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OCAL collimation problem

Astrophotography Collimation Equipment Reflector
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#1 nonfacciofoto

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Posted 25 May 2024 - 01:19 AM

Hi, recently I bought my first newtonian telescope (skywatcher quattro 200p). 

To collimate it I use OCAL 3.5 MAX, however I'm experiencing a strange problem.

After collimation, if I rotate the OCAL attached to the coma corrector the collimation shift.

I tried doing the same thing without the coma corrector and same thing happens, I also tried mounting a Ts-optics rotator and use it to move the OCAL and the problem still happens.

I'm using the windows or the Android version of the app with my personal serial number offset + manual offset as the manual teach.

Here a video showing the phenomena.

https://pixeldrain.com/u/ywZGUvVS
Is this normal or I'm doing something wrong?

Ps:

My focuser is the Cyck version that doesn't use 2 screw to hold the coma corrector like the included one. 



#2 Vic Menard

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Posted 25 May 2024 - 07:45 AM

I can see the OCAL wandering relative to the focuser (as the outermost gray ring rotates, the dark gap at 10 o'clock adjacent to the gray ring (which is clearly wider than the gap at 4 o'clock) gradually narrows until the dark gap at 10 o'clock is now narrower than the gap at 4 o'clock). 

 

If you were free rotating the OCAL, it could be precession. You should gently lock the rotation (using the same set screw or locking ring if there's more than one)) each time before you assess/image the alignment/centering. In this respect, the OCAL behaves identically to a sight tube (or a thin beam laser)--all three are sensitive to registration errors that impact the focuser axial alignment (note that the Cheshire alignment (primary mirror axial alignment) is effectively static throughout the rotation).



#3 nonfacciofoto

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Posted 25 May 2024 - 11:55 AM

Thanks for the detailed analysis.
I tested what you said and I found that even if I tight the screws of the rotator after each rotation I get the same result of the video.
There is any way to fix this problem or I need to live with it.
If there is a solution, what tool do I need? I thought that OCAL would be a "definite" purchase. šŸ˜…

#4 Vic Menard

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Posted 25 May 2024 - 01:35 PM

...I tested what you said and I found that even if I tight the screws of the rotator after each rotation I get the same result of the video.

How many "screws" are on the rotator?


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#5 nonfacciofoto

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Posted 25 May 2024 - 02:04 PM

3 screws at 120Ā°

#6 Vic Menard

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Posted 25 May 2024 - 02:35 PM

3 screws at 120Ā°

Did you use only one while rotating/testing? 


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#7 nonfacciofoto

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Posted 27 May 2024 - 12:37 AM

I gently loose all 3, and tighten all 3 after every rotation.

#8 Vic Menard

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Posted 27 May 2024 - 07:12 AM

I gently loose all 3, and tighten all 3 after every rotation.

Try tightening only one screw when testing (if the camera axis is horizontal during testing, use the topmost screw if the center of the gravitational load is inside the focuser drawtube--if the load is outside of/above the drawtube, use the most underneath screw).  Be sure to apply gentle pressure to the OCAL to ensure it's fully seated in the focuser. If the problem persists, the OCAL camera may be slightly decentered. This sensitivity to decentering is important to minimize parallax. 




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