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Veil Nebula fail - where did I go wrong?


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3 hours ago, imakebeer said:

more explicit, more detailed guide

If you like, post -a link to- e.g. three flat frames and three light frames and I'll make a video. It's very easy. 
Cheers

Edited by alacant
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1. I changed the filenames to contain only one '.'
2. The flat frames are incorrect. Have another go:

  • set the camera to Av
  • point it at an even source of light
  • adjust the light so the the exposures are around 2s
  • shoot around 15 frames.

Video here:

Edited by alacant
vínculo
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53 minutes ago, alacant said:

1. I changed the filenames to contain only one '.'
2. The flat frames are incorrect. Have another go:

  • set the camera to Av
  • point it at an even source of light
  • adjust the light so the the exposures are around 2s
  • shoot around 15 frames.

2024-08-22-12:42:54.204716781.mkv 40.61 MB · 1 download

Thank you so much for the video, I will take a look.

Re. flat frames - I think you're gonna tell me I've been doing it wrong all along, since the very get go.....

  • I always set the camera to M (manual) mode - is that not right?
  • For the flats I point the scope at the sky the morning after (not at the sun obviously, but somewhere where it is uniform looking, ideally clear blue sky) - wrong again?
  • I thought flats had to be the same ISO, exposure length and focus as the light frames, no, I thought that was the point? Wrong again?
  • Around 15 frames - well at least I don't score zero marks on this test! 🤣

I was just reading this actually and it's saying for flats with a DSLR you want the histogram (I assume!) 1/3 to 1/2 from left - any truth in that?

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4 minutes ago, TiffsAndAstro said:

For 3 frames this looks really good. 

It's all in the capture, the post-processing is just a minor detail, a mere afterthought 🤣

(I am kidding! Thanks again @alacant)

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10 minutes ago, imakebeer said:

any truth in that?

Yes. You are trying to eliminate anomalies such as dust and vignette in the optical train. Change nothing in the latter before shooting flat frames.

The Av method I posted above will get you exactly that. Whatever method you use, don't allow the shutter to fall much below 2s; the 12mp sensor is a devil for flicker and banding.

HTH

Edited by alacant
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1 minute ago, alacant said:

Yes. You are trying to eliminate anomalies in the such as dust and vignette in the optical train. Change nothing in the latter before shooting flat frames.

The Av method I posted above will get you exactly that. Whatever method you use, don't allow the shutter to fall much below 2s; the 12mp sensor is a devil for flicker and banding.

HTH

Just to be absolutely clear, I  want a shutter speed of >2s or <2s?

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1 hour ago, imakebeer said:

I thought flats had to be the same ISO, exposure length and focus as the light frames, no, I thought that was the point? Wrong again?

 Focus, yes. Otherwise very(!) wrong.

Edited by alacant
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Righto, I've been having fun with Siril, manually processing the entire stack (about 80 lights) using @alacant 's settings in the video. This included using the plot to throw away the dodgiest light frames.

Just some basic processing in Siril, a slight histogram tweak and a run of the star reduction script that uses Starnet & Pixelmath. Not too bad - I know I can do a lot more than this if I split it into starless + starmask and take it into GIMP and play with layers etc. I know I can push the colours more in the nebula without having to bring the noise in the farfield.

Still room for improvement but feels like a step in the right direction (and I still need to redo those flat frames!) 😊

Thanks again for the help, much appreciated 👍

reducedStars_final_RGN_sat_histo.thumb.jpg.8223237e872c4b4124c7a1f8e9b75016.jpg

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1 hour ago, imakebeer said:

Righto, I've been having fun with Siril, manually processing the entire stack (about 80 lights) using @alacant 's settings in the video. This included using the plot to throw away the dodgiest light frames.

Just some basic processing in Siril, a slight histogram tweak and a run of the star reduction script that uses Starnet & Pixelmath. Not too bad - I know I can do a lot more than this if I split it into starless + starmask and take it into GIMP and play with layers etc. I know I can push the colours more in the nebula without having to bring the noise in the farfield.

Still room for improvement but feels like a step in the right direction (and I still need to redo those flat frames!) 😊

Thanks again for the help, much appreciated 👍

reducedStars_final_RGN_sat_histo.thumb.jpg.8223237e872c4b4124c7a1f8e9b75016.jpg

this is a major improvement, but you'll fall out of your seat when you stack it again with better flats :)

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2 hours ago, imakebeer said:

Still room for improvement but feels like a step in the right direction (and I still need to redo those flat frames!) 😊

So pleased that you are making such good progress.

Ian

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  • 3 weeks later...

No news on this since it's been nothing but cloudy here for ages, and not looking like it's about to change 😒

However, I took some time to dig out the raw data from my initial stint learning DSO AP between about Oct 2022 - May 2023. I checked out the flat frames I took at the time and they are all completely wrong!!! I.e. where I'd used 30s or 60s exposures for my light frames I had used the same exposure length for my flats so they're all overexposed!

Bearing this in mind, the mind boggles how on earth I managed to get anything like the half-decent images I managed at the time! (e.g. M51, M81/M82)

I went back to the original sources, websites I'd looked at to learn what are light/dark/bias/flat frames, and even "Making Every Photon Count"... it's all there in multiple sources, set your camera to aperture-priority mode for the flat frames, so goodness knows how I missed that.

Still, lesson learned the hard way, now I'm just itching for some clear skies to put it into practice! 🙏🙏🙏🤞🤞🤞🔭🔭🔭

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On 08/09/2024 at 16:31, imakebeer said:

No news on this since it's been nothing but cloudy here for ages, and not looking like it's about to change 😒

However, I took some time to dig out the raw data from my initial stint learning DSO AP between about Oct 2022 - May 2023. I checked out the flat frames I took at the time and they are all completely wrong!!! I.e. where I'd used 30s or 60s exposures for my light frames I had used the same exposure length for my flats so they're all overexposed!

Bearing this in mind, the mind boggles how on earth I managed to get anything like the half-decent images I managed at the time! (e.g. M51, M81/M82)

I went back to the original sources, websites I'd looked at to learn what are light/dark/bias/flat frames, and even "Making Every Photon Count"... it's all there in multiple sources, set your camera to aperture-priority mode for the flat frames, so goodness knows how I missed that.

Still, lesson learned the hard way, now I'm just itching for some clear skies to put it into practice! 🙏🙏🙏🤞🤞🤞🔭🔭🔭

@imakebeer Hi again! mate a week or so ago I did a little experiment regarding calibration frames. I stacked my lights alone, about 2 hours worth, then I stacked them all again with properly done flats,bias,darks and the difference was like night n day! The whole image was so much cleaner, no vignetting, hardly any gradients etc etc!

Deffo worth doing them!

Clear Skies from Wes, Liverpool.

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58 minutes ago, wesdon1 said:

@imakebeer Hi again! mate a week or so ago I did a little experiment regarding calibration frames. I stacked my lights alone, about 2 hours worth, then I stacked them all again with properly done flats,bias,darks and the difference was like night n day! The whole image was so much cleaner, no vignetting, hardly any gradients etc etc!

Deffo worth doing them!

Clear Skies from Wes, Liverpool.

Looks clearish tonight, think I'll add more time to my version same target

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4 minutes ago, TiffsAndAstro said:

Looks clearish tonight, think I'll add more time to my version same target

@TiffsAndAstro I'm planning on getting outside myself, I'm getting more data on Soul nebula. If I'm able to, I'm also getting some videos of Saturn to process hopefully and get a nice final image.

That Vale nebula is stunning. I got about 2 hours on it recently, with an L-Extreme, which was superb. I might go for another 2-4 hours on it and see how much improvement it makes?

Edited by wesdon1
Forgot to mention something!
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22 minutes ago, wesdon1 said:

@TiffsAndAstro I'm planning on getting outside myself, I'm getting more data on Soul nebula. If I'm able to, I'm also getting some videos of Saturn to process hopefully and get a nice final image.

That Vale nebula is stunning. I got about 2 hours on it recently, with an L-Extreme, which was superb. I might go for another 2-4 hours on it and see how much improvement it makes?

More hours to see the difference is my plan too. Not up high as long as I thought, so I might get distracted :)

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As it happens I went out on a bit of a whim last night, followed by doing some flats the right(ish) way first thing this morning. I stacked manually in Siril this time (following the advice from @alacant) rather than relying solely on the scripts, plus a bit of tweaking in GIMP.

I think it's a little better but something is still going wrong somewhere as I'm still getting those damn dust bunnies! 😖 I can just about make them out in the flats so I'm not sure why they're not being removed once I calibrate, register and stack the lights 🤔 (it could do with cropping a bit anyway so I could crop them out, but that's cheating!)

simple02_01_stars100b.thumb.jpg.95096b20ebf7de00bc9bccc2ec36cf2f.jpg

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If you do flats before a session, any dust that arrives after that point won't be calibrated out.

I considered doing flats every hour or two, but just doing them once, at end of session seems to work well enough for me.

If you change filters you should probably do flats right after, but I've not tried that yet.

Ps your dust mote is in about best place it could be :)

take a new set of flats will probably sort it or crop it out :)

Edited by TiffsAndAstro
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Well wherever that dust is it was there when I started this thread a few weeks back!

I think it appeared while I was away from the hobby for a bit. I'm considering giving various parts a squirt of CO2 to see if that clears it.

Anyhoo, looking like another clear night so currently weighing up more time on the Veil Nebula vs. something different

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20 minutes ago, imakebeer said:

Well wherever that dust is it was there when I started this thread a few weeks back!

I think it appeared while I was away from the hobby for a bit. I'm considering giving various parts a squirt of CO2 to see if that clears it.

Anyhoo, looking like another clear night so currently weighing up more time on the Veil Nebula vs. something different

Your flats should deal with it, if it's dust. Maybe it's something else. That would be way above my pay grade though

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Hey @alacant quick question - I've been busy playing with more manual processing in Siril using the settings you showed me in your video..... In the stacking tab under Pixel Rejection -> Sigma Clipping, what actually is Sigma and why are the low/high values important? The default is 3 for both but I saw you set low=5 and high=2...

(I swear I saw an old post of yours on this the other day but damned if I can find it now)

I've searched the help and Googled more generally but can't find an answer, except it's maybe something to do with standard deviation so I suppose ultimately something to do with statistics....🤔

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