20" RC heads up

[garymck]

Andrews has on their GS page a 20" RC to be avaiolable November.....

Price?

Mount - think it would fit on my G11? :-)

cheers
Gary

[glend]

I was worried about some of the collimation issues with the smalller ones, until I looked through the details on Teleskop-Express - the focuser is de-coupled from the mirror carrier and separately collimatible. So I have rescrinded by concerns here with an edit.

[Somnium]

20" ... wow, it is probably going to weigh somewhere in the order of 50kgs. GSO keep on upping their RC aperture, you wonder how far they will go. i am yet to see some images from these big RCs, Paul uses the 12" and gets great results. i have been considering, for some time, the combo of the EQ8 and the RC14 but haven't pulled the trigger yet. 20" though ... we are definately experiencing a new era of amateur astronomy.

[g__day]

What would you mount it on? Will it come out with an EQ10?

[rustigsmed]

that is really getting pretty big, really big.
there is a guy in Italy using an EQ8 and RC 16" I haven't heard of anyone going any larger with the EQ8, perhaps you could get away with an 18" newt (with its lesser FL) but yes I think its heading to the serious mount territory... at 20"

TS has it on sale for about 5000 euro more than the 16"
http://www.teleskop-express.de/shop/product_info.php/info/p7545_TS-20-inch-f-8-Ritchey-Chretien-Astrograph---carbon-truss-tube.html

[rmuhlack]

What camera would you pair it with to get a useable image scale? at f8 that's a lot of focal length. Surely adaptive optics would be a must.

[gregbradley]

14,000 Euros would make it about AUD$27,000 landed. Hardly bang for your buck. There would be far better alternatives. They should hold off on the larger RCs until its completely certain their scopes are fully matured as designs and not a work in progress for someone else to complete. Unless the Aussie price is lower as that was Europe and they tend to have higher prices than we do.

$27K though puts it up against some seriously good scopes. TOA150 setup, AP140/155 both with a good camera, Planewave CDK 14 or its competitors IDK and Officina Stellare may start around there. FSQ130 and a good camera.

Add on a large mount to handle it (PME, AP1600, I don't know what else, Planewave Ascension, ASA DDMM ) and you're up over $50K for a GSO setup. Trash the focuser and throw in a FLI Atlas or at least a feathertouch and you're up another 4Gs.

Still it would be 20 inch. If you could overcome the inevitable half dones on the system then it could be good. The good thing about the GSO's as Paul has shown the optics seem fine.

Haven't seen any other GSO RC 12's or above images other than Pauls though.

Greg.

[Paul Haese]

Actually the collimation ring has been addressed some time ago. All scopes 12" and up have a rear collimation ring as part of the scope now. I had a bit to do with that development as the rig I am using is so heavy the old mirror assembly was not up to holding that sort of weight. Part of the solution was to develop a centring ring for the rear assembly.

I agree about the collimation being out but if you own a folding scope of any type you should know how to collimate it front and rear. I have never known a either a Newtonian, SCT or RC to never fall out of collimation when being moved by road transport. So being shipped overseas might just prove to disturb the collimation.

A long focal length will need a wide sensor I suspect if you are going to use it at native. As an example Martin Pugh is using a STXL11002 on his CDK17 and that does not produce really wide looking images. There is a nice even fit with that combination.

The 20" will need a big mount to carry it. An EQ8 could theoretically work but whether it will guide correctly or not is another matter.

Even if there is some teething problems with these big scopes they will still be a 1/4 of the price of their more prestigious cousins, so worth considering if you are on a limited budget.

I had considered the 16" but at present I am trying to eliminate other equipment problems. Cash is a little short too, so that kind of kills the idea for now.

[Paul Haese]

Hmm those prices across their entire range a huge. They are saying 3499 euro for the 12". Australian price is that in dollars. Euro is about double AUD so those prices are ridiculous.

[rustigsmed]

yep, actually if you log in with an Australian address it drops to 11,756 eu ... perhaps more comparable to what it will be in oz .

but then again compare the 12"

TS 12" = 2,940eu
Andrews 12" = $3799
ratio of 1.292

TS 16" = 5,461eu
Andrews 16" = $6999
ratio of 1.282

TS 20" 11,756 eu
Andrews 20" ?? maybe with a ratio of 1.287 = $15,129

a much better result if the ratios hold true.

Russ

[gregbradley]

If it were AUD$13990 here that makes more sense and a lot more tempting.

Greg.

[Paul Haese]

I need to make a correction about Euro. $1.48 to the Euro. Yep at 15K it would be a good deal for such a large aperture but it would still need a focusor, a shroud, a dew heater, adapters etc.

[netwolf]

A 20" RC at 16k is awesome, but still out of reach for me.

do you think my Pentax MS-5 could handle this, it had a C14 and 5" Pentax Refractor on it. Information i could find says it can handle 50kg but i think that is very conservative.
Pic from net of the mount carrying a Mewlon 300.
http://www.takayuki-astro.com/image/equip/m300.jpg

[clive milne]

Could always mount the secondary on a PDF located on the spider...

[glend]

Teleskop-express prices include VAT at 19% which is applicable inside the Euro zone but not on sales outside. So multiply their price by 0.81 and you should get the Euro amount to convert to AUD. That's how it has worked on car parts I have purchased from Europe. However it is up to the retailer to process the export exemption with their VAT payment process.

[Peter Ward]

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.

[sn1987a]

There's only one way to find out - we all stump up a thousand $ each and .... :P

[Somnium]

50 kgs ... that is some camera :) . GSO give you the body and the engine and a wad of cash to pay for whatever trim you like.

[Chris85]

Just thought I'd share my friend in Perth who's using the GSO 14" http://www.astrobin.com/users/ntk.thava/

[Peter Ward]

With a 50kg instrument rating there will be bugger-all flexure with say a 5kg CCD+CFW at the focal plane.

It will be interesting to see whether GSO deliver 5 micron spot sized across a 65mm field....which, to excuse the pun, is even more to the point :)

[rustigsmed]

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 :eyepop:

[gregbradley]

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.

[Paul Haese]

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.

[theodog]

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.:P

[Peter Ward]

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 :question: Might do a Marcus and document its deployment

[clive milne]

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/products-field-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.




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

[clive milne]

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.

[marc4darkskies]

Counting on it Peter! Will make interesting reading! :thumbsup:

[Peter Ward]

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.:shrug:

[clive milne]

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.

[Paul Haese]

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.

[xthestreams]

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!).

[Paul Haese]

Alex,

I don't think the 20" made the market here. The 16" was sold here as I have helped someone collimate one.

[DJT]

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.

[xthestreams]

Thanks PH, given your connection to GSO HQ do you know if they ever made it onto the wild anywhere?

Thoughts on the 16” ?

[xthestreams]

:-) of I’m going down that path I’d rather give my money to Sidereal/Astroworx and get something tailored to my needs.