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Strange pattern in the background

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#1 Astro_johnny

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Posted 21 May 2024 - 02:10 AM

Good morning everyone, my name is Giovanni and I have been doing astrophotography for a few years now.

I wanted to ask for help from those who are more experienced than me!

I live in Rome, Italy, and often go in search of clean and dark skies to take some photos of the sky.

My most common setup consists of an EQ6R-pro, an 80/480 OWL, an askar300, and a 115/800 triplet with an ASI294MC pro camera and optolong l-pro or l-ultimate filters.

Well, when I photograph in broadband, I often get a pattern of typically green patches on the background sky that are very annoying to remove. Can you tell me what I'm doing wrong or why they appear?

My processing workflow is quite standard: I do all the calibration frames and use PixInsight with gradient removal, color balancing, deconvolution, noise reduction, stretching, and post-processing.

 

reference: https://storage.goog...91-original.png


Edited by Astro_johnny, 21 May 2024 - 02:11 AM.

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#2 Chrisofweden

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Posted 21 May 2024 - 02:33 AM

Hi!

Looking at the image you linked, I think it looks OK. A little too “flat” for my taste, with the very dark background which is perhaps what you’re “forced” to do to hide the imperfections you describe?

That said, I note that you image with the 294MC Pro? I also own one these cameras and whilst I do like it, it can be finicky regarding calibration and in particular with Flats.
You may already be aware that the 294MC does not like short flats? Anything below about 2 seconds exposure and you risk getting into issues.
You need a light source for taking flats that allows you to expose longer than one normally would. That means it needs to be pretty dim…
I ended up buying a Flat Panel from Pegasus Astro - it’s adjustable and I could dim it enough to allow me to capture Flats at around 2,5 seconds. Doing this made the calibration process more reliable and I was able to deal with the “blotchy” background that I previously had to tackle.
My blotches were more red than green, but at the end of the day this is easy to try and if it helps then all good…

Hope you can work it out!

/Chrjs

Edited by Chrisofweden, 21 May 2024 - 02:36 AM.

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#3 bignerdguy

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Posted 21 May 2024 - 02:44 AM

Looks to me like you picked up a lot of nebulosity in that image.  Might simply be that.  Not sure otherwise.  Astrometry.net doesn't show any nebulas in that area so it might be molecular dust clouds arounds the three galaxies.  Nice image!



#4 astropgr

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Posted 21 May 2024 - 02:58 AM

Your flat frames arent calibrating properly orrr you dont have deep enough flats...



#5 Astro_johnny

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Posted 21 May 2024 - 03:47 AM

Thank you everyone! I'll try to make better flat smile.gif



#6 JF1960

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Posted 21 May 2024 - 12:38 PM

This could also just be normal background noise that you over-stretched.  Your galaxies look amazing.  Do you separate the stars and galaxies before stretching?



#7 Astro_johnny

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Posted 21 May 2024 - 03:05 PM

Thank you! Yes, I always separate stars from background after stretch..


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