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Narrowband filter weird results

Astro-Tech AT72EDII Filters Acquisition Narrowband Deep Sky
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Francois Donnet avatar
Francois Donnet avatar
Hi Everyone. So I had been testing a SVBONY 220 narrowband filter using an AT72edii and did also a testo with FMA180. I get very weird gradients on both lights and flats. It tends to disappear once stacking is done but nevertheless, I am clue less what could be the reason. Reflection maybe or something else? I use the 1.25" in front of the camera sensor as indicated by zwo. I also tried in from of the 1.25" tread for the FMA180 but get the same issues. UCH filter is better but still get this weird red and green things. If anyone have a clue to help? Filter is new and I am considering to contact SVBONY. I add one unprocessed 300s light of the rosette nebula here (bortle 8, low in the sky but still above 20degrees. Thanks
andrea tasselli avatar
andrea tasselli avatar
I'd suggest you process the images and if there are weird gradients after the lights are stacked then consider whether to return it to SVBONY. By the way, 20 degrees is pretty low in my book.
Chase Newtson avatar
Chase Newtson avatar
As long as they are calibrating out, you should be good.  My ASI294MC Pro gets even worse but similar gradients when I use my L-Ultimate.  As long as I take properly exposed flats per session, they calibrate out and I have none of that gradient in my images.  For my 294, I hear it is the nature of the sensor with narrowband filters, and not the filter itself.
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Joel Lee avatar
Joel Lee avatar
I have the same filter and I also get the same weird gradients but seemingly only on my flats. These average out later on in the master flat however. The following are all ASIFits Viewer auto stretch.

Two different single flats


A Light frame


The lights getting weird gradients could be related to your target being only 20 degrees above the horizon. I sometimes get terrible gradients even up to 40 degrees above.

Also if someone knows how to resize these uploaded images on the messages please let me know how, I'm sorry they are so large.
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Francois Donnet avatar
Francois Donnet avatar
Hi everyone, 

I agree it is very very low but I wanted to test the filter and we didn't have good clear sky for a while. So in the end it seems to be quite normal to have that and indeed it goes away when stacked. 
You can save the asifits as jpeg in asi studio this is how I posted them here. Thanks again for the help!