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Astrodon 3nm O3 Halos

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15 replies to this topic

#1 aarshad81

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Posted 29 November 2021 - 12:20 PM

I have a problem with some halo when taking picture of the Alnitak/horsehead/flame region. As you can see in the picture below. The filter is a 36mm unmounted filter with blackened sides all over. I dont see any damages or issues with the filter, but was wondering if this was normal or if not what i should look into

 

I am using it with an ASI1600MM pro / AT115EDT with the new Ver2 0.8 Reducer-Flattener and ZWO filter wheel.

 

The image below is at 600s and gain of 139 from bortle 7

Attached Thumbnails

  • O3_cropped.jpg

Edited by aarshad81, 29 November 2021 - 12:21 PM.


#2 AgilityGuy

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Posted 29 November 2021 - 12:28 PM

Looks like a microlens issue common to the 1600 camera.  Has nothing to do with the filter.  I use a 50mm unmounted Astrodon OIII filter with an ASI6200mm and there's no hint of halos. 



#3 aarshad81

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Posted 29 November 2021 - 01:01 PM

Its that faint disc 6-10 times the diameter of the star, it becomes more pronounced when stacking, i think the microlensing is the smaller pattern correct

 

the good thing is that i see it only on this star and only with this filter


Edited by aarshad81, 29 November 2021 - 01:49 PM.

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#4 aarshad81

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Posted 29 November 2021 - 02:17 PM

Ok I measured the reflection distance possibly from the CCD chip approx. And looks to be 26mm which is around where the astrodon O3 filter is. 

 

I am wondering why its causing that, from what i heard there is no correct orientation, i could try to flip the filter 

 

Sorry wasnt clear, but i am using CCD > ZWO FilterWheel > ZWO OAG > Reducer/Flattener > Focus/Scope

Attached Thumbnails

  • distance.JPG

Edited by aarshad81, 29 November 2021 - 02:22 PM.


#5 andysea

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Posted 30 November 2021 - 02:19 AM

I noticed a halo once with my 3nm Astrodon when shooting Gamma Cass. This is the link to the image.
https://flic.kr/p/zvK7Pd

#6 Endymion

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Posted 30 November 2021 - 03:51 AM

The filter would be at around 16 mm wouldn't it?   6.5mm for the sensor to camera boundary plus about 1/2 the 20mm thickness of the filter wheel?   

 

Is it possible that this is a reflection from the filter to the reducer lens?   10mm for the filter wheel to the OAG plus 16.5mm for the OAG then the lens of the reducer?



#7 Tayson82

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Posted 30 November 2021 - 05:15 AM

Halo is probably from Yours corrector.

Try to remove corrector and check it.

 

Maybe flip filter to another side, but I suppose this not help.



#8 sharkmelley

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Posted 30 November 2021 - 08:01 AM

Remember that the calculated value of 26mm is the total extra distance travelled by the reflected ray.  This will be twice the physical distance between the 2 reflective surfaces involved i.e. the physical distance between the reflective surfaces is 13mm.

 

Mark



#9 Endymion

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Posted 30 November 2021 - 02:52 PM

Mark,
I haven’t used that tool but the text on his screen capture suggests strongly that it calculates the distance between the reflecting elements and not the total light travel distance.

#10 aarshad81

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Posted 30 November 2021 - 03:36 PM

Ok thanks so far

 

I will measure all the components exact and try to troubleshoot one item at the time. 

 

1. Measure and look at most likely causes

2. Try Flipping Filter

3. Removing Reducer

4. Could still be multiple factors contributing to it but very curious if i can isolate it and report



#11 sharkmelley

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Posted 30 November 2021 - 06:36 PM

Mark,
I haven’t used that tool but the text on his screen capture suggests strongly that it calculates the distance between the reflecting elements and not the total light travel distance.

Yes, the description is potentially confusing but the equation (D x P x FR / 1000) makes it obvious that it is the total extra distance travelled by the reflected ray that is being calculated.

 

The CCDWare dust donut calculator gives the same distance of 26mm and it's pretty obvious that the dust donut calculator is calculating the total extra distance:

 

DustDonutCalculator.jpg



#12 aarshad81

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Posted 30 November 2021 - 07:27 PM

Thanks thats helpfull i will go outside soon to measure the setup up. I also did not know that



#13 aarshad81

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Posted 04 December 2021 - 10:34 PM

13mm is very small, looking at my measurements i cant find where it would be. I am thiningk of also trying to remove the OAG for now, although i am not sure if that would cause this. 

 

I only see it in O3 band. below an integrated picture of 2 hours approx, showing also Halos on other stars. The lower left halo is little offset as well from the star

 

For now I also flipped the filter just in case, but there is clouds everywhere so cannot trial that. The distance between filter and ccd chip is more than the calculated 13mm anyhow.

Attached Thumbnails

  • o3 halos.JPG
  • thumbnail_IMG_4701.jpg

Edited by aarshad81, 04 December 2021 - 10:37 PM.


#14 sharkmelley

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Posted 05 December 2021 - 02:09 AM

The distance between filter and ccd chip is more than the calculated 13mm anyhow.

What is your estimate of the distance between filter and sensor?  Surely it's not much more than 13mm.

 

Mark



#15 rockstarbill

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Posted 05 December 2021 - 02:15 AM

What is your estimate of the distance between filter and sensor? Surely it's not much more than 13mm.


Mark

I don't think it is either. The backfocus of the 1600 is 6.5mm IIRC and threaded directly into the wheel the filters would likely be 13mm.

Edited by rockstarbill, 05 December 2021 - 02:17 AM.

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#16 sharkmelley

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Posted 05 December 2021 - 03:09 AM

I've seen the following claim for a ZWO electronic filter wheel that accepts 36mm unmounted filters (my highlighting):

 

"The distance between the filter and sensor is around 10-12mm when you connect the ASI1600 to this EFW, so a 36mm filter won’t have vignetting with a scope with down to about f/1.2 focal ratio"

 

This distance is actually less than 13mm, not more.  But it may not be the same filter wheel the OP is using.

 

Mark




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