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HELP: Odd Star Shape

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#1 44maurer

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Posted 16 June 2019 - 01:02 AM

Can someone help me to understand what the problem is with my setup?

 

This is the 11" RASA, I have not had this problem previously, a year + ago, I had a problem that the lens unit came loose from the front/top plate. I had the scope repaired by Celestron and ever since then my stars look like the attached images. I have messed around with it thinking it was something I was doing wrong. Even though I was using the same setup as prior to the lens coming loose. I ended up putting it away. I did buy the Hotech Laser Collimator (yes that ridiculously expensive one) and made the adjustments.

 

I just set it up again with the plans of using the ASI1600 and NB, so I have not used this camera before on the RASA. Attached is a stack of 1 second exposures. My stars are really messed up and I'm not sure what I should be looking for. I did try rotating the camera and the odd shape stars rotate with the camera. 

 

If this could be camera tilt, how much would it need to move? I did try playing around a little with that, no luck.

 

Thank you in advance of any assistance.

 

Brian

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#2 PhilHoyle

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Posted 16 June 2019 - 03:25 PM

Looks like collimation.  It could be the camera is not perpendicular to the light path too.

 

Phil



#3 Monkeybird747

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Posted 16 June 2019 - 03:56 PM

+1 on collimation error. Looks like coma.



#4 44maurer

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Posted 16 June 2019 - 07:22 PM

I would like it to be collimation, but then that mean mean this HOTECH Advanced Laser Collimator isn’t working.

 

i don’t have a way to play with the tilt of the camera, so I may just try to place some shims in to see if it will change it.



#5 Monkeybird747

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Posted 16 June 2019 - 08:08 PM

If it was like that when it came back from Celestron for repair, then I'd contact Celestron and show them the pics. Is there really much that could be tilted in terms of the camera connections? Is your laser well collimated? I don't think it takes much to make a big difference at f2.

 

Can you do a defocused star test with the camera looping and make adjustments live? I'm looking at the manual for the rasa 11 under the Collimation section. I'm guessing you will see a star pattern similar to what is shown. Collimating on a defocused star may be your best bet.


Edited by Monkeybird747, 16 June 2019 - 08:13 PM.


#6 Stephen Kennedy

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Posted 16 June 2019 - 10:11 PM

Actually, those stars look a little out of focus to me. 


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#7 44maurer

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Posted 16 June 2019 - 10:40 PM

If it was like that when it came back from Celestron for repair, then I'd contact Celestron and show them the pics. Is there really much that could be tilted in terms of the camera connections? Is your laser well collimated? I don't think it takes much to make a big difference at f2.

 

Can you do a defocused star test with the camera looping and make adjustments live? I'm looking at the manual for the rasa 11 under the Collimation section. I'm guessing you will see a star pattern similar to what is shown. Collimating on a defocused star may be your best bet.

LaserS,  it’s their high end model that I figured was worth the price to get the fast F2 correct. I had done a collimation a few months ago and it’s just been sitting in my office, but maybe it got out a little.  Thanks  for the tip on manual, I’ll check that out. 



#8 44maurer

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Posted 16 June 2019 - 10:41 PM

Actually, those stars look a little out of focus to me. 

 

Actually, those stars look a little out of focus to me. 

I believe focus was very close. I know not perfect, very close. 



#9 44maurer

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Posted 18 June 2019 - 12:17 AM

Update: I check the collimation on an unfocused star and it is off a bit. I’ll work on that tomorrow.

 

I dont believe the focus was affecting this, Changing the focus only made the stars go from V’s to a more solid triangle/teardrop. 

 

Hopefully the collimation will fix fix my problem.



#10 Monkeybird747

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Posted 18 June 2019 - 01:20 PM

Once it is dialed in with the refocused star refocus and take some frames. If the stars look good pop your laser back in and see what it says. Should give you an indication of the accuracy of the laser collimation. *Disclaimer* I’ve only ever dealt with Newtonian collimation.

#11 44maurer

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Posted 01 July 2019 - 09:48 AM

 

I wanted to thank everyone for their help, I stayed up all night working on the collimation. I got 6 30 second images before the sky got too bright. Stars look pretty good now.

 

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Edited by 44maurer, 01 July 2019 - 09:49 AM.

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#12 Monkeybird747

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Posted 01 July 2019 - 09:57 AM

Those look much better! Did you use defocused star method? Curious if your laser was leading you astray. 



#13 44maurer

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Posted 01 July 2019 - 01:11 PM

Those look much better! Did you use defocused star method? Curious if your laser was leading you astray. 

No, I used the Hotech Advanced CT Collimator. It uses several lasers and what I did was set up the screen, adjust collimation, adjust screen, Collimate, and repeat. I did this a half dozen times. I’ve not seen it documented, but after each collimation, the original setup is changed slightly.




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