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SW 200P and CCD Inspector (Tilt)

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#1 SandyC8

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Posted 18 June 2021 - 05:06 PM

Hi,

 

I just bought a (new to me) SW 200P Quattro. I have a moonlite focuser and an ASI 294 MC Pro mounted. I took my first images a few nights ago.

 

To check the tilt and the collimation etc., I ran the images through CCD Inspector. I also have a RASA 8 so I'm fairly familiar with tilt issues.

 

To my surprise, CCD inspector said there was quite a lot of tilt (or sag) in the image. Please see the attached images. If it was my RASA, I would say it's a back focus issue.

 

I have train at the 90 degree point because I use a polemaster and if the train is vertical, it blocks the PM.

 

However, the back focus is exactly 55mm from the CC,  I'm using the SW coma corrector. So, the train is a Moonlite focuser, the Sky Watcher coma corrector, three zwo spacers equaling 48.5mm and then the camera (6.5 mm). 

 

The image posted below has no processing whatsoever...no calibration frames...nothing just a raw stack in APP. 

 

Let me know what you think....I don't know the first thing about newts.

 

Thanks

 

 

Attached Thumbnails

  • I1.jpg
  • I2.jpg
  • I3.jpg
  • I5.jpg
  • I4.jpg


#2 Jim Waters

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Posted 18 June 2021 - 05:22 PM

I have the same scope and the SW coma corrector.  I haven't checked for tilt yet.  Can't mirror alignment also cause these issues?  I would play around with back-focus and double check the alignment.   Make sure the focuser is aligned too.

 

EDIT - My camera is pointed down (180 degrees).  I use a PoleMaster and just swing the DEC 15 degrees out of the way during polar alignment.


Edited by Jim Waters, 18 June 2021 - 05:25 PM.


#3 SandyC8

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Posted 18 June 2021 - 06:48 PM

Thanks Jim,

 

The polemaster is mounted on the rail that the scope is mounted on....My mount is an Astro Physics Mach1 so there is no PM adapter for it. I thought about a RAPAS for the mount but I like the polemaster so.....

 

As you are using the same setup, I would really like to see about 30 of your subs. I would like to run them through CCDI and see how the look compared to mine.

 

Usually with my RASA, if the train was tilted, it showed on CCDI on one side of the other, not in the middle. It's a little strange that the collimation cross seems to be dead in the middle...

 

Don't shoot the messenger. As this is my first newt, I have no idea what I am talking about.  smile.gif


Edited by SandyC8, 18 June 2021 - 06:50 PM.


#4 SandyC8

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Posted 18 June 2021 - 07:41 PM

Jim...question...how do you collimate your scope....what tools are you using?

 

Thanks



#5 Jim Waters

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Posted 18 June 2021 - 07:50 PM

I use a laser collimator and a light pipe / sight tube.

 

https://agenaastro.c...collimator.html

https://www.astrosys...iz/coltlsm1.htm



#6 Jim Waters

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Posted 18 June 2021 - 07:52 PM

I don't have any good images.  There's too much smoke to image.



#7 Jim Waters

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Posted 18 June 2021 - 08:00 PM

Some links

 

https://skyandtelesc...ctor-telescope/

https://www.astro-ba...nian-reflector/



#8 SandyC8

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Posted 19 June 2021 - 09:53 AM

Thanks...read both articles....really good.

 

Now I need to figure out which tools to buy...I have a Hotech laser collimator which says that my scope is pretty well aligned but evidently there's more to it than that.



#9 mayhem13

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Posted 20 June 2021 - 05:21 AM

I can only share with you what I’ve read about the SW CC while I was researching which CC to get and the near unanimous reviews were that the SW produced the best images to the farthest EOV but nearly EVERYONE found the center of the image substantially softer than without the CC. I would run the inspector without the CC and see what comes back.



#10 SandyC8

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Posted 20 June 2021 - 10:14 AM

That's interesting ......maybe it's normal for SW CC.

 

As I said, I'm brand new to newts and on my RASA, I'd be pulling my hair out over a CCDI depiction like I have from my first subs with my SW.

 

I'll Google the CC and see what I can find.....

 

Thanks....
 

Lynn



#11 cmooney91

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Posted 24 June 2021 - 09:54 AM

Supposedly the SW Quattro Coma corrector is a rebrand of the "GPU aplanatic" coma corrector. 

 

For ~800mm focal length it wants closer to 53.66mm spacing. 



#12 Jim Waters

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Posted 24 June 2021 - 10:19 AM

Is that based on testing or the product spec sheet?


Edited by Jim Waters, 24 June 2021 - 10:20 AM.


#13 cmooney91

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Posted 25 June 2021 - 06:38 AM

53.66mm spacing at ~800mm FL came from the specs on the GPU product web site linked above.  

 

I recently changed my SW quattro CC + 8"F4 from 55mm to 53.66mm. It didn't seem to make anything worse.

 

I only do noncritical EAA. Usually mis-collimation, or focuser sag / tube flex dominate the edge aberrations, so it's hard for me to quantify an improvement. 

 

I've only been out once with the new spacing, and I recently purged my library of old EAA captures, so I don't have a good direct comparison. 



#14 bokemon

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Posted 25 June 2021 - 03:44 PM

The way to check tilt is to put on a bahtinov mask and see what an individual star looks like in the center vs sides of the image.




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