits or hunting for supernovae or comets with sensitive imaging capabilities.  But I don't think a refractor is *required.*  

 

On the ultra small side the solar GONG project uses a global array of 28 mm (that's right 1.1 inch objectives) to monitor the sun 24/7/365 in solar h-alpha.

 

But in general I think the use of refractors in professional astronomy is very much the exception not the rule.

 

Greg N



#56 gnowellsct

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Posted 02 August 2020 - 03:06 PM

The scientists at the U.S.N.O. use the vintage 26" Clark refractor every single clear evening for scientific study.  Actually though, a "tool" never does science, only the person wielding the toll can actually do science grin.gif  So any tool that works for the intended purpose, is just fine.

This is absolutely true about the person wielding the tool.  A zoologist counting migrating birds with a $100 pair of binoculars is doing science.  The same binoculars at a baseball game are not doing science....


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#57 Astrojensen

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Posted 02 August 2020 - 03:11 PM

As it turns out light scatter off a mirrored surface does cap the limiting magnitude of large instruments.  You can increase the aperture but not get more gains in faintness because light scatter creates noise in the images.  This happens around mag 28 or so.  

Source on that, please. The HST has imaged objects fainter than mag 30. 

 

 

Clear skies!
Thomas, Denmark



#58 gnowellsct

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Posted 02 August 2020 - 03:15 PM

Source on that, please. The HST has imaged objects fainter than mag 30. 

 

 

Clear skies!
Thomas, Denmark

Maybe it was 30 vs 32.  I put up a link to the Dragonfly.  It has had a lot of coverage these past few years.  It goes fainter than HST and has a much wider fov.

 

Greg N



#59 gnowellsct

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Posted 02 August 2020 - 03:19 PM

Here Thomas you can read this and let us know what it says.   The dragonfly has been around for a while.   There was a presentation about it at NEAF.  GN


Edited by gnowellsct, 02 August 2020 - 03:20 PM.

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#60 Astrojensen

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Posted 02 August 2020 - 03:33 PM

Here Thomas you can read this and let us know what it says.   The dragonfly has been around for a while.   There was a presentation about it at NEAF.  GN

Very interesting! I'll have to read it thoroughly, to make sure I grasp it all. Fortunately, it's well written and not boring. 

 

 

Clear skies!
Thomas, Denmark


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#61 gnowellsct

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Posted 02 August 2020 - 03:36 PM

Very interesting! I'll have to read it thoroughly, to make sure I grasp it all. Fortunately, it's well written and not boring. 

 

 

Clear skies!
Thomas, Denmark

There was also an article in S&T or Astronomy.  


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#62 Cotts

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Posted 02 August 2020 - 04:54 PM

How much do these scopes weigh?  My 312mm f2064mm dob-mounted Serrurier (75lb) is looking pretty good now...

Well, hello, there!  Your 12.5 inch has better resolution and better contrast transfer than a 10-inch TEC Refractor.  

 

Dave



#63 Freakshow

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Posted 03 August 2020 - 02:25 AM

How is the Dragonfly array different from stacking 24 subs?  



#64 Arcamigo

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Posted 04 August 2020 - 11:05 AM

Acquiring 48 images simultaneously, instead of sequentially, decreases the integration time, and allows the researchers to get a more accurate flat field calibration, which is key to their research. Also, the paper states that standard reflecting telescopes are limited to surface brightness levels of about 28 mag per square arcsecond. Absolute magnitude and surface brightness are not the same thing unless the object has an area equal to the unit area.




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