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Are my filters causing these reflections?

astrophotography CMOS dso imaging refractor
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#1 PhotonHunter1

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Posted 25 November 2017 - 04:02 PM

Below are two screen shots of IC434 I took the other night. Equipment is my ES 102 APO Triplet, my ASI1600mm-c with the EFW 7 and a Baader VariLock. Images shown are with the Ha and Green filters, 200/50 gain/offset, -20, 120 seconds and 60 seconds respectively. The larger circle also appear in the R and B channels (60s each) as well. I thought is was dew related but there was no dew whatsoever on the refractor. The forecast is for clear skies the next three nights and I'd love to resolve this issue so I can take advantage of the clear skies and get more time on IC434. Any suggestions what is causing these artifacts? Thanks in advance.

Attached Thumbnails

  • IC434 Ha 120s.jpg
  • IC434 G 60s.jpg


#2 Tapio

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Posted 25 November 2017 - 04:27 PM

Filters yes.
Some ($$) are better dealing with reflections than others but brighter stars are always challenge.

#3 PhotonHunter1

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Posted 25 November 2017 - 04:31 PM

Filters yes.
Some ($$) are better dealing with reflections than others but brighter stars are always challenge.

Thanks Tapio. Will the reflections be removed during calibration and integration with darks, flats and flat dark?



#4 scopenitout

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Posted 25 November 2017 - 05:01 PM

You don't mention the brand.
ZWO or Optolong by any chance?

#5 Salacious B Crumb

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Posted 25 November 2017 - 05:39 PM

My ZWO's do. Especially the OIII and SII ones. Would also like to know what's the best way to remove them during the post processing...

 

- Sal

 

Helo's.JPG



#6 PhotonHunter1

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Posted 25 November 2017 - 06:35 PM

You don't mention the brand.
ZWO or Optolong by any chance?

ZWO filters. 



#7 Tapio

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Posted 25 November 2017 - 09:35 PM


Filters yes.
Some ($$) are better dealing with reflections than others but brighter stars are always challenge.

Thanks Tapio. Will the reflections be removed during calibration and integration with darks, flats and flat dark?

No, calibration files will not eliminate those reflections.

#8 cfosterstars

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Posted 26 November 2017 - 09:38 AM

I started a thread about filters - I kind of regret it since it seems to be a sore subject for some - to discuss what you get for your money with more expensive filters:

 

https://www.cloudyni...ters-seriously/

 

Although I have no direct experience with Astrodon or other more expensive filters myself - I have ZWO 36mm LRGB and NB - many others responded that reflections and flair reduction is one advantage of more expensive filters.



#9 scopenitout

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Posted 26 November 2017 - 11:25 AM

I asked about the brand because there seems to be more problems with certain brands. Mostly those that have become popular due to pricing lower than the long-established brands.

If you cruise around Astrobin images and call up certain cameras and certain filter brands, you start to see a pattern of reflection artifacts.

#10 PhotonHunter1

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Posted 26 November 2017 - 08:20 PM

I started a thread about filters - I kind of regret it since it seems to be a sore subject for some - to discuss what you get for your money with more expensive filters:

 

https://www.cloudyni...ters-seriously/

 

Although I have no direct experience with Astrodon or other more expensive filters myself - I have ZWO 36mm LRGB and NB - many others responded that reflections and flair reduction is one advantage of more expensive filters.

I had read that thread when it was posted - good stuff. Guess I'll deal with the artifacts at this time as there are other things on my wish list to purchase at this time.



#11 PhotonHunter1

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Posted 26 November 2017 - 08:21 PM

+1 to process tips to remove the halos. Really appreciate any tips or steps. Thanks!



#12 pfile

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Posted 26 November 2017 - 10:59 PM

in pixinsight there is a script called StarHaloReducer but it is a real bear to use...

 

sometimes if you have a huge halo that's just one color, you can use ColorMask to make a mask and then paint out everything but the big halo, then use that mask to decrease the intensity of the halo using Curves thru the mask.

 

rob



#13 HillTop

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Posted 27 November 2017 - 10:30 AM

I'm finding Alnitak to be a real pain doing LRGB or NB.  Only time I've missed the old DSLR.  The halos differ substantially between filters (ZWO) - nasty.



#14 PhotonHunter1

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Posted 27 November 2017 - 10:48 AM

I'm finding Alnitak to be a real pain doing LRGB or NB.  Only time I've missed the old DSLR.  The halos differ substantially between filters (ZWO) - nasty.

Funny you mention this - I was thinking the exact same thing and strongly considering imaging this object with my modified T3i and astromnik Ha filter. 



#15 SandyHouTex

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Posted 27 November 2017 - 11:22 AM

I started a thread about filters - I kind of regret it since it seems to be a sore subject for some - to discuss what you get for your money with more expensive filters:

 

https://www.cloudyni...ters-seriously/

 

Although I have no direct experience with Astrodon or other more expensive filters myself - I have ZWO 36mm LRGB and NB - many others responded that reflections and flair reduction is one advantage of more expensive filters.

Except that in this thread there is a post which shows reflections with the Astrodons.  It's post #25.  There are reflections from Astrodons and Baaders, but non, or minimal with Astronomik.


Edited by SandyHouTex, 27 November 2017 - 11:24 AM.


#16 cfosterstars

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Posted 27 November 2017 - 03:53 PM

 

I started a thread about filters - I kind of regret it since it seems to be a sore subject for some - to discuss what you get for your money with more expensive filters:

 

https://www.cloudyni...ters-seriously/

 

Although I have no direct experience with Astrodon or other more expensive filters myself - I have ZWO 36mm LRGB and NB - many others responded that reflections and flair reduction is one advantage of more expensive filters.

Except that in this thread there is a post which shows reflections with the Astrodons.  It's post #25.  There are reflections from Astrodons and Baaders, but non, or minimal with Astronomik.

 

You are correct. I was just really providing the link to the thread so that the OP could get a feel for the subject and all the opinions. For me, I am still having a big problem with my ZWO 36mm NB for flat calibration issues. I am basically getting horrible results and have a lot of useless data. The LRGB filters have not had an issue to this point although I have not tried Alnitak yet. I suspect that they will also show halos. Right now halos are the least of my issues. I will be doing a longer post will all the flat comparisons and the NB data to show the problems, but I am basically out of ideas on how to fix these artifacts. I cant get rid of them with PixInsight DBE for all the effort I have put in. 



#17 Jared

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Posted 27 November 2017 - 05:53 PM

Below are two screen shots of IC434 I took the other night. Equipment is my ES 102 APO Triplet, my ASI1600mm-c with the EFW 7 and a Baader VariLock. Images shown are with the Ha and Green filters, 200/50 gain/offset, -20, 120 seconds and 60 seconds respectively. The larger circle also appear in the R and B channels (60s each) as well. I thought is was dew related but there was no dew whatsoever on the refractor. The forecast is for clear skies the next three nights and I'd love to resolve this issue so I can take advantage of the clear skies and get more time on IC434. Any suggestions what is causing these artifacts? Thanks in advance.

Filters are at least partially what's causing the reflections, but maybe not entirely.  You may notice that you actually have three halos around Alnitak of varying diameters.  The outermost, largest halo is almost certainly the filter, but particularly in the H-alpha image you can see two halos farther in (smaller diameter).  

 

The outer halo appears to be about 3.7mm across (just an approximation from looking at the pictures you posted).  Since your scope is f/7, that means the distance between the CMOS chip and the surface creating the outer halo is roughly 13mm.  Given the back focus distance of your camera at 6.5mm, and the thickness of the filter wheel at around 20mm, 13mm is almost perfectly in the center of the filter wheel, perhaps offset a bit towards the camera (though it's not like my measurements are precise).  Clearly the large halo is coming from one of the two surfaces of the filters.

 

What about the middle halo?  Its diameter of something like 0.7mm suggests it is from a surface roughly 2.5mm from the CMOS chip.  Clearly inside the camera, and likely caused by the cover glass for the CMOS chamber.  Hard to be certain since it could be from something closer in bouncing more than once, but a single reflection off the cover glass seems most likely.  Certainly, it's form a source inside the camera itself, so changing filter brands won't help with this middle halo.  

 

The final, inner most halo appears to have a diameter of about 0.3 or 0.4mm which suggests it is from a surface roughly 1.2mm from the chip.  Maybe related to micro lenses?  Hard to know for certain, but, again, definitely inside the camera.

 

So, the large halo is potentially something you could do something about by changing filter brands.  The inner two halos are almost certainly within the camera itself, so a change in filters won't help with those.



#18 PhotonHunter1

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Posted 27 November 2017 - 06:02 PM

 

Below are two screen shots of IC434 I took the other night. Equipment is my ES 102 APO Triplet, my ASI1600mm-c with the EFW 7 and a Baader VariLock. Images shown are with the Ha and Green filters, 200/50 gain/offset, -20, 120 seconds and 60 seconds respectively. The larger circle also appear in the R and B channels (60s each) as well. I thought is was dew related but there was no dew whatsoever on the refractor. The forecast is for clear skies the next three nights and I'd love to resolve this issue so I can take advantage of the clear skies and get more time on IC434. Any suggestions what is causing these artifacts? Thanks in advance.

Filters are at least partially what's causing the reflections, but maybe not entirely.  You may notice that you actually have three halos around Alnitak of varying diameters.  The outermost, largest halo is almost certainly the filter, but particularly in the H-alpha image you can see two halos farther in (smaller diameter).  

 

The outer halo appears to be about 3.7mm across (just an approximation from looking at the pictures you posted).  Since your scope is f/7, that means the distance between the CMOS chip and the surface creating the outer halo is roughly 13mm.  Given the back focus distance of your camera at 6.5mm, and the thickness of the filter wheel at around 20mm, 13mm is almost perfectly in the center of the filter wheel, perhaps offset a bit towards the camera (though it's not like my measurements are precise).  Clearly the large halo is coming from one of the two surfaces of the filters.

 

What about the middle halo?  Its diameter of something like 0.7mm suggests it is from a surface roughly 2.5mm from the CMOS chip.  Clearly inside the camera, and likely caused by the cover glass for the CMOS chamber.  Hard to be certain since it could be from something closer in bouncing more than once, but a single reflection off the cover glass seems most likely.  Certainly, it's form a source inside the camera itself, so changing filter brands won't help with this middle halo.  

 

The final, inner most halo appears to have a diameter of about 0.3 or 0.4mm which suggests it is from a surface roughly 1.2mm from the chip.  Maybe related to micro lenses?  Hard to know for certain, but, again, definitely inside the camera.

 

So, the large halo is potentially something you could do something about by changing filter brands.  The inner two halos are almost certainly within the camera itself, so a change in filters won't help with those.

 

Thanks for the detailed breakdown Jared - it’s extremely helpful!



#19 freestar8n

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Posted 27 November 2017 - 07:10 PM

The large halos are likely due to some large spacing between separate elements but the small ones could be a double bounce within a filter or window anywhere and the spacing doesn’t play a role. Only the thickness, index of refraction and f number matter.

T = h F n / 2

Where h is halo diameter F is fnum and n is index of refraction or around 1.5.

So for f/7 and 0.7mm it’s around 3mm thick. And it could be anywhere. And changing its distance from the sensor won’t matter.

Frank

#20 PhotonHunter1

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Posted 27 November 2017 - 11:48 PM

The large halos are likely due to some large spacing between separate elements but the small ones could be a double bounce within a filter or window anywhere and the spacing doesn’t play a role. Only the thickness, index of refraction and f number matter.

T = h F n / 2

Where h is halo diameter F is fnum and n is index of refraction or around 1.5.

So for f/7 and 0.7mm it’s around 3mm thick. And it could be anywhere. And changing its distance from the sensor won’t matter.

Frank

 

Thanks for the info Frank! It appears there’s not too much I can do to correct this - at least within my current filter setup. 



#21 SandyHouTex

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Posted 28 November 2017 - 10:56 AM

 

 

I started a thread about filters - I kind of regret it since it seems to be a sore subject for some - to discuss what you get for your money with more expensive filters:

 

https://www.cloudyni...ters-seriously/

 

Although I have no direct experience with Astrodon or other more expensive filters myself - I have ZWO 36mm LRGB and NB - many others responded that reflections and flair reduction is one advantage of more expensive filters.

Except that in this thread there is a post which shows reflections with the Astrodons.  It's post #25.  There are reflections from Astrodons and Baaders, but non, or minimal with Astronomik.

 

You are correct. I was just really providing the link to the thread so that the OP could get a feel for the subject and all the opinions. For me, I am still having a big problem with my ZWO 36mm NB for flat calibration issues. I am basically getting horrible results and have a lot of useless data. The LRGB filters have not had an issue to this point although I have not tried Alnitak yet. I suspect that they will also show halos. Right now halos are the least of my issues. I will be doing a longer post will all the flat comparisons and the NB data to show the problems, but I am basically out of ideas on how to fix these artifacts. I cant get rid of them with PixInsight DBE for all the effort I have put in. 

 

I'll be interested in what you find out.



#22 WesC

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Posted 28 November 2017 - 01:56 PM

I think that higher quality filters can only somewhat reduce, but not eliminate halos around extremely bright stars like Alnitak. I have 31mm Astrodons and I still have slight halos, but they are far less substantial than others I have seen.

 

get.jpg?insecure

 

I suspect the cover glass of the sensor plays a large role in this as well. And there are other factors... CCD sensor microlenses, exposure time blowing out the stars (particularly in narrowband), seeing conditions, especially humidity and particulates in the atmosphere, coating quality of the optics, etc...



#23 cfosterstars

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Posted 28 November 2017 - 01:59 PM

I think that higher quality filters can only somewhat reduce, but not eliminate halos around extremely bright stars like Alnitak. I have 31mm Astrodons and I still have slight halos, but they are far less substantial than others I have seen.

 

get.jpg?insecure

 

I suspect the cover glass of the sensor plays a large role in this as well. And there are other factors... CCD sensor microlenses, exposure time blowing out the stars (particularly in narrowband), seeing conditions, especially humidity and particulates in the atmosphere, coating quality of the optics, etc...

Beautiful image. FWIK, the sensors used in ZWO camera do not have AR on the sensor cover glass. They do have AR on the camera window that is about 5-6mm from the sensor.



#24 PhotonHunter1

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Posted 28 November 2017 - 11:30 PM

 

I think that higher quality filters can only somewhat reduce, but not eliminate halos around extremely bright stars like Alnitak. I have 31mm Astrodons and I still have slight halos, but they are far less substantial than others I have seen.

 

get.jpg?insecure

 

I suspect the cover glass of the sensor plays a large role in this as well. And there are other factors... CCD sensor microlenses, exposure time blowing out the stars (particularly in narrowband), seeing conditions, especially humidity and particulates in the atmosphere, coating quality of the optics, etc...

Beautiful image. FWIK, the sensors used in ZWO camera do not have AR on the sensor cover glass. They do have AR on the camera window that is about 5-6mm from the sensor.

 

WesC, No AR on the senser glass - that’s my understanding as well.



#25 CarlosUriarte

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Posted 29 November 2017 - 05:37 AM

In my case, the halo coming from the bright stars hurts me a lot.
So, I passed 31mm astrodon and the result with VISAC at f6.8 is promising

B33_V2-_Recuperado.png




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