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Edge HD vs. XLT

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#26 stevecoe

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Posted 26 July 2016 - 02:27 PM

Hello Daniel, et al;

 

It has become obvious to me that some eyepieces do a better job with some models of telescope.  I have a 2 inch diagonal, an iStar that I think I bought from you.  For wide field in the 9.25" SCT I use my Panoptics, 35mm and 27mm.  They provide an excellent flat and contrasty field of view and about one degree of the sky at a time.  I have had them for many years and have no need nor want to trade them in for something else.  Any Messier open cluster is excellent in this set up, sharp stars for over 80% of the field and a nice, dark background.  Right near the edge of the field, the stars are elongated 1.2X1, not enough to be a problem to my eyes.

 

I had heard that the Edge HD scope were aimed at imagers, I can't verify that, my astronomy club does not have any owners of the Edge SCT's.

 

Take care;

Steve Coe


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#27 contedracula

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Posted 29 July 2016 - 04:42 AM

There isn't difference between Edge HD and XLT in Visual Observation, any field corrector you need for observation.

 

The real problem is the seeing condition and the thermal issues for the big SCT.

 

The edge hd has the rear aperture for using the fans the XLT hasn't, when the seeing is good the diameter wins but if you live in a air bad layer zone you will waste the money  with a big diameter.

 

If you will use the telescope also for DSO and NOT only for Planets go for biggest telescope the seeing is a little bit less important.

I use the C14edge HD for Deep Sky photo at prime focus and with Hyperstar and Hi Res Imaging BUT for Planetary Observation I prefer the MakNewton 10" wins hands down in contrast!

 

Cheers


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#28 Stelios

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Posted 29 July 2016 - 09:54 AM

There isn't difference between Edge HD and XLT in Visual Observation

In theory, I'm sure you're right.

 

In practice, now having an Edge HD, I would not want to risk getting anything less. A couple of $100 amortized over 10 years of observing is nothing. 


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#29 contedracula

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Posted 29 July 2016 - 11:33 AM

Yes but the difference of 300 bucks C8 XLT vs EHD and 1100 bucks C11 XLT vs EHD for visual purposes, means wasting money... mostly for C11

 

Just my 2 cents

 

Cheers



#30 Penarin

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Posted 29 July 2016 - 01:06 PM

Reading this with interest because someday, if I'm lucky, I will be trying to decide between a normal 9.25, an edge 9.25, and a normal C11.  Strictly for visual use.


Edited by Penarin, 29 July 2016 - 01:16 PM.


#31 contedracula

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Posted 29 July 2016 - 01:46 PM

The best visual performer, my opinion, is the CPC11.

The Fork mount is more comfortable than the German Equatorial Mount



#32 Renae Gage

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Posted 21 November 2018 - 12:19 AM

The best visual performer, my opinion, is the CPC11.

The Fork mount is more comfortable than the German Equatorial Mount

This.

 

The most comfortable observing I ever did, hands down, was with a Nexstar 8" XLT.  Optically, it was meh, but ergonomically?  10/10.   I see all the deforked SCT's in the classifieds and shake my head in wonder.


Edited by Renae Gage, 21 November 2018 - 12:20 AM.


#33 SandyHouTex

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Posted 21 November 2018 - 11:21 AM

I've heard there is no difference visually.  Where the HD shines is if you have a large CCD sensor where the stars at the edge will be pinpoints instead of seagulls.



#34 NMBob

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Posted 21 November 2018 - 12:24 PM

On wide field eyepieces, like Naglers and above, you can start to see the difference between the two. And, of course, it depends on the sensor size and what you are going after for camera work whether it matters or not. I've never looked through a non-Edge with something like the Starizona focal reducer-flattener. It's supposed to be way better than the Celestron focal reducer, which just reduces. There's been a couple of threads on here about if non-Edge scopes can be coaxed into being as good as an Edge version.

 

Bob


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#35 Sarkikos

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Posted 21 November 2018 - 02:04 PM

I've never owned a standard 8" SCT, but I do own an EdgeHD 8", a C6 (my second) and two C5's (a new "spotting scope" and an old NexStar).  By far, the EdgeHD 8" has the flattest field and the sharpest image, even when the standard SCT's have an RC.  I can see the difference.  I am strictly a visual observer (isn't that redundant?).  I don't image, never did, never will.

 

Mike


Edited by Sarkikos, 21 November 2018 - 02:12 PM.

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#36 Jeffmar

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Posted 22 November 2018 - 12:24 AM

I own Celestron C8 Edge and C11 Edge scopes. I also have a nearly 30 year old C11 which can't compare with my C11 Edge as far as brightness and sharpness. I have had an opportunity to compare my C11 edge to a more contemporary standard C11 and I could not tell the difference. We were both using 68 degree eyepieces and there seemed to be no difference in brightness nor in sharpness. If you are doing mostly visual astronomy get the C11. If have 100 degree eyepieces to get wider field views or you are doing DSO photography get the Edge version. It really makes a difference with stars away from the center. Both of my edge scopes seem to have very good optics and give amazing views in good seeing conditions. I really can't tell you whether Edge scopes are sharper than standard scopes but both of mine are good and I am happy with them.


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#37 Sarkikos

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Posted 22 November 2018 - 08:12 AM

Most observers should notice the improvement in outer-field sharpness in the EdgeHD scopes when viewing through 80 degree or wider eyepieces.  But if they have only 68 degree or narrower eyepieces, they might not notice.  That's similar to observers with Newts maybe not being very aware of the outer field coma in Newts if they don't have wide-field eyepieces.

 

I wouldn't expect any difference in brightness, except dim objects in the outer field might be easier to see in the EdgeHD because of the sharper image there.

 

Mike


Edited by Sarkikos, 22 November 2018 - 08:17 AM.

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#38 Procyon

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Posted 22 November 2018 - 02:41 PM

I have often looked through my CPC1100 XLT (non Edge) vs a friend's C11 Edge OTA mounted on a CGEM. I found no significant differences visually. However, my friend was into AP and took some great pictures with his OTA. If photography will be important to you, go with the Edge; for visual purposes spend the money on a larger OTA.

 

Arizona Ken

Same here, and this. smile.gif

 

If weight is a non issue, get an 11, if it's an issue, get a 9.25..if weight is still an issue, get the 8. Can also get a CPC for a sturdier mount if you don't care about astrophotography much, not that it can't be done with a CPC though,,


Edited by Procyon, 22 November 2018 - 02:41 PM.


#39 junomike

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Posted 22 November 2018 - 05:21 PM

I have an 8" EdgeHD, C11 (NS11GPS) and C14 (CGE).  I do feel the optics in the EdgeHD are better than those in my other SCT's but Aperture can't be ignored.

I'd get the C11.

 

Mike

To update this, the 8" EdgeHD is long gone (just too small for DSO's and I not preferred for Planetary/Lunar).

The C14 is on It's way out also as although  I love the Aperture, I find the NS11GPS less work, better viewing position and better thermals (slight) and not too far off the

C14 for DSO's.



#40 charles genovese

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Posted 22 November 2018 - 05:26 PM

as for field curvature in a commercial Schmitt Cass - it is approximately 1/10th the focal length. For a refractor it is about 1/3rd. So the field curvature for a C14 is about the same as a 6"f/8 refractor and a C11 has about the same as a 5" f/7.5 refractor- I don't hear people complain about field curvature in refractors. (There is some coma  of course). And the Starizona reducer/correctors (the new type 2's are f/6.3) are as good as the Edge's correction for a lot less than the cost of an Edge. From comments here it appears the consistency now is overall better with newer scopes, but this would apply to the non Edge scopes also. For the smaller scopes the Edge correctors will make a bigger difference visually.  



#41 AxelB

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Posted 22 November 2018 - 05:53 PM

The reason some people can’t see the difference visually between Edge and regular sct is because they are probably younger and their eyes still have excellent focus adaptation. As you age, this adaptability gets lower and lower. It also varies between individuals. For that reasons, if you’re above 40 or just want to play safe, get the Edge hd. The difference will be visible when observing large open clusters with a wide field eyepiece (exemple: ES82 30mm or Nagler 31).

To go with your current mount, chose the 9.25, it’s already quite big and heavy. A C11 will be shaky on a cg5.

Another advantage of a smaller scope is its corresponding wider maximum field of view, which isn’t that wide on an f10 system.

Edited by AxelB, 22 November 2018 - 05:53 PM.

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#42 dscarpa

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Posted 22 November 2018 - 07:12 PM

 I have a  9.25" XLT that came with a CG5. It worked fine. After putting a Crayford, 80mm and   red dot finders it still worked but slewing got kind of loopy and the motors sounded none too happy. It's now on a Unistar which handles  it very well. The coma isn't bad and doesn't seem to effect lunar but the view in my IM715D mak is better for sure. If something happened to it I'd get a Edge. I have lots of 82* and 100* eyepieces. David


Edited by dscarpa, 22 November 2018 - 07:15 PM.

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#43 Sarkikos

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Posted 22 November 2018 - 10:58 PM

The reason some people can’t see the difference visually between Edge and regular sct is because they are probably younger and their eyes still have excellent focus adaptation. As you age, this adaptability gets lower and lower. It also varies between individuals. For that reasons, if you’re above 40 or just want to play safe, get the Edge hd. The difference will be visible when observing large open clusters with a wide field eyepiece (exemple: ES82 30mm or Nagler 31).

^^^^  As they say, "This."  ^^^^

 

Maybe some observers can't see the difference, because they can't see the difference.

 

The difference will be even more visible with hyper-wide field eyepieces (example 21 Ethos or 17 Nikon NAV HW).

 

Mike


Edited by Sarkikos, 22 November 2018 - 11:00 PM.


#44 ensign

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Posted 23 November 2018 - 07:53 PM

I've heard there is no difference visually.  Where the HD shines is if you have a large CCD sensor where the stars at the edge will be pinpoints instead of seagulls.

My experience has been somewhat different.  I do strictly visual with a 9.25 Edge, mainly deep sky, with premium eyepieces.

 

I observed for an entire year using only a C8 XLT, with and without a reducer/corrector.  The views were always soft in the XLT and this became starkly apparent when comparing views of Saturn side by side with several friends’ Dobs. The views in the Dobs were sharper and showed more detail.

 

I did not notice the vignetting produced by the reducer directly, but with the R/C the scope was behaving as if it had a good deal less aperture.  Some faint objects, that should have been visible with 8” of aperture, weren’t.

 

I had the same issues with a second sample of a C8 XLT.  But for EAA, it’s a fine scope, so I still have the second C8.

 

So I put up the cash for a 9.25 Edge. I have been observing with it now for several years.  I can say without qualification that the views in the Edge not only exceed the views in the XLT, they blow the doors off it.  No observable field curvature, no coma, and now, with a .7 reducer, only a trivial amount of vignetting with a reasonably wide field (1.5 degrees with a Pentax 40XL as measured using drift timing). And the views, while not exactly refractor-like, are acceptably sharp.

 

I had previously observed for several years with a very good 10” Dob. While a Paracorr cleaned up the views in the Dob rather nicely, I’d still give the Edge the edge.


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#45 Procyon

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Posted 23 November 2018 - 08:50 PM

I had the same experience, but I went from a 10" dob to an 8 Edge to an 11 XLT and never seen Planets and Globulars this bright, sharp and detailed. Galaxies from my backyard and PNe's are also very visible with the bigger aperture. Nebulae are obviously more detailed and brighter at dark sites, obviously because of the bigger mirror. My favorite open cluster scope to date as well.

I looked through my scope and an 11 Edge and although the outer field looked a bit flatter with the edge, it improved the view (for me, and this on a bad night with passing clouds) by 2-3% I'd say. Need to retest all this on better nights though. I had a a dielectric Baader Clicklock diagonal and a friend had a Stellarvue or ES diagonal (possibly Antares) but is switching to a Baader Clicklock so we should easily see the differences using the same eyepiece.

If I see a 10% difference or a much more enjoyable view on the outer field of a 25mm ES 100 I'll switch to an Edge, otherwise I'll wait for adaptive optics, lol. I also prefer the All Black OTA vs White/Beige/Orange Edge one.

Edited by Procyon, 23 November 2018 - 09:52 PM.


#46 Bill Barlow

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Posted 23 November 2018 - 08:59 PM

I have a very good C11 XLT, but have never observed through an Edge scope yet.  Will be interested in hearing how the comparison turned out.

 

Bill



#47 Daniel Mounsey

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Posted 25 November 2018 - 04:06 PM

There's no question that countless beginners have been mislead by a vast number of misunderstandings observers have about the Edge HD regarding the manner it performs. To this day, it still continues in epic proportions. It's the same problem you read in the refractor forums about the obsessions beginners have about glass types. I think the majority of the comments we hear about the Edge HD vs SCT debate also stem from vast number of users of older SCT's who were looking to update their SCT's. But I tell you, Celestron's optical QC is better than it's ever been (in China)! Even Meade's ACF's are nice. I was talking to my friend Steve Keene who's a member here on CN. This guy knows a ton about SCT's but very seldom posts on CN. He's a highly experienced and respected observer and we often talk about how the SCT has evolved over the years and he helped me regain a good respect for these popular telescopes. You guys want to know who hated SCT's more than anyone? Me! Nobody hated the image quality of SCT's more than I did. 

 

I've used and compared pretty much all there is to compare in this telescope industry from the finest Newtonian's to the worst Newtonian's. Royce, Kennedy, Zambuto, Coulter, Galaxy, Parks and numerous others. I've compared Quads, doublets, triplets, achromats, Edge HD's SCT's, VC's, VMC's, Custom Mak Cass's, Mak Newt's, ACF's, DK's, Classical Cats, bad SCT's, etc. All this over the course of the past 25 years. I said to myself....How do observers enjoy looking through these SCT scopes, they're too soft for my tastes? This is why I hardly ever participated in the Cat's forum back in the day. It was like they just rarely ever came to a crisp, hard focus like they did in Newtonan's and fine refractors for me. For that reason, I stayed away from SCT's for many years. I simply didn't like the image quality in them. When I looked at Jupiter for example, I usually found myself wanting to see more fine detail with higher contrast because of other optical systems I compared them too. Even with star clusters, I usually found something left to be desired. Today, its different though and there's never been a better time for mass produced Cats. I remember sitting in front of Alan Hale's desk several years ago who's like the Godfather of Celestron. Alan Hale is an amazing guy. I loved to hear his stories and this man is a telescope encyclopedia. He told stories that would blow my mind and there was one thing he said that was interesting. He said to me...The machining and production tolerances both mechanically and optically overseas are better than they ever were here in Torrance.

 

I'll admit that the Bob Goff C8 I have is the best SCT I've ever tested to date, but overall, the latest SCT XLT's are wonderful scopes and I've looked through a decent number of them now. We recently did another comparison between the Edge HD and SCT XLT with Dave Person and Darren Thibodeau who are both members here on CN. We used the Televue 41mm and 35mm Panoptic against the 31mm Baader Hyperion in both scopes. I encourage others to conduct similar tests to see for themselves how different eyepieces respond to these optical systems and be the judge. We looked at star fields using both eyepieces in each scope. After spending several minutes on the SCT XLT going back and forth between each eyepiece, I made my decision, then I had Dave and Darren take a look and decide. While using both eyepieces in the SCT XLT, we all enjoyed the views of the Hyperion and Panoptic pretty equally because eyepieces that are not corrected for angular magnification and other aberrations still work really well in SCT's, unlike most of these modern, fast Newtonian's we see today. The amount of coma an SCT exhibits is similar to that of an f6 or f7 Newtonian. Once again, the differences between the two eyepieces were not that great in the SCT and we all agreed the images were nice. This is one of the things I've always liked about SCT's in general. You don't need to spend tons of money on highly corrected eyepieces to get good performance. This is why you can still use simpler 30mm to 50mm Plossls or less expensive wide-field eyepieces and still achieve nice image quality. It depends on the eyepieces used.

 

We then did the same comparison with the Edge HD. We started with the 35 Panoptic. After several minutes taking a look, we all agreed that with the Panoptic, the Edge HD provided a slightly more uniform star field around the outer periphery which was slightly nicer than the standard SCT but it wasn't that much! You really had to look carefully. We then used the Hyperion in the Edge HD and the image looked the worse we had seen all night! Dave looked and was like... huh? I told Darren to be the judge and he said..... Yea, I see what you mean, it looks soft. The aberrations in the eyepiece itself just backfire on the observers eye. It really looked noticeably awful compared to the SCT and that's not an exaggeration in fact, only the very center in the Edge HD looked okay but the stars were not uniform and the aberrations around the Edge HD looked worse. The image was unacceptable. The same results occur when comparing a simpler classic 2" 50mm Axiom in the Edge HD vs the SCT. This is what many observers still don't understand about these optical systems and they keep going on about how the Edge is ALWAYS better. It's complete nonsense! You have to use the right eyepieces with these scopes. Not matching eyepieces to telescopes is one of the greatest blunders observers make to this very day, even experienced ones! I made this mistake myself long ago. Even John Hayes noticed the same thing and yet countless observers ignored his post and it's true! Observers continually get sold on the marketing hype because they think that whenever a telescope works better for imaging, that must mean it applies to observing as well. 

 

Many beginners walk in or call our store with these same curiosity as the OP because they often read forums like this where observers continually go on about the Edge HD, but they really don't understand why or if it's from observers who have constructively compared them. If beginners genuinely want to know about this before they buy, I always ask them... what eyepieces was the observer comparing in the review you read on the Edge HD? Nearly all of the time this question is asked to a beginner, they are either not informed or not made aware of this. Then I ask myself the next question. How am I going to help this person unlearn what they think they've already learned? Sometimes I feel bad for beginners or observers who already own a larger or smaller scope but are considering an SCT as an alternative. All they're trying to do is gather some opinions before they purchase and instead, they are bombarded with a great deal of confusion because there's this constant notion that the Edge is a superior scope visually, but there's almost never enough specifics as to why. Not only that, but many assumptions are completely false about the Edge. The answer is mostly, just get the Edge, it's better, you gotta have it. Many of those comments are from the same people that said the Edge acclimated faster than an SCT. Really? We know that's not true now and it's because observers have a bad habit of making assumptions because of these tiny vents the Edge has, but what tests are they actually performing to confirm that outcome? How do they know this? Not only that, many observers don't even understand how to test for this or what they should be looking for.

 

So, we are back to the same assumption that everything you look at is higher definition and better because it has a sticker that says HD on the side. People in the forums get so hyped and pumped up over marketing, it amazes me. Some people are just absolutely adamant they already know what they want and that's fine. I close the sale and move on, but some people really do have a genuine curiosity. So, before beginners jump into an Edge HD, they should be asking themselves some questions. Are you doing mostly astro imaging? Are you planning on spending several hundred dollars on highly corrected wide-fields like the Explore Scientific and Televue eyepieces? Are you mostly interested in viewing the solar system (thermals)? Are you planning to use a reducer/corrector? Do you feel okay collimating a telescope?

 

If a someone is more interested in imaging, then definitely go with the Edge HD. If you are married to the outer field of view AND you are willing to spend the extra money on highly corrected eyepieces, then get the Edge HD. Other than this, the Edge HD has nearly everything else working against itself which is why I've never bothered with one over an SCT. I can have just about any telescope I want, it's not a problem. The issue is that I genuinely have no interest in having an Edge HD over an SCT. Why?

 

The Edge HD takes longer to acclimate than a standard SCT. What about the vents? The vents are marginal at best but more importantly, the vents don't even address the real problem which is acclimating the light baffle inside. How could observers not notice this? What were they looking at? The light baffle is blocked off, away from the vents. When you defocus a star, you will see a heat spike or heat plume pouring upward or downward depending on which side of focus you are with an eyepiece. When you do a Schlieren test, it's even more obvious what goes on inside the tube. Even the most minute and slightest wave can be detected with the right amount of backlight using this method, it takes no prisoners. Most Imagers have even admitted seeing this problem worse compared to an ordinary SCT. This is mostly because heat remains stored inside the corrector at the bottom of the light baffle and pours out like a chimney. On a C14 Edge, it will never cool under most climates, so it's not even an option. What about fans? You can buy aftermarket fans but that means spending more money again and the results are marginal at helping the baffle because the inside of the baffle is tucked away. The idea is to exchange all the air inside the OTA but when the telescope is pointed up and you want to start observing, heat rises and that's where the problem resides and where the baffle pours off heat, not at the bottom where the vents are. Remember that warm heat rises and cool air falls down. With an SCT, you can simply open the visual back and ventilate the baffle prior to observation because it is not blocked by any corrector elements like it is on the Edge HD. No only that, but you have the mass of the primary surrounding the corrector which stores heat in the baffle. There's another fan you can buy that replaces the secondary on the Edge, but once again, this adds additional cost and then you have to ask yourself if you want to be doing this in the dark, not to mention slight tweaking to collimation incurred from its use if the socondary is not rotated in the gaps left or right prior to removing the secondary. Is this all practical? When it comes to planetary observing, this is a critical factor. Next is the reducer/corrector. Take a look at this field of view calculator and just play with the numbers. You can also add the reducers in CCD mode.

 

https://astronomy.to.../field_of_view/

 

Think practical about this. The reducer for the Edge HD is a minimal of $300 and up to several hundred dollars and there's absolutely nothing practical about this for visual use at all. Do you really want all this massive glass for visual? It throws the balance of the telescope way off. It's mainly for imaging and it's very heavy too. Now you're stuck with all the disadvantages of only having an f10 with a small field of view. With the standard 6.3 reducer which is designed for standard SCT's and can be used visually, you can drop a conventional SCT down from about 2032mm to about 1280mm. Now you have a compound telescope that has all the advantages of an 8" f6 Dobsonian packed into a small package.That's a huge advantage because it opens up another arena to see more extended subjects per a given eyepiece and the visual results with it are wonderful and well corrected. Not only that, but you can use less expensive, lighter weight 1.25" eyepieces to achieve greater fields. It will also work with many 2" eyepieces. Some eyepiece may vignette, but be smart about this and do some calculations. The reducer also doesn't cost very much and it works wonderful for deep sky!

 

What about collimation? This is something observers often underestimate and errors can degrade image quality, making an observer incorrectly think their telescope is somehow bad optically or they just don't even notice what it is causing it in the first place. Many observers use their telescope while out of alignment in fact IMO, most do not have their SCT's collimated correctly at all. I've been to countless star parties where I've checked this on other SCT's and it's amazes me people will continue to observe with them out of collimation. With an Edge HD, collimation is a bear. It amazes that nobody even talks about this or maybe it's because they haven't even collimated them either. An SCT XLT moves like silk by comparison. This is because the secondary in the Edge HD is placed as far away from the corrector in the baffle as possible. As a result, it's pressed up closer to the corrector plate, so there's very little room to adjust collimation. The screws can be extremely tight to adjust and to make matters harder, the screws are phillips heads. Now you have to either make sure you use the correct size screwdriver or push firmly which applies unwanted pressure to the corrector so the screw doesn't strip.

 

Next are these 99% dielectric diagonals and there's literally thousands of them still floating around and you might even own one yourself. Some of the earlier models had some obvious major issues to be aware of. Some companies were using thinner substrates than are in use today and this is what also contributes to degraded edge sharpness. You can perform this test in daylight easily with stunning results if you want to find out if your dielectric diagonal has this problem. The dielectric coating process requires multiple layers when they are applied. In theory an optical flat could lose three quarters of its wavefront accuracy just from applying this coating. When the coatings are applied, it places tremendous stress around the outer periphery of the substrate but it's even worse than that. There are several options or methods to create your own artificial star. Find a wall or a table to set up on and go into your cutlery drawer and grab a few forks and spoons and just lay them out in the sunlight far enough to reach focus. You can also use the top of a telephone poll insulator which is an old trick John Dobson popularized back in the day. Another option is a ballbearing you may have in your garage. Any of these methods can generate an artificial star, but you need something reflective.

 

Next, it is much better to use a highly corrected eyepiece like an Explore Scientific or Televue for example. These particular eyepieces are better corrected which make star sources look more like points around the outer field. The reason you want this is to help retain the star's diffraction pattern as much as possible so the aberrations in the diagonal are exposed as much as possible so the test is more obvious. During my tests, I used a 1.25" 13mm T6 Nagler. I compared four diagonals including a Televue dielectric. When the star is placed at the center of the field while looking through the eyepiece, you can de-focus it slightly till you see several rings or a diffraction pattern. BTW, your scope needs to be collimated properly for this. Slowly move the star left, right, up and down so it reaches each quadrant of the view towards the edge of the field. Don't panic if the pattern starts to look slightly oblong toward the outer field. You should expect to see this to some degree. What you are looking for is worse and appears inconsistent on all sides, almost like bananas. The cheaper dielectric diagonals revealed extremely inconsistent diffraction patterns in each quadrant of the FOV while the Televue Everbrite was consistently perfect on all sides.  This is with just a 1.25" eyepiece! This is not even a 2" and you can already see this problem, so imagine how much worse it is over the outer surface of the substrate. This too can affect the star quality of your telescope and should be considered. I then opened these diagonals and noticed that the substrates were a little over half the thickness of the Televue Everbrite or the AP Maxbright. Don't panic just because you have a lower cost dielectric diagonal. Some of them are actually okay, but many of the earlier ones were deplorable beyond measure and you may already have one.

 

Many observers think that because an astrograph produces pinpoint stars, that means it will do the same thing visually. No, it doesn't work that way and this is the assumption many observers are still making about the Edge HD. Eyepieces change the appearances you see through the telescope and they can not be ignored. The Edge HD will not work good with every eyepiece. To this day, I believe this controversy is one of the biggest myths in this industry and I'm willing to bet if I covered an SCT XLT and an Edge HD, most observers wouldn't even be able to see the difference taking the extremes of eyepieces into consideration. If you ever want to have a comparison, let me know. I'll gladly let anyone compare the two telescopes side by side with me so they can see this for themselves. One of my goals is to set these two telescopes up side by side at a star party while the tubes are covered and let several observers of any experience try to discern the differences. IMO, this whole fiasco has been exaggerated and greatly misunderstood because very few observers are accounting for how the views in the Edge are affected by eyepieces. It get's pumped up from marketing hype, parroting in the forums and from observers who are just generalizing or have never even compared these telescopes side by side. It's the same problem with all this nonsense we read about FPL53 in the refractor forums from people who have hardly compared refractors. There's just so much nonsense, it's incredible.

 

I understand if observers like their Edge HD's and I'm glad they're happy. The Edge HD's wonderful scopes, but observers seriously need to start taking into account how different eyepieces respond to different optical systems and where the blame is being placed. For me, the SCT XLT is my preferred choice of the two optical systems for the reasons I've explained, particularly when viewing planets. There is absolutely no reason that an Edge HD would produce superior planetary images. If anything, it would be theoretically inferior because the Edge HD takes longer to acclimate than an ordinary SCT and if observers are not aware of this (and it's obvious they are not), then too many assumptions get made. I'm sorry to sound so harsh, but I get so tired of hearing customers come in with their heads the size of balloons from all the nonsense their brains have been packed with. All telescopes display aberrations when used visually from a countless number of factors, they're supposed to.

Attached Thumbnails

  • D27E4FE4-223D-44FB-83AD-9491A55A1951.jpeg

Edited by Daniel Mounsey, 25 November 2018 - 08:45 PM.

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#48 Sarkikos

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Posted 25 November 2018 - 08:34 PM

The most important sentence of the post:

 

If a someone is more interested in imaging, then definitely go with the Edge HD. If you are married to the outer field of view AND you are willing to spend the extra money on highly corrected eyepieces, then get the Edge HD. 

 

All else is commentary.

 

Personally, I wouldn't think about an SCT for planetary.  Get a moderately-sized Newt with good optics and thermal control.

 

Mike


Edited by Sarkikos, 25 November 2018 - 08:41 PM.

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#49 starman876

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Posted 26 November 2018 - 06:00 PM

There's no question that countless beginners have been mislead by a vast number of misunderstandings observers have about the Edge HD regarding the manner it performs. To this day, it still continues in epic proportions. It's the same problem you read in the refractor forums about the obsessions beginners have about glass types. I think the majority of the comments we hear about the Edge HD vs SCT debate also stem from vast number of users of older SCT's who were looking to update their SCT's. But I tell you, Celestron's optical QC is better than it's ever been (in China)! Even Meade's ACF's are nice. I was talking to my friend Steve Keene who's a member here on CN. This guy knows a ton about SCT's but very seldom posts on CN. He's a highly experienced and respected observer and we often talk about how the SCT has evolved over the years and he helped me regain a good respect for these popular telescopes. You guys want to know who hated SCT's more than anyone? Me! Nobody hated the image quality of SCT's more than I did. 

 

I've used and compared pretty much all there is to compare in this telescope industry from the finest Newtonian's to the worst Newtonian's. Royce, Kennedy, Zambuto, Coulter, Galaxy, Parks and numerous others. I've compared Quads, doublets, triplets, achromats, Edge HD's SCT's, VC's, VMC's, Custom Mak Cass's, Mak Newt's, ACF's, DK's, Classical Cats, bad SCT's, etc. All this over the course of the past 25 years. I said to myself....How do observers enjoy looking through these SCT scopes, they're too soft for my tastes? This is why I hardly ever participated in the Cat's forum back in the day. It was like they just rarely ever came to a crisp, hard focus like they did in Newtonan's and fine refractors for me. For that reason, I stayed away from SCT's for many years. I simply didn't like the image quality in them. When I looked at Jupiter for example, I usually found myself wanting to see more fine detail with higher contrast because of other optical systems I compared them too. Even with star clusters, I usually found something left to be desired. Today, its different though and there's never been a better time for mass produced Cats. I remember sitting in front of Alan Hale's desk several years ago who's like the Godfather of Celestron. Alan Hale is an amazing guy. I loved to hear his stories and this man is a telescope encyclopedia. He told stories that would blow my mind and there was one thing he said that was interesting. He said to me...The machining and production tolerances both mechanically and optically overseas are better than they ever were here in Torrance.

 

I'll admit that the Bob Goff C8 I have is the best SCT I've ever tested to date, but overall, the latest SCT XLT's are wonderful scopes and I've looked through a decent number of them now. We recently did another comparison between the Edge HD and SCT XLT with Dave Person and Darren Thibodeau who are both members here on CN. We used the Televue 41mm and 35mm Panoptic against the 31mm Baader Hyperion in both scopes. I encourage others to conduct similar tests to see for themselves how different eyepieces respond to these optical systems and be the judge. We looked at star fields using both eyepieces in each scope. After spending several minutes on the SCT XLT going back and forth between each eyepiece, I made my decision, then I had Dave and Darren take a look and decide. While using both eyepieces in the SCT XLT, we all enjoyed the views of the Hyperion and Panoptic pretty equally because eyepieces that are not corrected for angular magnification and other aberrations still work really well in SCT's, unlike most of these modern, fast Newtonian's we see today. The amount of coma an SCT exhibits is similar to that of an f6 or f7 Newtonian. Once again, the differences between the two eyepieces were not that great in the SCT and we all agreed the images were nice. This is one of the things I've always liked about SCT's in general. You don't need to spend tons of money on highly corrected eyepieces to get good performance. This is why you can still use simpler 30mm to 50mm Plossls or less expensive wide-field eyepieces and still achieve nice image quality. It depends on the eyepieces used.

 

We then did the same comparison with the Edge HD. We started with the 35 Panoptic. After several minutes taking a look, we all agreed that with the Panoptic, the Edge HD provided a slightly more uniform star field around the outer periphery which was slightly nicer than the standard SCT but it wasn't that much! You really had to look carefully. We then used the Hyperion in the Edge HD and the image looked the worse we had seen all night! Dave looked and was like... huh? I told Darren to be the judge and he said..... Yea, I see what you mean, it looks soft. The aberrations in the eyepiece itself just backfire on the observers eye. It really looked noticeably awful compared to the SCT and that's not an exaggeration in fact, only the very center in the Edge HD looked okay but the stars were not uniform and the aberrations around the Edge HD looked worse. The image was unacceptable. The same results occur when comparing a simpler classic 2" 50mm Axiom in the Edge HD vs the SCT. This is what many observers still don't understand about these optical systems and they keep going on about how the Edge is ALWAYS better. It's complete nonsense! You have to use the right eyepieces with these scopes. Not matching eyepieces to telescopes is one of the greatest blunders observers make to this very day, even experienced ones! I made this mistake myself long ago. Even John Hayes noticed the same thing and yet countless observers ignored his post and it's true! Observers continually get sold on the marketing hype because they think that whenever a telescope works better for imaging, that must mean it applies to observing as well. 

 

Many beginners walk in or call our store with these same curiosity as the OP because they often read forums like this where observers continually go on about the Edge HD, but they really don't understand why or if it's from observers who have constructively compared them. If beginners genuinely want to know about this before they buy, I always ask them... what eyepieces was the observer comparing in the review you read on the Edge HD? Nearly all of the time this question is asked to a beginner, they are either not informed or not made aware of this. Then I ask myself the next question. How am I going to help this person unlearn what they think they've already learned? Sometimes I feel bad for beginners or observers who already own a larger or smaller scope but are considering an SCT as an alternative. All they're trying to do is gather some opinions before they purchase and instead, they are bombarded with a great deal of confusion because there's this constant notion that the Edge is a superior scope visually, but there's almost never enough specifics as to why. Not only that, but many assumptions are completely false about the Edge. The answer is mostly, just get the Edge, it's better, you gotta have it. Many of those comments are from the same people that said the Edge acclimated faster than an SCT. Really? We know that's not true now and it's because observers have a bad habit of making assumptions because of these tiny vents the Edge has, but what tests are they actually performing to confirm that outcome? How do they know this? Not only that, many observers don't even understand how to test for this or what they should be looking for.

 

So, we are back to the same assumption that everything you look at is higher definition and better because it has a sticker that says HD on the side. People in the forums get so hyped and pumped up over marketing, it amazes me. Some people are just absolutely adamant they already know what they want and that's fine. I close the sale and move on, but some people really do have a genuine curiosity. So, before beginners jump into an Edge HD, they should be asking themselves some questions. Are you doing mostly astro imaging? Are you planning on spending several hundred dollars on highly corrected wide-fields like the Explore Scientific and Televue eyepieces? Are you mostly interested in viewing the solar system (thermals)? Are you planning to use a reducer/corrector? Do you feel okay collimating a telescope?

 

If a someone is more interested in imaging, then definitely go with the Edge HD. If you are married to the outer field of view AND you are willing to spend the extra money on highly corrected eyepieces, then get the Edge HD. Other than this, the Edge HD has nearly everything else working against itself which is why I've never bothered with one over an SCT. I can have just about any telescope I want, it's not a problem. The issue is that I genuinely have no interest in having an Edge HD over an SCT. Why?

 

The Edge HD takes longer to acclimate than a standard SCT. What about the vents? The vents are marginal at best but more importantly, the vents don't even address the real problem which is acclimating the light baffle inside. How could observers not notice this? What were they looking at? The light baffle is blocked off, away from the vents. When you defocus a star, you will see a heat spike or heat plume pouring upward or downward depending on which side of focus you are with an eyepiece. When you do a Schlieren test, it's even more obvious what goes on inside the tube. Even the most minute and slightest wave can be detected with the right amount of backlight using this method, it takes no prisoners. Most Imagers have even admitted seeing this problem worse compared to an ordinary SCT. This is mostly because heat remains stored inside the corrector at the bottom of the light baffle and pours out like a chimney. On a C14 Edge, it will never cool under most climates, so it's not even an option. What about fans? You can buy aftermarket fans but that means spending more money again and the results are marginal at helping the baffle because the inside of the baffle is tucked away. The idea is to exchange all the air inside the OTA but when the telescope is pointed up and you want to start observing, heat rises and that's where the problem resides and where the baffle pours off heat, not at the bottom where the vents are. Remember that warm heat rises and cool air falls down. With an SCT, you can simply open the visual back and ventilate the baffle prior to observation because it is not blocked by any corrector elements like it is on the Edge HD. No only that, but you have the mass of the primary surrounding the corrector which stores heat in the baffle. There's another fan you can buy that replaces the secondary on the Edge, but once again, this adds additional cost and then you have to ask yourself if you want to be doing this in the dark, not to mention slight tweaking to collimation incurred from its use if the socondary is not rotated in the gaps left or right prior to removing the secondary. Is this all practical? When it comes to planetary observing, this is a critical factor. Next is the reducer/corrector. Take a look at this field of view calculator and just play with the numbers. You can also add the reducers in CCD mode.

 

https://astronomy.to.../field_of_view/

 

Think practical about this. The reducer for the Edge HD is a minimal of $300 and up to several hundred dollars and there's absolutely nothing practical about this for visual use at all. Do you really want all this massive glass for visual? It throws the balance of the telescope way off. It's mainly for imaging and it's very heavy too. Now you're stuck with all the disadvantages of only having an f10 with a small field of view. With the standard 6.3 reducer which is designed for standard SCT's and can be used visually, you can drop a conventional SCT down from about 2032mm to about 1280mm. Now you have a compound telescope that has all the advantages of an 8" f6 Dobsonian packed into a small package.That's a huge advantage because it opens up another arena to see more extended subjects per a given eyepiece and the visual results with it are wonderful and well corrected. Not only that, but you can use less expensive, lighter weight 1.25" eyepieces to achieve greater fields. It will also work with many 2" eyepieces. Some eyepiece may vignette, but be smart about this and do some calculations. The reducer also doesn't cost very much and it works wonderful for deep sky!

 

What about collimation? This is something observers often underestimate and errors can degrade image quality, making an observer incorrectly think their telescope is somehow bad optically or they just don't even notice what it is causing it in the first place. Many observers use their telescope while out of alignment in fact IMO, most do not have their SCT's collimated correctly at all. I've been to countless star parties where I've checked this on other SCT's and it's amazes me people will continue to observe with them out of collimation. With an Edge HD, collimation is a bear. It amazes that nobody even talks about this or maybe it's because they haven't even collimated them either. An SCT XLT moves like silk by comparison. This is because the secondary in the Edge HD is placed as far away from the corrector in the baffle as possible. As a result, it's pressed up closer to the corrector plate, so there's very little room to adjust collimation. The screws can be extremely tight to adjust and to make matters harder, the screws are phillips heads. Now you have to either make sure you use the correct size screwdriver or push firmly which applies unwanted pressure to the corrector so the screw doesn't strip.

 

Next are these 99% dielectric diagonals and there's literally thousands of them still floating around and you might even own one yourself. Some of the earlier models had some obvious major issues to be aware of. Some companies were using thinner substrates than are in use today and this is what also contributes to degraded edge sharpness. You can perform this test in daylight easily with stunning results if you want to find out if your dielectric diagonal has this problem. The dielectric coating process requires multiple layers when they are applied. In theory an optical flat could lose three quarters of its wavefront accuracy just from applying this coating. When the coatings are applied, it places tremendous stress around the outer periphery of the substrate but it's even worse than that. There are several options or methods to create your own artificial star. Find a wall or a table to set up on and go into your cutlery drawer and grab a few forks and spoons and just lay them out in the sunlight far enough to reach focus. You can also use the top of a telephone poll insulator which is an old trick John Dobson popularized back in the day. Another option is a ballbearing you may have in your garage. Any of these methods can generate an artificial star, but you need something reflective.

 

Next, it is much better to use a highly corrected eyepiece like an Explore Scientific or Televue for example. These particular eyepieces are better corrected which make star sources look more like points around the outer field. The reason you want this is to help retain the star's diffraction pattern as much as possible so the aberrations in the diagonal are exposed as much as possible so the test is more obvious. During my tests, I used a 1.25" 13mm T6 Nagler. I compared four diagonals including a Televue dielectric. When the star is placed at the center of the field while looking through the eyepiece, you can de-focus it slightly till you see several rings or a diffraction pattern. BTW, your scope needs to be collimated properly for this. Slowly move the star left, right, up and down so it reaches each quadrant of the view towards the edge of the field. Don't panic if the pattern starts to look slightly oblong toward the outer field. You should expect to see this to some degree. What you are looking for is worse and appears inconsistent on all sides, almost like bananas. The cheaper dielectric diagonals revealed extremely inconsistent diffraction patterns in each quadrant of the FOV while the Televue Everbrite was consistently perfect on all sides.  This is with just a 1.25" eyepiece! This is not even a 2" and you can already see this problem, so imagine how much worse it is over the outer surface of the substrate. This too can affect the star quality of your telescope and should be considered. I then opened these diagonals and noticed that the substrates were a little over half the thickness of the Televue Everbrite or the AP Maxbright. Don't panic just because you have a lower cost dielectric diagonal. Some of them are actually okay, but many of the earlier ones were deplorable beyond measure and you may already have one.

 

Many observers think that because an astrograph produces pinpoint stars, that means it will do the same thing visually. No, it doesn't work that way and this is the assumption many observers are still making about the Edge HD. Eyepieces change the appearances you see through the telescope and they can not be ignored. The Edge HD will not work good with every eyepiece. To this day, I believe this controversy is one of the biggest myths in this industry and I'm willing to bet if I covered an SCT XLT and an Edge HD, most observers wouldn't even be able to see the difference taking the extremes of eyepieces into consideration. If you ever want to have a comparison, let me know. I'll gladly let anyone compare the two telescopes side by side with me so they can see this for themselves. One of my goals is to set these two telescopes up side by side at a star party while the tubes are covered and let several observers of any experience try to discern the differences. IMO, this whole fiasco has been exaggerated and greatly misunderstood because very few observers are accounting for how the views in the Edge are affected by eyepieces. It get's pumped up from marketing hype, parroting in the forums and from observers who are just generalizing or have never even compared these telescopes side by side. It's the same problem with all this nonsense we read about FPL53 in the refractor forums from people who have hardly compared refractors. There's just so much nonsense, it's incredible.

 

I understand if observers like their Edge HD's and I'm glad they're happy. The Edge HD's wonderful scopes, but observers seriously need to start taking into account how different eyepieces respond to different optical systems and where the blame is being placed. For me, the SCT XLT is my preferred choice of the two optical systems for the reasons I've explained, particularly when viewing planets. There is absolutely no reason that an Edge HD would produce superior planetary images. If anything, it would be theoretically inferior because the Edge HD takes longer to acclimate than an ordinary SCT and if observers are not aware of this (and it's obvious they are not), then too many assumptions get made. I'm sorry to sound so harsh, but I get so tired of hearing customers come in with their heads the size of balloons from all the nonsense their brains have been packed with. All telescopes display aberrations when used visually from a countless number of factors, they're supposed to.

Great write up. This could be a very good white paper on the subject.  Thanks


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#50 Wildetelescope

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Posted 26 November 2018 - 07:13 PM

There's no question that countless beginners have been mislead by a vast number of misunderstandings observers have about the Edge HD regarding the manner it performs. To this day, it still continues in epic proportions. It's the same problem you read in the refractor forums about the obsessions beginners have about glass types. I think the majority of the comments we hear about the Edge HD vs SCT debate also stem from vast number of users of older SCT's who were looking to update their SCT's. But I tell you, Celestron's optical QC is better than it's ever been (in China)! Even Meade's ACF's are nice. I was talking to my friend Steve Keene who's a member here on CN. This guy knows a ton about SCT's but very seldom posts on CN. He's a highly experienced and respected observer and we often talk about how the SCT has evolved over the years and he helped me regain a good respect for these popular telescopes. You guys want to know who hated SCT's more than anyone? Me! Nobody hated the image quality of SCT's more than I did. 

 

I've used and compared pretty much all there is to compare in this telescope industry from the finest Newtonian's to the worst Newtonian's. Royce, Kennedy, Zambuto, Coulter, Galaxy, Parks and numerous others. I've compared Quads, doublets, triplets, achromats, Edge HD's SCT's, VC's, VMC's, Custom Mak Cass's, Mak Newt's, ACF's, DK's, Classical Cats, bad SCT's, etc. All this over the course of the past 25 years. I said to myself....How do observers enjoy looking through these SCT scopes, they're too soft for my tastes? This is why I hardly ever participated in the Cat's forum back in the day. It was like they just rarely ever came to a crisp, hard focus like they did in Newtonan's and fine refractors for me. For that reason, I stayed away from SCT's for many years. I simply didn't like the image quality in them. When I looked at Jupiter for example, I usually found myself wanting to see more fine detail with higher contrast because of other optical systems I compared them too. Even with star clusters, I usually found something left to be desired. Today, its different though and there's never been a better time for mass produced Cats. I remember sitting in front of Alan Hale's desk several years ago who's like the Godfather of Celestron. Alan Hale is an amazing guy. I loved to hear his stories and this man is a telescope encyclopedia. He told stories that would blow my mind and there was one thing he said that was interesting. He said to me...The machining and production tolerances both mechanically and optically overseas are better than they ever were here in Torrance.

 

I'll admit that the Bob Goff C8 I have is the best SCT I've ever tested to date, but overall, the latest SCT XLT's are wonderful scopes and I've looked through a decent number of them now. We recently did another comparison between the Edge HD and SCT XLT with Dave Person and Darren Thibodeau who are both members here on CN. We used the Televue 41mm and 35mm Panoptic against the 31mm Baader Hyperion in both scopes. I encourage others to conduct similar tests to see for themselves how different eyepieces respond to these optical systems and be the judge. We looked at star fields using both eyepieces in each scope. After spending several minutes on the SCT XLT going back and forth between each eyepiece, I made my decision, then I had Dave and Darren take a look and decide. While using both eyepieces in the SCT XLT, we all enjoyed the views of the Hyperion and Panoptic pretty equally because eyepieces that are not corrected for angular magnification and other aberrations still work really well in SCT's, unlike most of these modern, fast Newtonian's we see today. The amount of coma an SCT exhibits is similar to that of an f6 or f7 Newtonian. Once again, the differences between the two eyepieces were not that great in the SCT and we all agreed the images were nice. This is one of the things I've always liked about SCT's in general. You don't need to spend tons of money on highly corrected eyepieces to get good performance. This is why you can still use simpler 30mm to 50mm Plossls or less expensive wide-field eyepieces and still achieve nice image quality. It depends on the eyepieces used.

 

We then did the same comparison with the Edge HD. We started with the 35 Panoptic. After several minutes taking a look, we all agreed that with the Panoptic, the Edge HD provided a slightly more uniform star field around the outer periphery which was slightly nicer than the standard SCT but it wasn't that much! You really had to look carefully. We then used the Hyperion in the Edge HD and the image looked the worse we had seen all night! Dave looked and was like... huh? I told Darren to be the judge and he said..... Yea, I see what you mean, it looks soft. The aberrations in the eyepiece itself just backfire on the observers eye. It really looked noticeably awful compared to the SCT and that's not an exaggeration in fact, only the very center in the Edge HD looked okay but the stars were not uniform and the aberrations around the Edge HD looked worse. The image was unacceptable. The same results occur when comparing a simpler classic 2" 50mm Axiom in the Edge HD vs the SCT. This is what many observers still don't understand about these optical systems and they keep going on about how the Edge is ALWAYS better. It's complete nonsense! You have to use the right eyepieces with these scopes. Not matching eyepieces to telescopes is one of the greatest blunders observers make to this very day, even experienced ones! I made this mistake myself long ago. Even John Hayes noticed the same thing and yet countless observers ignored his post and it's true! Observers continually get sold on the marketing hype because they think that whenever a telescope works better for imaging, that must mean it applies to observing as well. 

 

Many beginners walk in or call our store with these same curiosity as the OP because they often read forums like this where observers continually go on about the Edge HD, but they really don't understand why or if it's from observers who have constructively compared them. If beginners genuinely want to know about this before they buy, I always ask them... what eyepieces was the observer comparing in the review you read on the Edge HD? Nearly all of the time this question is asked to a beginner, they are either not informed or not made aware of this. Then I ask myself the next question. How am I going to help this person unlearn what they think they've already learned? Sometimes I feel bad for beginners or observers who already own a larger or smaller scope but are considering an SCT as an alternative. All they're trying to do is gather some opinions before they purchase and instead, they are bombarded with a great deal of confusion because there's this constant notion that the Edge is a superior scope visually, but there's almost never enough specifics as to why. Not only that, but many assumptions are completely false about the Edge. The answer is mostly, just get the Edge, it's better, you gotta have it. Many of those comments are from the same people that said the Edge acclimated faster than an SCT. Really? We know that's not true now and it's because observers have a bad habit of making assumptions because of these tiny vents the Edge has, but what tests are they actually performing to confirm that outcome? How do they know this? Not only that, many observers don't even understand how to test for this or what they should be looking for.

 

So, we are back to the same assumption that everything you look at is higher definition and better because it has a sticker that says HD on the side. People in the forums get so hyped and pumped up over marketing, it amazes me. Some people are just absolutely adamant they already know what they want and that's fine. I close the sale and move on, but some people really do have a genuine curiosity. So, before beginners jump into an Edge HD, they should be asking themselves some questions. Are you doing mostly astro imaging? Are you planning on spending several hundred dollars on highly corrected wide-fields like the Explore Scientific and Televue eyepieces? Are you mostly interested in viewing the solar system (thermals)? Are you planning to use a reducer/corrector? Do you feel okay collimating a telescope?

 

If a someone is more interested in imaging, then definitely go with the Edge HD. If you are married to the outer field of view AND you are willing to spend the extra money on highly corrected eyepieces, then get the Edge HD. Other than this, the Edge HD has nearly everything else working against itself which is why I've never bothered with one over an SCT. I can have just about any telescope I want, it's not a problem. The issue is that I genuinely have no interest in having an Edge HD over an SCT. Why?

 

The Edge HD takes longer to acclimate than a standard SCT. What about the vents? The vents are marginal at best but more importantly, the vents don't even address the real problem which is acclimating the light baffle inside. How could observers not notice this? What were they looking at? The light baffle is blocked off, away from the vents. When you defocus a star, you will see a heat spike or heat plume pouring upward or downward depending on which side of focus you are with an eyepiece. When you do a Schlieren test, it's even more obvious what goes on inside the tube. Even the most minute and slightest wave can be detected with the right amount of backlight using this method, it takes no prisoners. Most Imagers have even admitted seeing this problem worse compared to an ordinary SCT. This is mostly because heat remains stored inside the corrector at the bottom of the light baffle and pours out like a chimney. On a C14 Edge, it will never cool under most climates, so it's not even an option. What about fans? You can buy aftermarket fans but that means spending more money again and the results are marginal at helping the baffle because the inside of the baffle is tucked away. The idea is to exchange all the air inside the OTA but when the telescope is pointed up and you want to start observing, heat rises and that's where the problem resides and where the baffle pours off heat, not at the bottom where the vents are. Remember that warm heat rises and cool air falls down. With an SCT, you can simply open the visual back and ventilate the baffle prior to observation because it is not blocked by any corrector elements like it is on the Edge HD. No only that, but you have the mass of the primary surrounding the corrector which stores heat in the baffle. There's another fan you can buy that replaces the secondary on the Edge, but once again, this adds additional cost and then you have to ask yourself if you want to be doing this in the dark, not to mention slight tweaking to collimation incurred from its use if the socondary is not rotated in the gaps left or right prior to removing the secondary. Is this all practical? When it comes to planetary observing, this is a critical factor. Next is the reducer/corrector. Take a look at this field of view calculator and just play with the numbers. You can also add the reducers in CCD mode.

 

https://astronomy.to.../field_of_view/

 

Think practical about this. The reducer for the Edge HD is a minimal of $300 and up to several hundred dollars and there's absolutely nothing practical about this for visual use at all. Do you really want all this massive glass for visual? It throws the balance of the telescope way off. It's mainly for imaging and it's very heavy too. Now you're stuck with all the disadvantages of only having an f10 with a small field of view. With the standard 6.3 reducer which is designed for standard SCT's and can be used visually, you can drop a conventional SCT down from about 2032mm to about 1280mm. Now you have a compound telescope that has all the advantages of an 8" f6 Dobsonian packed into a small package.That's a huge advantage because it opens up another arena to see more extended subjects per a given eyepiece and the visual results with it are wonderful and well corrected. Not only that, but you can use less expensive, lighter weight 1.25" eyepieces to achieve greater fields. It will also work with many 2" eyepieces. Some eyepiece may vignette, but be smart about this and do some calculations. The reducer also doesn't cost very much and it works wonderful for deep sky!

 

What about collimation? This is something observers often underestimate and errors can degrade image quality, making an observer incorrectly think their telescope is somehow bad optically or they just don't even notice what it is causing it in the first place. Many observers use their telescope while out of alignment in fact IMO, most do not have their SCT's collimated correctly at all. I've been to countless star parties where I've checked this on other SCT's and it's amazes me people will continue to observe with them out of collimation. With an Edge HD, collimation is a bear. It amazes that nobody even talks about this or maybe it's because they haven't even collimated them either. An SCT XLT moves like silk by comparison. This is because the secondary in the Edge HD is placed as far away from the corrector in the baffle as possible. As a result, it's pressed up closer to the corrector plate, so there's very little room to adjust collimation. The screws can be extremely tight to adjust and to make matters harder, the screws are phillips heads. Now you have to either make sure you use the correct size screwdriver or push firmly which applies unwanted pressure to the corrector so the screw doesn't strip.

 

Next are these 99% dielectric diagonals and there's literally thousands of them still floating around and you might even own one yourself. Some of the earlier models had some obvious major issues to be aware of. Some companies were using thinner substrates than are in use today and this is what also contributes to degraded edge sharpness. You can perform this test in daylight easily with stunning results if you want to find out if your dielectric diagonal has this problem. The dielectric coating process requires multiple layers when they are applied. In theory an optical flat could lose three quarters of its wavefront accuracy just from applying this coating. When the coatings are applied, it places tremendous stress around the outer periphery of the substrate but it's even worse than that. There are several options or methods to create your own artificial star. Find a wall or a table to set up on and go into your cutlery drawer and grab a few forks and spoons and just lay them out in the sunlight far enough to reach focus. You can also use the top of a telephone poll insulator which is an old trick John Dobson popularized back in the day. Another option is a ballbearing you may have in your garage. Any of these methods can generate an artificial star, but you need something reflective.

 

Next, it is much better to use a highly corrected eyepiece like an Explore Scientific or Televue for example. These particular eyepieces are better corrected which make star sources look more like points around the outer field. The reason you want this is to help retain the star's diffraction pattern as much as possible so the aberrations in the diagonal are exposed as much as possible so the test is more obvious. During my tests, I used a 1.25" 13mm T6 Nagler. I compared four diagonals including a Televue dielectric. When the star is placed at the center of the field while looking through the eyepiece, you can de-focus it slightly till you see several rings or a diffraction pattern. BTW, your scope needs to be collimated properly for this. Slowly move the star left, right, up and down so it reaches each quadrant of the view towards the edge of the field. Don't panic if the pattern starts to look slightly oblong toward the outer field. You should expect to see this to some degree. What you are looking for is worse and appears inconsistent on all sides, almost like bananas. The cheaper dielectric diagonals revealed extremely inconsistent diffraction patterns in each quadrant of the FOV while the Televue Everbrite was consistently perfect on all sides.  This is with just a 1.25" eyepiece! This is not even a 2" and you can already see this problem, so imagine how much worse it is over the outer surface of the substrate. This too can affect the star quality of your telescope and should be considered. I then opened these diagonals and noticed that the substrates were a little over half the thickness of the Televue Everbrite or the AP Maxbright. Don't panic just because you have a lower cost dielectric diagonal. Some of them are actually okay, but many of the earlier ones were deplorable beyond measure and you may already have one.

 

Many observers think that because an astrograph produces pinpoint stars, that means it will do the same thing visually. No, it doesn't work that way and this is the assumption many observers are still making about the Edge HD. Eyepieces change the appearances you see through the telescope and they can not be ignored. The Edge HD will not work good with every eyepiece. To this day, I believe this controversy is one of the biggest myths in this industry and I'm willing to bet if I covered an SCT XLT and an Edge HD, most observers wouldn't even be able to see the difference taking the extremes of eyepieces into consideration. If you ever want to have a comparison, let me know. I'll gladly let anyone compare the two telescopes side by side with me so they can see this for themselves. One of my goals is to set these two telescopes up side by side at a star party while the tubes are covered and let several observers of any experience try to discern the differences. IMO, this whole fiasco has been exaggerated and greatly misunderstood because very few observers are accounting for how the views in the Edge are affected by eyepieces. It get's pumped up from marketing hype, parroting in the forums and from observers who are just generalizing or have never even compared these telescopes side by side. It's the same problem with all this nonsense we read about FPL53 in the refractor forums from people who have hardly compared refractors. There's just so much nonsense, it's incredible.

 

I understand if observers like their Edge HD's and I'm glad they're happy. The Edge HD's wonderful scopes, but observers seriously need to start taking into account how different eyepieces respond to different optical systems and where the blame is being placed. For me, the SCT XLT is my preferred choice of the two optical systems for the reasons I've explained, particularly when viewing planets. There is absolutely no reason that an Edge HD would produce superior planetary images. If anything, it would be theoretically inferior because the Edge HD takes longer to acclimate than an ordinary SCT and if observers are not aware of this (and it's obvious they are not), then too many assumptions get made. I'm sorry to sound so harsh, but I get so tired of hearing customers come in with their heads the size of balloons from all the nonsense their brains have been packed with. All telescopes display aberrations when used visually from a countless number of factors, they're supposed to.

Great dialog!  Your description of the view with the 35 pan and the 8 inch edge captures exactly what I see, compared to what I have seen through standard scts.  For me, the difference is enough to make me glad I have the edge, but frankly not enough to make me want to change, if I had owned an xlt first. Would likely not have been able to tell the difference whe I first started out, for sure.   Following that thought a little further, I also have a standard C11 that I am very happy with and have zero desire to upgrade to an edge of similar aperture.  It has given me the best view of Saturn I have had to date.  To the op, Get what you can afford and can carry, and don’t look back;-)

 

Jmd




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