C/2020 F3 (NEOWISE): me too

I really wanted to go watching the comet, as could not watch the previous comets. I took this opportunity to try my small astro for the first time. Unfortunately here in the Caribbean, the atmospheric conditions are not ideal for astrophotography, we often have air pollution from sahara dust, high himidity and clouds.
Nevertheless, I had the chance to take some pictures of C/2020 F3, between clouds.
For this shot, I combined 6 images (ISO 800, 1x 60 sec., 5x 30 sec., Fujifilm X-T2, Samyang 85mm f/1.4 @ f/2.0) in Siril. I did the darkframe subtraction in ART and combined TIFFs in Siril because when I do darkframe subtraction in Siril I get a strong green cast (as if the green channel was multiplied by a factor of 2… any idea why?). Then the result was further processed in ART.
Not as beautiful as other images here, but anyways here’s my image:


Strong green cast is totally normal before color calibration.

Doesn’t the Remove green cast option work, after stacking?
I’ve learned that from your tutorial… :stuck_out_tongue:
Anyway, nice shot! The clouds add something to the composition.

Oh no. Never right after the staking!!! NEVER. You must apply a color calibration before.

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What’s the reason? I tried once the “Remove green cast” and ended up with an image that was not green, but also had lost most other color. Could have been that I applied it after stacking? How do you apply color calibration to all pictures in a sequence?

(In the end I solved the issue by using the normal color calibration, but again on the stacked image)

The remove green noise is destructive. You will loose color information.
Afher stacking your image is green and that is OK. You can retrieve color with color calibration tool

I agree, although in general it looked OK, once I checked carefully some parts it was clear that some information was lost.

Ah, OK. I understood you were saying to do green correction and color calibration before stacking. But you meant one should stack, color calibrate, and only then (if necessary), green noise removal. I got it right?

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Yes, once the image has been stretched.

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Wow, thanks all. I am guilty of performing Remove Green cast too early in the process… Thanks for the feedback

Wen I saw that strong green color after applying darks subtraction, I tried green noise removal right next and indeed it removed almost all color information, while color calibration didn’t.

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Here’s a new version, this time I used the raw files in Siril, and proceeded with a more careful Color calibration. Also for stacking I tried with Sum stacking instead of Averaging: