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C14 with good optics?

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#1 CHASLX200

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Posted 01 September 2016 - 05:26 AM

What are the chances to find a good used C14 with super optics? Now when when i say good i mean one in 10,000.  I am very picky and have world class seeing that allows me powers from 500x to 1100x in bigger scopes on the planets.  90% of my viewing is powers above 450x on the planets, almost no deep sky.

 

I want a C14 that can come close to what all of my Zambuto mirrors have done. I had a orange C14 i bought in 1996 that was very bad.  I sure don't want a repeat. My body is not up to throwing around big Newts like i have the last 40 years and the weight and size of a C14 would be perfect on my 2.5" shaft Cave mount.

 

 



#2 HenryB

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Posted 01 September 2016 - 05:56 AM

I would guess 1 in 10,000. However, my current C14 Edge has better optics than all my previous SCTs.


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#3 CHASLX200

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Posted 01 September 2016 - 06:06 AM

I would guess 1 in 10,000. However, my current C14 Edge has better optics than all my previous SCTs.

I know they vary big time from one OTA to another. I just don't wanna get stuck with another bad one.  Not sure how the Meade 14" SCT's are compared to a C14.  I never see much talk on the 14" Meade. I would think the last 20 years the C14 has better optics over the bad Orange tube days.



#4 happylimpet

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Posted 01 September 2016 - 08:05 AM

Exactly 1 in 10,000.

 

Next please.

 

EDIT: Actually perhaps my facetious answer is wrong. People with the 1 in 10,000 might be more inclined to hang onto them, so lets go with:

 

Less than 1 in 10,000.


Edited by happylimpet, 01 September 2016 - 08:06 AM.

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#5 *skyguy*

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Posted 01 September 2016 - 08:09 AM

Give Company 7 a call and find out about their optical testing and certification program.

 

http://www.company7.com/testing.html

 

They'll test any OTA you purchase from them ... for a fee ... and guarantee it will perform up to factory specifications. Or, send them a used OTA ... before you buy ... for certification testing. The certification service isn't cheap, but buying quality never is!

 

EDIT: BTW, I used to own a beach condo outside of Tampa on Sand Key. The unbelievably great seeing ruined me ... forever ... from doing any type of planetary observing or imaging from my home in New York State!


Edited by *skyguy*, 01 September 2016 - 08:32 AM.

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#6 dyslexic nam

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Posted 01 September 2016 - 08:58 AM

If you:

 

- are really interested in planetary (90%)

- have amazing seeing that allows for ludicrous magnification

- have a mount that can handle C14-class istruments

- are looking to make a significant hardware purchase for a new primary instrument...

 

...you could always consider one of the larger maks that are produced in small batches by some of the more 'boutique' shops.  They may go beyond your budget, but seem to have an assurance of optical quality that would likely be difficult to achieve with an off-the-shelf C14.  


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#7 Cotts

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Posted 01 September 2016 - 09:01 AM

Give Damian Peach a call.  He uses a C14 for unsurpassed planetary imaging.

 

http://www.damianpeach.com/best.htm

 

Maybe he will share where he bought his C14.....

 

Dave


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#8 Eddgie

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Posted 01 September 2016 - 09:20 AM

Give Company 7 a call and find out about their optical testing and certification program.

 

http://www.company7.com/testing.html

 

They'll test any OTA you purchase from them ... for a fee ... and guarantee it will perform up to factory specifications. Or, send them a used OTA ... before you buy ... for certification testing. The certification service isn't cheap, but buying quality never is!

 

 

Factory specification does not mean anything at all because Celestron only says their scopes are "Diffraction Limited" in quality.

 

Company 7 does not anywere imply that the scope you get from them will be in any way better than any scope you get from any other vendor.

 

Is all that Company 7 does is check that there are no serious optical defects.

 

I have challenged people in the past to prove to me that Company 7 guarantees that the scopes you get from them will be better than the scopes you get from anyone else, and no one to date has been able to substantiate that claim in any way.

 

Now, I think you wont get a "lemon" if you buy from Company 7, but I also don't think that this comes anywhere close to suggesting that if you buy from Company 7 that you will get a 1 in 10,000 C14.

 

If one is worried about getting a total lemon, then buying form C7 makes sense  but nowhere on their web page does Company 7 say that you will get the best optics Celstron makes.  They just say that you won't get a lemon. 

 

Again, I have made this challenge to -people before..  Show us in writing where Company 7 affirms that the quality of any Celstron scope they sell has anything but a diffraction limited promise.  Nowhere will you see them say anything like "We guarantee the Celestron Scopes you buy form us will have a guaranteed Strehl of .95" or anything like that.

 

I look forward to being proved wrong, but that has not happened to date.   If they were to say this on their web page, then one would then be able to expect (and demand) that this be the case, but don't be surprised if you can't find any such guarantee.

 

And I am not calling Company 7 bad..  They don't say you get a 95 Sthreal scope..  That is an urban myth started by communities like this one..  They can't be blamed for that.  They just say they inspect the scopes and reject any that have any serious error.


Edited by Eddgie, 01 September 2016 - 09:28 AM.

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#9 t.r.

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Posted 01 September 2016 - 09:23 AM

It depends on how you define "good"...if using the accepted optical standard of a "good" optic at .80 strehl (1/4 wave, diffraction limited) I think your chances of finding one are...good. :grin:  Finding one that is defined as "very good" at higher strehls (1/6 to 1/8 wave, better than diffraction limited)...not so good! :p

 

 



#10 Bill Barlow

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Posted 01 September 2016 - 09:29 AM

I have bought both Celestron and Meade SCT's from Company 7.  From what they told me, they call a supervisor at either Celestron or Meade and request the OTA the customer wants.  The supervisor then hand picks a very good optical sample to send to them to have a good chance to pass C7's inspection.  Neither Celestron or Meade sends C7 a scope from the warehouse sight unseen.  All of the scopes I have got from C7 have had excellent optical quality. 

 

Bill


Edited by Bill Barlow, 01 September 2016 - 09:34 AM.

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#11 HenryB

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Posted 01 September 2016 - 09:33 AM

I think that everyone who has been around SCTs has wondered the same thing - how to get a "excellent" one. I purchased an 8" SCT from Company 7 and did not think it was anything special. It would be nice if someone tested these scopes and offered the excellent ones for a premium price. Not sure if there is a market for this service.


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#12 Eddgie

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Posted 01 September 2016 - 09:36 AM

C14s like all Celstron SCTs can vary some in qualiity.

 

The most typical error in the C14, (which also shows up with regularity on the C11 and C 9.25) is an S-zone 8 inches out from center (and it is 8" out from center on the C11 and C 9.25.. This zone is almost for sure a zone that occurs from using sub-aperture polishers that are used on the C8. Since the C8 is probably polished in one pass, you don't see this zone but because the other scopes are polished in two passes, with the same 8" polisher on the center and then once around the outside, you get a zone.  Not a bad zone, but a zone none the less.

 

Coorrectors are made from float glass, and this glass (on all models) usually is not ground and [polished on both sides and this contributes to surface roughness in the final system.

 

Likewise, the mirror surfaces tend to have mirco-ripple.   

 

All of this does not mean you cant find really nice C14s, but it does mean that you will not easily find one with the optical quality you can get all day long from custom mirror makers.  The C14 just has a lot of surfaces and the ore surfaces there are, the more difficulty there is in getting them all perfect.

 

Don't obsess about it.   Most people on this forum would struggle to see the difference between as scope with .97 Strehl and one with .93 Strehl.  I you think you would be able to tell them apart on an in focus image, you are kidding yourself.  Star test will show even the tinest flaw, but the flaw needs to be quite serious to have a meaningful impact on the performance of the instrument 


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#13 Eddgie

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Posted 01 September 2016 - 09:46 AM

I have bought both Celestron and Meade SCT's from Company 7.  From what they told me, they call a supervisor at either Celestron or Meade and request the OTA the customer wants.  The supervisor then hand picks a very good optical sample to send to them to have a good chance to pass C7's inspection.  Neither Celestron or Meade sends C7 a scope from the warehouse sight unseen.  All of the scopes I have got from C7 have had excellent optical quality. 

 

Bill

Do you have an interferometer report on the quality?

 

Does Company 7  stipulate their quality criteria?

 

No proof of anything here and this does not mean that the scope will be better than any other scope out there.. According to Celstron, all of their scopes are high quality.

 

I am not trying to be mean here, but we see this all the time and no one has ever provided any substantiation that Company 7 gets the very best telescopes that Celstron makes.

 

Now, if they said "We guarantee  that the scope will have .97 Strehl" I would eat my words happily.. 

 

Alternately, if the community produced three interferomater tests of scopes bought from Company 7 and all had .975 or better Strhel, I would eat my words as well..

 

My point here is dead simple.. The OP wants a 1 in 10.000 C14 (which is in itself kind of dubious because as I previously mentioned, no one can easily see the difference between a .975 and .94 instrument..  The point is that Company 7 offers absolutely no assurance that the scope you buy from them will be the best C14 ever made.

 

And it would have to be the best C14 ever made to meet the OPs criteria because I doubt that more than a few thousand have ever been produced in all the years of C14 production..


Edited by Eddgie, 01 September 2016 - 09:47 AM.

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#14 Eddgie

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Posted 01 September 2016 - 09:54 AM

And if one wants to be absolutely positive of getting a killer 14" mirror, Zambuto will do the trick every time. 


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#15 *skyguy*

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Posted 01 September 2016 - 10:22 AM

Eddgie ... I think you're being a little too critical of Company 7.

 

From their website:

 

"The test methods employed in our routine quality control inspections of telescopes sold by our showroom include resolution testing, and or artificial or natural star testing. We also provide fee-based high precision testing with a system that will provide documentation. This is by means of a a professional Zygo GPI Large Aperture Phase-Measurement Interferometer that will provide a very accurate characterization of the telescope."

 

I'm sure that Company 7 and Celestron can provide a 14" SCT that meets the OP's optical specifications. It's gonna cost an "arm and a leg" ... but, that's the cost of quality!


Edited by *skyguy*, 01 September 2016 - 10:23 AM.

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#16 jhayes_tucson

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Posted 01 September 2016 - 11:40 AM

You are asking the wrong question but I'll come back to that in a moment.  Celestron makes telescopes that meet a diffraction limited "target."  Diffraction limited means that the image quality is limited more by the properties of light than by optical aberration.  That implies that the imaging performance of a diffraction limited system is very close to being indistinguishable from a theoretically perfect system.  The problem with Celestron as a company is that they don't have a very good way to tell if any telescope meets any quantitative spec--much less to tell if any given scope is within the theoretical diffraction limit.  As evidenced by the generally high optical quality that they ship, the performance targets are pretty good; but the final QC process is still mostly subjective and not very precise.  The controls are generally good enough to ship scopes that are diffraction limited but that's the reason why Celestron (and most amateur) scopes vary a bit in optical quality.

 

The thing that most amateurs don't appreciate is that it's actually pretty hard to accurately measure wavefront errors--quantitatively.  Simple tests like the star test or the knife edge test can provide some good information but neither is very quantitative and each can suffer from significant errors in reproducibility as well as repeatability.  In my view any notion that it's possible to visually detect the difference between a system with a Strehl of 0.8 and a system with a Strehl of say, 0.9 is urban myth.  With apologies to any radiologists out there, I suggest that you should be a bit suspicious of any test that requires an "expert" to interpret.  Reproducibility demands that two independent operators produce the same results.  There are so many subtle issues that can affect image quality such as micro-ripple, stray light, obscuration ratio, tube currents, and overall seeing that it's impossible to sort all that stuff out in the field.  It takes a controlled measurement of each parameter in a lab to accurately measure the factors that affect image performance.

 

Getting back to your question, I suggest that if you want a good telescope, you should be asking, "How do I get the highest quality optical system possible?  I'd answer that question by telling you to go buy something like a RCOS system.  RC Optical System had two things going for them.  First, they used ion-beam figuring to achieve very high surface accuracy and second, they used a 4D Technology Phasecam interferometer to measure both the components and the final system performance.  RCOS also knew what they were doing in terms of mechanical design.  These are superb systems that included an interferometric test report with each system (though from what I've seen, the report was not from the Phasecam.)  There are other companies that also use good, quantitative test procedures.  PlaneWave uses a double pass Shack-Hartman test that seems to work well.  The folks at AG Optical have an interferometer (though I don't know much about their process.)  Any of those scopes have well documented optical performance.  (Most of them also have fairly large obscuration ratios so they may not be very well suited to planetary imaging.)  You'll pay more, but you'll also have a better idea of what you are getting.

 

Instead, I suggest that you try to find just a "good" Celestron--they are everywhere.  I've measured a couple of C11s and a C8 Edge systems on a 4D FizCam and all three showed single pass wavefront performance with a Strehl>0.8.  But, I agree with others that if you want the single best scope out of 10,000, your odds are somewhere north of 1:10,000 of finding that one.  Of course, you'll need to understand how to test it.  It might take a lifetime of looking and maybe a few million dollars to find that one.  I also suspect that when you find that one, you'll  find that it might only be different from the other 5,000 at the top of the heap by a milli-wave or two.  On the other hand, if you want an inexpensive system and you don't want to search forever, buy a Celestron, try it and if you don't like it sell it and try again.  I suspect that Damian Peach and Christopher Go probably just ordered a system and then went about learning out how to get the best imaging performance out of it.  Otherwise, pony up and pay for a "high-quality" system that's been manufactured and measured to real specs.

 

John


Edited by jhayes_tucson, 01 September 2016 - 11:40 AM.

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#17 CHASLX200

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Posted 01 September 2016 - 12:48 PM

If you:

 

- are really interested in planetary (90%)

- have amazing seeing that allows for ludicrous magnification

- have a mount that can handle C14-class istruments

- are looking to make a significant hardware purchase for a new primary instrument...

 

...you could always consider one of the larger maks that are produced in small batches by some of the more 'boutique' shops.  They may go beyond your budget, but seem to have an assurance of optical quality that would likely be difficult to achieve with an off-the-shelf C14.  

I have all the above but not the cash, Don't wanna go past $5k for a OTA. Already had a 7" Q that would never seem to cool so Maks are out. Plus a good one in the size i want would be 20k or more.


Edited by CHASLX200, 01 September 2016 - 12:48 PM.


#18 CHASLX200

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Posted 01 September 2016 - 12:53 PM

It depends on how you define "good"...if using the accepted optical standard of a "good" optic at .80 strehl (1/4 wave, diffraction limited) I think your chances of finding one are...good. :grin:  Finding one that is defined as "very good" at higher strehls (1/6 to 1/8 wave, better than diffraction limited)...not so good! :p

It has to be close to what a Zambuto Newt can show in the same size. I would never expect a C14 to be the same as a Zambuto Newt. A Newt is gonna beat out a SCT everytime, but the size and weight of a big Newt is out in my book. 

 

I have owned 50 or more SCT's and only 4 of them stood out as great and 4 others, AKA LX200's were very good. I had a 1984 C8 that could laugh at 500x and ask for more.  So i know there are some freak SCT's with great optics, just most give a ho hum image or bad image.  Buying a used C14 will be tricky as what someone else says is good could be my bad. I have the seeing to allow me to know right off the bat if i got good optics or not.  People with normal seeing never really know what they got or don't know better.


Edited by CHASLX200, 01 September 2016 - 12:57 PM.


#19 CHASLX200

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Posted 01 September 2016 - 12:55 PM

And if one wants to be absolutely positive of getting a killer 14" mirror, Zambuto will do the trick every time. 

Yes it will, but my days of throwing around a 100lb OTA are over. And i don't like fast scopes due to coma and shallow focus.



#20 Bill Barlow

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Posted 01 September 2016 - 02:34 PM

 

I have bought both Celestron and Meade SCT's from Company 7.  From what they told me, they call a supervisor at either Celestron or Meade and request the OTA the customer wants.  The supervisor then hand picks a very good optical sample to send to them to have a good chance to pass C7's inspection.  Neither Celestron or Meade sends C7 a scope from the warehouse sight unseen.  All of the scopes I have got from C7 have had excellent optical quality. 

 

Bill

Do you have an interferometer report on the quality?

 

Does Company 7  stipulate their quality criteria?

 

No proof of anything here and this does not mean that the scope will be better than any other scope out there.. According to Celstron, all of their scopes are high quality.

 

I am not trying to be mean here, but we see this all the time and no one has ever provided any substantiation that Company 7 gets the very best telescopes that Celstron makes.

 

Now, if they said "We guarantee  that the scope will have .97 Strehl" I would eat my words happily.. 

 

Alternately, if the community produced three interferomater tests of scopes bought from Company 7 and all had .975 or better Strhel, I would eat my words as well..

 

My point here is dead simple.. The OP wants a 1 in 10.000 C14 (which is in itself kind of dubious because as I previously mentioned, no one can easily see the difference between a .975 and .94 instrument..  The point is that Company 7 offers absolutely no assurance that the scope you buy from them will be the best C14 ever made.

 

And it would have to be the best C14 ever made to meet the OPs criteria because I doubt that more than a few thousand have ever been produced in all the years of C14 production..

 

Company 7 will provide an interferometer report if you want to pay for it.  By going through C7 you eliminate the chance of getting a lemon.  Since Meade and Celestron hand pick the scopes that are sent to C7, you will likely be getting one of their best.

 

Their testing adds about 5-10% more to the cost of the OTA.  

 

Bill


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#21 CHASLX200

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Posted 01 September 2016 - 02:38 PM

If i bought new i would want to return anything i am not happy with. I wonder what the track record is like on A Meade 16" SCT OTA?



#22 Cotts

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Posted 01 September 2016 - 02:40 PM

Your wants, as I understand them:

 

+/- 14" of aperture.

Somewhat portable/lighter than 100 pounds  (A C14 is not exactly easy to 'throw around')

to fit nicely on your Cave mount.

long focal ratio to reduce coma + more generous focus 'sweetspot'...

Very high Strehl optical system.

No photography for you, just high magnification planetary observing

 

A couple of questions:  Are we talking about a permanent observatory set-up or are you having to set the whole thing up at remote sites?  There is a very important distinction here...   A permanent home observatory can have a heavier/bulkier scope which you won't have to "Throw around"..  A bigger Mak Cass or Mak Newt could fit the bill. Even 100 pounds or more - get some friends to help mount the scope on the Cave and leave it there.   These two types of scopes can be bought (at no little expense) with apertures up to 16". The cooling issues these sorts of scopes have can be ameliorated by air-conditioning the observatory - if you have one...   

 

If you have to schlep your scope/mount combo to a remote site (or even from house/garage to driveway or backyard) each time you observe then I believe the answer is clear - you need a longer f/ratio 'planet-killer' dobsonian with Sevo-Cat tracking.  A 14", f/6 or f/7 is easily moveable in pieces to your vehicle and thence to your observing site.  I have a 12.5" f/6.5 Teeter dob with a Mike Lockwood mirror which is perfect on planets and would surely make you as happy as I am.   There is absolutely zero issue with coma in an f/6 or longer for planetary observing - you're only looking at the central arc minute or less of the field....  At last year's Winter Star Party a very well-known telescope maker and dealer described the views of Jupiter through my scope as "the best on the entire observing field"...  Detail inside the Red spot, albedo markings on Ganymede...  Such a scope is easy to move with the wheelbarrow handles and assembles in 10 minutes or less, including collimation...  

 

I do realize you said a big Newt is not what you want....

 

but no scope is the perfect combination of exactly what you want.   

 

Dave


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#23 CHASLX200

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Posted 01 September 2016 - 02:57 PM

The mount will stay outside in my back yard.  I never plan to take it anywhere.  Just plop on the OTA and view planets when they are in prime time.  Jupiter being the main target 2 months a year. I know all about Zambuto and Newts, having owned over 220 scopes and many Zambuto scopes and no mattter how ya cut it a 12.5" f6 OTA is gonna be heavy and bulky.  I have a 12.5" F/6 OTA just sitting that i will never lift onto the mount.



#24 cam1936

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Posted 01 September 2016 - 03:02 PM

Just curious, what about a tracking dob with a premium mirror At F6 or so? Should be easier to set up and transport than a eq mounted C14. No? Plus you know the optics are going to be superb.

#25 CHASLX200

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Posted 01 September 2016 - 03:14 PM

Just curious, what about a tracking dob with a premium mirror At F6 or so? Should be easier to set up and transport than a eq mounted C14. No? Plus you know the optics are going to be superb.

Done with Dobs.  After that bad Tectron i want no more. 




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