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Reflection Artifacts in the ASI6200

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#451 sn2006gy

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Posted 30 September 2020 - 02:04 PM

Dithering only offsets the subs from each other, but the pattern (reflection) is still there, and will align with the star alignment process when stacking the subs. So you're right back at square one again.

I wonder if you could do some cheat, like an ROI frame around bright stars and then somehow used that to calibrate out aberrations... or instead of star focus do a field focus?

 

just thinking out loud.. you're right, it would be aligned but i guess some creativity could help clean it out besides the usual PI tricks



#452 Lead_Weight

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Posted 30 September 2020 - 02:07 PM

I was actually wondering if you could take Mark's equation that calculates the precise location of the reflections, and put that into PixelMath creating an artificial flat, that you could then use to subtract from the image, completely erasing the halos.


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#453 Peter in Reno

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Posted 30 September 2020 - 03:39 PM

I guess my question is, would dithering more subs help remove/reduce this pattern on integration?

If you are referring to FPN, then yes. FPN is not always "Fixed".

 

Peter 


Edited by Peter in Reno, 30 September 2020 - 03:43 PM.


#454 rockstarbill

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Posted 30 September 2020 - 10:06 PM

I wonder if you could do some cheat, like an ROI frame around bright stars and then somehow used that to calibrate out aberrations... or instead of star focus do a field focus?

 

just thinking out loud.. you're right, it would be aligned but i guess some creativity could help clean it out besides the usual PI tricks

Field focus I can test here in a moment, but I dont think it will have any effect at all. 

 

I think the lesson on Vega is, dont image Mag 0 stars. It wont end well. Alnitak is Mag 2 so would have less of a chance of causing the problem. I do think its fascinating that the TOA130 produced very prominent grid effects with the IMX455 while the KAF-16803 had to crank the exposure time up.

 

The per um^2 read noise of these cameras isnt that different:

  • FLI 16803 - 9 micron (81 micron squared) - 8e noise - 0.10e noise per micron
  • ASI 6200 -  3.76 micron (14.14 micron squared) - 1.6e noise (at 100 gain, bin 1x1) - 0.11e noise per micron

The QE is different, but I am not so sure that is enough to cause the discrepancy. The 16803 is much further away from the filters, which may be providing a dampening effect on the appearance of the grid pattern.


Edited by rockstarbill, 30 September 2020 - 10:07 PM.


#455 sharkmelley

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Posted 01 October 2020 - 02:54 AM

I was actually wondering if you could take Mark's equation that calculates the precise location of the reflections, and put that into PixelMath creating an artificial flat, that you could then use to subtract from the image, completely erasing the halos.

You just need to look at this earlier example in post #329 from Monkeybird747 to understand why that will never work:

 

gallery_279392_14518_1542511.png

 

We don't even understand why each reflection exhibits a gradient in brightness, let alone attempt to simulate it.

 

Mark


Edited by sharkmelley, 01 October 2020 - 06:00 AM.

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#456 Astrobarn_

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Posted 01 October 2020 - 06:26 AM

Recently received my 3nm Chroma set, will hopefully get it under the stars soon. Worth noting that all 3 NB filters (ha,oiii,SII) have mirrored coatings on both sides. No way to tell which way should be up.

#457 Lead_Weight

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Posted 01 October 2020 - 06:51 AM

Recently received my 3nm Chroma set, will hopefully get it under the stars soon. Worth noting that all 3 NB filters (ha,oiii,SII) have mirrored coatings on both sides. No way to tell which way should be up.

Look here.   https://www.cloudyni...2#entry10423297


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#458 Der_Pit

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Posted 01 October 2020 - 04:18 PM

The per um^2 read noise of these cameras isnt that different:

  • FLI 16803 - 9 micron (81 micron squared) - 8e noise - 0.10e noise per micron
  • ASI 6200 -  3.76 micron (14.14 micron squared) - 1.6e noise (at 100 gain, bin 1x1) - 0.11e noise per micron

The QE is different, but I am not so sure that is enough to cause the discrepancy. The 16803 is much further away from the filters, which may be providing a dampening effect on the appearance of the grid pattern.

 

 

We don't even understand why each reflection exhibits a gradient in brightness, let alone attempt to simulate it.

I wonder if that is just the pixel size.  After all, to create a diffraction pattern, the star image must illuminate the pixels/microlenses.  And the amplitude of such an interference would depend on the number of 'emitters' involved.  I could imagine that therefore larger pixels (at the same telescope, i.e., same star image size) create weaker patterns, and maybe the gradients are partially illuminated microlenses?


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