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Need help with totally off collimation on my SCT

Cassegrain Collimation DIY Equipment SCT Celestron
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#26 davidc135

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Posted 17 September 2021 - 03:56 PM

Your plan of having an artificial star at 100ft sounds fine. That distance will cause 0.3 waves over-correction in your 11'' sct which won't affect collimation and, hopefully, the air will be steady enough to show the Airy disc.

 

It'll show what the scope can do but you may have to adjust the collimation in actual use at altitude.

 

David


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#27 dudleyjohn

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Posted 18 September 2021 - 01:51 PM

I read that I should set up the star at 25x FL. That would be 70 m for my CPC 1100. I paced it off today and I think I might be able to try it out this evening.



#28 dudleyjohn

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Posted 18 September 2021 - 06:25 PM

Well, I went out and tried to collimate this evening. No luck. I can't get the artificial star to resemble anything like a circle. It looks like a V. I've been able to get it to point in different directions, but I've adjusted the collimation screws practically to what I think is their limits in every direction. I'm sure I haven't exhausted all possibilities, but I feel like I'm making no progress at all. Any ideas? BTW: The vertex of the V is where it is brightest. If I just had a clue which direction to go when the V is pointing in a direction (tip the secondary toward the vertex or away?), I might have a starting point, at least.


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#29 dudleyjohn

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Posted 18 September 2021 - 07:01 PM

I finally got it! I followed directions provided by pcaritj in the forums to look through the corrector plate to get all the images concentric. I'd tried this before, but I was too close to see the picture I needed to see. That got me close enough that I could see a circle with a shadow using the artificial star. Then it was just a few minutes before I had it centered. I can now at least focus Jupiter and its moons. Next comes the star collimation. Thanks for all the helpful advice.


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#30 teashea

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Posted 18 September 2021 - 07:36 PM

I finally got it! I followed directions provided by pcaritj in the forums to look through the corrector plate to get all the images concentric. I'd tried this before, but I was too close to see the picture I needed to see. That got me close enough that I could see a circle with a shadow using the artificial star. Then it was just a few minutes before I had it centered. I can now at least focus Jupiter and its moons. Next comes the star collimation. Thanks for all the helpful advice.

Congratulations.  Your persistence has paid off.




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