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Why are there circles in image?

astrophotography cassegrain equipment imaging Meade SCT
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#1 adamchicago

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Posted 27 September 2020 - 05:14 PM

Why are there two circles in this image from an SCT?  I also have a refractor that uses the same filter wheel and camera where this doesn't occur.

 

I'm pretty certain this is also after correctly focusing.

 

1. Meade 10" F10 SCT

2. SCT crayford adapter

3. Feather Touch crayford focuser

4. Optec 0.62 recucer

5. 50mm extension tube

6. 15mm extension tube

7. ZWO OAG

8. ZWO 2" 7 place filter wheel...I believe set to luminance filter in this image

9. ZWO 1600mm main camera

Attached Thumbnails

  • Image with circles2.jpg
  • SCT Optical Train SMLv4.jpg

Edited by adamchicago, 27 September 2020 - 05:15 PM.


#2 TOMDEY

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Posted 27 September 2020 - 05:41 PM

Those are ghosts from the light from the brightest star bouncing off various surfaces... SCTs and relateds are notorious for this, one of the most offensive ghosts bouncing off the corrector plate. All of the stars are doing that, but only the brightest one overtly shows it. Here's a picture I took with a 250mm F/1.65 Maksutovish Camera. Same thing. Nothing you can do about it, other than to keep bright stars out of the field. Recently, a contributor  thought that he might have discovered a comet... but it turned out to be one of these things.    Tom

 

~click on~ >>>

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  • 54 Vega Tom's Super-Schmidt 1st light.jpg

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#3 adamchicago

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Posted 27 September 2020 - 05:50 PM

Ok thanks.  I'm glad it's just because I was aimed at very bright Deneb for tracking-calibration purposes, so hopefully won't be an issue for most normal targets.

 

Those are ghosts from the light from the brightest star bouncing off various surfaces... SCTs and relateds are notorious for this, one of the most offensive ghosts bouncing off the corrector plate. All of the stars are doing that, but only the brightest one overtly shows it. Here's a picture I took with a 250mm F/1.65 Maksutovish Camera. Same thing. Nothing you can do about it, other than to keep bright stars out of the field. Recently, a contributor  thought that he might have discovered a comet... but it turned out to be one of these things.    Tom

 

~click on~ >>>

 




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