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Cause of this artifact and any ideas for mitigating it during acquisition or processing.

Steffen Hirtle GraXpert Processing Deep Sky Artifacts Emission Nebula
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John Stephens avatar
John Stephens avatar
Can anyone explain the pattern of color I have in the background of the Rosette Nebula and a good method for dealing with it?
The attached image is 12hrs in a Bortle 4/5 using a Canon R5 200mm @ F3.5 and has been calibrated with Bias, Darks, and Flats then Processing: Graxpert/Subtract, BlurX/Correct Only, SPCC, BlurX, NoiseX, StarX. The attached image just has the initial STF stretch applied after SPCC.

I did manage to process this earlier in my integration 8.5hrs with fair results but was hoping adding more data would help separate the pattern from the target but doesn't seem to be the case.
Processed Rosette 8.5hrs
Engaging
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
What does it looke like pre/post flat calibration?
Die Launische Diva avatar
Die Launische Diva avatar
How confident are you on your flat-taking procedure? Keep in mind that the consequences of poor flats eventually will show in long integrations. And also keep in mind that modern DSLR/Mirrorless cameras are introducing artifacts on their own, see Mark Shelley's article.
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andrea tasselli avatar
andrea tasselli avatar
Avoid using unfiltered cameras, that's my best advice with widefield images under less than pristine skies.
Well Written
John Stephens avatar
John Stephens avatar
What does it looke like pre/post flat calibration?

That's a very good question, and forgot that is one of the intermediate files PI leaves behind but I just deleted the uncalibrated files literally a few minutes before checking for replies here. Stacking files from a 45mp camera eats up storage this folder was nearly 600Gb but I will que the stack up again tonight and post the results tomorrow.
John Stephens avatar
John Stephens avatar
Die Launische Diva:
How confident are you on your flat-taking procedure? Keep in mind that the consequences of poor flats eventually will show in long integrations. And also keep in mind that modern DSLR/Mirrorless cameras are introducing artifacts on their own, see Mark Shelley's article.

Reasonably confident, I have run into the flats changing brightness when using the auto flat function in the ASIAIR that I cannot explain. I have tried t-shirt and ipad screen on a white background and t-shirt and sky and have observed the same behavior on both methods. I have blinked the flats though and removed the copies that had significant changes in exposure. I have looked at that article and there is nothing listed for the R5. 


andrea tasselli:
Avoid using unfiltered cameras, that's my best advice with widefield images under less than pristine skies.

I have thought about adding a filter, but haven't seen much info on how much impact it would have in a bortle 4/5 sky. So not sure if any improvements would outweigh the potential issues with halos or other artifacts that seem to come with light pollution filters.
andrea tasselli avatar
andrea tasselli avatar
John Stephens:
I have thought about adding a filter, but haven't seen much info on how much impact it would have in a bortle 4/5 sky. So not sure if any improvements would outweigh the potential issues with halos or other artifacts that seem to come with light pollution filters.


A moderately wide NB filter such as the Optolong L-enHance would drastically reduce your background (and relative noise) if you are shooting emission nebulae. There might or might not be issues with haloes on some bright stars but those can be dealt with and certainly is going to be much better than what I see here. Obviously acquiring a cooled astro-camera is going to improve things considerably by appreciate it isn't cheap.
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