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Comparing Apples to Diamonds

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#1 mic1970

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Posted 16 April 2019 - 11:06 AM

I'm somewhat close to trading my some scopes and buying an 8" Edge HD.  I've been reading reviews that compare it to refractors.  I understand the comparison and appreciate the time someone took to review the two, but all the ones I've seen compared the $1K SCT to multi-thousand refactors or Taks.  How does it compare to a $1000 refractor?  That is what I would like to know.  

 

Sorry... done with my soap box.   



#2 Cotts

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Posted 16 April 2019 - 11:46 AM

What kind of $1000 refractor?  For visual?  For imaging?  For both?

 

A $1000 triplet APO refractor is very likely no larger than 80mm.  An 8" EDge (200mm) will easily outperform it in all aspects of visual performance except field of view.  The APO will be a far better imaging instrument...

 

A $1000 ED or "Semi"-APO refractor will probably be no larger than 5" (125mm.)   The advantage of the 8" EDge over a 5" or  scope will be less but still noticeable in visual use....  The ED scope will need careful management of Chromatic Aberrations if used for photography.

 

A $1000 Achromatic refractor would likely be a 6-incher and be very subject to chromatic aberration in visual and absolutely unuseable for photography (exception - mono camera and color filters.....).  The 8" Edge would still outperform it slightly but noticeably in the visual realm..... 

 

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#3 MrRoberts

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Posted 16 April 2019 - 12:11 PM

I loooove my C-8/E. I store and use it for visual in southern AZ these days where my parents live. I did use it a few times to take some short run shots of Jupiter when I was first dabbling in AP, but be aware this is not really a good scope to learn ap with. Its easy to set up (size/weight) and although I use it on an Ioptron AZM Pro I have seen others set up on smaller manual mounts. Its quite a cost and visually effective OTA no matter how you mount it.

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#4 HenryB

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Posted 16 April 2019 - 01:50 PM

SCTs are more fussy than small refractors. This includes collimation and thermal management. You need to learn about these things to get good performance, unlike a small refractor. If you are willing to do this, the brighter images of a C8 HD will be the better choice. I have used SCTs for a long time, and my current C14 HD is the best of the lot.



#5 bobhen

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Posted 16 April 2019 - 02:35 PM

I'm somewhat close to trading my some scopes and buying an 8" Edge HD.  I've been reading reviews that compare it to refractors.  I understand the comparison and appreciate the time someone took to review the two, but all the ones I've seen compared the $1K SCT to multi-thousand refactors or Taks.  How does it compare to a $1000 refractor?  That is what I would like to know.  

 

Sorry... done with my soap box.   

Those reviews were “performance” reviews not “dollars per-inch of aperture” or “value” reviews.

 

What you are doing is taking one of the refractor’s weaknesses (cost per-inch of aperture) and comparing it to a scope that costs less per-inch.

 

One could also ask: Why pay $1,000 for only an 8-inch SCT optical tube when one could get a larger Newtonian and on a Dobsonian mount to boot for that $1,000? So why are you selecting an 8-inch SCT when a Newtonian will gather more light for less money?

 

One could also ask: Why would I want an 8-inch telescope that performs worse than an 8-inch telescope of another design?

 

A) If one is interested in the most aperture per dollar, the Newtonian wins.
B) If one wants the best contrast, light throughput and definition per inch, the apo refractor wins.
C) If one wants the most compact tube per inch then the SCT wins.

 

That $1,000 will buy you one from A, B or C from the above.

 

Once a budget is set, everything else becomes a compromise or tradeoff.

 

Bob


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#6 mic1970

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Posted 16 April 2019 - 02:55 PM

Well said.

Those reviews were “performance” reviews not “dollars per-inch of aperture” or “value” reviews.

 

What you are doing is taking one of the refractor’s weaknesses (cost per-inch of aperture) and comparing it to a scope that costs less per-inch.

 

One could also ask: Why pay $1,000 for only an 8-inch SCT optical tube when one could get a larger Newtonian and on a Dobsonian mount to boot for that $1,000? So why are you selecting an 8-inch SCT when a Newtonian will gather more light for less money?

 

One could also ask: Why would I want an 8-inch telescope that performs worse than an 8-inch telescope of another design?

 

A) If one is interested in the most aperture per dollar, the Newtonian wins.
B) If one wants the best contrast, light throughput and definition per inch, the apo refractor wins.
C) If one wants the most compact tube per inch then the SCT wins.

 

That $1,000 will buy you one from A, B or C from the above.

 

Once a budget is set, everything else becomes a compromise or tradeoff.

 

Bob



#7 Astrojedi

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Posted 20 April 2019 - 08:31 AM

It is very simple...

 

While the APO will be easier to use, cool faster and provide a larger fov it will be significantly limited in aperture which is the achilles heel of the refractor design.

 

A $500-$1000 8” - 9.25” SCT will significantly outperform any $1000 APO in all other respects. 

 

A $700 10” Dob will slightly outperform the 8” SCT and significantly outperform the $1000 apo

 

My suggestion would be to first get the 8” SCT or 10” dob depending on the ergonomics you prefer and then adding a small refractor as a second scope. They are very complimentary.

 

And the worst thing you can do in the hobby is blindly chase optical quality. It is great for bragging rights but little difference at the EP especially in larger apertures (>6”)


Edited by Astrojedi, 20 April 2019 - 08:37 AM.


#8 SeattleScott

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Posted 20 April 2019 - 08:39 AM

4” Apo and 8” SCT is not an either/or question. The correct answer is both. They are very different scopes that compliment each other nicely. I would never trade an 8” SCT for a 4” Apo but adding the 4” Apo in addition to the SCT would be awesome.

Scott
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