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What did the postman bring today? - Hint: It is heavy!

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#51 HenkSB

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Posted 23 April 2024 - 05:39 AM

I have some time now so let me explain my experiences.  The GSO provides an impressive value for the money.  I paid $800 for my 12" GSO a few years ago.  It worked OK for AP, but I have plenty of trouble with mount related issues, so it was not easy to figure out which problem goes where.  After a while I noticed that the collimation laser dot moved around quite a bit when slewing the telescope, over a length about twice the size of the donut.  I had a few suspects in mind: (1) vanes not tight enough, (2) secondary is too heavy for the vanes, (3) primary is rolling around, (4) the tube is sagging.  I started with (2) by making a counterweight in a tube that was attached to the vanes near the secondary.  It did not make much difference.  About (3), I added shims to make the primary tight, that also did not fix it.  I created a harness for (3) with cables to tighten up the tube just to see if that was the problem.  It also did not make a difference - but that doesn't mean it is not the problem, I probably used the wrong test.  Eventually I took the OTA off and moved the two tube rings around the focuser, and also tightened the vanes beyond reasonable, adding large washers on the outside.  That seemed to have effect.  So, I put myself on the Agena watch list for another pair of 14" GSO rings.  They have been on backorder for a half year now.  It was just postponed until end May.  Until then I won't use the telescope because I do AP and it's not suitable for that until the problem is fixed.  I would like to hear other people's experiences or suggestions.

I now realize that this is about the 12" GSO Dob while the one I discussed is the 12" F/4 GSO astrograph.  So maybe my comments don't apply to your scope.  I have the 12" Z12 Dob too that has some parts in common.  I modified it into a collapsible for transportation purposes so I can't check if its collimation changes as the scope slews.  It's easy to check with a laser collimator if you like.


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#52 TheChosen

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Posted 23 April 2024 - 06:57 AM

I now realize that this is about the 12" GSO Dob while the one I discussed is the 12" F/4 GSO astrograph.  So maybe my comments don't apply to your scope.  I have the 12" Z12 Dob too that has some parts in common.  I modified it into a collapsible for transportation purposes so I can't check if its collimation changes as the scope slews.  It's easy to check with a laser collimator if you like.

I will be testing it out .. so far I've managed to assemble the base and put some wheels on it. I refuse to use a DOB unless it has wheels mounted to the base smile.gif

 

The azimuth motion is so much better than the three teflon pads of the Sky Watcher. The size/weight of the base is not that bad.

 

Only problem is, the little guy has appropriated the base as his new car, he loves me driving him through the apartment, especially the fact the base can rotate and while rotating it makes some rolling sounds :)

 

Screenshot_2024-04-23-13-52-28-856_com.miui.videoplayer-edit.jpg


Edited by TheChosen, 23 April 2024 - 06:58 AM.

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#53 MeridianStarGazer

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Posted 23 April 2024 - 08:46 AM

The flex tube is basically the same weight. I thought about it but decided it was not worth the trouble and extra money... Not to mention collimation and needing a shroud etc.


I'll take a truss that fits in a trunk. But needing to pay $1xx for a shroud is a bummer.
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#54 25585

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Posted 23 April 2024 - 02:29 PM

I'll take a truss that fits in a trunk. But needing to pay $1xx for a shroud is a bummer.

I agree, trusses should be sold with a shroud included.



#55 TheChosen

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Posted 24 April 2024 - 04:28 AM

Finally got the time to assemble the whole thing.

 

Now I need to install the carrying straps (no go without them) and also collimate the scope. Just by looking through the focuser I can tell it needs it badly.

 

Might be also a good idea to dismantle the primary mirror holder and check if it is not too tight. Sometimes I heard they tighten it too much in these new bigger scopes because of transportation and pinch the mirror.. anybody heard of that?

 

CL.jpg


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#56 HellsKitchen

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Posted 24 April 2024 - 06:16 AM

Finally got the time to assemble the whole thing.

 

Now I need to install the carrying straps (no go without them) and also collimate the scope. Just by looking through the focuser I can tell it needs it badly.

 

Might be also a good idea to dismantle the primary mirror holder and check if it is not too tight. Sometimes I heard they tighten it too much in these new bigger scopes because of transportation and pinch the mirror.. anybody heard of that?

 

attachicon.gif CL.jpg

 

That can certainly be the case, definitely worth checking it. 



#57 HenkSB

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Posted 24 April 2024 - 10:18 AM

Finally got the time to assemble the whole thing.

 

Now I need to install the carrying straps (no go without them) and also collimate the scope. Just by looking through the focuser I can tell it needs it badly.

 

Might be also a good idea to dismantle the primary mirror holder and check if it is not too tight. Sometimes I heard they tighten it too much in these new bigger scopes because of transportation and pinch the mirror.. anybody heard of that?

 

attachicon.gif CL.jpg

If it ain't broke, don't fix it.  The metal ring is large enough and can't be changed, the mirror is held down by rubber holders each with 2 screws with limited travel.  IMHO it is well made.  Unless you have evidence of pinching I would leave it alone.


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#58 TheChosen

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Posted 24 April 2024 - 10:26 AM

If it ain't broke, don't fix it.  The metal ring is large enough and can't be changed, the mirror is held down by rubber holders each with 2 screws with limited travel.  IMHO it is well made.  Unless you have evidence of pinching I would leave it alone.

Yeah , I figured it is not worth the trouble right now. I'll star test it first .. then it is going off eventually anyway for some cleaning. I already cleaned my 8" so it is not a big deal.

 

I meant only checking if the rubber holders are just the right distance (usually paper thin distance) from the mirror, which is standard after a cleaning. Not messing with anything else.


Edited by TheChosen, 24 April 2024 - 10:28 AM.

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#59 HenkSB

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Posted 24 April 2024 - 10:49 AM

Yeah , I figured it is not worth the trouble right now. I'll star test it first .. then it is going off eventually anyway for some cleaning. I already cleaned my 8" so it is not a big deal.

 

I meant only checking if the rubber holders are just the right distance (usually paper thin distance) from the mirror, which is standard after a cleaning. Not messing with anything else.

The distance won't be paper thin, more like 1 mm.  At least not with the one I have (the Z12).  With my F/4 12", which has an identical mirror holder AFAICT, I added some shims when I noticed the collimation problems that I mentioned.  It did not turn out to be critical.  Worst case it would yield a 2 mm difference for the primary collimation, practically nothing to worry about compared to tube and vane flexure, and the error margins of the collimation tool.

 

Was the scope delivered with a dirty mirror?  With every cleaning you can still scratch it or leave skin oil residues.


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#60 TheChosen

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Posted 24 April 2024 - 10:51 AM

The distance won't be paper thin, more like 1 mm.  At least not with the one I have (the Z12).  With my F/4 12", which has an identical mirror holder AFAICT, I added some shims when I noticed the collimation problems that I mentioned.  It did not turn out to be critical.  Worst case it would yield a 2 mm difference for the primary collimation, practically nothing to worry about compared to tube and vane flexure, and the error margins of the collimation tool.

 

Was the scope delivered with a dirty mirror?  With every cleaning you can still scratch it or leave skin oil residues.

No the mirror is very clean .. but based on my 8" , it takes about 20 observations for it to become dirty.

 

I have the cleaning process nailed down with no risk of scratching. Yeah , the distance recommended is something like a paper business card, which is around 1mm.

 

https://youtu.be/6XeBl8eCPsc



#61 TheChosen

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Posted 25 April 2024 - 05:23 AM

I now realize that this is about the 12" GSO Dob while the one I discussed is the 12" F/4 GSO astrograph.  So maybe my comments don't apply to your scope.  I have the 12" Z12 Dob too that has some parts in common.  I modified it into a collapsible for transportation purposes so I can't check if its collimation changes as the scope slews.  It's easy to check with a laser collimator if you like.

I just finished collimating my 12" .. took me an hour to get it at a really good place. I have the say the adapters and focus holders of GSO are a lot better than Sky-Watcher 8". I finally got the laser to agree with the Cheshire.

 

Then I started slewing the telescope in all directions , even I went as far as to point it about 20 degrees towards the ground to see if the primary is tight into place or there is a little bit of freedom. It seems it is not tightened but there is a tiny bit of freedom (just as it should be).

 

No change to collimation , the laser stayed directly in the center.


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#62 MeridianStarGazer

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Posted 25 April 2024 - 09:36 AM

...

CL.jpg


The bases look the same size.

#63 TheChosen

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Posted 25 April 2024 - 09:53 AM

The bases look the same size.


Same angular size maybe.. but the 8 is 530mm.. the 12 is 630mm 😉
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