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Sensor tilt or focuser sag?

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#1 Squanto

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Posted 21 June 2021 - 01:51 PM

Hey guys I was testing out my ASI071MC Pro last night and noticed that my images had vignetting that was off center and when I looked at the corners I noticed that the stars weren’t round in the top two corners in the attached single sub of the pelican nebula. The top right corner looks worse. My question is what could be causing this issue? 
 

My telescope is TS Photoline 130 f/7 with 3.7” deluxe focuser, and the 3” TS .79x reducer/flattener. 
I am using the ZWO spacer that is included with my 071Mc Pro along with a filter drawer that houses my Baader UV/IR cut filter. The image was guided with guidescope and ASI290mm mini camera. The sub was 120sec, 175 gain and auto stretched in the ASIAir Pro.

 

Image train: scope>reducer>16.5mm spacer>21mm filter drawer with uv/ir filter>071MC pro.  Total backspace=55mm

Any insight would be appreciated. Thanks 

 

Attached Thumbnails

  • A7E899A7-868A-4F70-BCEF-9E98913E1312.jpeg

Edited by Squanto, 21 June 2021 - 04:56 PM.


#2 Tapio

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Posted 21 June 2021 - 02:59 PM

Can you provide full image and crop of corners ?



#3 Jim Waters

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Posted 21 June 2021 - 03:52 PM

Test without the Filter Drawer.  Can you wiggle the focuser?  



#4 Squanto

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Posted 21 June 2021 - 04:56 PM

Can you provide full image and crop of corners ?

Sorry I totally forgot to post the image. I edited my original post to include image. You can zoom in to see the corners. 


Edited by Squanto, 21 June 2021 - 04:58 PM.


#5 Squanto

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Posted 21 June 2021 - 04:57 PM

Test without the Filter Drawer.  Can you wiggle the focuser?  

I’ll have to wait till the next time I have time to image to test without the filter drawer. As far as having wiggle in the focuser there isn’t any. It’s a robust 3.7” focuser 



#6 Squanto

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Posted 22 June 2021 - 08:16 PM

I take it nobody has any idea as to what might be the cause? 



#7 ChrisWhite

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Posted 22 June 2021 - 09:11 PM

You can test the focuser to see if it's sagging. Take an image above the eastern horizon, then slew to the western horizon and take another image. If the two images have star shapes in the same spots then it's not sag.

If its the sensor you can try to shim some threads with aluminum foil or use the camera tilt plate. Trial and error to see if it gets better.

I'm on my phone and can't see your inage well, but it looks like the top is bad and the bottom is good?

#8 Squanto

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Posted 22 June 2021 - 11:24 PM

You can test the focuser to see if it's sagging. Take an image above the eastern horizon, then slew to the western horizon and take another image. If the two images have star shapes in the same spots then it's not sag.

If its the sensor you can try to shim some threads with aluminum foil or use the camera tilt plate. Trial and error to see if it gets better.

I'm on my phone and can't see your inage well, but it looks like the top is bad and the bottom is good?

Yes the bottom os nice and round and the top is bad especially the top right corner where the stars look elongated. Aside from that the other thing that puzzles me is that the image shows more vignetting on the right side vs the left side. 




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