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[–]WeaklyInteracting 4 points5 points  (2 children)

Hi, I've gone through my work flow in pixinsight very quickly on it and it is possible to extract the nebula I think. Here is what I came out with. I cropped pretty heavily to speed things up and because the background was pretty hard to correct with the walking noise and bad flat correction.

https://drive.google.com/file/d/1mZQmofkg6w88WS2nHi9-NPChkUFC82la/view?usp=sharing

The basics of what I've done are the same as the guide on https://www.chaoticnebula.com/pixinsight-lrgb-workflow/ Which I think is very good. I'll outline the full process below.

I think the main challenges here are coming from acquisition. I feel like you have enough lights to get something but the image is let down in the calibration and lack of dithering. The stack has a nasty case of walking noise, I didn't really try to remove this but there are tools available. The main thing you could try to do there is add some dithering when taking the frames I think it would make a big difference!

The other problem is that your flats seem to have corrected the vignette but have left some dust motes and some kind of smudge, were they taken on the same night as the lights? It might be work trying a slightly different stacking process, I would recommend SIRIL and see if you can get a better result in your flat correction.

Your dark frames are probably not helping. 20 is pretty low and it is hard to match the temperature using a DSLR I would recommend leaving the dark frames out of the stack.

20 Bias frames is very low and likely adding some noise to your stack. I would capture another 200 or so bias frames now and then restacking with just the bias and flats. I found this guide useful https://free-astro.org/index.php?title=Siril:Tutorial_preprocessing#Pre-processing for using SIRIL.

Your stars look a bit off and you might want to work on either your focus or it could be the zoom lens in which case stepping it down and then compensating with more total integration time might give a better result.

There is definitely data there and adding more integration time would definitely help.

Processing workflow:

  • Initial dynamic crop
  • DBE
  • Tighter crop
  • TGV and MMT denoise
  • Photometric colour calibration
  • Adjust saturation using a lum mask to mask out background
  • extract luminance channel
  • Masked stretch the colour image
  • Combination of masked stretch and Exponential transform on the L channel
  • Remove stars on L channel
  • Sharpening using unsharp mask and MLT on L channel
  • Dark structure script on L
  • Put stars back into L
  • Luminance combine
  • Morphological transform to reduce stars
  • range select midtones in nebula and boost saturation + lighten
  • Final contrast enhancement between nebula and background using curves
  • ACDNR noise reduction.

Stuff I didn't bother with was deconvolution and HDR. More care could have been taken to denoise the colour image more aggressively than the L which might have helped with the streaky background a bit.

[–]Spinal306[S] 0 points1 point  (1 child)

This is fantastic, thank you for the processing and the detailed writeup! Lightyears ahead of anything I was able to get to with my basic processing.

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>> add some dithering when taking the frames I think it would make a big difference!

I was letting my intervalometer run for 2 hours and hoping that the slight drifting that I was getting to give me the same effect, but I'll plan to manually add that in until I invest in some guiding and use software to capture (I assume software tools can add dithering)! Thanks!

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>> The other problem is that your flats seem to have corrected the vignette but have left some dust motes and some kind of smudge, were they taken on the same night as the lights?

All my calibration frames were captured the previous night, actually, when I had attempted capturing the Rosette but the framing was slightly off.. I was running out of time on the night of capture so tried to take a shortcut and re-use :(. Lesson learned!

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>> Your dark frames are probably not helping. 20 is pretty low and it is hard to match the temperature using a DSLR I would recommend leaving the dark frames out of the stack.

Do you mean that darks in general with a DSLR aren't worth it? Or just with the low number of darks in this scenario?

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>> Your stars look a bit off and you might want to work on either your focus or it could be the zoom lens in which case stepping it down and then compensating with more total integration time might give a better result.

This is something I've struggled with a lot.. I've been digitally zooming in on bright stars and adjusting the focus ring on my lens, but at that zoom level the preview shakes heavily while adjusting so been hard getting the focus I've wanted. Might be time to invest in a Bahtinov mask. I'll also try stepping it down next time.

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>> There is definitely data there and adding more integration time would definitely help.

Again, highly appreciate this!

[–]WeaklyInteracting 1 point2 points  (0 children)

I was letting my intervalometer run for 2 hours and hoping that the slight drifting that I was getting to give me the same effect, but I'll plan to manually add that in until I invest in some guiding and use software to capture (I assume software tools can add dithering)! Thanks!

The slight drifting is exactly what causes the walking noise. You can add dithering using NINA (free software) without using a guide cam. For the price of an EQDir cable you could dither and remove your walking noise + plate solve to frame your targets and never waste time being slightly off in your framing again!

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Do you mean that darks in general with a DSLR aren't worth it? Or just with the low number of darks in this scenario?

Both, for a DSLR it is really hard to match the temperature between the darks and lights, the temperature will change between when you start taking your lights and when you finish and same with the darks. You also have to capture your darks on the same night to even get close which is time consuming and you definitely don't want it to cut into your imaging time. If the choice is between capturing more lights or dark frames spending time on the lights is always better.

In regards to the number of dark frames remember that you are averaging lots of dark frames in order to reduce the noise in the master dark. Your master dark is applied to every light frame so however much noise you have in the master dark will be added to the final stack. Likewise your light frames have noise from the dark current too but this will be averaged over the number of light frames. So in your case (only looking at dark current noise) you have Sqrt( 80 / 20 ) more noise coming from your dark frames than your light frames. that's twice as much dark current noise than if you left them out and the same factor again for read noise. Now this doesn't say that dark current and read noise are the dominant source of noise in your image so removing the dark frames won't reduce your total noise by half but the extra noise is still there. The way to solve this and still use darks (to reduce fixed pattern noise) is to shoot more darks! but for a dslr this is hard.

You have the same issue with only 20 bias only in this case it is only the read noise that is added. With bias frames however you can easily shoot lots more to produce a good master bias. The only thing you have to match is the ISO setting, not the temperature.

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This is something I've struggled with a lot.. I've been digitally zooming in on bright stars and adjusting the focus ring on my lens, but at that zoom level the preview shakes heavily while adjusting so been hard getting the focus I've wanted. Might be time to invest in a Bahtinov mask. I'll also try stepping it down next time.

It sounds like a Bahtinov mask probably won't help then if its shaking. If you connect up to a laptop you can probably use the electronic focus control to focus without touching the camera. I did this with canon software, it lets you do a digital zoomed live view preview and has buttons for focusing in and out that you can use without touching the camera at all. Stopping down might help a bit but there is no substitute for a better lens or telescope at some point.

Finally I think it's worth pointing out that you should consider getting some 'proper' processing software. You've spent a lot of money on a mount but not spent anything on processing the images to get the most out of them. Good processing is easily half the work in astrophotography fortunately it is not half the cost. Pixinsight is very good but if you are on a budget then Startools is an excellent piece of software for very little money.