211 replies to this topic

[luxo II]

But the airflow from the fans is bupkiss….

[CHASLX200]

Not really.  Not sure if it’s still standard procedure, but back in the day Celestron hand figured their optics. As noted earlier, my ‘83 C8 was the personal scope of one of the opticians in Torrance. He spent extra time with the final figure and the results speak for themselves. Freaky sharp to slop bucket would depend upon who was working the line. 

 

Charles

They slipped up on mine and left the factory dead near perfect.  Every orange C8 i had was ok to lack luster and a gray 2004 C8 was total slop.

[Illinois]

Roger Tuthill also inspected the C8s he sold. My ‘75 was one of his…superb optics. I recall a conversation with him prior to my purchase during which he stated that Torrance sent him the “cream of the crop” to avoid costs associated with returned units that didn’t cut it. Based upon my experience, combined with others I know who also purchased one of his inspected C8s, I would agree that this was very much the case. 

 

Charles

Yes Roger Tuthill and other is Company Seven do inspect scope before send to customer.  I bought dew from Tuthill for my C8 and wonderful catalog to read.  I remember Super C8 and I can’t afford at that time so I bought Super Polaris C8 is good for me because I am not astrophotographer.  

[Procyon]

? good enough? 

 

[quilty]

looks like some tilt?

[Procyon]

looks like some tilt?

Wish I knew quilty, optics seem very fine though. Was a simple ronchi test. It'd be cool if everyone did it with a simple ronchi eyepiece, they sell for a few bucks.

Edited by Procyon, 21 May 2025 - 09:10 AM.

[azure1961p]

An opened back cassegrain isn't enough. It needs active cooling as well if you want the sharpest images.

 

Pete

[BGazing]

But the airflow from the fans is bupkiss….

Lymax cools my C8 very, very quickly. C11 takes a bit more time, but still very reasonable.

Now, it also requires stuffing it in ocassionally as the temp drops during the night.

[Procyon]

Maybe I'm ultra careful about my scope's interior, but I just don't want any air coming from outside inside my scope. Makes no sense to me, over time won't that accumulate particles no matter the filter?

 

I look at the interior of my CPC 1100, bought in 2016...I still don't see anything in there. I take it out at night say right after the first heat wave has dissipated from the ground, around 10pm, 10:30pm is better. 

 

Than I go out around 11:30pm and I can still see it hasn't fully acclimated yet. But around 12am-12:30am, everything looks crystal. Yeah, I know more people are in a rush for good reasons, just thought I'd throw this out there, I'm sure most of you know this routine anyhow.

[thierry martin]

Imagine if Celestron offered a "Deluxe" or "Special" version of their SCT's where the optics had been worked on for an extended time, with hand figuring and testing, plus came with a test certificate and numbers. Say 1/8 wave actual tested. And to get this the customer would pay about 100% more for the SCT. 

 

It would be a small "sideline" of, say 5% production, that would say "look what we can do" and be for discriminating imagers and picky customers... or just visual observers who want real consistent quality aperture in the light weight Catadioptric package.

 

This idea stems from the old discontinued no longer available Russian made Maksutov optics from Intes, Alter Intes, Intes Micro, Santel etc., which were available to the customer in different optical grade usually 1/6 or 1/8. That came with actual test certificates.

 

I know. Dream on, right?

 

All the comments  never involve the optical configuation as an arguments,  about making  a Deluxe version.The SCT is  still dependant of composition of optical parts . The simulation is using optimal theorical polishing surfaces. Therefore the main concern is always the remaining defects to tackle in order to make better SCT. The test on the optical bench will not see  the shift of the spectrum , The Schmidt corrector is the problem  . To improve the SCT the Schmidt correct must be built like achromatic  doublet,  even its power is small.  The other aberrations are already corrected to some extend, with the aplanatic SCT or Edge SCT. Of course a deluxe SCT means for me, the secondary is used as a focuser with a battery remontly controlled by wifi blutooth. No more shift during the nigth.  The primary has to be very close to the exist baffle for  longer back spacing,  shorter baffle with bigger entrance  .Bigger full ligth illumination field.

 

Today  optics quality  is not an issue  for a big compagny, the computer is controling the process.Just need to ask more precision Even the test bench can be done by IA. It is over the time a good optician having gold in the hands to make perfect optical SCT. It s like coating under vaccum . Today every thing is automatically controlled. Of course the assembly must be still hand made. 

 

Now when you buy in an small compagny, you get a better result just because their clients accept to pay more. Celestron is making  millions SCT for a good price. It migth work with partners to make special requests . I supposed Meade did it and eventually  it took ages to produce a reducer. Today compagny are managed with commercials to make money .  Why Celestron will bother to make a Deluxe version for the optical design when Meade did a much better SCT and had failed?. 

[RichA]

? good enough? 

 

Full.jpg

Take it down to three bands.

[RichA]

Lymax cools my C8 very, very quickly. C11 takes a bit more time, but still very reasonable.

Now, it also requires stuffing it in ocassionally as the temp drops during the night.

Yes, honestly, a 1 inch computer fan could evacuate a C8/C11 tube very quickly.

[Brain&Force]

My answer to the title question: nah. What I would pay money for is a better Ritchey–Chrétien.

 

GSO optics appear to be excellent in quality, so it's not about better wavefronts. Aside from some of the mechanical bugbears, a design with a slightly smaller central obstruction (but still enough to fully illuminate an APS-C sensor) would be great. That is, while keeping it at f/8, which could be done by reducing the focal length of the primary and increasing the magnification of the secondary. As a side effect this would also reduce the field curvature.

 

As an imager, I wanted something that could handle the near IR or UV, so an all-reflecting setup was the obvious choice. But even as a visual observer I found myself leaning towards getting an RC instead – sure, there's a bigger central obstruction, but it can give me wider and better-corrected fields, and I spend most of my time at very low powers (38x!) I know I'm losing contrast on the planets and other small objects, but it's a tradeoff I'm okay with.

[azure1961p]

Lymax cools my C8 very, very quickly. C11 takes a bit more time, but still very reasonable.

Now, it also requires stuffing it in ocassionally as the temp drops during the night.

Trouble is you need the active cooling full time.  It's so worth it. It truly is.  That or wrap it up in reflectix. 

[thierry martin]

My answer to the title question: nah. What I would pay money for is a better Ritchey–Chrétien.

 

GSO optics appear to be excellent in quality, so it's not about better wavefronts. Aside from some of the mechanical bugbears, a design with a slightly smaller central obstruction (but still enough to fully illuminate an APS-C sensor) would be great. That is, while keeping it at f/8, which could be done by reducing the focal length of the primary and increasing the magnification of the secondary. As a side effect this would also reduce the field curvature.

 

As an imager, I wanted something that could handle the near IR or UV, so an all-reflecting setup was the obvious choice. But even as a visual observer I found myself leaning towards getting an RC instead – sure, there's a bigger central obstruction, but it can give me wider and better-corrected fields, and I spend most of my time at very low powers (38x!) I know I'm losing contrast on the planets and other small objects, but it's a tradeoff I'm okay with.

The RC is F8 for smaller focal very use full when using the Lepus . The backspacing is generous to accomodate reducers with generous backfocus for moder cameras for DSO. The camera is not conerned by contrast because it is collected photons for seconds compare to our eye limited by 1/10 of second. Therefore for 1 deg of field the astigmatic aberation is inside the Airy spot. That if very good. The only thing will be a flattener to mach the size of the camera sensor and the focus tolerance. concerning visual observation you are rigth. The central obstruction is bad for visual use. Regarding the baffle. This is a problem with the full field illumination. The SCT from Celestron was originally built to match full format camera , at the focus without straigt light interferences. With 34% obstruction the constast was well preserve with some  full field illumination at the centre ( 0.1deg of field ) and slowing the vignetting reaching 40% at the 19mm of axis. Which it is not a problem for our eyes. 

The RC is for imaging , but you can always watching: at least enjoying tiny stars

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[photoracer18]

Never trust any statement from the 50's to the 70's when it comes to optical quality of essentially mass produced telescopes. That is not to say they did not make good ones but frankly testing at those price levels was not really going to happen. Since all the Newtonian dealers in the days around when Celestron started advertised that their optics were 1/10 wave or better (yet testing has proven that while their best might make that claim the majority might not) the average buyer had no way to test whether that was true and they knew that. Most important thing was whose name on the back of the mirror who made it was more important (or who was in charge of the optical shop during that era). So I am pretty sure that Celestron advertised the same quality as the others without actually testing every one of them. Nowadays optical makers need to differentiate their output from the their competitors  So instead of good enough they may have to reach another level. If its not too costly. That is why so many turn to DPAC testing after purchase. Even a bad mirror will look pretty good at low power, especially if the mirror is big enough.

[RichA]

When Sky & Tel compared Meade and Celestron 8 inch SCTs back in the 1980s, they found the Meade's had smoother optics, while the Celestron's had more accurate curves.  Too bad they couldn't be combined in those days.  Because both had some issues in that era, but how many out of 100 no one knows.  Today, I'd suggest they are consistently better, but you will never see a DPAC test on an 8 inch SCT that'll match a five inch apo refractor.  But, as C14 users have proven with their planetary shots, sheer aperture trumps absolute optical quality.  No question.

[quilty]

I don't know if C are right with their just oversized primary mirror by just 1.5 mm.
They seem to ignore the usually poor outmost part of the mirror with a hanging edge.

[CHASLX200]

When Sky & Tel compared Meade and Celestron 8 inch SCTs back in the 1980s, they found the Meade's had smoother optics, while the Celestron's had more accurate curves.  Too bad they couldn't be combined in those days.  Because both had some issues in that era, but how many out of 100 no one knows.  Today, I'd suggest they are consistently better, but you will never see a DPAC test on an 8 inch SCT that'll match a five inch apo refractor.  But, as C14 users have proven with their planetary shots, sheer aperture trumps absolute optical quality.  No question.

I had my best and worst SCT's from C and the Meades pre 1993 were all ok at best but never a total slop bucket.  The later 90's LX200's were all good since i had 8 of them and only one soft 12" LX200.

[RichA]

Imagine if Celestron offered a "Deluxe" or "Special" version of their SCT's where the optics had been worked on for an extended time, with hand figuring and testing, plus came with a test certificate and numbers. Say 1/8 wave actual tested. And to get this the customer would pay about 100% more for the SCT. 

 

It would be a small "sideline" of, say 5% production, that would say "look what we can do" and be for discriminating imagers and picky customers... or just visual observers who want real consistent quality aperture in the light weight Catadioptric package.

 

This idea stems from the old discontinued no longer available Russian made Maksutov optics from Intes, Alter Intes, Intes Micro, Santel etc., which were available to the customer in different optical grade usually 1/6 or 1/8. That came with actual test certificates.

 

I know. Dream on, right?

 

Comments?

There has been an optically-improved Celestron 8 since C8's have been around, it's called the Questar 7.  Guess what? The Questar costs 7 times as much,  Questar is just about dead now because too few people bought them to allow Questar to hire qualified people and contract competent optical shops to do the work.  It's hard to employ engineers at $80,000 to $100,000 a year when numerous defense contractors will pay double that.  I should point out, I had two Q7s, a SW 180 Mak an Intes and dozens of 8 inch SCTs and of them all, I'd still take a C8 for overall performance, portability, acclimatizing characteristics and ease of use.

[Foehammer]

I'd definetely choose one that had:

-Improved secondary mating to corrector (no twisting)
-Improved secondary mount / collimation mechanism (not pressure based, no more trefoil)
-No mirror flop during focusing (no locks)
-Active cooling built in.

As far as optics quiality, I think most people can't appreciate the difference either through lack of experience or conditions.

Having said that, I'm perfectly happy with mine.

[azure1961p]

There has been an optically-improved Celestron 8 since C8's have been around, it's called the Questar 7.  Guess what? The Questar costs 7 times as much,  Questar is just about dead now because too few people bought them to allow Questar to hire qualified people and contract competent optical shops to do the work.  It's hard to employ engineers at $80,000 to $100,000 a year when numerous defense contractors will pay double that.  I should point out, I had two Q7s, a SW 180 Mak an Intes and dozens of 8 inch SCTs and of them all, I'd still take a C8 for overall performance, portability, acclimatizing characteristics and ease of use.

If I recall the Q7 didn't have a primary mirror large enough to contain the correctors light cone so it's working at 6.6" or some such.  I'd bet it outdoes the C8  on Mars but never ever on deepsky.

 

Pete

[Rasfahan]

I can‘t say anything about SCT optical quality - all I‘ve seen is tests of the full system and not the single components. Problems i. The system can stem from all kinds of known mechanical problems, starting with decentered secondary, miscollimation due to mirror shifting, inadequate mirror holders, acclimatisation problems, etc. If GSO is able to churn out hyperbolic mirrors of high quality for low prices, I‘ld be surprised if the Celestron mirrors are actually the culprit for bad performance.

 

I think the problem lies in the mechanics. Looking at my RASA that whole construction was agrarian - very rough, basic and partly just barely adequate and partly inadequate for the purpose. That is not easily fixed but needs newly designed components (mirror holders/cells, focuser mechanism, etc). Some of that has been introduced with the V2 but that doesn‘t fix the main problems of the design. It also needs not only new tooling, and better QC but a different attitude towards quality. Splurting grease around a badly made focusing mechanism just doesn‘t cut it.
 

If you want good optics with good mechanics, it‘s going to come at a cost. Not only in money, but also in weight. And then there‘s just no more advantage to the SCT design compared to, e. g. a (corrected) DK or a nice CC. And those can be easily had with impeccable mechanical and optical components and don’t have the inherent compromises of the too-shortly-spaced SCT. So, I‘ld say there is no market for a better SCT because that market is covered by these other designs.

 

I think the point has been made above, but I couldn‘t fond the post when I looked for it.

[quilty]

If I recall the Q7 didn't have a primary mirror large enough to contain the correctors light cone so it's working at 6.6" or some such.  I'd bet it outdoes the C8  on Mars but never ever on deepsky.
 
Pete

Such a pricy scope and they don't even manage to provide it at true 7" ?

The 3.5" was aimed as 4"?

[NinePlanets]

If they made say, a C10, 11 or 12 at F/14 or F/16 or F/18 with a smaller central obstruction so the 1st diffraction rings weren't so bright and planets a bit more contrasty (and forgetting about accommodating large format eyepieces and cameras), then I might be the first in line.