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GSO 12" F/5

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#1 tboss70

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Posted 14 May 2021 - 12:41 PM

I received a GSO 12" F/5 last fall around the Mars opposition as I was looking for cheap, large aperture, and an excellent mirror lol.gif

The huge box arrived and appeared in descent condition but the OTA did have a couple small dents in it. Otherwise, everything appeared in good condition.

The focuser is the " LB upgrade" (Linear Bearing Crayford Focuser) but to be honest, while it does work okay, it doesnt feel like a great focuser. And for the price I guess that is to be expected.

The mirror takes a while to cool but it does include a fan. During the few times I have used it I dont think its ever been fully acclimated. Star testing appears to show slightly softer rings on inside focus and well defined outside focus.

I used a Ronchi eyepiece to check the mirror and I see straight lines, no signs of astigmatism, or TDE. Pretty sure I can identify TDE from my Orion 8" F/4.9 mirror. You can see the curve at the edge of the mirror.

I see zero of that in the GSO.

 

I've been wondering how good the secondary mirror is on this newt as I've read that they are the weaker link in some of the cheaper newtonians. 

Another thing a little off with this one is the primary mirror cell can be shifted slightly as the screws dont appear to  hold it well. I did try to tighten them but for the weight of that cell/mirror and the tubing, its just borderline useable/tolerable. I find I have to point to my object, then collimate and enjoy. If I move the scope in another direction my collimation is off again a little.

Does anyone know where to purchase 14" diameter tubing that might be better support? I'd spring for that if I could find some but I dont know where to get it. And I think I would prefer aluminum or metal.

 

At the tail end of the Mars opposition last fall I did get a few good images. I cant wait to try it on Jupiter and Saturn once they get higher.

 


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#2 Ben the Ignorant

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Posted 14 May 2021 - 01:46 PM

I've been wondering how good the secondary mirror is on this newt as I've read that they are the weaker link in some of the cheaper newtonians.

You tested the secondary and primary simultaneously with the Ronchi, the combo is good as the lines are straight.


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#3 tboss70

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Posted 14 May 2021 - 03:09 PM

Thats a good point, thank you.



#4 bokemon

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Posted 16 May 2021 - 02:43 PM

The primary mirror cell has a major problem in that the collimation bolts have a lot of room to slide around in the holes.  U need to find some bushings at the hardware store to take up the extra slop.

The steel tube is very flimsy.  I replaced mine with an aluminum version, but I had to get the sheet metal myself and have a local shop roll it into a tube. You need to get the dimensions exactly right to fit into the original caps at the ends.



#5 tboss70

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Posted 16 May 2021 - 08:42 PM

The primary mirror cell has a major problem in that the collimation bolts have a lot of room to slide around in the holes.  U need to find some bushings at the hardware store to take up the extra slop.

The steel tube is very flimsy.  I replaced mine with an aluminum version, but I had to get the sheet metal myself and have a local shop roll it into a tube. You need to get the dimensions exactly right to fit into the original caps at the ends.

Thank you. How thick was the aluminum? Is it sufficient enough? I may need to go this route myself and possible get a different mirror cell. 



#6 bokemon

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Posted 16 May 2021 - 10:17 PM

I used 0.080" 6061 aluminum, and it is RIGID.


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#7 stargazer193857

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Posted 20 May 2021 - 04:24 PM

The primary mirror cell has a major problem in that the collimation bolts have a lot of room to slide around in the holes.  U need to find some bushings at the hardware store to take up the extra slop.

...

That is true of most nuts and bolts. I wonder if Teflon tape would help. I plan to have screws digging into predrilled holes sized for the right amount of friction. Then there is matching friction so stuff starts turning smoothly.
 


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#8 tboss70

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Posted 28 May 2021 - 05:02 PM

I went over this tube again and tried to see if anything was loose. I could certainly tighten a few screws better that i had not noticed before. Apparently this helped as I collimated the scope again and threw the lazer pointer in and as I moved the scope around i saw no shift in collimation. We'll see if this sticks but I'm hoping so.


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