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ACF vs EDGE HD vs Nexstar GPS optic (viewing only)

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#1 daslolo

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Posted 26 March 2020 - 06:19 PM

The ACF I had was sharp til the edge, no chromatic aberration on the moon, and also seemed bright on nebula for an 8"

But Meade mount and software were not my cup of tea so I'll go Celestron

How do the old starbright of the GPS series or new Xlt edge and non edge compare in term of sharpness, CA and brightness?

 

Interesting in viewing only.



#2 junomike

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Posted 26 March 2020 - 08:43 PM

I've had all three and IMO the EdgeHD was the brightest and offered the most aesthetically pleasing view due to flatness and neutral tone.

The 10" ACF seemed a tad sharper than my NS11GPS but as both exhibited some tone/tint (seen mainly on Luna) and the Celestron was a Fork Mount

I kept it instead.


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#3 daslolo

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Posted 26 March 2020 - 08:54 PM

awesome! thanks

 

i'm happily surprised to hear that the edge is brighter, i thought the extra flattening lenses would absorb a bit more light



#4 junomike

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Posted 26 March 2020 - 09:07 PM

awesome! thanks

 

i'm happily surprised to hear that the edge is brighter, i thought the extra flattening lenses would absorb a bit more light

Probably a bad term by me as these weren't all the same Aperture.

If by brightest you mean, light gathering, then Aperture wins regardless of design as the difference isn't great enough

to overcome even 1" difference (IMO).

 

I was referring to more of the purity/cleanliness/whiteness of the Image.  For that the EdgeHD seemed to rival a good Newt whereas

I find all other SCT's have a distinct yellow tint to them (noticeable on Luna).


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#5 Eddgie

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Posted 27 March 2020 - 09:28 AM

If your are not imaging then the benefit of the EdgeHD would be largely influenced by the kind of eyepeices you use and your tolerance to off axis aberrations (field curvature and coma). 

 

If used with well corrected eyepieces like the Panoptic 41mm, the standard SCT will give very good across the field performance (not as good as the EdgeHD, but perhaps acceptable if you are not bothered by stars that are not quite perfect at the edge).

 

If you use modern ultra wide types like the 31mm Nagler, and you are sensitive to off axis aberrations, then the EdgeHD will be a better choice.

 

As to the center of the field (for planetary observing) the EdgeHD has zero benefit and here it is all up to the fabrication quality.  The quality on these scopes can vary a lot, and you might get an EdgeHD with medium quality finish and a standard SCT with near perfect optics, or you might get a dog standard SCT and an EdgeHD with very good optics. Sample by sample, Celestron scopes do vary in quality of manufacture.

 

Now over the last decade and a half, I have seen a huge number of posts from people that say that they only care about what is at the center of the field, and could care less about off axis performance, and there are people like me that are quite concerned with off axis performance (because once you have enjoyed it, it is hard to go back to scopes that are aberrated at the edge) so which is best I think can be greatly influenced by your tolerance to off axis aberration and the kinds of eyepieces you are planning to use with it.


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#6 Jeffmar

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Posted 28 March 2020 - 05:00 PM

I have a 30+ year old C11 and a much newer C11 EdgeHD. The difference was pretty obvious. It was like the newer scope was 3 or 4 inches bigger. Images were sharper and brighter. I have also compared a much newer C11XLT to my C11 Edge. Visually they were both very good. Using the same 68 degree eyepieces I could not tell a difference. 


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#7 daslolo

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Posted 28 March 2020 - 10:59 PM

I have a 30+ year old C11 and a much newer C11 EdgeHD. The difference was pretty obvious. It was like the newer scope was 3 or 4 inches bigger. Images were sharper and brighter. I have also compared a much newer C11XLT to my C11 Edge. Visually they were both very good. Using the same 68 degree eyepieces I could not tell a difference. 

what do you think causes the new tube to look 3" brighter?



#8 junomike

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Posted 29 March 2020 - 07:24 AM

what do you think causes the new tube to look 3" brighter?

I've experienced this as well and IMO It's a combination of the coatings being of older vintage (less initial transmission) as well as slight deterioration over time which

causes the overall transmission of the system to be lower resulting in what appears to be less Aperture as compared to newer OTA's.



#9 daslolo

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Posted 29 March 2020 - 10:30 AM

I read about old tubes using silver and that tarnishes after a while



#10 carolinaskies

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Posted 29 March 2020 - 10:54 AM

I've experienced this as well and IMO It's a combination of the coatings being of older vintage (less initial transmission) as well as slight deterioration over time which

causes the overall transmission of the system to be lower resulting in what appears to be less Aperture as compared to newer OTA's.

This is correct. 

A 30 year old Celestron would have lower transmission coatings from the start.  When the XLT Starbright coatings started to be used in very late 90's it upped the game significantly in old coatings to new coatings comparison.  Also, these were not silvered like certain early models so they did not tarnish, but coatings do degrade from factory to a nominal figure over time as proven by research at big optical facilities and observatories.  So a 30 year old effective transmission might be 75-80% where a new-10 year old might be 90-96%. 

Another thing which has to be added into any comparison is the external pieces and their quality (and coatings).  A standard mirror diagonal vs dielectric coated diagonal will transmit less light so that comparisons can be apples to oranges if this difference isn't also taken into account by swapping these externals between two telescopes.  

 



#11 Jeffmar

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Posted 29 March 2020 - 01:06 PM

what do you think causes the new tube to look 3" brighter?

I think it was a combination of the older coatings and some degradation over the years. 

 

The newer scope was a sharper example, getting more details, which also might look like an image from a larger scope.


Edited by Jeffmar, 29 March 2020 - 01:12 PM.

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#12 daslolo

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Posted 02 April 2020 - 02:58 AM

Interesting.

 

Tonight was the first night with the Nexstar 11 GPS.

Light gathering I could tell was slightly better than the new 8 ACF by looking at Orion through binoviewers and a pair of el cheapo swony 18mm and Orion was maybe 10 degrees lower, almost in the trees. It looked almost as bright as the ACF through the excellent 2" ES82 18mm.

Star crispness: the ACF wins hand down as the NS had double wings. This could be the tube that hasn't yet acclimated, those carbon tubes take longer and I waited no more than 20 minutes smile.gif

 

Eyepieces matter a lot. What 1.25" under 50$ a pop do you guys recommend for brightness?



#13 Bill Barlow

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Posted 02 April 2020 - 01:33 PM

The NS11 should be noticeable brighter than the 8" Meade at similar magnifications since it has double the light grasp.  



#14 daslolo

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Posted 02 April 2020 - 04:44 PM

Does a 2" 82* eyepiece show images brighter than a 1.25" 72* eyepiece of the same mm?

 

Here are more details:

All is from memory since I don't have the ACF nor the es82.

Binos with 18mm 72* eyepieces on the 11" provide similar perceived magnification as es82 18mm on the 8" acf (math don't add up so maybe it's a perception thing due to the AFOV difference, I'll check with a single 72* on the 11")

In this setup the 11" looks a bit dimmer than the 8", and less crisp (I'll try after leaving the scope outside for an hour or two).

Bino on the 8" looked way dimmer but I don't remember which eyepieces, it might have been 9mm so yeah...

When I swapped the binos for a single 1.25" that gave half magnification, orion showed an extended part which I couldn't see before using wide eyepiece.

The viewing conditions are also less favorable than when I had the ACF/ES with a half moon and loads of air turbulences.



#15 Bill Barlow

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Posted 02 April 2020 - 07:38 PM

For the same magnification/exit pupil you would need a 13mm eyepiece for the 8" scope while using the 18mm in the C11. The C11 would have a larger exit pupil vs. the M8, so it should be a bit brighter.  Seeing conditions/turbulence might cause the C11 images to be affected more because of its greater resolution over the M8.  


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