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Visual Only: 150mm Triplet APO vs 14" Dobsonian

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#76 Daniel Mounsey

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Posted 26 July 2018 - 10:56 PM

Greg, do you recall any time you may have had a chance to use an 8” apo?



#77 gnowellsct

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Posted 26 July 2018 - 11:38 PM

Greg, do you recall any time you may have had a chance to use an 8” apo?

Yessir at least 3  equal to or greater than 7 inches and two of them side by side with the ol' tin can.

 

Greg N



#78 dr.who

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Posted 27 July 2018 - 02:22 AM

What is the advantage of a thinner mirror?
 
Personally the all aluminum design of the Obsession UC is more attractive to me than the classic looking wooden Dobs. But if I am sacrificing performance I would go for a wooden Dob from Teeter or New Moon instead.  I do have the opportunity to buy a used but still brand new Obsession UC 22 for only 9k with go-to, which is actually worth about 16k from Obsession.


Cooling. The thicker the mirror the longer the cool down time. I believe Dave K. still uses 2” mirrors. They take quite a while to cool. And the Obsessions are, if I remember right, f/4.5. In the 15” UC I had that wasn’t horrible in terms of using a ladder but the bigger 18” and above models did need at least a step stool. Sub f/4 gets you away from that.
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#79 CHASLX200

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Posted 27 July 2018 - 06:04 AM

A SCT is the last thing i would want for planets. Never wanted a Dob over 18" so they are out.  So my only choice is APO's under $4k or a long focus newt in the 8 to 12.5" Range.  I have a SW150 Mak that does a very good job for the price, but my TMB 105/650 does just as well on Jupiter.



#80 starman876

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Posted 27 July 2018 - 09:19 AM

I love all scopes.  The more glass the better.   Optics are really fascinating.   To be able to look back into time at objects that might not even be there anymore.  I never found a scope I did not like.  Maybe some were a bit bothersome, but there was something about each one that I liked.   I guess not buying just anything that came along helped with that attitude.   some scopes I have had for years.   I only sell them when I need to make room for a new scope.   It is nice to have a variety of scopes to choose from on different nights.  I choose the Zeiss 60mm on nights when seeing is not so great.  It always punches through and gives me a good view.  When the seeing improves I get out the TMB or Tak 100mm scopes.  when it really gets good I bring out the big guns.  The 6" AP or the 12.5" portaball.   I have found that some of these inexpesive Orion 8" Newts are not that bad.  Sure give good views of Jupiter and Saturn.  Maybe the best scope on the used market for around $200 or less.    So if you choose carefully you can have a good selection of scopes for just about any night.  


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#81 janapier

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Posted 27 July 2018 - 11:17 AM

A SCT is the last thing i would want for planets. ...

I guess you never observed Jupiter through a C11 in good seeing...


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#82 Astrojedi

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Posted 27 July 2018 - 11:43 AM

A SCT is the last thing i would want for planets. Never wanted a Dob over 18" so they are out.  So my only choice is APO's under $4k or a long focus newt in the 8 to 12.5" Range.  I have a SW150 Mak that does a very good job for the price, but my TMB 105/650 does just as well on Jupiter.

 

For observing planets my C9.25 delivers the contrast of a high quality color free 6" apo (i.e. a very expensive scope) and the light gathering of a 9" scope and resolution of a 9.25" scope for just $1000. For deep sky I can observe galaxies and galaxy clusters that are out of reach of a 6" APO... and weights just 20lbs and works on my M2C mount. Whats not to like! I will take that deal any day. : )


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#83 starman876

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Posted 27 July 2018 - 12:29 PM

For observing planets my C9.25 delivers the contrast of a high quality color free 6" apo (i.e. a very expensive scope) and the light gathering of a 9" scope and resolution of a 9.25" scope for just $1000. For deep sky I can observe galaxies and galaxy clusters that are out of reach of a 6" APO... and weights just 20lbs and works on my M2C mount. Whats not to like! I will take that deal any day. : )

I agree, the C9.25 is the best SCT in the Celestron line up.  Also, the best tested with DPAC of any of their SCT's


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#84 gnowellsct

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Posted 27 July 2018 - 06:18 PM

For observing planets my C9.25 delivers the contrast of a high quality color free 6" apo (i.e. a very expensive scope) and the light gathering of a 9" scope and resolution of a 9.25" scope for just $1000. For deep sky I can observe galaxies and galaxy clusters that are out of reach of a 6" APO... and weights just 20lbs and works on my M2C mount. Whats not to like! I will take that deal any day. : )

..and you can put a refractor on a 9.25. However there are people who'd rather have their teeth extracted without anaesthetic than admit a 9.25 or even a c14 could hold its own against a 6" apo.

In the refractor forum I would suggest it's provocative to suggest otherwise. Anyhow it's great having people who buy large refractors and given the costs (even of the inexpensive ED doublets) and mount difficulties it's not like they're going to put much of a dent in the sct market.

And one thing about scts is that at f/10 and longer they really can't touch the wide fields of refractors. My 5" apos have convinced me that it's a very good idea for other people to buy and operate the 6 inch and larger apos and I'm very appreciative if offered a view. GN

Edited by gnowellsct, 27 July 2018 - 06:22 PM.


#85 CHASLX200

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Posted 27 July 2018 - 06:52 PM

I guess you never observed Jupiter through a C11 in good seeing...

Did thru my friends 1982 C11 and it was so mushy it would not come to focus.  I know people think SC's are great, but try some Zambuto Newts in my seeing and you won't be going back to SCT's.  And i am talking about 11 to 18" Zambuto Newts not some small 6" APO.


Edited by CHASLX200, 27 July 2018 - 06:57 PM.


#86 gnowellsct

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Posted 27 July 2018 - 07:07 PM

Did thru my friends 1982 C11 and it was so mushy it would not come to focus.  I know people think SC's are great, but try some Zambuto Newts in my seeing and you won't be going back to SCT's.  And i am talking about 11 to 18" Zambuto Newts not some small 6" APO.

This is what I have often said about SCTs.  Because they have been in continuous production for around 50 years people feel OK pulling any one out of the historical line up and generalizing across the entire species.  Celestron has been bought and sold about four times since 1980 and undergone several changes of management as well as changes in the production techniques and the production site.  It's basically a succession of four or five companies, in a sense.

 

I used look through a 1978 Newt that hadn't been recoated in 40 years and it was so mushy....for sure all Newts are bad...doesn't make much sense does it?

 

Greg N


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#87 EJN

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Posted 27 July 2018 - 07:21 PM

4 pages? Call the OCD hotline.



#88 CHASLX200

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Posted 27 July 2018 - 07:26 PM

This is what I have often said about SCTs.  Because they have been in continuous production for around 50 years people feel OK pulling any one out of the historical line up and generalizing across the entire species.  Celestron has been bought and sold about four times since 1980 and undergone several changes of management as well as changes in the production techniques and the production site.  It's basically a succession of four or five companies, in a sense.

 

I used look through a 1978 Newt that hadn't been recoated in 40 years and it was so mushy....for sure all Newts are bad...doesn't make much sense does it?

 

Greg N

Well then lets talk the last 2 C6's i had. One was made in 06 and was bad and the last was made 2 years and i had to return it.  So i guess i have bad luck or i am just more picky than others and will only want the best optics i can buy.  Now i will say that 1984 black C8 was a one in a million freak that would take 500x and ask for more. So i know more than anyone THERE ARE SOME INSANE SHARP SCT's out there.  Just they don't come often, at least for myself.



#89 starman876

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Posted 27 July 2018 - 08:11 PM

or you do not have had very many that were in proper alignment.   It takes only a very small bit out of adjustment and an SCT is total mush.   I have shown that in DPAC.   Just take one screw a 1/4 turn the wrong way and the lines that were almost straight now start looking like circles.    SCT's are so sensitive to alignment that I will not even look through one at a planet until I am sure it is properly aligned.  



#90 CounterWeight

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Posted 27 July 2018 - 08:48 PM

I viewed through SCt's exclusively until about 9 years ago, several Meads 10-12" and a C11 towards the end.  I always wished for a simpler collimation method (At times that was to have someone else turn the screws while I was eyeballing)... and something to deal with acclimation (like a lightweight non deformable mirror?), moving main mirror for initial focus...   Other than the dew and cooling issues, getting used to collimating, i really enjoyed them and even today sometimes think about getting a 9.25. If we are mentioning Celestron and it's change up's we should include Meade there as well.  Not happy with the scopes I started getting from about 2002? on, the Celestron was a welcome reprieve.  Not trying to stir up old dust, but  though 10" and above SCt's can be very nice to view with, I have never felt their build was done in a way to facilitate easy deployment or collimation. 

 

In ways the design as we can buy them today is a combination of everything very difficult in a folded optic with a closed tube.  Still, i enjoyed the c-11 quite a bit though i felt it was not at all something I could quickly use in my usual climate.  That solved by setting out early and as often as possible leaving out while covered.  I still sometimes recommend an 8" SCt for folks as I feel for some it may be all they ever need or want.


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#91 Astrojedi

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Posted 28 July 2018 - 01:29 AM

Well then lets talk the last 2 C6's i had. One was made in 06 and was bad and the last was made 2 years and i had to return it.  So i guess i have bad luck or i am just more picky than others and will only want the best optics i can buy.  Now i will say that 1984 black C8 was a one in a million freak that would take 500x and ask for more. So i know more than anyone THERE ARE SOME INSANE SHARP SCT's out there.  Just they don't come often, at least for myself.

Actually quite the opposite. These days quality control is significantly better. I have looked through about 20 Celestron scts (post 2005 models) and 90% had very good to excellent optics. I would say 99% of bad reports are due to miscollimation and/or poor thermal management. Further, I have owned 3 C9.25 scts and they have all been super sharp.



#92 Jon Isaacs

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Posted 28 July 2018 - 03:23 AM

Actually quite the opposite. These days quality control is significantly better. I have looked through about 20 Celestron scts (post 2005 models) and 90% had very good to excellent optics. I would say 99% of bad reports are due to miscollimation and/or poor thermal management. Further, I have owned 3 C9.25 scts and they have all been super sharp.

 

SCTs are made to a price point.  John Hayes article on interferometically testing 2 C14 Edge's is pretty informative. 

 

https://www.cloudyni...elescopes-r3095

 

Not quite in Zambuto-Lockwood range.  Imagine you had an SCT that looked like this:

 

158978001.hTCMVDeD.jpg

 

An 8 inch F/25 with a 20% CO, a properly mounted mirror and optics produced by professional optician working for the Dutch Space Agency..  This is what a truly premium SCT looks like.  

 

Jon


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#93 starman876

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Posted 28 July 2018 - 07:26 AM

Actually quite the opposite. These days quality control is significantly better. I have looked through about 20 Celestron scts (post 2005 models) and 90% had very good to excellent optics. I would say 99% of bad reports are due to miscollimation and/or poor thermal management. Further, I have owned 3 C9.25 scts and they have all been super sharp.

That is what I have been saying all along about the SCT's.  Miscollimation is responsible for most of the bad reports.  It has been a good thing though.  These guys that sell the SCT because they cannot align it sell them for a song.\smirk.gif


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#94 CHASLX200

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Posted 28 July 2018 - 07:41 AM

Actually quite the opposite. These days quality control is significantly better. I have looked through about 20 Celestron scts (post 2005 models) and 90% had very good to excellent optics. I would say 99% of bad reports are due to miscollimation and/or poor thermal management. Further, I have owned 3 C9.25 scts and they have all been super sharp.

Most of the 1's i bought were pre 2002.  Had two great 10" LX200's and one 12" and one mushy 12" LX200.


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#95 RolandosCY

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Posted 28 July 2018 - 07:59 AM

As you can see from my signature I am the happy owner of n Obsession 18" Classic, a great 5-inch APO (Tak FS128), but also of a 6" achro. I am mostly a deep-sky guy, only occasionally observing the Moon and planets during the few days around full Moon. Well, the star images in my 128 are by far the best and most pleasing. But there is no way I can observe faint Hickson galaxy groups with my Tak. And on some nights of amazing seeing, the 18" with its superb OMI mirror readily beats the Tak 128 on planetary detail, for it can readily handle more than 800X (the max I can achieve with my 128 is 439X). As I do observe from my backyard, both scopes are ready to go out in just a couple of minutes (the 18" is on wheel barrows, the 128 sits on a dolly-mounted altaz mount). But the 18" needs a lot more time to acclimatize. My most used scope is the Tak FS128, but I do have the "luxury" of pulling out the 18" whenever I feel doing so. 

 

There is an additional thing to take into account: Set-up hassle if you need to haul the scopes to dark sites. Until 2014, I used to live in a 50,000 city, and my sky conditions meant that I had to load and unload the 18"  in my car, a huge effort. Now I live under rural skies slightly exceeding SQM 21, and I no longer take the 18" to really dark skies. The FS128 is far more manageable for taking along to a trip. The TOA 150 is signifcantly heavier though, so you will need to take this into consideration.

 

If the set-up is of no consideration, I would rather go with the 15", and get a refractor later on, possibly a decent 4 or 5 inch instead of a six inch. There is no doubt that the really clean, contrasty image given by a high quality refractor can not be matched by a relector (simple laws of physics), but I would rather get the extra aperture along with its resolving power.

 

As you might have noted I did not say anything about my 6-inch achro. I do love that scope, and often use it for the wider fields given compared to the 128, but the extra weight it has (and to a lesser extend the star images) mean I use it less than the 128 or the 18" which are my primary scopes.


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#96 Astrojedi

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Posted 28 July 2018 - 09:55 AM

SCTs are made to a price point.  John Hayes article on interferometically testing 2 C14 Edge's is pretty informative. 

 

https://www.cloudyni...elescopes-r3095

 

Not quite in Zambuto-Lockwood range.  Imagine you had an SCT that looked like this:

 

158978001.hTCMVDeD.jpg

 

An 8 inch F/25 with a 20% CO, a properly mounted mirror and optics produced by professional optician working for the Dutch Space Agency..  This is what a truly premium SCT looks like.  

 

Jon

Yes, I understand they are made to a price point and that they are not ‘premium’ scopes but the ones I have used are darn good and not lemons like it is often implied on these forums.

 

Also I can only speak to my experience. John tested one... I have looked through 20+ newer ones (and maybe 40+ in all) but I admittedly I have only looked through a couple of c14s.

 

I have 30yrs of experience with SCTs and all I can say is that the quality is much better and more consistent than ever before especially the C9.25s. It is very rare to get a lemon when you buy new. The only reason the SCT quality myth keeps propagating on these forums is because there are so many older SCTs around.

 

Also while I see the point you are trying to make, to me this picture does not tell me anything about the quality vs. price of the SCTs in question. I once saw a ‘premium’ and pretty tricked out 10” dobsonian with very fine custom machining which cost $10k+. Does that mean that all 10” dobs that cost less than $10k are duds? That last 5% of quality always costs many times more... sometimes 5-10x more.


Edited by Astrojedi, 28 July 2018 - 10:11 AM.

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#97 Jon Isaacs

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Posted 28 July 2018 - 10:25 AM

Yes, I understand they are made to a price point and that they are not ‘premium’ scopes but the ones I have used are darn good and not lemons like it is often implied on these forums.

 

Also I can only speak to my experience. John tested one... I have looked through 20+ newer ones (and maybe 40+ in all) but I admittedly I have only looked through a couple of c14s.

 

I have 30yrs of experience with SCTs and all I can say is that the quality is much better and more consistent than ever before especially the C9.25s. It is very rare to get a lemon when you buy new. The only reason the SCT quality myth keeps propagating on these forums is because there are so many older SCTs around.

 

Also while I see the point you are trying to make, to me this picture does not tell me anything about the quality vs. price of the SCTs in question. I once saw a ‘premium’ and pretty tricked out 10” dobsonian with very fine custom machining which cost $10k+. Does that mean that all 10” dobs that cost less than $10k are duds? That last 5% of quality always costs many times more... sometimes 5-10x more.

 

 

On the other hand, premium is about attention to detail. My gut feeling is that the views through the 8 inch F/25 will be substantially better than a commercial SCT. Thermal management, proper spacing, proper alignment and support of the mirror, not just near perfect optics.

 

 

Jon



#98 starman876

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Posted 28 July 2018 - 10:37 AM

another thing that does not help the reputation of any scope is the same people telling their experience from 10 years ago or more and not having tried any of the newer ones with the current quality control.  some people love spinning negative stories about scopes they have had.   in most cases they could not resist a bargain on a poor scope and afterwards voiced their oponion that all the scopes in that line up were bad.  heaven knows that everyone is looking for super optics for a bargain

  one thing i have learned that they are very rare.7


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#99 Astrojedi

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Posted 28 July 2018 - 10:39 AM

Hard to say how much better as I have never looked through one. I try not to speculate.

 

But I can tell you this... I have ‘fixed’ countless SCTs by collimation and explaining to the user the need for cool down.


Edited by Astrojedi, 28 July 2018 - 10:42 AM.


#100 gnowellsct

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Posted 28 July 2018 - 11:58 AM

One of the things that never gets discussed is that premium optics fare better with premium owners. Obsession sold scopes with nylon slings that did not hold collimation all sky for something like ten years. It drove my friend nuts on his 15". He tried several different sling designs one was Kevlar or some such. At some point the Glatter system came out and he was happy. You have to be highly motivated to keep at something like that. His first OMI mirror was also a dog. Before the Obsession 15 he had a c11 that was terrible and unfixable (print through). Then he had a discovery 12 that was poor. It took about two years to get the obsession 15 performing well. He used it for about ten years and sold it (to my dismay) and got a newer c11 that is a strong performer on planets.

Pete's an engineer loves to work with equipment. He has been essential in helping with many of my mods on out and tube. If you think a premiere newt is a ticket to out of the box first class performance guess again. Once you got it all going well, there are the non trivial issues including collimation mirror cleaning and recoating.

I'm sure many Newts with inferior mirror support are still out there. I'm sure poor newt mirrors are also out there. There's even a minor industry in refiguring the imports. Or was till they started using inferior glass blanks.

Pete's 15 inch sometimes outperformed my c14 but most of the time it was pretty even and there were many occasions on which the c14 did better on planets. For whatever reason the 15 never did as well on red/blue jovian detail though more than once it offered unsurpassed detail in the browns. Saturn was whiter which it always seems to be in Newts.

Towards the end of his obsession 15 ownership I was urging him to get a recoat because the c14 seemed to be bringing in fainter stars.

You have to wonder about that. Jon is very fond of calculating light loss on an sct but never throws in anything for the dust or failing coatings on newts. Think of how gradual this reflectivity loss was. Initially his scope had a clear advantage on Andromeda G1 but after years I finally bring to his attention that there is a visible difference in luminance. That means for years he was losing aperture relative to the c14, by the time I'm complaining about a VISIBLE difference, the loss must have been substantial.

Light loss and scatter due to infrequent cleaning is another issue.

I kept griping he needed a recoat, he complained the rocker box was a back killer and sold it for a c11 g11 combo.

In 16 years of comparison with not just this but other high performance Newts I've never once felt the need to get rid of this crummy ol sct. If scts were vaporized, as seems to be secretly wished by their numerous critics, I'd get a dob and I'd try to get a good one. But I'm pretty good with what I've got.

I do think there MUST be some kind of luminance loss on scts but there's no data. Whatever the curve is it must be slow decline because towards the end the light loss on the 15 outpaced the light loss on the c14 (whatever that is). Certainly it's trivial to clean a corrector plate compared to a Newt primary.

All that said it would take some seriously deficient optics and owner operator error for a 14" Newt not to outperform a 6" apo on on most visual aspects of performance.

Wide fields, tracking accuracy, wind stability, ease of observing at zenith, ease of optics maintenance at close to out of box levels, compatibility with binoviewing or h alpha viewing, balance, the advantages are likely to be with the 6" assuming the money spent on the mount is roughly equal to money spent on the OTA. If you're intending to put a 6 inch apo on a cheap GEM forget it. Get the 14 dob.

GN


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