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ED80CF collimation issue?

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#1 nikivan

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Posted 11 July 2020 - 03:33 AM

I've recently purchased used ED80CF. Did a first light today and it is quite evident there is an issue with the star shapes. Is this a collimation issue?    

 

ED80CF issue.jpg



#2 PETER DREW

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Posted 11 July 2020 - 04:20 AM

It's either collimation or tilt somewhere in the imaging train. My money would be on the latter.

#3 ButterFly

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Posted 11 July 2020 - 05:24 AM

The rotating focuser is a source of tilt error if not locked well.  But the coma looks uniform over this part of the field.  Tilt would leave some part of the field more in focus than another.  Move a bright star around the field to check, especially near the edges.

 

Collimating this scope is rather easy when you have done it a few times.  Get a collimated laser for adjusting the focuser and a cheshire for adjusting the cell.  The focuser tube rides on pads with a hair trigger, so that will take the longest time to get to a nice balance between centering and friction.  I take mine on shortish hikes so I collimate about once every two months or so.



#4 nikivan

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Posted 11 July 2020 - 11:35 AM

The rotating focuser is a source of tilt error if not locked well.  But the coma looks uniform over this part of the field.  Tilt would leave some part of the field more in focus than another.  Move a bright star around the field to check, especially near the edges.

 

Collimating this scope is rather easy when you have done it a few times.  Get a collimated laser for adjusting the focuser and a cheshire for adjusting the cell.  The focuser tube rides on pads with a hair trigger, so that will take the longest time to get to a nice balance between centering and friction.  I take mine on shortish hikes so I collimate about once every two months or so.

Thanks for the reply. What can be adjusted in the cell and how do you do it properly? I am searching for more info, but so far I've read the triplets are hard to collimate and better not to touch.



#5 ButterFly

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Posted 11 July 2020 - 06:19 PM

Thanks for the reply. What can be adjusted in the cell and how do you do it properly? I am searching for more info, but so far I've read the triplets are hard to collimate and better not to touch.

Adjusting the tilt is easy and quite the same as for a doublet.  It is done by the three pairs of big screws at the front of the cell.  Centering a triplet is hard.  NEVER touch the screws at the side of the cell.  Only let either ES or Orion handle that - those screws are usually locked with loctite.

 

Read all you can from a search for <refractor collimation cheshire laser>.  They procedure will become clear.  Focuser first, then the cell.



#6 nikivan

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Posted 13 July 2020 - 12:02 PM

Adjusting the tilt is easy and quite the same as for a doublet.  It is done by the three pairs of big screws at the front of the cell.  Centering a triplet is hard.  NEVER touch the screws at the side of the cell.  Only let either ES or Orion handle that - those screws are usually locked with loctite.

 

Read all you can from a search for <refractor collimation cheshire laser>.  They procedure will become clear.  Focuser first, then the cell.

I'll bring the scope to our local telescope shop for them to take a look. I would never touch the cell screws myself. I did another test by rotating the focuser and the entire image train by 180 degree. The direction of the distortion didn't change. Am I correct to assume the issue is not related to a focuser tilt?  



#7 ButterFly

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Posted 13 July 2020 - 09:43 PM

I did another test by rotating the focuser and the entire image train by 180 degree. The direction of the distortion didn't change. Am I correct to assume the issue is not related to a focuser tilt?  

Yes.  It is likely way off collimation.  Not a big deal at all.

 

 

I'll bring the scope to our local telescope shop for them to take a look. I would never touch the cell screws myself.
 

Sure you will - once you learn which ones to touch.   Being able to adjust the cell tilt is a very nice feature.  Fixing tilt errors in the cell is something you should do from time to time, depending on how the scope is handled.  Centering a triplet (having the center of each element placed correctly in relation to one another) is beyond the capabliity of most amateurs - that needs microns of accuracy.  Those are different sets of screws.




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