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RC telescope collimation or reflection or other issues?

Optics Equipment Collimation Classic Catadioptric
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#1 lihao19943

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Posted 30 December 2024 - 10:13 AM

I have an RC18 telescope, and recently during the imaging process, some moderately bright stars at various off-axis locations have a bright semicircular halo toward the center of the light axis, and a slightly dimmer halo in the other direction of the axis. Is this a collimation problem of the optical axis or is there some kind of reflection in the telescope system?
It is worth noting that this halo is only clearly resolved when FWHM<2".

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#2 Tapio

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Posted 30 December 2024 - 10:39 AM

Alluna RC18?
What a scope!

So there shouldn't be internal reflections.
Is it shrouded?

What components are there in optical path?

Edited by Tapio, 30 December 2024 - 10:39 AM.

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#3 rzep8

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Posted 30 December 2024 - 11:20 AM

I don't think this is a collimation issue as the stars do not appear to be oval or astigmatic. Are you using a filter? Possible reflections off the filter might be my guess.


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#4 lihao19943

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Posted 30 December 2024 - 01:14 PM

Alluna RC18?
What a scope!

So there shouldn't be internal reflections.
Is it shrouded?

What components are there in optical path?


Yes, in the optical path of the Alluna RC18, there are a CAA, an extension adapter, an OAG, a filter wheel, filters, and a camera.

#5 lihao19943

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Posted 30 December 2024 - 01:24 PM

I don't think this is a collimation issue as the stars do not appear to be oval or astigmatic. Are you using a filter? Possible reflections off the filter might be my guess.

Viking

Yes,I using the Chroma filter.

When installing the filter, make sure the bottom of the text on the filter faces the camera.

Because I am using the filter wheel of the Morivian C3-61000EC-pro camera, only three screws with rubber retaining rings are used to fix the filter during installation. This results in a part of the screws being "protruding" inside the filter. I don't know if this will cause such artifacts to appear. Should I replace it with a circular retaining ring like the ZWO filter wheel to fix the filter?



#6 lihao19943

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Posted 31 December 2024 - 07:07 AM

Tonight I'm going to flip the filter over and test it to see if it fixes the problem.

#7 rzep8

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Posted 01 January 2025 - 06:21 PM

Viking

Yes,I using the Chroma filter.

When installing the filter, make sure the bottom of the text on the filter faces the camera.

Because I am using the filter wheel of the Morivian C3-61000EC-pro camera, only three screws with rubber retaining rings are used to fix the filter during installation. This results in a part of the screws being "protruding" inside the filter. I don't know if this will cause such artifacts to appear. Should I replace it with a circular retaining ring like the ZWO filter wheel to fix the filter?

Oooh.. that much I can't answer. My only thought on that is taking the camera off and looking down the connection to the filters. Possibly shine a light down there and see if anything reflects back.



#8 lihao19943

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Posted 02 January 2025 - 12:43 AM

Oooh.. that much I can't answer. My only thought on that is taking the camera off and looking down the connection to the filters. Possibly shine a light down there and see if anything reflects back.

I took the filter off and ran some tests. I found that the halo problem still existed. I put it into virtual focus to make the problem more obvious. From the image, it seems that there are two strange diffraction rings, and they are oriented towards the center of the optical axis at all four corners of the focal plane.

Therefore, I judge whether this is a problem caused by some protruding structure or burr in the optical path or uneven pressure ring of the main mirror and other defects?

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