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Filters causing really bad star halos, any advice?

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#1 stefannebula

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Posted 22 May 2020 - 11:38 PM

Hello, 

 

I am experiencing really nasty halos around some stars that I'm sure is coming from my narrowband filters. 

These halos are noticeable in single subs, and are very pronounced when stacked. It's happening for stars that aren't even that bright!

Is this to be expected with the filters that I'm using or is there something that I can optimize to reduce these? 

 

Any advice appreciated... 

 

Equipment

SharpStar 150HNT (F2.8, 420mm focal length hyperbolic newtonian)

Optolong 6.5nm Ha, Oiii and Sii filters

ZWO ASI183MM-Pro

 

The following is an Oiii master stack of 50*300s subframes (gain 100, offset 10, -20C)

 

[ ]

 

FULL IMAGE:

3ZgQN5m.jpg



#2 stefannebula

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Posted 22 May 2020 - 11:42 PM

I'll add that this is an image of NGC6357, and the brightest star in the image (HD 157486) is only Magnitude 6.17



#3 SoDaKAstroNut

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Posted 23 May 2020 - 04:51 PM

Those are some unusual refraction spikes...never seen dashed ones.



#4 Der_Pit

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Posted 23 May 2020 - 05:16 PM

Are those mounted or unmounted filters?  If unmounted, have a try at reversing them.  Many filters have AR coating only on one side, and that side has to face the sensor....


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#5 stefannebula

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Posted 23 May 2020 - 08:49 PM

Those are some unusual refraction spikes...never seen dashed ones.

I'm no expert but I believe this is to be expected with a monochromatic filter. As I understand, the light diffracts into a spectrum and because the filter is monochromatic it only selects for only that color (blue in this case). When I combine the narrow band filters into a color image you can start seeing the rainbow. 

 

rQzJU8x.jpg

 

 

It may be especially pronounced in my case because my secondary spider veins are very thick (2.5 mm) and I think that geometry has an affect on the amount of diffraction. Again, I'm no expert so I may be very wrong on that :p 


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#6 stefannebula

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Posted 23 May 2020 - 08:50 PM

Are those mounted or unmounted filters?  If unmounted, have a try at reversing them.  Many filters have AR coating only on one side, and that side has to face the sensor....

Thanks for the suggestion. My filters are unmounted, I inserted them the way the manufacturer specified but I will try reversing them just in case.

Thanks



#7 PhotonHunter1

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Posted 23 May 2020 - 09:02 PM

My current ASI camera and ASI filters create some nasty halos. Here a link to my latest image and the lovely multiple halos created by Alnitak. https://www.cloudyni...ad-and-friends/

 

While a new set of filters will solve some of my problem, the clear lens in front of my sensor can also be a contributing factor. Not sure but it may be a factor for you as well??



#8 stefannebula

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Posted 23 May 2020 - 09:08 PM

My current ASI camera and ASI filters create some nasty halos. Here a link to my latest image and the lovely multiple halos created by Alnitak. https://www.cloudyni...ad-and-friends/

 

While a new set of filters will solve some of my problem, the clear lens in front of my sensor can also be a contributing factor. Not sure but it may be a factor for you as well??

Thanks for sharing, and yeah looks similar, I've heard that the old ZWO filters are re-branded optolong filters (may be incorrect) so it may just be an issue with these filters. Looks like there is some microlense diffraction around Alnitak as well, which shouldn't be an issue in my case as I'm using an ASI183 not ASI1600. 

Love your image though, so much signal! 




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