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Old 13-11-2021, 07:03 PM
AdamJL
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Sensor Tilt?

Hi all

In a recent image I noticed that the stars on the left all had some strange "horizontal diffraction" spikes. I know it's not true diffraction like with a reflector, but I was puzzled as to why this was happening on a refractor.

Spoke to someone today who thought it could be sensor tilt, so I downloaded CCD Inspector and decided to give it a look.

I loaded up a frame from the night (1), and also a frame from earlier in the night (2). Then compared to a night a couple of months ago (3).

I'm guessing amounts of 12-18% is pretty bad?

I don't know specifically how to determine whether it's my camera (which can be fixed with the tilt adjustment screws) or if it's somewhere else on my imaging train. First guess would be to turn the camera 90 or 180 degrees and see if the image changes or not? If it changes then the problem is in the imaging train, if it doesn't change then it's the camera.. is that right?
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Last edited by AdamJL; 13-11-2021 at 07:54 PM.
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  #2  
Old 13-11-2021, 07:18 PM
AdamJL
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I've just analysed the 21 images I used for that picture.
Average of 18.8 (19%) tilt. One of them is 23%. Yuck.
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Old 13-11-2021, 07:41 PM
AdamJL
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Interestingly, the only image from that sequence that didn't have the strange spikes was the first (and only) image taken after a Meridian flip
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Old 13-11-2021, 07:52 PM
AdamJL
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Also decided to use ASTAP's built in CCD inspector (hey it's free).

First image is from about 5 frames into the sequence, showing "moderate" tilt 0f 19%. That's off by a little bit compared to CCD Inspector (which showed 22% for the same image) but the trend is the same.

Comparing this to the image post-meridian flip again, which was down to 12% (mild tilt).

I think the fact that the meridian flip seems to have "fixed" the issue, tells me the issue is probably in the imaging train? Maybe something not tightened enough.

Adding to this, there are some definite back-focus issues which I already know needs fixing.. boy this is going to be a fun project to fix
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  #5  
Old 13-11-2021, 08:42 PM
Startrek (Martin)
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Adam,
Enjoy the challenge , it is satisfying finally resolving these sorts of issues
I spent a month sorting out coma with my coma corrector in my 2 newts when I started using my new 2600MC
You will get to the bottom of it I’m sure
Martin
PS: To ensure the tilt plate on my 2600MC was level , I used a piece of A4 paper in the gap between the tilt plate and camera body and adjusted the Allen screws until the paper could just slide along all edges
A bit antiquated but it worked ok

Cheers
Martin
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Old 13-11-2021, 09:34 PM
AdamJL
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Quote:
Originally Posted by Startrek View Post
Adam,
Enjoy the challenge , it is satisfying finally resolving these sorts of issues
I spent a month sorting out coma with my coma corrector in my 2 newts when I started using my new 2600MC
You will get to the bottom of it I’m sure
Martin
PS: To ensure the tilt plate on my 2600MC was level , I used a piece of A4 paper in the gap between the tilt plate and camera body and adjusted the Allen screws until the paper could just slide along all edges
A bit antiquated but it worked ok


Cheers
Martin
Martin, that's genius

Cheers mate!
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