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Is this tilt?

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#1 Hypoxic

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Posted 30 June 2020 - 08:08 AM

So as some of you know, I've been struggling with my gear for a while now trying to figure out what's going on with the elongated stars. Today I learned how to do a little image analysis in PixInsight. I'm not really sure how to read the FWHM images but to me things don't look that great. I'm beginning to suspect that my Flat61A is not threaded straight.

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  • DSC_1213_eccentricity.jpg
  • DSC_1213_FWHM.jpg
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Edited by Hypoxic, 30 June 2020 - 08:12 AM.


#2 sharkmelley

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Posted 30 June 2020 - 08:55 AM

Tilt is definitely a big part of your problem.  But the FWHMEccentricity script is not telling you anything that is not already obvious from the looking at the image.

 

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#3 Hypoxic

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Posted 30 June 2020 - 10:00 AM

Tilt is definitely a big part of your problem.  But the FWHMEccentricity script is not telling you anything that is not already obvious from the looking at the image.

 

Mark

That's pretty much what I figured but wanted to post them anyway, just in case there was something more to be had.

At the moment I'm researching a way to get a camera tilt compensator into my imaging train. I think I see a way to do it with some bits from TS.



#4 MarcoAstro

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Posted 30 June 2020 - 01:53 PM

That's pretty much what I figured but wanted to post them anyway, just in case there was something more to be had.

At the moment I'm researching a way to get a camera tilt compensator into my imaging train. I think I see a way to do it with some bits from TS.

I think that you've seen my post in the other topic.

 

First thing that I would do is make sure that you focuser, field flattener and any other bits are aligned as best as possible. That is assuming they have some kind of adjustment available.

 

Is the tilt that you are seeing repeatable i.e. it's always the same no matter what you do? I expect that you also have an issue with the back focus distance being a little short (or long), but you need to fix the tilt first.


Edited by MarcoAstro, 30 June 2020 - 01:57 PM.


#5 Hypoxic

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Posted 30 June 2020 - 02:34 PM

I think that you've seen my post in the other topic.

 

First thing that I would do is make sure that you focuser, field flattener and any other bits are aligned as best as possible. That is assuming they have some kind of adjustment available.

 

Is the tilt that you are seeing repeatable i.e. it's always the same no matter what you do? I expect that you also have an issue with the back focus distance being a little short (or long), but you need to fix the tilt first.

Yes, I saw your post. 

 

This is what I’ve finally found. That little gap, right...there:

 

if I rack the focuser a little tighter, I can see a very slight shift to that side as it seats flush. But if I let the focuser go, it opens up again.

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#6 MarcoAstro

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Posted 01 July 2020 - 04:15 AM

Yes, I saw your post. 

 

This is what I’ve finally found. That little gap, right...there:

 

if I rack the focuser a little tighter, I can see a very slight shift to that side as it seats flush. But if I let the focuser go, it opens up again.

That looks very similar to the issue that I solved with the adhesive PTFE tape. Is that field flattener threaded onto the focuser, or is it using the compression fitting? It looks screw-on, but I'm not 100% sure. If it is threaded then you are almost certain that it is focuser draw tube slop. If you are happy to dismantle the focuser, then I would take a look and see if the PTFE tape is a possible solution. It's cheap and easy to try.



#7 Hypoxic

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Posted 01 July 2020 - 12:44 PM

That looks very similar to the issue that I solved with the adhesive PTFE tape. Is that field flattener threaded onto the focuser, or is it using the compression fitting? It looks screw-on, but I'm not 100% sure. If it is threaded then you are almost certain that it is focuser draw tube slop. If you are happy to dismantle the focuser, then I would take a look and see if the PTFE tape is a possible solution. It's cheap and easy to try.

The Flat61A threads into the draw tube with M54 threading. But honestly, I think it’s not threaded straight. The draw tube itself is very rigid.



#8 MarcoAstro

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Posted 02 July 2020 - 03:51 AM

I just looked at some drawings of the Flat61A and I see what you mean about how it threads on.

 

You say "if I rack the focuser a little tighter, I can see a very slight shift to that side as it seats flush. But if I let the focuser go, it opens up again." which makes me think that it might be possible to adjust this out at the focuser. Have you tried stripping it down to see what it looks like in there?




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