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Celestron SCT Double Vision Question

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9 replies to this topic

#1 nevada-jason

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Posted 19 April 2024 - 04:14 PM

Hey all, question for the experts.  Hope it's an easy one.

 

Last year, I made the move from an Apertura 10" reflector to a used 9.25 SCT because I wanted to be able to use a go-to mount.  I did lots of lucky imaging using an equatorial platform with the 10" and I learned how to collimate the reflector while recognizing the signs of not having that done. While I've had reflectors for decades, this is my first SCT.

 

Some of my images with the SCT have double vision artifacts that almost leave me cross eyed. I've seen the same effect on some of the images posted in this forum but not sure what causes it and how to fix it.

 

Is it a matter of collimating the SCT and dialing in the secondary mirror?  Or is it a processing artifact and the images aren't being stacked properly?  Or am I seeing issues at the edge of the field of view that can't be helped?  It seems to have a double image throughout the entire image.  I want to say the more I sharpen the worse it gets, but I still see detail, just double.

 

I'm using the same imaging processing that I was using before.  Sometimes ordering by quality in PIPP, stacking using AutoStakkert then sharpening using RegiStax6 followed by final tweaks in PhotoShop.

 

I've attached some images below of what I'm seeing.  The bright mountain tops have a secondary image that outlines the bright spots.  The Hadley Rille looks double.

 

Thanks in advance and I really enjoy seeing everyone's images here!

Attached Thumbnails

  • Screenshot 2024-04-19 135645.png
  • Screenshot 2024-04-19 135712.png


#2 ShaulaB

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Posted 19 April 2024 - 04:17 PM

A used scope? It probably is out of collimation. Yes, SCTs need collimation too. It's fairly easy. Many YouTube videos and threads here discuss how to do it.



#3 MarkMittlesteadt

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Posted 19 April 2024 - 04:20 PM

Hey all, question for the experts.  Hope it's an easy one.

 

Last year, I made the move from an Apertura 10" reflector to a used 9.25 SCT because I wanted to be able to use a go-to mount.  I did lots of lucky imaging using an equatorial platform with the 10" and I learned how to collimate the reflector while recognizing the signs of not having that done. While I've had reflectors for decades, this is my first SCT.

 

Some of my images with the SCT have double vision artifacts that almost leave me cross eyed. I've seen the same effect on some of the images posted in this forum but not sure what causes it and how to fix it.

 

Is it a matter of collimating the SCT and dialing in the secondary mirror?  Or is it a processing artifact and the images aren't being stacked properly?  Or am I seeing issues at the edge of the field of view that can't be helped?  It seems to have a double image throughout the entire image.  I want to say the more I sharpen the worse it gets, but I still see detail, just double.

 

I'm using the same imaging processing that I was using before.  Sometimes ordering by quality in PIPP, stacking using AutoStakkert then sharpening using RegiStax6 followed by final tweaks in PhotoShop.

 

I've attached some images below of what I'm seeing.  The bright mountain tops have a secondary image that outlines the bright spots.  The Hadley Rille looks double.

 

Thanks in advance and I really enjoy seeing everyone's images here!

To me it just looks blurry, which could be one (or all) of three things...

 

Scope is not collimated well enough.

It's still out of focus.

Seeing conditions (most likely atmospheric turbulence...similar to wavy lines on hot pavement at a distance).



#4 nevada-jason

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Posted 19 April 2024 - 04:30 PM

To me it just looks blurry, which could be one (or all) of three things...

 

Scope is not collimated well enough.

It's still out of focus.

Seeing conditions (most likely atmospheric turbulence...similar to wavy lines on hot pavement at a distance).

Definitely could be seeing. I just never saw this effect with the reflector.  And I need to get better at collimating the SCT.

 

My best images with the reflector was when I added an EAF and I haven't done that yet either.



#5 DeepSky Di

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Posted 19 April 2024 - 04:51 PM

Collimation advice from the planetary forum is in this faq: https://www.cloudyni...d-january-2023/



#6 Migwan

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Posted 19 April 2024 - 06:05 PM

Looks to be out of focus to me.  That can be tricky in an SCT, especially in bad seeing.   Keeping a proper focus distance of around 105-110mm can help a tad.

 

Along with collimation, bad seeing & not quite being in focus, acclimation could be adding to the problem.   You might want to consider double wrapping the tube with Reflectix or similar.    That really limits any thermal activities that might occur within the tube. 


Edited by Migwan, 19 April 2024 - 06:08 PM.


#7 davidc135

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Posted 20 April 2024 - 03:45 PM

I think they are diffraction effects which isn't very helpful as I don't know how they can be avoided.  David



#8 nevada-jason

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Posted 22 April 2024 - 12:18 AM

Thank you to everyone who responded.  Hope this helps the next person with this.

 

I wanted to post a follow up since my outdoor workflow is at fault.  I'm 80% sure it is a focusing issue. Maybe 20% collimation.  I checked and adjusted collimation prior to another run at the moon.  Seeing wasn't allowing the later collimation steps, plus I'm still new to the process on a SCT.  I have room to improve.

 

What I didn't do during the run with the moon was adjust my focus.  My images got worse as I went on so I really need to follow my own past workflow.  Even with my 10" reflector, I adjusted focus constantly.

 

I'm just glad it wasn't a problem with post processing.  

Attached Thumbnails

  • Screenshot 2024-04-21 221125.png

Edited by nevada-jason, 22 April 2024 - 12:22 AM.

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#9 davidc135

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Posted 22 April 2024 - 02:03 AM

That's a great shot of Gassendi. It looks like you've resolved the problem.  David



#10 Borodog

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Posted 22 April 2024 - 06:53 AM

If you have not insulated your scope yet, I would recommend doing it ASAP. 2 layers of Reflectix will do the trick. Not only will you avoid the lengthy cooldown phase; it will greatly reduce the need for frequent refocussing.
  • nevada-jason likes this


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