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How many really good SCT's are out there

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#26 Justlooking456

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Posted 23 June 2019 - 02:45 AM

One man's bad SCT could be another's best scope ever. Some people swear by Chevrolet and some swear at them.

 

I read Rod's Used SCT Buyer's Guide and narrowed it down to a couple then bought a new one after looking at what was floating around CL and Ebay. This last one was the first scope I have had in 10 years. Yeah I bought a Meade, y'all can toss rotten tomatoes at me if you want, but the next one just might be a C11 Edge.



#27 yellobeard

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Posted 23 June 2019 - 04:03 AM

Yep, C11 edge: higher pricetag, means more narrow factory tolerances, so bigger chance to obtain a good one!

Good decission..

#28 petely

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Posted 23 June 2019 - 05:09 AM

I wonder if many of the bad SCT's people have complained about are the same ones just being passed around and the really good ones are being kept

Yes, that's my view, too. I understand that there are a few people who simply get bored with the "same old telescope" after a few months and some will be forced to sell due to circumstances. But for the most part the reason I suspect most scopes go on the second hand market is because they fail to live up to the original buyer's expectations.
Now, that could be because they expect too much, or it could be because there is something wrong that they hope a buyer won't spot until it's too late.

 

But the issue is also magnified, as we hear a lot more about the problems people have than about their successes. And horror stories tend to get repeated and exaggerated, as well.


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#29 CHASLX200

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Posted 23 June 2019 - 05:44 AM

I am just curious, if you owned so many, why did yuo decide to stop  at #60, and not # 10, or whatever? 

Just had to keep buying scopes over the last 42 years. Done with it now.  What may be good to one person may not be good to my eyes. Many people don't know what really good is.  Once you have owned the best then these SCT's don't look so hot.



#30 CHASLX200

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Posted 23 June 2019 - 05:51 AM

I wonder if under near perfect seeing conditions a good (not excellent) SCT will out perform an excellent, but substantially smaller aperture telescope of another design. I suppose it depends on the subject - double star, planetary details, DSOs, etc. I've been quite happy with my 3 SCTs (C-5, C-8, C-11) in over 45 years of observing. I would expect that these would fit in the bell curve as described. I have no idea how they would test out. But I doubt any were in the lower 20%. If any was in the upper 20% it would be unlikely I would recognize that. Seeing is usually the big variable in my experience. The ease of use, aperture versus weight/length, cost have been why I've used an SCT for most of my career.

 

I've had 3 Newtonians (6-, 8-, and 10-inch), only one (the 8) had tracking. Only one (the 10 inch Dob) had push-to DSC object finding. That one was briefly carried by my G-11 mount with tracking and go-to. But for the last 10+ years the SCTs (C-8 or C-11) have been on the G-11 mount. For me that setup has been the "best", most used telescope. Now with the C-11 and 115mm APO riding on top, I can compare the views given by a (likely average) SCT and a good APO refractor. I enjoy both. Rather than being concerned over which is "best" I get on with the viewing. The entire Veil Nebula fits in the refractor's FOV. The view of Jupiter is better in the SCT if seeing allows.

 

That's my two cents, for what it's worth.

 

Best Regards,

Russ

My freaky good 1984 C8 sure came close to MANY WELL MADE 8" f/8 Newts i have owned over the years. So while some people think i am putting down all SCT's well that is not true.  So we all know there can be some super good sct's out there. But they all vary so much from mush dogs to super sharp.



#31 CHASLX200

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Posted 23 June 2019 - 06:01 AM

What is odd is that there are oodles of bad Newtonians, and Newtonians that are poorly maintained, uncollimated, and have bad figures on bad glass...there used to be a small industry refiguring mainland mirrors, but no more, they're not up to the polishing process.  But to the best of my knowledge you have no SCT owners who make a point of being on the Newtonian group saying bad things about Newts.  We do however have our share of trolls here in the Cats & Casses who repeat the same tired nostrums year after year.   

 

In any case there are a fair number of hangers on in this forum who don't use cats, don't like cats, have nothing to contribute on the topic of cats, and who, most interestingly, mechanically cite the limitations of cats completely oblivious to the many limitations of their preferred alternative optics.  

 

But I guess it's better than television, and it keeps them off the streets.  

Had a few bad Newts as well and even a 7" Meade ED so it is not like i am picking on SCT's only.


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#32 HxPI

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Posted 23 June 2019 - 08:29 AM

My own opinion:  I would say that a very large percentage of telescope owners really don't know how to do an accurate objective analysis of their optics.  

 

After a decade of encouraging people to read Suiter's book on telescope testing, I still hear people that totally dismiss the validity of the star test.  

 

I often think this because maybe they looked at their defocused patterns and it did not look perfect (few scopes do though) and they wanted to justify their subjective opinion of the optics because who wants to think their telescope is not a great telescope?

 

I have just pointed to dozens and dozens of tests that show that a high Strehl SCT is not very common, but the vast majority of owners on CN say "Oh yeah, my Cx has really great optics!"  The objective data makes it very difficult to believe that. 

 

When you have star tested a truly perfect optic though, it looks just like the pictures of perfect optics in Suiter's book.  It kind of just jumps out at you.

 

The three perfect optics I have owned and star tested were two Intes Micro Mak Newts and my Astro-Physics 6" (and I don't own any of these anymore... Just because it is perfect does not mean I will keep it forever). Now I have owned a fair number of excellent scopes (near perfect) but a really perfect optic just looks exactly like Suiter says it will.  Once you see it, you can see less than perfection at a glance. 

 

And now people will quote Roland Christen, but clearly they did not really read his full commentary.  He even says in his often quoted work that he did not use a 33% obstruction for his MCT, but Suiter's tests are built around the 33% obstruction.  His rationaly was that a 33% obstrucition would be no better than an SCT, but the point is that the obstruction is not there for actual use, but rather to conduct the test and reduce the effects of higher order spherical aberration.  Likewise, I would wager that most of these people have not read Suiter's book, where he addresses these issues. 

 

Every Takahasi owner thinks because their scope is a Tak, it will have perfect optics.  I can point to several bench tests that cast serious doubt on that widely accepted belief.  Just a couple of days ago, I pointed to a test of a Takahasi with a Strehl of .922Heck that is peak of the bell curve Celestron quality... Most Tak reflector owners just don't want to believe that their scope could possibly have optics that are no better than a mass produced C8.

Is Suiter’s book $34.00 or $230.00? I ordered the $34.00 version from Willmann-Bell; for some reason the same book is over $200 new on Amazon! Very confusing. Hopefully the $34 version is legit....



#33 treadmarks

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Posted 23 June 2019 - 09:03 AM

After my past few nights of observing, I feel like the real question is: how many really good nights of seeing are there? Or how many really good SCT users are there? Because you may have a 1/8 wave or a .95 Strehl SCT, but if your seeing is bad it's performing as a 1/2 wave or worse telescope 95% of the time. Same thing if you don't collimate it. Oh and you may be impatient and not wait for a moment of good seeing, etc. etc.

 

Anyway, right about now I'm feeling like the saving grace of my SCT is its ability to gather a lot of light, quality optics are for people who live in Florida and California. If I didn't look at DSO, I may as well just use a 70mm scope frown.gif 



#34 starman876

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Posted 23 June 2019 - 09:13 AM

I have had a good number of SCT's.  still do.   Only couple let me down.  The rest always put up an image I could be happy with and study the features of the object I wanted to know more about.   I wish I knew more about how to refigure optics.   I would be trying to improve on all of them.  These are large aperture optics so you do need good seeing to appreciate one.  It is not like you can use them every single night.  Another fact which has been stated before.  If the optics in all these mass produced optics had a high Strehl I doubt many of us would be able to afford them.   We must keep cost, optical quality and build quality in their proper prospective when it comes to cost and performance. 



#35 CHASLX200

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Posted 23 June 2019 - 09:27 AM

I would still love another shot at a super good C14. And i know there are some good 14's out there. I just need a seller to back his scope up and offer a refund if i am not happy.  I just got a bad C14 and it is simple as that.  



#36 Astrojedi

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Posted 23 June 2019 - 10:24 AM

Let’s break this question up. This question by the op is not well phrased and just invites uninformed and secondhand opinions.

 

EdgeHDs: Very consistent quality. I am yet to find a bad one (10+). Almost all I have looked through / owned / collimated for others have been 1/5 wave or better. Superb performers and pinpoint stars once cooled and collimated. The flat field is unmatched in cats. Mechanicals are much better. Quality is a notch above other SCTs..

 

Newer XLT SCTs (post 2006-07): in the past 10+ years I have looked through / helped collimate at least 30-50+ of these. At least 90-95% were 1/4 wave or better. The C9.25s are the best. I never looked through one I did not like.

 

Pre 2005 SCTs: Much more variable quality 70-80% were good

 

Classics: Worst of the bunch in terms of sample variation. Some were superb and others were just terrible. I remember one I used about 20yrs ago. SA was so bad that I just could not find a sharp focus point. Boggled my mind as to how it got through QA.


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#37 starman876

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Posted 23 June 2019 - 10:26 AM

Yep, C11 edge: higher pricetag, means more narrow factory tolerances, so bigger chance to obtain a good one!

Good decission..

Most people seem to be happy with the Edge HD they got.  I wonder if the only difference is the corrector lens in the baffle tube or did they make other adjustments?



#38 CHASLX200

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Posted 23 June 2019 - 10:31 AM

Let’s break this question up. This question by the op is not well phrased and just invites uninformed and secondhand opinions.

 

EdgeHDs: Very consistent quality. I am yet to find a bad one (10+). Almost all I have looked through / owned / collimated for others have been 1/5 wave or better. Superb performers and pinpoint stars once cooled and collimated. The flat field is unmatched in cats. Mechanicals are much better. Quality is a notch above other SCTs..

 

Newer XLT SCTs (post 2006-07): in the past 10+ years I have looked through / helped collimate at least 30-50+ of these. At least 90-95% were 1/4 wave or better. The C9.25s are the best. I never looked through one I did not like.

 

Pre 2005 SCTs: Much more variable quality 70-80% were good

 

Classics: Worst of the bunch in terms of sample variation. Some were superb and others were just terrible. I remember one I used about 20yrs ago. SA was so bad that I just could not find a sharp focus point. Boggled my mind as to how it got through QA.

Like i said, they vary so much.  Now i can't say how good the Edge is on avg or the Meade ACF's.  Meade made some clunkers back when they first came out around 1981, but they hit the sweet spot in the mid and late 90's with the LX200's with some very good optics. Celestron was all over the map in the 70's and 80's with bad to great OTA's.   


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#39 Paul Hyndman

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Posted 23 June 2019 - 10:33 AM

Is Suiter’s book $34.00 or $230.00? I ordered the $34.00 version from Willmann-Bell; for some reason the same book is over $200 new on Amazon! Very confusing. Hopefully the $34 version is legit....

That's the book. I have the original version (which also came from Will-Bell) and have no idea why/how some are charging such a high price for the second edition. Rest assured, Will-Bell is a legit publisher/dealer that has served the scientific community for decades. 


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#40 starman876

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Posted 23 June 2019 - 10:57 AM

That's the book. I have the original version (which also came from Will-Bell) and have no idea why/how some are charging such a high price for the second edition. Rest assured, Will-Bell is a legit publisher/dealer that has served the scientific community for decades. 

I will have to buy one before the whole world starts to charge a couple of hundred dollars.  sounds like a book we all should have to evaluate a scope properly under the stars.

 

I looked through the catalog from Bell and ordered three books.  

 

Thanks for the heads up on where to buy them.


Edited by starman876, 23 June 2019 - 11:04 AM.


#41 jgraham

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Posted 23 June 2019 - 11:02 AM

I just did a quick count in my garage and I currently own 16 SCTs from 4" up to 10", and from about 1977 to 2014, being careful to step over the Halley years (from about 1985 to 1988). (I really gotta stay out of the classifieds!) To be honest, there's not a bad scope in the bunch. Some are optically better than others, and anything built this century has been consistently very good, but I would not rate any of my scope any worse than fair, and that's really only one scope, a spotter version of the Meade 2045. I also have an LX3 version of this same scope and it is outstanding!

 

Having bought nearly all of my scopes off of the used market I am usually buying someone else's problem, and I have yet to see an SCT whose problem wasn't the same; collimation and acclimation. The most problematic members of my SCT family have been the Meade f/6.3 Wide Field SCTs. These have a reputation for spotty optics and my first (a 10" f/6.3) seemed to confirm this. Before giving up on it I spent and entire evening zeroing-in the collimation using a camera, and it blossomed into a solid performer. I liked it so much that I bought another 10" f/6.3 for visual and an 8" f/6.3 for EAA, both went through the same teething pains and both ended up with the same result. For these 'fast' SCTs, close is not good enough. But once adjusted and the screws snug, they have remained in great shape for several years.

 

Just for reference; I was an active ATM for 30 years (from about 1968 through 1998), and I built something like 30 scopes from a 4.25" f/8 up to my Green Monster 16.5" f/6.5, so I like to think that I know my way around at least basic optical testing, but I could be wrong about that. smile.gif

 

Soooo, I think that if anyone is in the market for an SCT built in the past 20 years by one of the main manufacturers you have a good chance of getting a good performing SCT. Just take the time to let it acclimate and keep an eye on the collimation.

 

My latest baby...

 

Lightswitch 8 ACF (6-10-2019)-1.jpg

 

...a Meade LS 8 ACT with a micro-focuser. I had this out last night DSO-hopping from Scorpius northward up through Cygnus (with a stop-over at Jupiter). Loverly!

 

And one for the older members of the family...

 

Sandcast C8 Setup (3-23-2018)-2.jpg

 

These kinda book-end my SCT gear. :)

 

Enjoy!

 


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#42 Astrojedi

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Posted 23 June 2019 - 11:05 AM

Like i said, they vary so much.  Now i can't say how good the Edge is on avg or the Meade ACF's.  Meade made some clunkers back when they first came out around 1981, but they hit the sweet spot in the mid and late 90's with the LX200's with some very good optics. Celestron was all over the map in the 70's and 80's with bad to great OTA's.   

 

My point is exactly that the newer ones don’t vary as much. I don’t think it is appropriate to lump 30yr old OTAs with newer OTAs together as ‘SCTs’ and then make a generalized statement about ‘SCTs’. This is exactly the issue I have with some folks here who constantly mis-characterize SCT quality and performance.


Edited by Astrojedi, 23 June 2019 - 11:08 AM.

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#43 starman876

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Posted 23 June 2019 - 11:10 AM

My point is exactly that the newer ones don’t vary as much. I don’t think it is appropriate to lump 30yr old OTAs with newer OTAs together as ‘SCTs’.

That is a valid point.  It appears as though the manufacturing of scopes with quality optics from China is on the rise.  That is a good thing.   I would presume that the use of automated manufacturing has really helped in this process.   I am wondering when american manufacturers are going to start using the automated process in america.  would love to see a reasonably priced SCT which is american made.usa.gif



#44 vahe

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Posted 23 June 2019 - 11:17 AM

Ahh of course! I indeed forgot that very important fact !

Perhaps because I so much forced myself earlier to accept the downpart of those F/2 primaries, easier as they indeed allow us to play with very compact scopes, I just forgot all about it!

 

 

Design and construction of SCT's involves for two major optical compromises;
1 - F/2 Primaries discussed earlier.
2 - Vacuum method of producing correctors. Vacuum method was invented by Celestron and is responsible for making the low cost production of these scopes possible but there is a catch to it, the vacuum method produces a close approximation of highly complex aspheric Schmidt curve, to improve on it hand figuring by highly skilled opticians will be required resulting in unaffordable SCT.
I have looked through good many SCT’s, they all produce relatively soft images compared to high end refractors and Maksutovs, but no need to compare SCT’s to expensive scopes, all one needs to do is to compare SCT’s to Meade 7” Mak to see the difference in image quality.

.

Vahe


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#45 starman876

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Posted 23 June 2019 - 11:35 AM

Design and construction of SCT's involves for two major optical compromises;
1 - F/2 Primaries discussed earlier.
2 - Vacuum method of producing correctors. Vacuum method was invented by Celestron and is responsible for making the low cost production of these scopes possible but there is a catch to it, the vacuum method produces a close approximation of highly complex aspheric Schmidt curve, to improve on it hand figuring by highly skilled opticians will be required resulting in unaffordable SCT.
I have looked through good many SCT’s, they all produce relatively soft images compared to high end refractors and Maksutovs, but no need to compare SCT’s to expensive scopes, all one needs to do is to compare SCT’s to Meade 7” Mak to see the difference in image quality.

.

Vahe

The Meade 7" Mak is a great scope.  I took the counterweight out of mine.   I should use it more.   



#46 SandyHouTex

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Posted 23 June 2019 - 11:42 AM

All of the SCTs I own, except the Meade, are diffraction limited, often considered as 1/4 wave or better.  The reason is that I returned any which were worse than that.  How many were worse than that - 0.  They all shipped to me that good or better.  I did exchange my C14 because of a thumb print on the aluminized surface.



#47 jgraham

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Posted 23 June 2019 - 11:54 AM

Indeed. I have a pair of de-weighted Mak 7s; one for visual and one for imaging. I didn't include them in my list 'cause they are MCTs not SCTs. The Mak 7s are by far the best optics that I have seen in a production scope and at the tippy top of the list of how I would rank the optics in my Cats. The two ACFs that I have aren't bad. If fact, they are quite good, just not on par with the Mak 7s.



#48 Astrojedi

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Posted 23 June 2019 - 12:04 PM

Design and construction of SCT's involves for two major optical compromises;
1 - F/2 Primaries discussed earlier.
2 - Vacuum method of producing correctors. Vacuum method was invented by Celestron and is responsible for making the low cost production of these scopes possible but there is a catch to it, the vacuum method produces a close approximation of highly complex aspheric Schmidt curve, to improve on it hand figuring by highly skilled opticians will be required resulting in unaffordable SCT.
I have looked through good many SCT’s, they all produce relatively soft images compared to high end refractors and Maksutovs, but no need to compare SCT’s to expensive scopes, all one needs to do is to compare SCT’s to Meade 7” Mak to see the difference in image quality.

.

Vahe

None of the newer SCTs I have owned have produced soft images once collimated and in thermal equilibrium. You will be surprised how many folks who own SCTs don’t realize how to use one. Thermals in the OTA are almost indistinguishable from SA for practical purposes.

 

Beyond the typical differences between refractors and cats, the contrast and sharpness are a function of optical quality not optical design. My EdgeHD 8 holds its own very well against any 7” Mak and even 6” refractors. The only objects that look better in a high end 6” APO are Jupiter and Mars.

 

If you are ever in San Diego please visit the SDAA dark site. I go there often and do outreach as well. I would be happy to change your mind.



#49 Eddgie

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Posted 23 June 2019 - 12:21 PM

I wonder if under near perfect seeing conditions a good (not excellent) SCT will out perform an excellent, but substantially smaller aperture telescope of another design. 

Absolutely.  I have had the great pleasure of owning an Astro-Phycics 6" triplet and as one would expect, the optics were textbook.   Perfect spherical aberration correction in green (tested with a narrow pass green filter and 33% obstruction) no zones, turned edge, and a figure so smooth that it has to be believed to seen how perfect a star test can look. 

 

As perfect at it was, and as unobstructed as it was, my C14 easily showed a huge amount of detail that was out of the reach of the 6" Apo.  In one of my posts, I described how I was able to actually resolve surface detail on Ganymede, and could easily see polar shading on Io using my C14. I was never able to duplicate these observations using the 6" Astro-Physics.  In fact, the only refractor observation I have ever read where I felt the observer may have seen a similar amount of actual detail (not just albedo shading) was done with  hugely expensive 8" Apo. 

 

And considering that a C14 not only costs a tiny fraction of a high quality 8" apo (about $62,000 less for the C14), and is lighter (an 8" Apo weighs 61 lbs, vs 52 for a C14), more compact, easier to mount, and more comfortable to use, it makes one wonder why someone would buy an 8" Apo for planetary observing???? 

 

And heck, my mass market 12" dob does better on planets than the 6" Apo did.  Sure, it takes a night of good seeing, but here is what I have to say about that.   Even when seeing is perfect, you are not going to see the actual shape of Galileo Regio on Ganyemende using a perfect 6" apo.  Never-ever did I achieve that kind of result with the AP.  It does not have enough resolution and contrast transfer to do this.  So, the choice is to have as good or even better view in a 6" Apo on nights of poor or bad seeing, where there is little point in even bothering to try to look at solar system objects, or have ocassions where you can see far more with the less expensive, easier to mount, and more comfortable to use large SCT?

 

The break-even on winning out against a top quality 6" Apo is the C11, but to do this, the C11 is going to have to be at the upper end of the quality range, and yes, the seeing will have to be very good, and if less than excellent, the observer will have to be very patient.  

 

To answer your question though, it is not at all difficult for a larger, less perfect, obstructed aperture to beat out a meaningfully smaller perfect aperture.  I have done it with a very wide variety of comparisons.  Seeing is seeing, but patience will almost always give the significantly larger aperture the upper hand. 

 

(Roland Christen once told me that if my main goal of being on the 155EDF wait list was to do planetary observing, he suggested that I drop off the list and get a high quality 10" reflector because it could do a better job.   He very politely explained that where the big advantage of the 155ED would be realized was when one was imaging with large sensors.  I took his word for it, and have since concluded that he was correct).  


Edited by Eddgie, 23 June 2019 - 12:43 PM.

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#50 Eddgie

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Posted 23 June 2019 - 12:41 PM

Is Suiter’s book $34.00 or $230.00? I ordered the $34.00 version from Willmann-Bell; for some reason the same book is over $200 new on Amazon! Very confusing. Hopefully the $34 version is legit....

$34.  Yes, that is the one.

 

https://www.willbell.com/tm/tm5.htm

 

For whatever odd reason, if a book is out of print (as is the case with the original version of Suiter's book, which is the one I saw on Amazon when I looked) book sellers will often put a stupid high price on it, I guess hoping someone will think that it is the only way to get the book anymore?  I don't know why really, but I have seen it with other out of print books, but in this case, the original was simply superseded by a second (and improved) edition.

 

The first version is really good, but the Second Edition is much better.  In addition to just telling how to star test (and even here, there are improvements) it also goes into quite a bit of telescope design.  For example, Suiter looks at things like the design limits of the inexpensive small, all spherical f/12 MCT design, and goes into comparison between polychromatic Strehl (something that the refractor forum almost completely ignores) and visual weighted Strehl.  

 

It is far more than a book about how to test telescopes.   I  consider it a must read by people that really want to understand how contrast transfer is affected by design and fabrication, and there is a great deal of information about different designs as well. 

 

It is a treasure chest of all things to do with optics and optical quality. 


Edited by Eddgie, 23 June 2019 - 12:59 PM.

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