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Edge correction changes when the camera is turned in a 200mm F4

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9 replies to this topic

#1 Andre Moutinho

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Posted 04 August 2020 - 01:07 AM

Hi,

 

I am having different edge performance when I rotate the camera in the focuser.

 

 Setup:

 Newtoniano GSO 200mmf4

 ASI 1600MM Cool

 GPU

 

Notice that A is worst 

 

B is a bit better (rotated 180 degree from A)

C is the best (rotated 90 degree from A)

 

What may be causing it? sensor tilt?

The images bellow are in the order: B, A and C.

 

 

 

 

Thanks

Andre

Attached Thumbnails

  • A.JPG
  • B.JPG

Edited by Andre Moutinho, 04 August 2020 - 11:04 AM.


#2 sharkmelley

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Posted 04 August 2020 - 05:20 AM

One of the images has "smeared" stars even in the centre of the image.  This could be because of a tracking error and it makes the image difficult to interpret.

 

Mark


Edited by sharkmelley, 04 August 2020 - 11:07 AM.

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#3 andysea

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Posted 04 August 2020 - 10:34 AM

In order to eliminate any tracking error it is best to take an exposure that is only a few seconds. Typically ~5 seconds in a rich star field produce enough stars to analyze the image.
How long were those exposures?


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#4 Andre Moutinho

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Posted 04 August 2020 - 10:57 AM

In order to eliminate any tracking error it is best to take an exposure that is only a few seconds. Typically ~5 seconds in a rich star field produce enough stars to analyze the image.
How long were those exposures?

Hi, exposure time was 20s.. and it was guiding so it should not be a problem. But it should be better 5s in a star field to avoid any tracking doubts.



#5 Andre Moutinho

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Posted 04 August 2020 - 11:10 AM

Hi,

 

I am having different edge performance when I rotate the camera in the focuser.

 

 Setup:

 Newtoniano GSO 200mmf4

 ASI 1600MM Cool

 GPU

 

Notice that A is worst 

 

B is a bit better (rotated 180 degree from A)

C is the best (rotated 90 degree from A)

 

What may be causing it? sensor tilt?

The images bellow are in the order: B, A and C.

 

 

 

 

Thanks

Andre

Attached Thumbnails

  • C.JPG


#6 andysea

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Posted 04 August 2020 - 03:41 PM

Hi, exposure time was 20s.. and it was guiding so it should not be a problem. But it should be better 5s in a star field to avoid any tracking doubts.

I think 20s is still fine. I would exclude tracking errors. How is the camera connected to the focuser? If it is through a nose piece, it is possible that there might be some minor tilt introduced when you tighten it down. 

Threaded connections are always better. F4 is fast enough to exacerbate any little imperfection. 



#7 Andre Moutinho

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Posted 04 August 2020 - 03:51 PM

I think 20s is still fine. I would exclude tracking errors. How is the camera connected to the focuser? If it is through a nose piece, it is possible that there might be some minor tilt introduced when you tighten it down. 

Threaded connections are always better. F4 is fast enough to exacerbate any little imperfection. 

Hi, ok.. Everything (camera, EFW, spacer are threaded into the GPU coma corrector and the GPU is connected into a low profile moonlight 2" focuser.

 

 

Best

Andre



#8 GregsCNAccount

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Posted 05 August 2020 - 04:53 PM

Is the GPU coma corrector inserted fully into the focuser draw tube?  If the flange on the GPU is not flush with the flange on the draw tube, any slop between the draw tube and the GPU diameters could allow tilt to be introduced randomly each time the setup is tightened down.  I had this issue with a Moonlite focuser and an ES HDCC.  If you can't rack out the draw tube far enough to do this, add a spacer under the focuser.  Moonlilte sells various thicknesses.



#9 jtrezzo

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Posted 05 August 2020 - 05:47 PM

I believe sensor tilt it would not change when you rotate so I'd be ruling that out. How are you collimating, what tools? My initial guess would be collimation or as someone else said, focuser slop. Are you using a stock focuser or a good one like FT or Moonlite? The stock one on my 250mm Newt was garbage and I wouldn't even have tried imaging on it.



#10 GregsCNAccount

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Posted 05 August 2020 - 07:37 PM

I'm not suggesting sensor tilt within the camera.  I presume that his focuser does not have camera rotation provision.  Presuming that is the case, he has to unlock the GPU in the draw tube to rotate it.  I'm suggesting tilt caused by the difference in the outside diameter of the coma corrector and inside diameter of the draw tube, i.e., slop.  Unless the draw tube and GPU flanges are flush, there is no way to ensure that the slop hasn't allowed the GPU to be locked in the draw tube with some tilt.  This could change every time the GPU is locked down, as when rotated.




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