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Edge HD vs. XLT

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#51 Edrow10

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Posted 26 November 2018 - 10:38 PM

Daniel, that's a very nice write-up. Thanks, enjoyed it.

 Best,



#52 glmorri

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Posted 27 November 2018 - 11:47 PM

Daniel, I appreciate having the benefit of your experience and analyses on this and many other occasions.  Thank you for taking the considerable time it required to write your post. 

 

Awhile back I posted a piece that made a statistical comparison of the interferometry tests of, among other things, Edge alone vs. XLT+Edge 8” and 11” SCTs (manufactured by Synta in China):

 

https://www.cloudyni...a-c11s-and-c8s/

 

The summary statistics showed little, if any, difference in the Strehls for the Edge compared to the overall Synta SCTs.

 

“The Edge SCT test results were included in the Synta category, but were also looked at separately.  Edge SCT average Strehls  did not appear different from all Syntas for either the C8s (.894 vs .904) or the C11s (.909 vs .914).  This is not surprising, since the purpose of the Edge optics is to correct off-axis aberrations inherent in conventional SCTs, but interferometry evaluates optics on-axis.  Indeed, if we compare on- and off-axis Strehl ratios for a conventional SCT  (figure 9.6, Telescopes, Eyepieces and Astrographs) versus an aplanatic Flat-Field SCT (figure 9.17) that “…differs only slightly from that of Celestron’s EdgeHD” (p. 256), we see that the Edge design has a slightly lower (-.08) Strehl on-axis, but a better and much wider acceptable performance range off-axis”

 

These interferometry findings are consistent with your conclusions about the Edge vs, XLT SCTs.

 

Best Regards,


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#53 Sarkikos

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Posted 28 November 2018 - 06:56 AM

The EdgeHDs are SCTs with built-in correctors.    That's basically what the tests show.

 

Mike


Edited by Sarkikos, 28 November 2018 - 07:05 AM.


#54 WyattDavis

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Posted 28 November 2018 - 07:22 AM

This has been a very interesting thread. My take-aways so far are that if I do the following with my EdgeHD 8":

  • Keep it in tight collimation
  • Use my "stage 1" DSP TEMPest fan in the Fastar port before viewing to cool the baffle and the scope in general (I usually do this for about 30 minutes).
  • CAREFULLY replace the secondary in the same orientation it was in before I removed it to use the fan (so as to keep collimation)
  • Use my "stage 2" active vent fans throughout an observing session to keep the primary/interior of the OTA at ambient temperature
  • Not care about using a reducer and keep the scope at its native f/10ish focal length
  • Use well-corrected eyepieces (TV Ethos, Nagler, Panoptics in my case).

Then, I should have a well-performing scope that puts up cleaner images off-axis/at the edges of the FOV vs a regular XLT C8 and that will otherwise be about the same in performance on-axis. To get this increment of additional performance (which is mostly useful for wider-field viewing in any case), I will have had to have spent more for the EdgeHD itself over the XLT and buy/power/use the fans.

 

Failing to use both types of fans as described, I might actually end up with a scope that actually cools off more slowly than a standard C8 XLT...

 

Is that a fair summation?


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#55 ensign

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Posted 29 November 2018 - 09:01 PM

Daniel, that's a very nice write-up. Thanks, enjoyed it.

 Best,

Nice?  Maybe.  Lengthy?  Certainly. Argumentum verbosium?  Possibly.

 

In any case, doesn’t jibe with my experience.

 

Is it too far-fetched to believe that Celestron actually achieved their design goals?

 

https://s3.amazonaws...paper_final.pdf


Edited by ensign, 29 November 2018 - 09:44 PM.


#56 Procyon

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Posted 29 November 2018 - 09:43 PM

We need a pepsi/coke showdown with xlt's vs edges on different objects, after 2-3 hours of acclimation and 3-5 eyepieces. :)
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#57 ensign

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Posted 29 November 2018 - 09:45 PM

We need a pepsi/coke showdown with xlt's vs edges on different objects, after 2-3 hours of acclimation and 3-5 eyepieces. smile.gif

Yup! grin.gif 



#58 Daniel Mounsey

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Posted 30 November 2018 - 09:32 AM

I’m going to do this challenge with a group as soon as it’s possible with several types of eyepieces.  Come to think about it, I should also do an fpl53 challenge since beginners far more often completely ignore the fact that opticians can use various mating glass’s to achieve the same color correction. I’ve even had one optician in particular tell me...I defy them to see the difference. In short, some of these astronomical myths need some serious dispelling.


Edited by Daniel Mounsey, 30 November 2018 - 10:00 AM.

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#59 Sarkikos

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Posted 30 November 2018 - 11:53 AM

I have an EdgeHD 8" and am very happy with the images I see through it.  It provides me built-in correction at all times.  I don't have to install a reducer/corrector to achieve better corrected outer fields.  But if I want, I can install a reducer.  So the result is a wider range and variety of magnifications and fields of view, while maintaining a well-corrected field across the entire range.

 

Mike


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#60 beanerds

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Posted 30 November 2018 - 01:45 PM

We need a pepsi/coke showdown with xlt's vs edges on different objects, after 2-3 hours of acclimation and 3-5 eyepieces. smile.gif

And please don't forget the BIG Dob's 20 inch plus ,, You just gotta see the galaxy clusters in a 20 inch plus Newt from the dark skies of the NT of Australia ( where these were taken )  Jupiter is as bright as the full moon  , Here are my observing buddies setting up and sorry if I side tracked a little but as you ask ,,, the light gathering drops off the enjoyment levels  the bigger a scope gets  ( that's my iStar 127mm refractor in the background ready for dark at 12 degrees south ) .

 

APERTURE RULES !  my friend ,,, at a cost so think seriously about 11in  vrs 9.25 in as as said the C11 is a big boy  .

 

 

Sorry can't help myself as I love and use 100mm - 127mm refractors but when the seeing is just right ,,,, out comes the XLT C9.25 .

Here she is , a great telescope so powerful but easily used .

 

Beanerds .

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Edited by beanerds, 30 November 2018 - 02:14 PM.

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#61 BillP

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Posted 30 November 2018 - 08:27 PM

APERTURE RULES !  my friend ..

 

I see this expression off and on and can never find the rules when I Google for them.  So are these set of rules for aperture only privy to some secret society of astronomers or something like the Ancient and Honorable Order of Turtles has?  Just makes no sense to me why people here and there like to shout out aperture rules when the rules are no where to be found.  All that usually happens when this phrase is yelled, as far as I can tell, is a bunch of people with sore backs making trip after trip from their car with telescope pieces while I'm observing nodding their heads.  Just don't get it.  Oh well.


Edited by BillP, 30 November 2018 - 08:28 PM.

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#62 BillP

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Posted 30 November 2018 - 08:40 PM

People in the forums get so hyped and pumped up over marketing, it amazes me.

 

Great post Daniel waytogo.gif   I'll add that marketing is not always obvious too.  A lot of marketing goes on between the lines in discussion forums in subtle ways that most never realize as well.  A lot to navigate in this hobby that's for sure...and breadth of experience is about the only way to cut through all the misconceptions out there.  Good job on sharing some of that hard earned experience bow.gif


Edited by BillP, 30 November 2018 - 08:40 PM.

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#63 Procyon

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Posted 30 November 2018 - 09:05 PM

Nothing like some good mid aperture, comfort and a cup of hot joe. :)

Edited by Procyon, 30 November 2018 - 09:06 PM.

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#64 jjack's

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Posted 01 December 2018 - 05:41 AM

Sometime aperture doesn't rules...i have seen doubles stars with beautifull airy patterns and so sweet tiny circles around when the skies were steady, using refractors or my C8. I have never seen that with my 14"dob.


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#65 SandyHouTex

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Posted 01 December 2018 - 06:08 AM

I see this expression off and on and can never find the rules when I Google for them.  So are these set of rules for aperture only privy to some secret society of astronomers or something like the Ancient and Honorable Order of Turtles has?  Just makes no sense to me why people here and there like to shout out aperture rules when the rules are no where to be found.  All that usually happens when this phrase is yelled, as far as I can tell, is a bunch of people with sore backs making trip after trip from their car with telescope pieces while I'm observing nodding their heads.  Just don't get it.  Oh well.

From Harvard University:

 

http://www.icq.eps.h...u/MagScale.html



#66 Sarkikos

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Posted 01 December 2018 - 02:20 PM

I see this expression off and on and can never find the rules when I Google for them.  So are these set of rules for aperture only privy to some secret society of astronomers or something like the Ancient and Honorable Order of Turtles has?  Just makes no sense to me why people here and there like to shout out aperture rules when the rules are no where to be found.  All that usually happens when this phrase is yelled, as far as I can tell, is a bunch of people with sore backs making trip after trip from their car with telescope pieces while I'm observing nodding their heads.  Just don't get it.  Oh well.

There are no rules for aperture.   You can observe with whatever aperture you like.

 

But larger aperture does have greater light grasp, and if done right, greater resolving power.  In those ways, aperture does rule.

 

On the other hand, personally I don't think I'd own an aperture more than 14" or so.  Just too much hassle moving them around.

 

Mike


Edited by Sarkikos, 01 December 2018 - 02:23 PM.

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#67 BillP

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Posted 02 December 2018 - 04:45 PM

From Harvard University:

 

http://www.icq.eps.h...u/MagScale.html

 

lol.gif  So let's see...there are about 217,000 stars I understand visible down to mag 9, so within reach of 50mm binoculars quite easily.  Have any of the aperture rules folks actually observed each of those 217,000 carefully before moving to larger apertures to view dimmer ones?  If not then they would have no idea what they've actually missed!  Hmmm.  Those aperture rules sure are strange looney.sml.gif


Edited by BillP, 02 December 2018 - 04:51 PM.


#68 SandyHouTex

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Posted 02 December 2018 - 07:25 PM

lol.gif  So let's see...there are about 217,000 stars I understand visible down to mag 9, so within reach of 50mm binoculars quite easily.  Have any of the aperture rules folks actually observed each of those 217,000 carefully before moving to larger apertures to view dimmer ones?  If not then they would have no idea what they've actually missed!  Hmmm.  Those aperture rules sure are strange looney.sml.gif

You’re confusing me.  Why do I have to observe all the stars at a particular aperture before I can move on?  “Aperture rules” means that when I look at Omega Centauri with my 80 mm EON i see a smokey circle in the field of view.  When I use my 16 inch Teeter/Zambuto I see something much grander.  A bigger, much brighter circle with hints of resolved stars.


Edited by SandyHouTex, 02 December 2018 - 07:26 PM.


#69 Jeffmar

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Posted 02 December 2018 - 07:27 PM

I went to Harvard. Spent the afternoon and bought a hat. Nice architecture.

 

 

Not from Harvard University


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#70 BillP

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Posted 03 December 2018 - 07:32 PM

You’re confusing me.  Why do I have to observe all the stars at a particular aperture before I can move on?  “Aperture rules” means that when I look at Omega Centauri with my 80 mm EON i see a smokey circle in the field of view.  When I use my 16 inch Teeter/Zambuto I see something much grander.  A bigger, much brighter circle with hints of resolved stars.

 

Nope...you must view each and every one before you move on...them is the observing rules lol.gif   I'm just funnin'.  Anyway...Hmmm.  6" scope at dark site, but not super dark, in New Mexico showed Omega Centauri filled with oodles and oodles and oodles of resolved stars.  I observed it in larger scopes, up to 18" while there...preferred the view in the 6" Apo.  I recommend you skip your 16 and take a smaller scope to a darker site and enjoy the view.  Well worth it as it is quite grand.  Nice to see it once in its glory...the memory is sufficient now for me as time to get back to those 217,000 stars wink.gif


Edited by BillP, 03 December 2018 - 07:33 PM.


#71 ensign

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Posted 03 December 2018 - 09:42 PM

*Great post Daniel waytogo.gif   I'll add that marketing is not always obvious too.  A lot of marketing goes on between the lines in discussion forums in subtle ways that most never realize as well.  A lot to navigate in this hobby that's for sure...and breadth of experience is about the only way to cut through all the misconceptions out there.  Good job on sharing some of that hard earned experience bow.gif

Maybe.  But my goal was to have a similar experience at the eyepiece to what I had with my 10” Dob in a smaller, lighter package.  It took a fair amount of experimentation and expense, and having  been called overly demanding of equipment in the past, I finally reached my goal with the 9.25 Edge and particularly so with the new .7 reducer.

 

With 12 years of avid visual observing (however much I may have lacked experience selling astronomy gear) under my belt, I like to think I have built up at least some small immunity to marketing hype and that I too, have at least some infinitesimal quantity of that hard-earned experience.


Edited by ensign, 03 December 2018 - 09:55 PM.

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#72 Sarkikos

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Posted 04 December 2018 - 06:46 AM

Maybe.  But my goal was to have a similar experience at the eyepiece to what I had with my 10” Dob in a smaller, lighter package.  It took a fair amount of experimentation and expense, and having  been called overly demanding of equipment in the past, I finally reached my goal with the 9.25 Edge and particularly so with the new .7 reducer.

 

With 12 years of avid visual observing (however much I may have lacked experience selling astronomy gear) under my belt, I like to think I have built up at least some small immunity to marketing hype and that I too, have at least some infinitesimal quantity of that hard-earned experience.

Hmmm... Maybe I should get a 9.25 Edge when I finally let my 10" Dob go.

 

:grin:

Mike



#73 ensign

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Posted 04 December 2018 - 07:22 PM

Hmmm... Maybe I should get a 9.25 Edge when I finally let my 10" Dob go.

 

grin.gif

Mike

Just reading your sig, I figure it will be a frosty Friday on Venus before that ever happens.wink.gif


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#74 Procyon

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Posted 05 December 2018 - 12:12 AM

Hmmm... Maybe I should get a 9.25 Edge when I finally let my 10" Dob go.

:grin:
Mike

Probably better for 2 flights of stairs than the 11 lol.

Would you get a CPC model? Or can you place the OTA on a cpc heavy tripod or a tad lighter and lighter mount?

A 9.25 will do a great job on so many more objects, I like the 11 for it helps me see faint Galaxies also from the backyard. Not that a 9.25 wouldn't but considering I use my 11" 90% of the time from an easily accessible backyard patio 5 feet away, I may as well get the biggest aperture I'd feel ok carrying in one shot. 5 feet is just 5 feet. :)

A lighter CPC mount/model in the future would be great.

The 11 is quite daunting in the beginning, but as a backyard patio grab n go it seems to work well. I take it to dark sites as much as possible, the OTA and attached mount sit in the front seat first class. You can pretty much make the tripod and tray turn into the size of a golf club bag.

Edited by Procyon, 05 December 2018 - 01:22 AM.


#75 Sarkikos

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Posted 05 December 2018 - 07:24 AM

Just reading your sig, I figure it will be a frosty Friday on Venus before that ever happens.wink.gif

Yes.  It is much easier to buy a telescope than to sell it.  You know, the packaging and shipping and all.

 

See anything you like?

 

:grin:

Mike




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