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What is the cause of banding on Ha solar images?

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#1 Averton

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Posted 23 January 2022 - 12:30 AM

As per our other thread of "The sun on 21/1/2022 from Melbourne Australia" a number of people suggested we should take mono images.

In fact, on the first light of the scope when we took the images we already posted we did in fact also take two monochrome videos using our only monochrome camera which is an ASI120MM Mini guide camera.

We didn't post any images because of quality issues that we thought we might be able to fix later.

However, we haven't been able to fix it and it appears as banding across the solar disk as per the images attached.

This camera works in all other respects and we have used it successfully in white light images with no banding issues.

Having done a bit of research it appears that folk have had banding issues with solar images but the causes suggested don't apply in this case.

1. The video was captured in raw 16 bit format

2. The gain was 0 and the exposure was 1.798 ms

3. The capture software was ASICap (there was a suggestion on one thread that FireCapture had caused banding and SharpCap did not)

 

The first file is just the stacked images from the video with no processing and looks exactly like what was on the computer screen at the time and was in the video captured.

The second file is just the sharpened version where the bands are still visible.

 

Any ideas??

 

Clare & Peter

Attached Thumbnails

  • 2022-01-21-0141_3-2022-01-21-0140_7-Sun_pipp_grad6_ap65_Drizzle30.jpg
  • 2022-01-21-0141_3-2022-01-21-0140_7-Sun_pipp_grad6_ap65_Drizzle30_20220123_144930_WSL2_0_WV10_10_10_269_503_662.jpg


#2 Tapio

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Posted 23 January 2022 - 01:49 AM

They are called Newtons rings and are common problem with Sun Ha imaging.

 

https://brierleyhill...tons-rings.html


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#3 Mikoka

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Posted 23 January 2022 - 10:26 AM

Hi Clare, hi Peter,

 

you can use an ADC (Atmospheric Dispersion Corrector) in the lightpath between the blockfilter and the Camera.

That will solve the problem. May be you have to turn the ADC untill the newton fringes vanish.

 

best regards  Michael


Edited by Mikoka, 23 January 2022 - 10:27 AM.

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#4 Tapio

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Posted 23 January 2022 - 11:27 AM

Hi Clare, hi Peter,

you can use an ADC (Atmospheric Dispersion Corrector) in the lightpath between the blockfilter and the Camera.
That will solve the problem. May be you have to turn the ADC untill the newton fringes vanish.

best regards Michael


That is the first time I read that ADC could remove Newton rings.
But yeah, why not. And it can be used for its original purpose too.
But trying flats or using tilt adapter might be cheaper solution.
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#5 Averton

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Posted 23 January 2022 - 10:32 PM

They are called Newtons rings and are common problem with Sun Ha imaging.

 

https://brierleyhill...tons-rings.html

Thanks for this, it explains the phenomenon very well.  It accounts for why two other cameras worked perfectly on the day but this one did not.

In this case the easiest thing is not to use this particular camera.



#6 Averton

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Posted 23 January 2022 - 10:33 PM

Hi Clare, hi Peter,

 

you can use an ADC (Atmospheric Dispersion Corrector) in the lightpath between the blockfilter and the Camera.

That will solve the problem. May be you have to turn the ADC untill the newton fringes vanish.

 

best regards  Michael

Thanks Michael.  Unfortunately we don't have an ADC but it is something that would be useful for our planetary imaging so maybe it is a consideration in the future.




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