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Specular Reflections

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#1 Umasscrew39

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Posted 28 October 2020 - 03:46 PM

This was a new one for me, specular reflections, i.e., stray light from a bright star, that is trying to ruin my image (lower left corner). This is just a few calibrated frames of the Pacman nebula which I took with the new ZWO ASI294MM Pro using a chroma Ha filter on an 80 mm apo triple refractor (300s subs). I used darks which got rid of the amp glow, as well as dark flats and flats. At first I thought this was an error on my part but realized it was probably stray light from Schedar (mag 2.2). Good news is that it is not impinging upon the nebula itself but bad news it is nearly impossible to remove. I see my options as cropping it or perhaps remove the stars and use clone stamp and then put the stars back. It was suggested that perhaps rotating the camera might help.

 

I'm curious if others have had this problem to deal with and what did you try.

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#2 Dan Crowson

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Posted 28 October 2020 - 03:59 PM

I've seen this one quite a bit with my refractor. There didn't seem to be much I could do other than trying to reframe or try it on the opposite side of the meridian.

Dan


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#3 vakulenko_sergiy

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Posted 28 October 2020 - 04:03 PM

I had similar nasty reflections when I point my ED80 scope to the Pelican Nebula.

 

I think Starnet and Clone stamp can easily fix it once nebula is not directly affected.


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#4 Stelios

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Posted 28 October 2020 - 08:26 PM

It can be at least partially removed with very aggressive DBE. Large boxes saturating the region. Adam Block has the technique in one of his videos. 


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#5 Umasscrew39

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Posted 29 October 2020 - 05:37 AM

Thanks for the input.  I got the same results from both sides of the meridian and when I tried the default DBE the other night (I forgot to mention that in my initial post) it had no real effect.  However, Adam got some removal of his reflection with his aggressive settings as you noted. So, I'll try that as well. If that has no effect, looks like Starnet and clone stamp might be worth a try or finally cropping.

 

------------

 

Update from Adam Block who responded to my question:

 

Use GAME (script) to create a small elliptical mask in that area.
Create another range or star mask that includes everything that is "real" except the background.
Subtract this from the elliptical mask. Now you have a white elliptical mask with black stars and things (protected).
Apply MMT of the Residual layer to this area with the mask in place to get the right local sky brightness.
Finally add noise and match the surrounding sky.

The nice thing about the above is that there is no cloning. Real objects are kept (based on threshold brightness).

(I demonstrate this technique in my tutorials.) 



#6 ngc1535

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Posted 29 October 2020 - 02:32 PM

It can be at least partially removed with very aggressive DBE. Large boxes saturating the region. Adam Block has the technique in one of his videos. 

Indeed..this is another solutions... albeit a brute-force-hammer solution. lol

-adam




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