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6" RC collimation

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7 replies to this topic

#1 DWM

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Posted 19 July 2021 - 10:54 PM

I bought a 6" RC scope basically to play with until my Stellarvue SVX is delivered. 

Like so many of these scopes, collimation is poor.

 

Looking through the scope with a Cheshire eyepiece I can see the primary is out of alignment, but what might be a bigger problem is that there isn't a small white dot in the center as shown in the collimation instructions.

 

Can anyone clarify what might cause this?

 

Dave



#2 Sky King

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Posted 20 July 2021 - 01:00 AM

The RC's are difficult to collimate and after a lot of study what I found is:

 

1) Don't touch it and do a star test in and out of focus. It could need nothing. Many people say fooling with the collimation only makes it worse. 

 

2) iOptron has a manual with instructions if it fails the star test. 

 

3) This method is considered best by a number of people.

 

4) A GSO Focuser Collimation Ring / Tilt Adapter is also highly recommended.

 

I've been trying to get up to speed on this before I actually have to do it, so maybe someone with direct experience can help you more. Good luck! 



#3 bjulihn

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Posted 20 July 2021 - 01:51 AM

Hi DWM;

 

I would heartily agree with the #3 recommendation above for Deep Sky Instruments process. It seems difficult at first glance but it is actually pretty simply because it tells you exactly what to do with various issues and gives photographic examples. The first time I really gave it a try my stars tightened right up and my images improved significantly. Also, they go to some extent explaining why the center spot can be misleading. They use a method that does not require a center spot. I recommend you give it a look.

 

Brad



#4 quilty

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Posted 20 July 2021 - 04:28 AM

My latest method is quite simple and needs no further equipment, though maybe not perfect

 

1. See if the mirrors are fixed

2. adjust primary mirror watching from the front and see if everything looks concentric

3. adjust collimation ringmark without eyepiece by turning the three collimation screws of the secondary

4. fine collimation at a medium star at high power by the secondary mirror

 

This led me to a reproducable collimation state


Edited by quilty, 20 July 2021 - 04:56 AM.


#5 DWM

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Posted 20 July 2021 - 01:51 PM

Thanks to all. As it looks like my Stellarvue is still a few months away I'll try these recommendations. 

After 40 years with various SCT's I got out of those because of collimation issues and now I've jumped back in. 

 

When I decide to sell it, it will go our my door better than when it came in. Ha.

 

Dave



#6 Sky King

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Posted 21 July 2021 - 07:48 PM

This vendor (not affiliated with me) posted a new collimation device that they claim works with RC's. If it works it could be a great last resort tool. 



#7 sunrag

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Posted 21 July 2021 - 08:08 PM

Interesting! I can see by looking through the focuser that i am not seeing concentricity. I don’t have a tilting adapter for the focuser. I also don’t want to take apart the OTA for collimation. So looking for easier way to collimate.

#8 quilty

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Posted 22 July 2021 - 01:32 AM

GSO cassegrains happen to have lose mirrors. Any collimation in that state is pointless. Fixing the mirrors is the only reason to disassemble the OTA though inevitable sometimes. The collimation itself doesn't need to. Just turning the collimation screws till everything looks concentric


Edited by quilty, 22 July 2021 - 01:35 AM.



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