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Old 17-05-2018, 07:30 PM
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GSO Carbon Truss Newtonian Review

I have had a long association with GSO since the first sales of the RC8 in Australia. There were some teething problems with the RC's along the way which have subsequently been resolved. Problems like the need for longer and better primary baffles, carbon trusses rather than steel tubes, better primary mirror cells and focuser centring rings to name a few.
So when GSO announced it would be producing a new fast Newtonian with a truss system I immediately thought it would be on my list of purchases, given that a lot of experience would be put into these scopes from previous developments, or so I thought.
Last year I took delivery of the 12” version and began commissioning of the OTA into one of my remote observatories. I removed the stock focuser and bought a focuser from a reputable manufacturer (which I have had to also replace with an Atlas focuser I had already because the new focuser was flexing too!).
What I like about the Newtonian:
· Conical mirror which aids in fast cooling.
· Primary mirror cell holds the mirror on a large thick plate, which prevents pinching of the optics.
· Optics test quite well with no apparent aberrations.
· Carbon truss OTA, makes the telescope lighter than a steel tube and probably more economical than a carbon tube.
· Images show sharp detail of both terrestrial and astronomical objects. I have produced quite a few images which show good detail despite the stiffness issues in the OTA.
· Fast imaging speeds with an f4 telescope. Subexposures are greatly reduced with a fast f ratio and a responsive camera.
What I found was problematic with the Newtonian:
My first imaging run showed the presence of astigmatism in images. Nice neat little crosses appeared where every star was on the first download. Rotating the primary showed it was the secondary that was at fault. With consultation it was suspected that the glue holding the primary onto the secondary stalk was at fault. Removing the silastic which had hardened on the outside and was still sticky on the inside; replacing it with aquarium grade silicone solved that problem. The silastic’s uneven cure was causing the secondary to distort and produce astigmatism.
Next I found like others that the secondary cage was flexing a lot and this was causing huge distortions to stars shapes when pointing at varying parts of the sky. I installed aluminium tubes with threaded rods (8 of them) and locking nuts. Star shapes had improved and star shape changes were now less severe.
With the help of a friend who is a machinist in the Astronomical Society of South Australia (Alan) we installed a counter weight to the secondary assembly. The thinking here was that the secondary was rotating perpendicular to the optical line and needed to be balanced. Again the modification helped a little but still there was movement in the shape of the stars from one side of the meridian to the other.
My next move was to glue the secondary shroud to the secondary assembly rings with Loctite. This created further stiffness but has sadly, did not remove the several pixels of movement left I was seeing in star shapes.
The final resort will be to rebuild the secondary cage and assembly. I think the focuser board needs to be a lot bigger and there needs to be another board on the other side of the secondary assembly too. The secondary spider also needs to be replaced with a far sturdier one than the one that is provided. The current vanes are too flimsy and have no way of tightening them either. Gravity is therefore causing the secondary to rotate and that is causing star shapes to change across the sky.
So would I recommend this OTA as an imaging scope? I am unhappy to say the answer at present is no. Whilst the optics do produce sharp images, the OTA cannot produce consistent results. The secondary cage, spider and focuser plate are way under engineered. It all needs beefing up to be usable as an astrograph or to be sold as an astrograph. When GSO fix the current stiffness problems, it should be a great astrograph for the price.
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Old 17-05-2018, 07:58 PM
glend (Glen)
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Thank you Paul. Comprehensive review, as always. Has GSO indicated if they will be taking your advice on board for a Gen 2 model?
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Old 17-05-2018, 08:19 PM
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Wow Paul, you have certainly spent a lot of time and effort to improve the telescope and unfortunately it is still unsatisfactory. I am surprised that you cannot tighten up the spider vanes, that is usually one of the basic requirements for building a Newt that you have spider vane adjustment.

Where are you at now, still persevering or had enough?

Sorry to hear this.

Cheers
Bill
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Old 17-05-2018, 08:43 PM
glend (Glen)
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Paul, I seem to recall a Newt builder in NZ, I think it was, used high 'E' guitar strings to stabilise his secondary. I have also seen photos of secondaries held in location in space, as it were, by thin guitar strings. I suppose 'hacking' it is not a solution for all buyers and GSO should fix it.
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Old 17-05-2018, 08:53 PM
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Glen I think that was Rolf Olsen who did the guitar string trick on a truss newt.
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Old 17-05-2018, 10:35 PM
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Quote:
Originally Posted by glend View Post
Thank you Paul. Comprehensive review, as always. Has GSO indicated if they will be taking your advice on board for a Gen 2 model?
Hi Glen, I have sent several emails off to GSO and to date have heard nothing back regarding making just some of the more basic improvements on the scope. I have got sick of being a beta tester without any response from the manufacturer. They were once quite responsive but that has changed.

Quote:
Originally Posted by billdan View Post
Wow Paul, you have certainly spent a lot of time and effort to improve the telescope and unfortunately it is still unsatisfactory. I am surprised that you cannot tighten up the spider vanes, that is usually one of the basic requirements for building a Newt that you have spider vane adjustment.

Where are you at now, still persevering or had enough?

Sorry to hear this.

Cheers
Bill
Should the AG12 I have bought turn out to be very good, I will then devote time to retrofitting a completely new secondary cage and spider. It's going to take some time to develop properly but that is on my list of fixes. I like the optics, they just need some work holding it all together.

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Originally Posted by glend View Post
Paul, I seem to recall a Newt builder in NZ, I think it was, used high 'E' guitar strings to stabilise his secondary. I have also seen photos of secondaries held in location in space, as it were, by thin guitar strings. I suppose 'hacking' it is not a solution for all buyers and GSO should fix it.
It could have been Rolf, but I cannot remember who that might have been. If there was a complete fix and it could be marketable it might be worth someone building these things and selling them as modified units.
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Old 18-05-2018, 09:11 AM
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I’ll certainly give you credit for tenacity, but given the on going problems this may be a catalyst for others to look at other affordable solutions. For example the occasional “pre loved” RCOS that comes up for sale. These beautifully engineered and instruments often go for a song compared to their new pricing.
I suspect if you asked Planewave or similar to ship with Zerodur ion-milled optics you’d “need a Bex and a lie down” after hearing the price.

I am puzzled as to why they don’t get snapped up when they appear, but suspect even if the optics are not expensive, the cost of getting a suitable mount puts many off.

As for Orion..I hope that goes well and wait with interest to hear your experiences and results with the new beastie in due course.
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Old 19-05-2018, 03:02 PM
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H Paul,

Well done in doing this review, trying to provide feedback to the manufacturer and also letting others know how the product performs and what they will be up against.

Why GSO (and others) would not use reviews and amateur forums to listen more to potential customers is beyond me. In this case, it may just be a question of cost, or it's just in the too hard basket for them to update tooling, increase the product price etc.

In the age of social media etc, I'm afraid you simply cannot hide these days when you release products that don't cut it at certain levels.

Hope you retro your scope as I have always felt GSO's offered so much potential but could not fully deliver in the age of digital imaging which at a pixel level particularly, and at higher focal lengths, is just so unforgiving.

John K.
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Old 19-05-2018, 03:12 PM
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Thanks Paul, you have me worried about GSO carbon fibre, trusses and tubes. I was thinking about an 8" tube - I know its different, but ...
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Old 19-05-2018, 07:26 PM
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Hi Paul

Please dont give up.

You know the problems and no doubt you can solve all issues.

You have invested a great deal in working up the unit and it would be unfortunate if you gave up before you have the unit working perfectly.

No doubt you are losing patience and perhaps enthusiasm ... and that is totally understandable particularly if you get no appreciation from the manufacturer.

Let me say there will be many folk who will be happy with your development of the unit ...

But I know you can do it.

Your energy is taking a beating but heck its only a scope so make it do what you expect of it.

At the pointy end of any game folk buy stuff and improve it...think race cars or bikes.
And as to race bikes and cars each week they do something to make it better than last week.

It seems you are close to turning the unit into a great scope.

And on the positive you seem to have identified the problems and really you have been making wonderful progress.

Knowing the problems enables you to fix them..imagine how annoying it would be if no matter what you did saw no result and you were left wondering why.

Maybe a night imaging something with something else but just for fun as they say and recover some of your enthusiasm.

Does it play up everywhere or just some orientations?

If so that is reasonable..Its like guitars to a degree they all have their strong points and their weak points but I suggest you work within the region of what the unit does well...pointing straight up should work ok??

I wish you luck and must say I for one really enjoyed reading your various posts on bringing the unit up to scratch.

Good luck.

alex
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Old 20-05-2018, 06:10 AM
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I purchased my AG12 about the same time Paul and have had many of the same issues. I was lucky enough to be spared from the secondary astigmatism.

Ive added carbon rods to the upper housing which work well however Im still left with the rather flimsy secondary which cant be tightened in the same way you can in a tube design.

I agree that the focuser plate needs beefed up. Even the main mount dovetail could be more heavy duty.

Ill that said, kudos to GSO for the conical mirror which was rather unexpected. Why they don't advertise the fact is beyond me.

The main takeaway here is that an imaging f4 system is rather unforgiving and requires to be designed and manufactured within an f4 imaging requirement in mind. I dont think this scope quite does this.

Perhaps this is an opportunity for a company like teleskop-express to come up with an upgrade package.

I have attached an image with the carbon tubes i have added.

Dave
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Old 20-05-2018, 07:54 AM
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Great review Paul and even better explanation of your numerous corrective actions, will be useful to many.
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Old 20-05-2018, 08:53 AM
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Paul, thanks for the review. I was interested to hear your comments re needing to change out the focuser - I'm assuming you are referring to your NiteCrawler? How did you determine the focuser was flexing when you also have issues with the focuser mounting plate?

The youtube video for the Nitecrawler has a demonstration of it holding position with a 16lb load. You must have a heavy camera!

https://www.youtube.com/watch?v=azcv1b6u3jo
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Old 20-05-2018, 09:45 AM
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Quote:
Originally Posted by DaveNZ View Post
I purchased my AG12 about the same time Paul and have had many of the same issues. I was lucky enough to be spared from the secondary astigmatism.

Ive added carbon rods to the upper housing which work well however Im still left with the rather flimsy secondary which cant be tightened in the same way you can in a tube design.

I agree that the focuser plate needs beefed up. Even the main mount dovetail could be more heavy duty.

Ill that said, kudos to GSO for the conical mirror which was rather unexpected. Why they don't advertise the fact is beyond me.

The main takeaway here is that an imaging f4 system is rather unforgiving and requires to be designed and manufactured within an f4 imaging requirement in mind. I dont think this scope quite does this.

Perhaps this is an opportunity for a company like teleskop-express to come up with an upgrade package.

I have attached an image with the carbon tubes i have added.

Dave
Dave how much weight is hanging off the side of that top section? I get the impression from the GSO build that they are expecting folks to use a DSLR (non-modded, non-cooled), or something like an ASI1600 and filter wheel as its heaviest load.
I wonder if you were just doing manual focus and rotation with a light camera, would the scope design be ok?
Given Paul's experiences with GSO scopes, it seems that they do not test with these sort of imaging loads (or perhaps don't test at all). Do we need to accept that these are not Planewave category scopes, but basic designs built to a budget entry point with reasonable optics?
I agree there is a limited market for customisers to step in and take a basic scope and hotrod it. Sort of like Holden's HSV unit. Is the volume there to justify a business line for TS or others? Obviously, someone like Paul could become that customiser, if that excited him.

That leads to asking, if you have to invest to upgrade, why not just buy the high end scope in the first place? Or is it the challenge of making a stock budget production model into an HSV?
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Old 20-05-2018, 11:15 AM
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ZeroID (Brent)
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Quote:
Originally Posted by Paul Haese View Post
.... It could have been Rolf, but I cannot remember who that might have been. If there was a complete fix and it could be marketable it might be worth someone building these things and selling them as modified units.
Yes it was Rolf on his previous Serrurier build, the 10F5. I am not sure if his new 12" build is the same. I copied his 'E string' idea on my 8F8 reasonably well. It is very stable, I am still using it on the 8F6 successor to the 8F8 but with thin nylon which is more forgiving on over tightening.
Pretty sure the build photos are still on Rolfs website.
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Old 20-05-2018, 11:21 AM
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Dave how much weight is hanging off the side of that top section? I get the impression from the GSO build that they are expecting folks to use a DSLR (non-modded, non-cooled), or something like an ASI1600 and filter wheel as its heaviest load.
I wonder if you were just doing manual focus and rotation with a light camera, would the scope design be ok?
Given Paul's experiences with GSO scopes, it seems that they do not test with these sort of imaging loads (or perhaps don't test at all). Do we need to accept that these are not Planewave category scopes, but basic designs built to a budget entry point with reasonable optics?
I agree there is a limited market for customisers to step in and take a basic scope and hotrod it. Sort of like Holden's HSV unit. Is the volume there to justify a business line for TS or others? Obviously, someone like Paul could become that customiser, if that excited him.

That leads to asking, if you have to invest to upgrade, why not just buy the high end scope in the first place? Or is it the challenge of making a stock budget production model into an HSV?
Good points Glen. Yes, I'm probably expecting too much from the price point.

Not sure off the top of my head of the combined weight of the Litecrawler and QSI683. I have solved the "weight issue" with the carbon fibre rods which was low cost. (rods from Ebay)

The real issue is the secondary. You would have the same issue I'm guessing with the original GSO focuser and a light weight camera. I was getting movement with my collimation laser with no camera attached and my lighter Moonlite focuser.

Cheers Dave
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Old 20-05-2018, 11:44 AM
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Good points Glen. Yes, I'm probably expecting too much from the price point.

Not sure off the top of my head of the combined weight of the Litecrawler and QSI683. I have solved the "weight issue" with the carbon fibre rods which was low cost. (rods from Ebay)

The real issue is the secondary. You would have the same issue I'm guessing with the original GSO focuser and a light weight camera. I was getting movement with my collimation laser with no camera attached and my lighter Moonlite focuser.

Cheers Dave
Both the GSO dobs I have owned, a 12" and a 16", suffered from secondary sag at various altitudes, easily observed with a laser collimator in place. The 12" was a solid tube model and the 16" was the strut model. I managed to control it in the 16" by using "string bracing" of the top section, as used in Dennis Steele's string dobs ( on the Dob Stuff website).

The 'string' I used was actually non-stretch Dynema synthetic boat running rigging, 2mm; attached to small turnbuckles secured to the top and bottom section rings in triangulated arrangement. It only took three of this strings to correct the top section movement.
I figured using steel guitar strings on the big Dob would introduce expansion/contraction with temperature fluctuations. I know my guitar goes out of tune with temperature changes.
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Old 20-05-2018, 03:55 PM
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May sound crazy but what about fishing line. Strong thin low expansion and cheap and available.
You could lace the whole thing in a web a fishing line.☺
If it flexes anothor lash down.
Alex
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Old 21-05-2018, 05:06 PM
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Thanks everyone for the thoughts and discussion, that was my purpose for putting up the review. Manufacturers ought to take more notice of feed back.

Both Dave and I have conversed quite a lot about the issues. It's been great to bounce ideas off each other to try to find the problems.

Quote:
Originally Posted by xelasnave View Post
Hi Paul


........Does it play up everywhere or just some orientations?

If so that is reasonable...........pointing straight up should work ok??
...
....
alex
It's a non repeatable problem. In part of the sky the eastern imaging may be ok and on the west terrible, or the meridian might be terrible and parts of either eastern or western are good. The problem can be minor to down right infuriating. Each imaging run has resulted in hours of data being ditched. I have been generally doing research work on some part of the night and then pretty picture images on the part of the sky that I know is ok for that particular object. Trying to work around the problem a little.

Quote:
Originally Posted by peter_4059 View Post
Paul, thanks for the review. I was interested to hear your comments re needing to change out the focuser - I'm assuming you are referring to your NiteCrawler? How did you determine the focuser was flexing when you also have issues with the focuser mounting plate?

The youtube video for the Nitecrawler has a demonstration of it holding position with a 16lb load. You must have a heavy camera!

https://www.youtube.com/watch?v=azcv1b6u3jo
No it'd not the nitecrawler, that is on the RC and that works fine. It's holding up the STXL, with filter wheel, filters and the AOX. It's a tank. The problem was with the 2.5" heavy duty Moonlite Newtonian focuser. That could not hold the load very well. Ron has apparently made some modifications to those focusers now.

I could easily move the draw tube up and down with that particular focuser.

Quote:
Originally Posted by glend View Post
Dave how much weight is hanging off the side of that top section? I get the impression from the GSO build that they are expecting folks to use a DSLR (non-modded, non-cooled), or something like an ASI1600 and filter wheel as its heaviest load.
I wonder if you were just doing manual focus and rotation with a light camera, would the scope design be ok?
Given Paul's experiences with GSO scopes, it seems that they do not test with these sort of imaging loads (or perhaps don't test at all). Do we need to accept that these are not Planewave category scopes, but basic designs built to a budget entry point with reasonable optics?
I agree there is a limited market for customisers to step in and take a basic scope and hotrod it. Sort of like Holden's HSV unit. Is the volume there to justify a business line for TS or others? Obviously, someone like Paul could become that customiser, if that excited him.

That leads to asking, if you have to invest to upgrade, why not just buy the high end scope in the first place? Or is it the challenge of making a stock budget production model into an HSV?

I have the QSIWSG-8 with filter wheel, adapters and Atlas focuser. Not a huge load but perhaps enough to cause flex.

Yeah there is a price point issue here but it should hold a QSI as a minimum. No one expected it to hold a big camera. Though you're right you would expect a few mods to be done but not a total rebuild.

Having bought a high end scope (well I hope so, it is yet to ship) it cost nearly 12000 more dollars, so I am expecting something a lot better. I know their secondary assemblies are better in any event. It is just the optics that might be risky.
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Old 21-05-2018, 05:11 PM
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Ahh that makes sense.
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