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  #21  
Old 07-08-2015, 10:49 AM
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rustigsmed (Russell)
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looking at planewave etc a 20" RC are generally over 60kgs so you're not going to get it onto a EQ8 (but you could get a 20" ASA newt astrograph..just).

so 17-18" instruments would really be the stretched upper limit for an EQ8. realistically you will need something like a Paramount ME II for the GSO 20".

Before spending all that coin you really would like to see a review, as Peter W points out that really is a lot of weight on parts, 20" is big big leap from 16
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  #22  
Old 07-08-2015, 10:49 AM
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So far the GSO RCs optics don't seem to be the weak point. A number of sharp images show that. Its more the difficulty of collimation, the poor focuser, the lack of flatteners, the lack of a flattener that corrects the whole field, mounting of the primary mirror at one stage seemed sus with just some silicone and clips in a 3 spots.

But as an emerging scope maker the option to make it work is still pretty amazing as 20 inch RC/STL11 images by some well known top names from 8-10 years ago still have not been bettered today.

If I were to get one (which I am not planning to) I would treat as a potential project that may take some effort to get into a workable system and that is part of what your discounted price is taking into account. 5 years from now they may have upped the focuser, flexure, reducers/flattener and temp control issues better.

Greg.
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  #23  
Old 07-08-2015, 12:32 PM
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Quote:
Originally Posted by Peter Ward View Post
OK it's a 20"...but...does it have the following?
  • A 50kg instrument payload
  • 100mm diameter instrument adapters
  • 90mm diameter fully corrected reducers and field correctors
  • Zero image shift, servo controlled secondary focuser
  • Integrated touch-screen focus, environment and instrument rotator control
  • Zerodur optics with a 98% strehl and 96% reflectivity.
  • Finite point analysis and machining to reduce dead weight by 80% or better
  • Remote mirror shutters.

Large and elegantly engineered imaging telescopes up until now have not been cheap...hence, to use an automotive analogy, I'd very much like to see whether a Great Wall ute would seriously challenge the latest S-Class.

My money is still on the Benz.
Well you certainly get the bells and whistles but then again you pay the bells and whistles prices. The adapters from the back end at 100mm right from the 12" up.

The other components you have listed are not included in a GSO package clearly. I am reliably told though that a flattener is in the planning.

As I understand it all the big scopes have a multi point mirror assembly unlike how the 12" has been supported in the past. The 12" will be supported by this assembly in coming models. Logan showed this new development a month of so ago now.

I guess the bottom line is that you get what you pay for and what you can afford. I doubt anyone is suggesting a GSO 20 will be like some of the Merc's or Ferrari's out there but it will no doubt have good performance in the end.
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  #24  
Old 07-08-2015, 12:46 PM
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theodog (Jeff)
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Quote:
Originally Posted by Paul Haese View Post
.......I guess the bottom line is that you get what you pay for and what you can afford. I doubt anyone is suggesting a GSO 20 will be like some of the Merc's or Ferrari's out there but it will no doubt have good performance in the end.
Well said. Amateur astronomy should be an inclusive bunch. I sometimes feel that some are becoming a little exclusive.

However, the 20" would be a little to large for me and my budget.
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  #25  
Old 07-08-2015, 01:03 PM
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I have two 20" (German) RCs to install later this year...and frankly a GSO simply didn't make the cut for a number of reasons.

Not the least of which is, while amateurs can and do successfully modify, not just GSO scopes, but a hole bunch of gear (EQ mod comes to mind) as they have the luxury of tinkering plus the time to trail and error various solutions, and often get a very usable instrument....something you wouldn't expect an institutional user to have to deal with.

My own 16RC will be arriving next month...and I have to say I'm getting quite excited about its impending arrival. The test images (courtesy amazing German QC) look awesome.

Hummm Might do a Marcus and document its deployment
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  #26  
Old 07-08-2015, 01:06 PM
clive milne
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Quote:
Originally Posted by Peter Ward View Post
OK it's a 20"...but...does it have the following?
  • A 50kg instrument payload
It's debatable whether that is necessary, but easily achievable by simply putting the focuser on the spider.
  • 100mm diameter instrument adapters
They quote M117mm thread pattern on the instrument flange.

  • 90mm diameter fully corrected reducers and field correctors.
If you are using Alluna as your reference point, their corrector and reducer have usable fields of 65mm and 60mm respectively (not 90mm) http://www.alluna-optics.com/product...corrector.html

The after market corrector and reducer from ASA have fields of 80 & 60mm.
http://www.astrosysteme.at/eng/correctors_rc.html

Under what circumstance is it necessary (or even desirable) to have a 90mm field?

  • Zero image shift, servo controlled secondary focuser.
Simple, mount the secondary on an FLI PDF. Incidentally, strictly speaking there is no such thing as a zero shift focuser but there are several with tolerances which are adequate. (the PDF being one of them)
And forgive me if it comes across as unsporting, but I have to point out that the necessity of purchasing an aftermarket focuser because the manufacturer supplied unit is inadequate is not really indicative of engineering incompetence.... If that is not the case, tell me what function is served by the thing bolted to the back of your Riccardi Honders? (The Atlas focuser that is)

  • Integrated touch-screen focus, environment and instrument rotator control
Why not automate these functions?

  • Zerodur optics with a 98% strehl and 96% reflectivity.
GSO use quartz which is arguably better than Zerodur. They also quote 99% reflectivity in their coatings. The one thing I don't like about them is that they are dielectric so a complete pita to re-coat.

  • Finite point analysis and machining to reduce dead weight by 80% or better
A better question would be; is the mechanical stiffness adequate? and is the weight of the ota manageable? When the majority of the ota is a carbon fibre truss, there is little extra dead weight to reduce. (I'm guessing your are quoting an Alluna brochure?)

  • Remote mirror shutters.
Available as an aftermarket option.


Quote:
Originally Posted by Peter Ward View Post
Large and elegantly engineered imaging telescopes up until now have not been cheap...hence, to use an automotive analogy, I'd very much like to see whether a Great Wall ute would seriously challenge the latest S-Class.

My money is still on the Benz.
Well, if the task at hand was carrying a couple of 44 gallon drums across a freshly plowed paddock, my first choice would be a Toyota Hilux. The Great Wall would be somewhat down the list, but not nearly as far down the list as the Benz. Moral of the story: refinement is a wonderful thing, but gold plating a bucket doesn't help it carry water, it simply reduces the size and number of buckets that you might conceivably own.

best
c

Last edited by clive milne; 07-08-2015 at 02:13 PM.
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  #27  
Old 07-08-2015, 01:26 PM
clive milne
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Incidentally... I think it also needs to be stated that for a 20" RC
it isn't necessary (and is actually counterproductive) to use a field corrector
for CCD's up to the size of the KAF8300 chip.

And... let's be real, the cost of the GSO ota wouldn't even cover the deposit
for a set of 20" RC optics from Mike Jones.
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  #28  
Old 07-08-2015, 01:30 PM
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marc4darkskies (Marcus)
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Quote:
Originally Posted by Peter Ward View Post
...

Hummm Might do a Marcus and document its deployment
Counting on it Peter! Will make interesting reading!
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  #29  
Old 07-08-2015, 02:20 PM
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Quote:
Originally Posted by clive milne View Post
  • A 50kg instrument payload
It's debatable whether that is necessary, but easily achievable by simply putting the focuser on the spider.
[LIST]
Without going through the entire list, sure I accept you could modify a GSO to include any number of enhancements....my point was: the GSO simply doesn't have these enhancements out of the box.

I am also privy to some real-world test data on the reflectivity of GSO optics. It was not actually close to that claimed, in fact only 86%.

Lastly, Roland Christien at AP advised me that di-electric layering of primaries is fraught with danger. The surface tension of the layers invariably distorts the optic underneath. AP struggled with this just on their 2" star diagonals...but eventually worked out a process to prevent distortion of a small optic.

Perhaps GSO have some proprietary process for coating their primaries, but one wonders why no-one else is following their lead.
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  #30  
Old 07-08-2015, 02:30 PM
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Yep fair enough....
If I was in a position to buy one I would look at it from the perspective of an atm project where most of the hard work is already done. (at a fire sale price) And I would definitely stipulate that the optics be delivered un-coated to an address somewhere in Florida.

Still, you get my point.
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  #31  
Old 07-08-2015, 02:32 PM
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Quote:
Originally Posted by Peter Ward View Post
I have two 20" (German) RCs to install later this year...and frankly a GSO simply didn't make the cut for a number of reasons.

Not the least of which is, while amateurs can and do successfully modify, not just GSO scopes, but a hole bunch of gear (EQ mod comes to mind) as they have the luxury of tinkering plus the time to trail and error various solutions, and often get a very usable instrument....something you wouldn't expect an institutional user to have to deal with.
I hear what you are saying Peter. If I had the money I would be buying into the more expensive system myself. The scope I have was the cheap part of my long focal length observatory and it was always a temporary part of the equation.

The only really annoying thing that I have found with GSO scopes is the back focus measurements from the rear plate are not well defined and that can make for a lot of guessing when using an Atlas you might imagine.

I think one can really see that for those with a budget in mind and don't mind a bit of tinkering you would buy the cheaper imaging platform and those that have the money and little time for tinkering then the paying for the solution is the way to go. Personally I am tired of tinkering, I want to image night after night, but my budget does not allow for that at present.
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  #32  
Old 14-04-2021, 01:27 PM
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xthestreams (Paul)
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Exhuming an old thread here as I've been looking into getting a 16" RC from Andrew's while I save up the pennies for the 17" PW.

Got me wondering, did the 20" beast ever make it to market? I've seen them listed on TS site in Germany, but cannot find any references to images from them anywhere.

I assumed they were either too hard to make and/or the target market for them (small institutions and/or crazy amateurs) preferred the value proposition of a name brand product at that scale.

While we're here, anyone know of the 16" in deployment in Australia? I've had fun trying to get my 12" working to the best of its abilities - worth the effort if you're patient (and throw out the Tak!).
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  #33  
Old 14-04-2021, 02:46 PM
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Alex,

I don't think the 20" made the market here. The 16" was sold here as I have helped someone collimate one.
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  #34  
Old 14-04-2021, 09:51 PM
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Quote:
Originally Posted by xthestreams View Post
Exhuming an old thread here as I've been looking into getting a 16" RC from Andrew's while I save up the pennies for the 17" PW.

Got me wondering, did the 20" beast ever make it to market? I've seen them listed on TS site in Germany, but cannot find any references to images from them anywhere.

I assumed they were either too hard to make and/or the target market for them (small institutions and/or crazy amateurs) preferred the value proposition of a name brand product at that scale.

While we're here, anyone know of the 16" in deployment in Australia? I've had fun trying to get my 12" working to the best of its abilities - worth the effort if you're patient (and throw out the Tak!).
Ooh..fun!
Try and persuade CFF to spin up the 16” on one of their frames
The GSOs of the world can create a great mirror, really, but the challenge is the structure that surrounds the mirror. I have a CFF 10” RC and it is solid and on a par with PW in terms of handling collimation.
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  #35  
Old 16-04-2021, 10:23 PM
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xthestreams (Paul)
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Quote:
Originally Posted by Paul Haese View Post
Alex,

I don't think the 20" made the market here. The 16" was sold here as I have helped someone collimate one.
Thanks PH, given your connection to GSO HQ do you know if they ever made it onto the wild anywhere?

Thoughts on the 16” ?
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  #36  
Old 16-04-2021, 10:25 PM
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xthestreams (Paul)
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Originally Posted by DJT View Post
Ooh..fun!
Try and persuade CFF to spin up the 16” on one of their frames
The GSOs of the world can create a great mirror, really, but the challenge is the structure that surrounds the mirror. I have a CFF 10” RC and it is solid and on a par with PW in terms of handling collimation.
:-) of I’m going down that path I’d rather give my money to Sidereal/Astroworx and get something tailored to my needs.
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