23 replies to this topic

[GTom]

I see black tube "C8 XLT", Orange tube "Nexstar 8SE", grey tube "Evolution 8" models on the second hand market, with probably further units down the road. What are the optical differences among these?/Any particular series are more reliable/blessed with better QC?

[Sheremy01]

I’m curious as to the answer as well. I’ve often wondered.

[KJR]

I purchased a new C8 Black Tube XLT in June 2023. I don’t think optically there is a difference. Older ones without Fastar May not have the ability to easily add a Hyperstar. Not sure about the QC over the years, can’t keep track like autos. 
 

if I was in the market I would get the C8 Edge HD. The extra optics in the end of the baffle flattens out the image.

 

KJR

[photomagica]

I agree with KJR. Buy a recent model, Edge if possible. Recent C8's seem to exhibit consistently higher quality optics than older models .  I bought a C8 Evolution shortly after that model came out and optically it is very good and the Evolution mount generally works very well. I owned, used and tested a number of C8s before I bought the Evolution and it is the best of the lot optically. I agree there isn't an optical difference among recent C8's except with the Edge.

Bill

[quilty]

I'd take a past insane freaky sharp one :-)

[Eddgie]

I see black tube "C8 XLT", Orange tube "Nexstar 8SE", grey tube "Evolution 8" models on the second hand market, with probably further units down the road. What are the optical differences among these?/Any particular series are more reliable/blessed with better QC?

The optical prescription among the standard C8s is essentially identical. 

 

While some will say that later made SCTs have better optics, I have seen no proof of that and would be skeptical of such claims. Also, the EdgeHD optics are not made to a higher standard than the non EdgeHD optics, though the EdgeHD optics by design will have far superior off axis performance. This is important if you are going to use exotic wide field eyepieces like the 31mm Nagler, where the off axis aberrations of the design will be easily visible. This is nothing to do with optical quality, it is just a function of the design, which has pretty strong field curvature and coma. 

 

The primary design difference performance wise is the coatings.  The later scopes usually have XLT coatings and this does provide a bit better transmission than the Starbright coatings, but if the optics were the same quality of an XLT and non XLT scope, the contrast would be the same. 

 

As compared to early C8s, the XLT coatings make a difference that can be seen, but the difference between Starbright and XLT is at the very edge of visible perception. 

 

Original orange tube optics are somehow thought to be better optically than newer ones, but I have owned three, and none of them were anything special. 

 

The difference in performance between any two SCTs that would be big enough to be seen are simply random. You would have to have a unicorn perfect sample with one that should have not gotten through QC, and there are not many of those out there. Otherwise, the difference between this one and that one is simply too small to really be easily seen.  I have owned six  standard C8s over the decades, and only one had essentially perfect optics and it was a 90s scope.  

 

The later standard SCTs are all the same optically and the performance difference is typically difficult to see. They  all use the same optical design. 

Edited by Eddgie, 01 November 2024 - 07:37 AM.

[skyjim]

I  have owned both the standard C8, one that was also made by Skywatcher plus a C8HD. Like the above post the C8HD had a falter FOV which helps with some wide field EP's and also when you dive into AP but the down side since the time I owned the HD was the cooling when I lived in up state NY. Yes there are aftermarket fans to be had cause those toy vents did nothing but the standard C* I always placed the scope upside down so the heat would rise out of the ota when there was nothing placed inside the visual back.

 

When you were looking at planetary targets and the object was centered in the FOV there was really not any real difference between the standard C8 and the HD but as far as years they were made and were they were made I can only attest to two C9.25's I had owned. The first one was back around 2002, it was made in the USA and the focuser was sub par which forced me to use an aftermarket focuser on the back of the OTA and the optics were OK. The last one was around 2010, this one was a Synta made in China C9.25, the focuser was very good on this sample and the optics were one of the best I have ever owned. I would have to say all the C8's I owned were made in China as well but the overall quality was right were you would want them to be. I hope this may help.

[MrRoberts]

This goes back a few years, but when I bought C-8e vs the std xlt the price difference was only $300 ish. Have loved the views ever since.

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[GGK]

Some info below on the two primary options one must decide upon for visual use.  Otherwise, and as others have already said, the difference in tubes, other than age, is more about how it was packaged for retail and marketed.  

 

Edge HD vs. the classical design without the integrated flattener. Here's the Celestron Edge HD white paper: https://s3.amazonaws...per_final.pdf  

 

- Note that the Celestron SCT 0.63X focal reducer reduces coma and improves field flatness of the classical design.

 

Coatings - Latest Starbright XLT coatings vs. earlier Starbright coatings.  Here's a related Celestron article: https://www.celestro...ptical-coatings

 

This is a nice video showing other differences between the classical and Edge HD designs:

https://www.bing.com...89BD1&FORM=VIRE

 

Gary

[rfcooley]

All C8 are designed and mechanically the same and have been for the 50ish years (except the Edge.). The difference is the coatings  used on the mirror and corrector. I own several C8's early ones with no coatings, ones with StarBright coatings and ones with Starbright XLT coatings. I can tell a small difference between the non coated and the StarBright coated. The StarBright coated has a little better contrast and a tad sharper. My StarBright XLT has a very noticeable difference between the non coated, and a little better than the Starbright. However, the differences are really only noticeable under very good sky conditions (around 21.5/ 22+ Mg/Arc²) in my experience. So the question is how often to we have good enough skies to see a noticeable difference on any given night at our usual observing site?  Now days the Cat line comes with the Starbright XLT and the C series are still basically the same until the Edge design came about. We can argue endlessly about the newer mirror manufacturing better or worse. In some models of the C  Series the mirrors and correctors are touted to be worse. Is this so? Since the basic design has been unchanged for 50 ish years. Coatings have been improved. What about the mirrors or correctors?  Are they better or worse? Have the type of substrate of the mirror blanks changed significantly?  They may be more consistent but what are the tolerances for that measure of consistency?  Are those tolerances narrower or broader over the years?  Are the mirrors thinner or thicker?  All of these things can make a difference in the scopes performance.

 

I have seen it touted that some people claim they can see a difference of 1 or 2 percent in coatings and or mirror configuration. Ummm..   My eye Doctor is an Ophthalmologist, as in MD. I have an Optometrist that writes, diagnoses my eyes and changes my prescription for my glasses. I have an Optician that makes sure my glasses fit properly and are occasionally adjusted. Now my Ophthalmologist and Optometrist  say that the human eye is not able to discern that small of a percentage in changes of acuity. So I ask what percentage of acuity can be come noticeable?  There answers were interesting. A very few, they called rare, might be able to discern a change of 10 to around 15 percent change in acuity. Many will see a change of above 15 percent and most will see a change around 20 percent. But, we need to keep in mind this can vary from person to person and further variances are possible due to other conditions, large pupil, small pupils, depth perception, lens distortion, blood pressure and many other conditions that can exist in our eyes.  Just like in our hobby. There are several variables that can make a difference in our viewing pleasures such as Seeing, Transparency, Clouds, acuity of our optics, how good our eyes are or are not.

 

So how much improvement in optics of a telescope is necessary to make a noticeable difference for you or I?  If we have really good eyes (rare), we might discern a 10 to 15 percent improvement in acuity. If we have good eyes we should be able to discern 15 to 20 percent improvement in acuity. If we have normal eyes we should be able to discern a 20 percent improvement in acuity.

 

Now lets take this a step further. I have 4 2inch diagonals. One is a standard inexpensive diagonal, One advertises a 90% reflectivity, one is 95% reflectivity, and one is 99% reflectivity.  I can tell under normal observing conditions a difference between my inexpensive diagonal and my 90% very slight but noticeable. I can tell a more noticeable difference between my inexpensive diagonal and my 95% reflectivity diagonal. However, I can not discern much of a difference between my 95% and my 99% diagonal under normal observing conditions. When I get to dark skies (around 21.5+Mag/Arc²) I can tell a significant difference between all 4 diagonals. So, how often do I have skies that support the premium diagonal  or for that matter premium eyepieces. Not that often. This can also be applied to which telescope is better. Do you live in skies that consistently measure above 21.5 Mag/Arc²?  In that case you want the newest coatings, tube and lens designs and premium accessories. At least I would. However, if most of my observing is done in 20 Mag/Arc² or less than the additional cost of premium scopes and accessories may not be worth the additional cost. In other words, since I can not take advantage of premium sky conditions do I really need premium optics and accessories?

 

In answer to the OP question about which C8 should he get? I don't think it makes too much difference unless you live in an area with real dark skies, that have excellent seeing, transparency, cold temperatures, or higher altitudes. 

 

The important thing is how much observing you will be able to do?  Will it be mostly in so,so skies or in excellent skies. I would purchase at C8 at a cost that is most comfortable to you so that you have room to grow. You can always purchase better accessories has your experience increases. But for now I would go with what you feel comfortable in spending $ on.  While you explore the hobby and enjoy the views through the eyepiece. C8s are generally pretty good optically, they are versatile and able to keep you busy observing for quite some time.

 

I just noticed you are in the Highlands of Scotland. I visited there while I was in the service. Our team were guests of your Black Watch Regiment. Fine soldiers they were. As I remember what I learned was how to drink warm Beer/ Ale and throw darts. I also remember cold, fog, rain and Bagpipes. so I am not sure how much observing you will do.

 

In any case enjoy your time at the eyepiece there is a lot to see.

 

Clear Skies Never Lose the Wonder

From the other side of the Pond.

 

RF

[GTom]

Rain and bagpipes we have plenty, unfortunately clouds too. However, when these clear, my own backyard is B4 and B2 is just 30min ride from here. A good long, wide eyepueve and a quality field corrector, such as the Alan Gee II are defo on the list. I am not going for the Edge version: that one sells at a thousand pounds premium here even second hand! The best correctors cost about a third of that.

[quilty]

I think, too, the edge version isn't likely to be the best one.
Maybe you consider an ACF or the 9.25. The 9.25 has about half the coma amount and visually doesn't need a corrector. The ACF anyway that's for sure everything else what period was best is guesswork

Edited by quilty, 02 November 2024 - 04:22 AM.

[GTom]

I think, too, the edge version isn't likely to be the best one.
Maybe you consider an ACF or the 9.25. The 9.25 has about half the coma amount and visually doesn't need a corrector. The ACF anyway that's for sure everything else what period was best is guesswork

The 9.25 is unfortunately a full step up in both weight and size: 20lbs from 13, OTA diameter adds 35mm, which combined means very significant additional demands re mount choice. I suspect an AM5 class harmonics or even smaller gets away with the c8 + full AP gear without counterweights while the C9.25 will need counterweights = even more weight to carry.

Edited by GTom, 02 November 2024 - 07:00 AM.

[quilty]

I quite know, just an idea. I think the C9 is the largest my stable EQ5 can take properly. But the 9 is definitely another size
When too large I'd prefer an 8 ACF over an edge.
My 41 year old 2080 does well and I prefer the C9 just for the reduced coma. I think a good 8 ACF could replace both.

[thierry martin]

The 9.25 is unfortunately a full step up in both weight and size: 20lbs from 13, OTA diameter adds 35mm, which combined means very significant additional demands re mount choice. I suspect an AM5 class harmonics or even smaller gets away with the c8 + full AP gear without counterweights while the C9.25 will need counterweights = even more weight to carry.

I have a respaced C8 . There is no problem for the Ioptron HAE29. 

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[Notdarkenough]

This is a common question. It is propagated in part by Celestron's marketing folks. They tend to introduce "packages", not pieces of kit. An 8SE is an 8"OTA with an SE mount. And Evo 8 is an 8" SCT with an Evolution mount. AVX8? Same thing, an AVX mount with an 8" SCT. CPC 0800? CPC-mounted 8" SCT. 

 

Once we decouple the mount, we have, in this example, an 8" SCT. The coatings on different production years 8" SCTs aren't all the same. The newest coatings are Starbright XLT. So, the current base model 8" SCT is an XLT. Celestron then designed an internal field flattener inside some SCT OTAs, these have the designated EdgeHD, or HD. Thus, a new rig may well be an Evo 8HD with XLT coatings. Prior to the XLT coatings process, other terms were used for selling 8" OTAs, and most folks simply call them "C" for Celestron and the OTA aperture, 8" is the 8. A C8 may well be an older 8" SCT before XLT, or a 8" SCT with XLT. Does this difference matter? If you are buying or selling, it is a huge difference. In practical terms, most uses of the "C8" designation simply refers to any 8" Celestron SCT. 

 

The same naming convention is true of the C6, C8, C9¼, C11 and C14. 

[thierry martin]

This is a common question. It is propagated in part by Celestron's marketing folks. They tend to introduce "packages", not pieces of kit. An 8SE is an 8"OTA with an SE mount. And Evo 8 is an 8" SCT with an Evolution mount. AVX8? Same thing, an AVX mount with an 8" SCT. CPC 0800? CPC-mounted 8" SCT. 

 

Once we decouple the mount, we have, in this example, an 8" SCT. The coatings on different production years 8" SCTs aren't all the same. The newest coatings are Starbright XLT. So, the current base model 8" SCT is an XLT. Celestron then designed an internal field flattener inside some SCT OTAs, these have the designated EdgeHD, or HD. Thus, a new rig may well be an Evo 8HD with XLT coatings. Prior to the XLT coatings process, other terms were used for selling 8" OTAs, and most folks simply call them "C" for Celestron and the OTA aperture, 8" is the 8. A C8 may well be an older 8" SCT before XLT, or a 8" SCT with XLT. Does this difference matter? If you are buying or selling, it is a huge difference. In practical terms, most uses of the "C8" designation simply refers to any 8" Celestron SCT. 

 

The same naming convention is true of the C6, C8, C9¼, C11 and C14. 

What is for you a huge difference? So far Celestron doesn't provide an optical test report for its telescopes. Celestron suggests to get a better coating because everything is made  during the same process thank to the technolgy evolution during the last 60 years. Of course it should be better ligth at the focuswith the XLT coating .  But In an C8 on any SCT , it is entrance of the baffle the crical issue.  This could have been improved. The Edge version gives less vigneting that the classical version, because the corrector is inside the baffle. Of course a second hand modern C8 OTA is sold for more money than the 70th version which were very well controlled individually.  . And this is a good news for the worlwide astronomers community  to have 60 years of C8! Which company can beat Celestron for this sucess? The C8 remains the first telescope having  a big mirror in a small volume than even a Lady can handle it. Owning one it is always a good asset to start this hobby. 

[maroubra_boy]

I see black tube "C8 XLT", Orange tube "Nexstar 8SE", grey tube "Evolution 8" models on the second hand market, with probably further units down the road. What are the optical differences among these?/Any particular series are more reliable/blessed with better QC?

Unless you do a side by side test of each OTA and only after giving each OTA the requisite TLC (release the corrector & collimate taking mirror shift/flop into account), it is impossible to to say which is better. The mount each OTA comes with MEANS NOTHING. I have seen outstanding OTAs on both high end & low end mount options & rubbish also with each.

Age means nothing too. I help my Club mates collimate & tune their SCTs so I have seen a spread of OTAs spanning more than 40 years & I cannot see an improvement or drop in OTA quality across the years. Still more scopes I wouldn't lay my money down for than I would be happy to spend my hard earned cash for.

[C0rs4ir_]

2004 seems to have been a excellent year of production. I would opt for early syntha years if i would get another one.

[quilty]

It's like wine, he?
I wouldn't completely deny but crazy though. the true connoisseur knows what production years must be favoured or shunned

Edited by quilty, 03 November 2024 - 04:49 AM.

[C0rs4ir_]

It's like wine, he?
I wouldn't completely deny but crazy though. the true connoisseur knows what production years must be favoured and shunned

You read my mind. Chapeau!

Edited by C0rs4ir_, 03 November 2024 - 04:33 AM.

[quilty]

And what do you recommend how long to store them in the cellar before degustation?

[C0rs4ir_]

And what do you recommend how long to store them in the cellar before degustation?

Consume right away once you get one of them. The previous owner of mine sadly didnt store it in an oak barrel but it catched a bit of mold in his basement. After i got it i cleaned it and made it fit for use it showed its rich bouquet on the night sky. Just make sure its wrapped in insulation and dew shield on.

[quilty]

Quite in fact I have stored two Maks because they were not all ok.
But the Mak5 last night looked through for the first time since long seemed to optically level the C9. What a performance at Sat and Jupe and Gany's transit!
Maybe that storing is the final trick to let them shine :-)

Time to see to my Mak7, the problem is principally solved.

Since last night I consider possible a 7" Mak or Mew 180 to outperform the C9

Edited by quilty, 03 November 2024 - 05:28 AM.