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SKywatcher 80mm collimation issue?

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11 replies to this topic

#1 sonshadowcat

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Posted 13 February 2018 - 11:52 AM

I was attempting to take some photos last night when I noticed that I was getting extreme coma and elongated stars no matter my exposure time (15, 60, 120, 240sec). I had previously taken  images of Orion not long ago and my stars were perfect with no focus or coma issues. As far as I could tell, focus was fine. Is there a possibility it's a collimation issue? Is there a way to test my SW80 without having to buy a specialized tool or send it off somewhere (I wouldn't even know where to start)?

 

I'm attaching an image showing samples from a 240sec shot to show the elongation and coma issues.

 

IC1848_LIGHT_240s_3200iso_45f_20180212_21h47m07s155ms_ABE.jpg

 

Any help would be greatly appreciated!



#2 msl615

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Posted 13 February 2018 - 12:26 PM

I don't do much astrophoto, and I suspect the experts here will have much better answers, but I do have a guess.

 

Unless you dropped the SW80 or something else that would have tweaked the front objective, my guess is that the OTA is not the issue.

I am thinking that somehow the attachment of the camera to the OTA was off plane....that the camera was tilted compared to the OTA.  My first test would be to inspect the joint for something obvious, remove the camera, remount and try again.  What kind of camera were you using?

 

Mike



#3 einarin

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Posted 13 February 2018 - 12:52 PM

What Skywatcher scope and do you use flattener/reducer with it ?



#4 aneeg

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Posted 13 February 2018 - 12:54 PM

I agree with Mike. 

Try to look through your scope, if it is ok visual, the scope should not be blamed.

Arne



#5 skyward_eyes

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Posted 13 February 2018 - 01:19 PM

What scope are you using?

 

What camera are you using? 

 

Are you using a field flattener? 



#6 mikerepp

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Posted 13 February 2018 - 01:42 PM

Looks like it might be your tracking.  But the pic in the upper right corner does exhibit some astigmatism. 


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#7 sonshadowcat

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Posted 13 February 2018 - 04:01 PM

What scope are you using?

 

What camera are you using? 

 

Are you using a field flattener? 

Skywatcher 80mm

Canon 6D

Yes

 

Mikerepp: That's what I thought at first too but it happens at every exposure I tried at, even 15sec. If it were a tracking issue then shouldn't the stars get progressively worse with longer exposure? They don't.

 

Could it be the focus tube tightening screw? I only applied minimal tightening but perhaps that somehow affected the plane?



#8 skyward_eyes

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Posted 13 February 2018 - 04:13 PM

Which 80mm model? The ED doublet or Esprit? 



#9 sonshadowcat

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Posted 13 February 2018 - 04:16 PM

Ed doublet

Edited by sonshadowcat, 13 February 2018 - 04:16 PM.


#10 einarin

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Posted 14 February 2018 - 12:37 AM

Then I'd say it's flattener-camera distance issue and maybe tilt.

How does it look without flattener ?



#11 LewisM

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Posted 14 February 2018 - 04:03 AM

That's definitely a tilt and possible spacing distance error in the flattener. I'd be checking the T-ring mount (horrible **** things!), and cinch up the little grub screws on the bayonet attachment. You also may have drawtube sag causing this - unfortunately this is VERY common with the rather poor SW ED80 focuser. Plenty of tutorials describing how to fix them (or better still, replace them)



#12 jring

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Posted 14 February 2018 - 06:14 PM

Hi,

 

my money is on tilt somewhere in the image train too. If you got the 80ED with the kit, now is the time to mount the diagonal and EPs and have a look through the instrument. If stars look good then, go on searching the problem in the image train. If you can see a problem visually, then the scope might have a problem.

 

Joachim




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