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| https://www.astrobin.com/7383oi/?nc=user Hi all, this was my first attempt at a nebula and also my first dive into PixInsight so I am sure there's a lot I didn't get right. What confuses me most is how I wound up with the color balance I did- the stars seem to show a normal color range but where are the reds in the nebula? I would really appreciate any feedback. |
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Hi Zara, This is a great first effort with PI (I’ve been using it for 9 months and am still a n00b). I think the reds you are referring to only come out when you shoot narrowband (H-Alpha, someone else please confirm). Pixel-peeping, you do have some issues with your stars — the odd brown halos around the brightest stars and some of the cores are darker than their surrounding halos. For me, this is usually due to improper masking (masking when I shouldn’t). Also, the core of M42 is completely blown out (looks like bright clipping) with a very hard edge, I’d be less aggressive with your stretching and see if you could keep the core from clipping like that. The background looks pretty good so I’d say your background extraction and noise reduction went well. Again, a very nice first effort — keep it up! Clear Skies! Clint |
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Hi Zara, very nice result, especially with a relatively short integration time. You managed to get extensive nebulosity around the nebula itself, and the Running Man looks fabulous. I'd agree with Clint above that the core is burnt out. This is one of the key points with M42 as the core is so bright compared to the rest of the nebula. Ideally you should be able to see the four main Trapezium stars, and the three 'pointer' stars (Theta 2 Orionis) close by. Many people will take a second set of short exposure images and blend them in. If your main lights are 180s, maybe a few at 60s would capture the core? I think the colour overall is what you would expect. Red generally comes from Hydrogen emission lines and is picked up by Ha narrow-band filters. It's also present in the Red filter image, but that's a much broader spectrum unless you mix Ha in with the red channel to accentuate it. The blue comes from reflected light from the nebula's young stars, and is generally a broadband spectrum similar to that of the stars themselves, so this will be picked up by your LRGB filter set. By the way, did you capture Luminance as well as RGB? |
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Padraic Moran: Thank you for the feedback! How is this blending normally done? Does the process have a name? This makes a lot of sense, in this case the core was as seen even in the unstretched images so I suppose my exposure was just too long. I did get just a few luminance frames but they were even brighter. |
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| I'm afraid I can't help with Pixinsight - I don't use it myself - but you would use masks and layers in PS or Gimp. Not a particularly difficult job once you have the data. |
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Hey Zara, there is a process in PI called ‘HDR Composition’ and here’s a basic tutorial from Light Vortex Astronomy I’ve done an HDR composition of M42 with 5, 15, and 40s subs. You can see my result here: https://www.astrobin.com/937txx/ If you’d be willing to share your channel masters (xisf files) I’d be happy to take a look and see if the core is recoverable in any way. (I’ll document my process for you). Modern cameras have very good dynamic range and it’s possible you could bring out the core detail without having to shoot multiple exposure lengths. Of course, if you want to try an HDR comp — have at it! It will almost certainly improve the result. P.S. I may have wrongly assumed that you shot channels individually, if you shot this OSC (one shot color) then all I would need is the master light file (again, if you would like me to take a look). CS |
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Clint: That would be fabulous, thank you! What is the best way to share those with you? |
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Clint: @zara the usual way we share these big files is over something like dropbox, google drive or one drive -- any cloud storage solution really, because Astrobin doesn't allow such large files. Once uploaded, you can PM me the link or share it here (and let others have a go too) |
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| If the Orion nebula is red then there is no reason why the Running Man shouldn't be red as well, not brown. |
