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  #1  
Old 12-05-2014, 08:58 AM
loc46south (Geoffrey)
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First Impressions of GSO 12" R/C Truss

I have had a number of PM's regarding the 12" GSO TRuss I purchased a few weeks ago - a few members were considering purchasing one in the near future. Here is my experience so far :-

The telescope has been set up on a Losmandy G-11 mount - I understand that the OTA is nearing the max load specs for the G-11 but providing that it is carefully balanced it performs without any hiccups - as a precaution I reduced the slew speed to 500 otherwise no changes were made.

Last friday night the skies cleared enough for me to attempt to collimate the unit, a preliminary check with a Takahashi Collimation scope had shown it to be out of alignment. The stock focuser was removed and replaced with a Moonlite CSL 2.5in Motorised Crayford and the camera used was a SBIG ST10XME.

Preliminary images showed the unmistakable sign of badly pinched optics - subsequent investigations over the weekend show that this is a common fault with 12" GSO R/C's and the matter has now been refered back to the Retailer. I would caution anone considering a similar purchase to think carefully before buying. It is now a matter of watch this space.

Cheers
Geof Wingham
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  #2  
Old 12-05-2014, 12:32 PM
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multiweb (Marc)
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Might want to check your primary retaining clips. Easily fixed.
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  #3  
Old 12-05-2014, 01:57 PM
loc46south (Geoffrey)
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Originally Posted by multiweb View Post
Might want to check your primary retaining clips. Easily fixed.
Wish it was that easy - that is only part of the problem. Spent the last 3 days doing a fair bit of research on the subject. Pricipal problem is the design and construction of the mirror retaining cell.

Cheers
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Old 12-05-2014, 02:19 PM
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Quote:
Originally Posted by loc46south View Post
Wish it was that easy - that is only part of the problem. Spent the last 3 days doing a fair bit of research on the subject. Pricipal problem is the design and construction of the mirror retaining cell.

Cheers
This thread might give you some ideas to start with.
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  #5  
Old 12-05-2014, 04:29 PM
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Sorry to here about your issues Geof.

As 'just down the road' I was hoping you would have better luck as I was interested in one of the truss tube GSO RCs.

There are many threads of people having issues with the 12" tube GSO RCs. However the good news is many get there in the end.

With my 10" GSO newtonian. I had pinched optics(retaining clip issue)primary centre spot was out by 6mm. Secondary was too close to primary by a large amount and collimation isn't holding well.However I'm slowly working through the issues.
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  #6  
Old 12-05-2014, 05:01 PM
loc46south (Geoffrey)
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Cause of problem

Thanks for the link Marc - the problem is caused by the focuser tube being attached to the Primary mirror cell - The weight of the focuser, camera etc acts as a lever and deforms the cell at the 3 collimation points on the outer rim. The 8in and 10 in R/C does not have this problem as the collimation screws are located closer to the mirror centre.

There are a number of fixes out there that work with differing results and if you don't mind the expense a conversion kit is available to replace the existing 3 point suspension cell with an 18 point suspension cell - cost 1350 euros.

My biggest ***** is that this is a new design telescope produced with a known documented problem. I didn't know about it at time of purchase but I am well aware of it now -

Cheers
Geof Wingham
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  #7  
Old 12-05-2014, 06:05 PM
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The rear assembly has been redesigned and I am sure I will be receiving the new rear assembly in the near future. It will prevent movement. However the problem you have is not caused by the rear mirror assembly. I currently have the heaviest imaging rig hanging off the back of one of those scope at 11Kg and I don't get that at all.

You need to check the primary and secondary mirror assemblies. The mirror cell issue produces elongated stars are certain angles, not pinched optics.

I have read all the threads about this and nearly every one has come to the wrong conclusions.

Once the rear cell is available you need only ring and ask for it. The scope has a two year warrantee in Australia. It might be another month or so yet before the assembly will be freely available.

Best of luck.
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Old 12-05-2014, 08:41 PM
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Nothing at all constructive to add, but it is for these reasons I am a staunch refractor nut.

Collimation drives me nuts, and I want a scope to work right, out of the box, and not need to recollimate it every time I used it.

Aperture fever has never bitten. Glad about that too.

Good luck with it. Seems even the high end OS's have collimation issues too.
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  #9  
Old 12-05-2014, 09:37 PM
clive milne
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Quote:
Originally Posted by Paul Haese View Post

You need to check the primary and secondary mirror assemblies. The mirror cell issue produces elongated stars are certain angles, not pinched optics.

.
Paul... I am struggling to understand what you are saying here?
Could you please elaborate.
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  #10  
Old 13-05-2014, 04:50 AM
loc46south (Geoffrey)
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Quote:
Originally Posted by Paul Haese View Post
The rear assembly has been redesigned and I am sure I will be receiving the new rear assembly in the near future. It will prevent movement. However the problem you have is not caused by the rear mirror assembly. I currently have the heaviest imaging rig hanging off the back of one of those scope at 11Kg and I don't get that at all.

You need to check the primary and secondary mirror assemblies. The mirror cell issue produces elongated stars are certain angles, not pinched optics.

I have read all the threads about this and nearly every one has come to the wrong conclusions.

Once the rear cell is available you need only ring and ask for it. The scope has a two year warrantee in Australia. It might be another month or so yet before the assembly will be freely available.

Best of luck.
Paul - Thanks for the info. I have been in contact with the retailer I bought the scope off and he is consulting with GSO - I am waiting for an outcome. I am aware of the optical issues and have checked the optics with laser, Tak Collimation Scope, visually and with software analysis - all give similar results - that the scope is near collimation but one thing I did notice was that with change in elevation the mirror appeared to shift within its cell.

I am relieved to hear you comment concerning the weight you have on your scope, as I intend using it with a MOAG,AO-8 and ST10XME Camera

At this point I have not cracked open the telescope body and will not do so untill I hear back from the Retailer.
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  #11  
Old 13-05-2014, 04:56 AM
loc46south (Geoffrey)
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Quote:
Originally Posted by LewisM View Post
Nothing at all constructive to add, but it is for these reasons I am a staunch refractor nut.

Collimation drives me nuts, and I want a scope to work right, out of the box, and not need to recollimate it every time I used it.

Aperture fever has never bitten. Glad about that too.

Good luck with it. Seems even the high end OS's have collimation issues too.
Hi Lewis - depends on the scope - I own a mixed bag but in there I have a Tak Mewlon 250S - That scope arrived in perfect collimation after a trip from Japan to America to NZ and I have carted it around to various dark sites over the last 5 years on the back of a 4 x 4 vehicle and the collimation has never moved - in all that time I have never had to touch it or even had to realign the finderscope.
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  #12  
Old 13-05-2014, 08:47 AM
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Quote:
Originally Posted by clive milne View Post
Paul... I am struggling to understand what you are saying here?
Could you please elaborate.
The mirror cell directly screws into the rear adapters. So any heavy weight on the back end acts like a lever to the entire mirror cell. It cannot create pinched optics as the cell is very rigid and does not twist. I have tried to do that and had to exert a lot of force with a two foot lever on a spare cell I had just to test if this was the problem. The only thing that is holding the mirror cell in place is three screws and the lock screws that go with it. The screws are quite good but are sprung loaded and it is the springs that are moving a little to create the elongation of the stars. In all the tests I did I never saw triangular shaped stars. This problem only seems to come up with heavy loads. I had not such trouble when I tested the scope with the QSI or when I had the STL and focusor on the back. However, once I started putting things on like a rotator and STXL and its heavy filter wheel things changed.

GSO are working on the problem and I am awaiting the modified rear cell assembly. It will have an adapter which bolts directly onto the rear face and then the imaging train screws onto that. There will be a centring adjustment to sort out optical alignment too.
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Old 13-05-2014, 08:54 AM
loc46south (Geoffrey)
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Quote:
Originally Posted by Paul Haese View Post
The mirror cell directly screws into the rear adapters. So any heavy weight on the back end acts like a lever to the entire mirror cell. It cannot create pinched optics as the cell is very rigid and does not twist. I have tried to do that and had to exert a lot of force with a two foot lever on a spare cell I had just to test if this was the problem. The only thing that is holding the mirror cell in place is three screws and the lock screws that go with it. The screws are quite good but are sprung loaded and it is the springs that are moving a little to create the elongation of the stars. In all the tests I did I never saw triangular shaped stars. This problem only seems to come up with heavy loads. I had not such trouble when I tested the scope with the QSI or when I had the STL and focusor on the back. However, once I started putting things on like a rotator and STXL and its heavy filter wheel things changed.

GSO are working on the problem and I am awaiting the modified rear cell assembly. It will have an adapter which bolts directly onto the rear face and then the imaging train screws onto that. There will be a centring adjustment to sort out optical alignment too.
Hi Paul - there was no heavy load on mine at the time - the stock focuser had been swapped out for a CR/2 motorised Moonlite and a ST10XME camera - that was all so either something is very loose inside or something else ie wrong.
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Old 13-05-2014, 09:12 AM
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Theres a number of waves of distortion there - it would take a pretty decent force on the primary or secondary to do that -

How many points is the float cell and how many edge clips are there ? That info could help rule some things in or out. A non rotationally symmetric error in a component is obviously another possibility which hasn't been mentioned , I have seen it in larger optics.
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Old 13-05-2014, 09:17 AM
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Quote:
Originally Posted by Satchmo View Post
Theres a number of waves of distortion there - it would take a pretty decent force on the primary or secondary to do that -

How many points is the float cell and how many edge clips are there ? That info could help rule some things in or out. A non rotationally symmetric error in a component is obviously another possibility which hasn't been mentioned , I have seen it in larger optics.
Mark, there are three edge clips and really only three points. The whole mirror which is flat and it sits on the mirror cell which has lots of support but the whole assembly is sitting on three screw points. So really it is three points.
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Old 13-05-2014, 09:18 AM
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Quote:
Originally Posted by loc46south View Post
Hi Paul - there was no heavy load on mine at the time - the stock focuser had been swapped out for a CR/2 motorised Moonlite and a ST10XME camera - that was all so either something is very loose inside or something else ie wrong.
My guess is that the edge clips are too tight and need to be loosened off. That weight is nothing and should not produce any distortion from my experience with these scopes.
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Old 13-05-2014, 09:23 AM
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Mark see the link below for the images of the mirror cell

http://www.iceinspace.com.au/forum/s...d.php?t=117425

That will give you an idea of what I am talking about.
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  #18  
Old 13-05-2014, 09:43 AM
loc46south (Geoffrey)
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Hi - here is a link that may explain the problem from another perspective and the solutions used. http://stargazerslounge.com/topic/18...-rc-dissambly/

Cheers
Geof Wingham
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Old 13-05-2014, 09:45 AM
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Paul ,I can see there are three massive clips but I can't see whats behind the primary - is it a 9 point or 3 point cell? If the weight of the camera is bending the back plate it should only cause a change in collimation - not twist the mirror- unless it is bonded hard to the cell in which case its not really a flotation cell.
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Old 13-05-2014, 10:50 AM
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Mark in that thread, you can see a photo of the mirror cell without the mirror in it. The fans on the back plate can be seen from behind. It is the fourth photo in the first post of my thread. There are little metal tabs that the mirror sits on and there are six in all. That is what the mirror sits on and it is held in place by the baffle assembly. Now if the baffle is too tight and the clips on the edge are too tight it might cause pitch optics.
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