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Do CATs have Premium Optics

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#1 Asbytec

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Posted 19 May 2018 - 05:24 AM

I have been trying to understand the MCT design for a long time and why I like mine so much. I always attribute the great views to the above average seeing and thermal cooling in the tropics. Both of which allow a very high level of collimation. All of this matters. 

 

A question for MCT is (and SCT, too, it's related), how can you take a highly curved meniscus that, apparently, puts out a lot of secondary spherical aberration and toss in a fast primary mirror with a ton of primary spherical aberration and make it work at all. Not only work in many cases, but work quite well. Certainly a scope with that much aberration is not on the same par with a premium scope (except maybe an unobstructed APO). I still believe we can characterize mass production as something of a hit and miss proposition, not saying otherwise. But can we say some premium scopes are being delivered at or above the bell curve? And if so, do those lucky enough to have one, can it be said we have premium optics? 

 

Even though it's massed produced, is it also what we might consider premium? I do not mean premium in the way amateur glass pushers craft well made premium mirrors and professionals deliver sensibly perfect optics to a very satisfied market, and thank God for them, but the way machines might do it. We will often hear that mass produced scopes will be no better than 1/4 LSA, plus a few more aberrations, especially as the system is tested at the eyepiece. So, the popular implication seems to be they simply cannot be premium. Impossible. I might argue otherwise. 

 

An IF certainly takes no prisoners and may well tell us our scopes have 1/4 pvw LSA and a host of other aberrations at a few points sampled, but I can say the (my) star test is most certainly not indicative of a smooth fully 1/4 wave of undercorrection across the defocused pattern as they are argued to be...that they must be, for some reason. Apparently because it cheaper to leave them at 14 pvw LSA. Roddier is probably good test, and DPAC is arguably a good test, as well. But, what if all of these tests show us nice results? Is our scope premium in the level of its performance regardless of whether it's finely handcrafted? 

 

Like many others, I know I have simply been impressed with the MCT design, as others have with their SCT. I have seen some amazing things and discussed observations with other premium owners. Premium owners seem to have a some level of advantage over what I have seen, mostly in terms of "sharpness" (I think I know what that means.) However, that difference may well have boiled down to the size of our obstructions (or lack of), and to some extent the mechanical execution such as baffling, coatings, focuser movement, or glass quality. I am not so sure it's always the premium optics that are making the difference in all cases. So, it dawned on me, if not, then do I have a premium scope. And do you?

 

The question remains, well, even if it is premium how do you know it is? And at what level of performance can we say it is premium? Maybe it boils down to some scale of Strehl ratios, but it also may not be that simple. Or are premium optics simply hand made and tested (sometimes with a certificate or simply a reputation) to show they are? 


Edited by Asbytec, 19 May 2018 - 05:34 AM.

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#2 CHASLX200

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Posted 19 May 2018 - 05:32 AM

Some do, but you are paying much more for them.  The avg SCT is mass made and the optics are all over the map chap. While one SCT can be super sharp the next can be a mush dog.

 

The Tak Cats seem to be very good, but you are paying 3 to 5 times the price.   It is just a optics lotto with the cheaper made stuff.  It does seem like the China stuff has got much better over the last 10 years and is much better vs 20 years ago.  


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#3 Asbytec

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Posted 19 May 2018 - 05:47 AM

Part of my interest lay with your ETX 125 (and one I star tested) and your recent brief, but positive SW 150 first light as much as my own. Still interested in hearing more about how your SW turned out.

 

I think I agree, it's (less of) a crap shoot with mass production and finely crafted Tak Cats as well as hand crafted MCTs are consistently the best any scope can be. (Premium Newts, too, but off topic really as CATs are more complex and in the CAT forum I don't want to diverge to Newt mirror quality). I also agree scopes coming out of China are not as bad as they might have been. Astronomics is turning out pretty nice AT ED refractor run. Lots of examples out there of very good scopes.  

 

My primary interest is understanding how you can take such a convoluted thing as a MCT design and make it perform. It's somethign I am waiting for you to test on your SW 150, and somethign I experience with my China cheapo MCT. But, the conversation may apply to SCTs and CATs in general. I know they are good, but can they premium?


Edited by Asbytec, 19 May 2018 - 06:06 AM.


#4 sg6

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Posted 19 May 2018 - 06:30 AM

Not really "premium" unless someone somewhere has spent the time almost hand crafting parts or at least putting in a fair bit of human time.

 

A premium mirror is likely one where they are checked by a person or a machine at more numerous stages and it is decided what work has to be done. So the work performed is therefore customised a bit. Kind of grind the first stage, check all is as expected, make adjustments if/as necessary, check at second stage and again adjust grinding as necessary. Make it a 6 stage set of checks and it would be better then one that has say 3 checks. But those additional 3 are time and money. The final stage may be a finer grind for a better surface fimish. The final grind may be a normal grind and a fine grind.

 

Lens will be much the same someone will check each lens, and lens surface, at each stage, if a radaii is on the high side (too flat) then the grind may be altered to rebalance it  Same if the radaii is too tight they may alter the grind to give a more optimal greater radaii.

 

But they all take additional time and work and that is cost.

 

Optical components will be checked for performance as they are completed and I would expect that they are graded accordingly. So a "good" manufacturer is likely and simply paying extra for the Grade A items. However you will accordingly get a higher cost for the equipment.

 

SCT's, Maks etc operate a lot based on the seperation of the 2 mirrors, that has to be precise.



#5 db2005

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Posted 19 May 2018 - 06:36 AM

I've been wondering about that myself. Intes make some MCTs which are held in very high regard by owners, but I've never tried one, and I've never felt compelled to spend APO money on an MCT.

 

However, I finally got myself a Celestron C8 XLT recently, my first CAT after several years using only refractors and Newtonians. I am delighted by the C8's performance and convenience, and I'm still trying to understand why the C8 performs so well despite not having perfect optics. No, the images are not as tightly defined and as contrasty as a premium 100 mm APO, but at 30% of the price of a much smaller APO I can't really complain. Despite the C8 not delivering perfect pinpoint sharpness like my FC-100 I still find it enjoyable to use because of its superior light gathering power which makes many observing targets much more enjoyable. Performance on Jupiter is roughly on par with my FC-100, but with slightly better resolution and slightly less contrast.

 

My guess is that CATs can get away with good-but-not-perfect optics by means of their sheer aperture advantage (you know "aperture wins", as they say). And the C8 is definitely better than any of the inexpensive Newtonians I've tried and much more convenient to use.

 

I'll be following this thread, as I look forward to other people's experiences with this.


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#6 macdonjh

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Posted 19 May 2018 - 06:41 AM

I think people here generally use "premium" as an adjective for the brand, rather than the level of quality a scope or mount is made to.  By that I mean a "premium brand" consistently produces high quality gear.  The non-premium or mass market brands produce good, sometimes excellent, gear, but the variation in quality from sample to sample is higher than with a premium brand.  Look at all those older posts where somebody is waxing poetic about that C8 or Cave Newtonian they once had with excellent optics.  



#7 WadeH237

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Posted 19 May 2018 - 06:54 AM

Even though it's massed produced, is it also what we might consider premium? 

I have two answers for this:

 

1) Who cares?  What matters is how the scope performs, not what you call it.

 

2) Cars tend to have more consistent quality than most telescopes, but there is still some variation.  If you were to buy a new Ford Festiva, and it happened to be the one produced at the far right of the quality bell curve, would it then be considered a premium automobile?


Edited by WadeH237, 19 May 2018 - 06:56 AM.


#8 rolo

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Posted 19 May 2018 - 06:59 AM

Only one way to know for sure, bench test or experienced star testing, which is rare. To me premium means more than 1/4 wave smooth well corrected optics and in more cases than not mass produced is usually less than that.  

 

I've had and compared a few ETX90 vs a Questar and while the ETX is good the Questar 3.5 is excellent. Main difference is aspherized optics in the Q and smoother as well. Same thing with the ETX125, focus on bright star and see three or four rings around it and its a sure sign of Spherical aberration. The Double-pass Auto collimation test showed the same results. Same problem with two Orion 6" Maks(red) and two Orion 90mm Maks, acceptably smooth but SA was obvious. It doesn't make it a bad scope but premium they're not and made to be that way.Best test I've seen was SW 150 at 1/5 wave but a little bit rough. I'm sure it performed great.

 

Below are some DPAC tests I've done of Celestron, Meade Criterion Dynamax 8. Despite the less than perfect results the Celestron gives excellent views, the Meade was good and Dynamax well, pretty bad good for maybe 150x. First two are of Celestron SCT's and both were very good to excellent at the eyepiece. The Maks tested better in smoothness but seemed to show a hole in the center around the secondary and bit of bowing of the lines from inside to outside of focus. I'll see if I can dig up one those pics. And no I'm not an Expert at these tests, I use them for my and friends reference.

 

The last one is Vixen ED102SS.

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Edited by rolo, 19 May 2018 - 07:05 AM.

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#9 Asbytec

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Posted 19 May 2018 - 07:00 AM

Not really "premium" unless someone somewhere has spent the time almost hand crafting parts or at least putting in a fair bit of human time.

 

<snip>

Yes, it's a great point (along with the rest of your comment) and a definition I use to kind of tell them apart. The idea is a lot of care is made to ensure great premium performance. And those scopes are definitely premium and worth the money. Never any question to my mind. But, if it is about performance, the line may blur a little. To me it's interesting the MCT specifically (and maybe other CATs generally) can be so atrocious in terms of lower order and higher order spherical and yet the system comes together nicely. Nicely enough? 



#10 Asbytec

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Posted 19 May 2018 - 07:05 AM

I've been wondering about that myself. Intes make some MCTs which are held in very high regard by owners, but I've never tried one, and I've never felt compelled to spend APO money on an MCT.

I guess that is what I am driving at as well. I have no doubt my particular sample is obstructed and not giving the same image as a great APO. But, to within it's "diffraction limit", it is giving me /maybe/ very nearly the best image possible. No scope is perfect. I am just amazed at how they do that with highly curved, and likely very aberrant surfaces. Likewise, I am not compelled to upgrade to an APO, for example. When I come in from a night of observing, I am not left wanting. So, it makes me wonder...


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#11 Asbytec

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Posted 19 May 2018 - 07:08 AM

I think people here generally use "premium" as an adjective for the brand...

Yes, that, too. Great point. Along with a premium build. No question. But, at some point, it's about the image, too. How good does it have to be? I have my opinion, and of course it probably be as good as it possibly can be. But, how do you get there with an obstruction, for example. The optics almost have to be "premium", if you will. 



#12 Asbytec

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Posted 19 May 2018 - 07:11 AM

1) Who cares?  What matters is how the scope performs, not what you call it.

 

I'll leave the car analogy for later, its apt I guess. 

 

But, yes, who cares. Kind of true. I think we want to know we're not getting a lemon, and by extension getting good images. So, we might care a little or a lot. But, I think the point you are making is the same as mine. Who cares, so long as the image is jaw dropping, sharp, snappy, or whatever. That's where the rubber meets the road. And that's what we pay for at any price. But, yes, again...it's more about actually enjoying the darn thing rather than worrying about it. So, in that sense, who cares outside of an interest in how it all comes together. 


Edited by Asbytec, 19 May 2018 - 07:57 AM.


#13 rolo

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Posted 19 May 2018 - 07:16 AM

Yes, that, too. Great point. Along with a premium build. No question. But, at some point, it's about the image, too. How good does it have to be? I have my opinion, and of course it probably be as good as it possibly can be. But, how do you get there with an obstruction, for example. The optics almost have to be "premium", if you will. 

I'll put it this way, at a mini star party at a friends house years ago the two 6" Orion Maks were no match against a Vixen 102 F/9 Fluorite. Compared them to the host's AP 130GT and it was night & day difference. Same thing with Tak CN212 it was most excellent in Cassegrain mode. Main Subect was Mars.



#14 Asbytec

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Posted 19 May 2018 - 07:23 AM

Only one way to know for sure, bench test or experienced star testing, which is rare. To me premium means more than 1/4 wave smooth well corrected optics and in more cases than not mass produced is usually less than that.

Yes, premium are not made to be that way. I agree. I think I also agree at or somewhere above 1/4th wave and smooth optics is a good starting point for a sensibly good image (including the obstruction). The MCT is interesting because, and as your DPAC show, they do have some obvious SA, but are also capable of some pretty good rms values if done correctly. This is the part that interests me most. When I test mine, it is kind of confusing because the resulting star test resembles Suiter's 1/8 pvw LSA, but I know that is not right because I'm sure we're not seeing pure LSA alone. It only resembles the pattern fairly closely. My assertion might be, if it resembles that 1/8 pvw LSA pattern maybe performance can be expected to be the same. If that's so, then is it premium if we ignore the mass produced build? 



#15 rolo

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Posted 19 May 2018 - 07:25 AM

Norme, You seem to obsessed with this subject. Have your scope bench tested and be done with it. Talking about it forever is not going to change anything. If you're happy with your scope, who cares what anyone else has to say? Mass Produced is just that, thousand s made to make as much profit as possible. You're not going to get a Z06 Corvette out of a Chevrolet Spark production line.  



#16 Asbytec

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Posted 19 May 2018 - 07:28 AM

I'll put it this way, at a mini star party at a friends house years ago the two 6" Orion Maks were no match against a Vixen 102 F/9 Fluorite. Compared them to the host's AP 130GT and it was night & day difference. Same thing with Tak CN212 it was most excellent in Cassegrain mode. Main Subect was Mars.

MCTs and premium refractors are also two different scopes. A premium refractor, despite it's aperture, has the advantage of operating at it's Strehl while the MCT is necessarily degraded by its obstruction. As above, it may be possible the MCT was giving the best image possible and all scopes involved had a nice > 0.9 Strehl. Which is why I said the question might not be that simple. To come close to any of your comparison samples, the MCT has to be exceptionally well made with a very modest obstruction. But, even with an obstruction, the MCT is being the best it can be, or nearly so, if rms is much below 0.074. If it's the best it can be, is it premium despite the obstruction effects? 



#17 Asbytec

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Posted 19 May 2018 - 07:36 AM

Norme, You seem to obsessed with this subject. Have your scope bench tested and be done with it. Talking about it forever is not going to change anything. If you're happy with your scope, who cares what anyone else has to say? Mass Produced is just that, thousand s made to make as much profit as possible. You're not going to get a Z06 Corvette out of a Chevrolet Spark production line.  

It's just a discussion on a cloudy night as rainy season sets in. I'm interested in understanding my equipment and why I like it so much despite the company making a profit. I could care less about the latter, and more about what I see through it and why. Recent topics on seeing and premium, and premium and C14s cause me to consider a lot of things and learn a little. I'm particularly interested in how a scope can throw aberrations all over the place like the MCT and still put up a nice image. If you don't mind, I'd like to explore the topic. How they do that interests me far more than any car analogy of putting a big engine on a racing chassis or not. There are always better cars out there and better scopes. That's not the point. 


Edited by Asbytec, 19 May 2018 - 07:51 AM.

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#18 HarryRik9

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Posted 19 May 2018 - 07:37 AM

I note that only one comment addressed the issue of the overall design. Basically SCTs and MCTs being shorter have advantages for the observer. The overall mechanical design, stability of the mount, is as important as the premium optics. 


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#19 rolo

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Posted 19 May 2018 - 07:53 AM

It's just a discussion on a cloudy night as rainy season sets in. I'm interested in understanding my equipment and why I like it so much despite the company making a profit. I could care less about the latter, and more about what I see through it and why. It interests me far more than any car analogy. Recent topics on seeing and premium, and premium and C14s cause me to consider a lot of things and learn a little. If you don't mind, I'd like to explore the topic. I'm particularly interested in how a scope can throw aberrations all over the place like the MCT and still put up a nice image. How they do that interests me. 

I don't mind at all.  All I'm saying is you've been down this road many, many times and I would like to be at peace with it. Maybe a profession optician can explain how a scope with multiple abberation can put up a good image. I can tell you this much,Even the horrible Dynamax 8 I tested was usable so no, perfect optics are certainly not needed for good views. All things being equal the difference between a 1/4 wave and an 1/8 wave is not a night and day difference at the eyepiece. To me premium optics are worth it but for general observing not necessary. Maybe a local Astronomy club in your area would be good place to compare your scope to a premium scope.



#20 rolo

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Posted 19 May 2018 - 07:56 AM

I note that only one comment addressed the issue of the overall design. Basically SCTs and MCTs being shorter have advantages for the observer. The overall mechanical design, stability of the mount, is as important as the premium optics. 

That's a good pointwaytogo.gif . Could you imagine an unfolded C14 at f/11, it would be nearly 13ft long!!



#21 Jon Isaacs

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Posted 19 May 2018 - 07:58 AM

2) Cars tend to have more consistent quality than most telescopes, but there is still some variation.  If you were to buy a new Ford Festiva, and it happened to be the one produced at the far right of the quality bell curve, would it then be considered a premium automobile?

 

A Ford Festiva that was out on the endof the bell curve would still drive and generally behave like any other Ford Festiva , the inherent qualities that characterize a Festiva are in the design.  It would have fewer problems but it would still ride the same, the noise level would the same,  the seats and interior room would be the same. 

 

A telescope is different because the quality of the optics are so important to the quality of the view. Each scope must be evaluated on an individual basis. Still,  much about a telescope is determined by the design. The size of the CO,  the coatings on the mirrors , the coatings on the corrector,  these are determined by the manufacturing processes used , scope to scope variation would be small. 

 

Can an affordable Mak have premium optics? Probably. 

 

The Synta 127 mm I recently owned did not have provide "premium" views. 

 

Jon


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#22 rolo

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Posted 19 May 2018 - 08:03 AM

An IF certainly takes no prisoners and may well tell us our scopes have 1/4 pvw LSA and a host of other aberrations at a few points sampled, but I can say the (my) star test is most certainly not indicative of a smooth fully 1/4 wave of undercorrection across the defocused pattern as they are argued to be...that they must be, for some reason. Apparently because it cheaper to leave them at 14 pvw LSA. Roddier is probably good test, and DPAC is arguably a good test, as well. But, what if all of these tests show us nice results? Is our scope premium in the level of its performance regardless of whether it's finely handcrafted?

 

I would say so. Many mass produced Meade, Cave, Edmund,OpticCraft,Criterion and other Newtonians have excellent optics but less than excellent build quality. I would say they are premium in their level of optical performance. So is your Mak if that's the case.


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#23 Asbytec

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Posted 19 May 2018 - 08:03 AM

I note that only one comment addressed the issue of the overall design. Basically SCTs and MCTs being shorter have advantages for the observer. The overall mechanical design, stability of the mount, is as important as the premium optics. 

Portability, ease of set up and use, all that...yes. My scope has some small amount of image shift, too. I guess in that sense, the build is not premium. Sometimes I am still amazed at how quickly I'm setup and observing compared to earlier scopes (like goto calibration, imaging set up especially, and whatever.) Just plop it down and go.


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#24 Asbytec

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Posted 19 May 2018 - 08:08 AM

I don't mind at all.  All I'm saying is you've been down this road many, many times and I would like to be at peace with it. Maybe a profession optician can explain how a scope with multiple abberation can put up a good image. I can tell you this much,Even the horrible Dynamax 8 I tested was usable so no, perfect optics are certainly not needed for good views. All things being equal the difference between a 1/4 wave and an 1/8 wave is not a night and day difference at the eyepiece. To me premium optics are worth it but for general observing not necessary. Maybe a local Astronomy club in your area would be good place to compare your scope to a premium scope.

Yea, I wish. I'm pretty much by myself out here. CN is my astronomy club. I have been down this road, too, a few times. I am still not sure, after talking with experts, I really got a handle on the answer. But, I think I am close, and the reason I made this thread...to discuss it. I agree with you premium optics are worth it in every way.

 

I like mine so much I am torn between it being cheap or pretty good. I think it's the latter and I am thankful. But, how and why and do I understand it? I already understand my scope cannot compete with a 6" APO, maybe not a 4" APO in many ways, not a C14, either, and probably will not best an 8" Dob. I don't expect it to, but barring those expectations...gosh, I like it. But, why? Is it the tropical seeing? (Well, yes...that's it, too.) 

 

One of the influential threads of late was the discussion of seeing on premium vs all others. I argued the effects of seeing on the image in all scopes, but I learned a comparison was the right (better) thing to do. This means you are able to tell something about your scope and how it behaves in seeing to determine whether premium is the way to go. It made me realize maybe I have nothing to complain about with either the seeing or the optics. It made me realize maybe I am not at the proverbial junky 1/4 LSA that degrades when a gnat farts.

 

So, I began to try to understand the complex and interesting MCT design, again. From what I can gather, I actually think it's quite ingenious. Yes, it's no secret I am a fan of the design since I first laid eyes through it 8 years ago. I just want to know why. Maybe others do, too. I actually want to explain what I understand, but waiting for the right moment. I am kind of leery about being completely wrong. LOL


Edited by Asbytec, 19 May 2018 - 08:26 AM.


#25 rolo

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Posted 19 May 2018 - 08:09 AM

I've seen some of your Jupiter drawings and they're excellent. I would be very happy with a scope like that.waytogo.gif


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