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Looking for some help and direction on my Jellyfish Nebula photo. https://www.astrobin.com/3g78ii/ This is 6:42 worth of data collected over several nights in a bortle 4 area. I used a Canon T5 (full spectrum mod) with an astronmik L2 UV/IR filer, SharpStar 61 EDPH II, .8x reducer/flattener, AVX mount, and Orion SSAG. My lights were 120s@ 800iso, and I had accompanying darks and flats. The main areas I'm concerned about are the halos around almost all the stars that are pretty pronounced, and just a general softness to the image. Any other areas of advice are certainly appreciated. My basic workflow is this: Manual calibration and integration in PI. Dynamic Crop Dynamic Background Extraction Background Neutralization and Color Calibration SCBR to reduce green. Multiscale Median Transformation on Chrominance then on Luminance Maybe Deconvolution (i don't think I did on this one) Arcsihn Stretch then some Histogram Transformation Non linear I do: Multiscale Linear Transform to sharpen Morphological Transformation for some star reduction ACDNR Finally some Curves transformation for contrast and saturation Then I sent it over to Photoshop for some selective brightening. Thanks, everyone. Anything is very much appreciated. |
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| Weird halos you got all over the place. Were they there before the non-linear processing bits? It looks like un-focused light but you wrote you had the UV/IR cut so it seems unlikely. Again, without access to the raw stack up hard to say why. I'd try to minimize the halo avoiding going through the ArcSinh stretch first but that is just a wild guess from my part. |
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andrea tasselli: It definitely seems they are there in the linear stack, though maybe a bit smoother. Would you like to see the master? |
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| That would help, yes please. |
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andrea tasselli: Here you go! https://drive.google.com/file/d/1cGI4y0h04RX8pBOV8igf6voi7vm0gr2O/view?usp=sharing |
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| Quick question: did you use LocalNormalisation as part of your process? |
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| OK. Got it now. You have significant longitudinal chromatic aberration and the halos are all poorly focused deep blue-violet light. I'm processing the thing now and see what can be made out of it.... |
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andrea tasselli: Just out of interest, how did you manage to work that out? I did split the master into its three channels and noticed that the halos were much bigger in the blue channel and wondered why. |
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Chris Barthel:andrea tasselli: Well, I managed to reduce the halo somewhat by removing the magenta component from the star mask AND from the starless nebula then recombine the two. The rest is HystogramTransformation and selective curves on stars and nebulae. Note how now the structure of the nebula is so much more evident than in the orginal. I just added a touch of noise removal courtesy of MultiscaleLinearTransform. I wouldn't push any noise removal in the final image as it is deleterious to the visibility of the fine structure in IC443.  |
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Andy Wray: If you see bloated stars in the blue channel that is the clue. I would add the image also suffer from lateral chromatic aberration (you can see that the halos in the 3 channels don't overlap anymore as you move out from the center of the image). The only question is: where it comes from? Scope or reducer? |
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This just to show the 1x image of IC443 (that is pixel peeping purposes): |
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Andy Wray: i did, yes. |
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andrea tasselli:Andy Wray: Well, hmm. First of all thank you so much for looking at it. This was certainly not the direction I was expecting this to go, and it's a bit discouraging. I just did some reading on lateral and longitudinal aberration. That seems entirely like an optics problem and I'm not really sure how I can solve that whether that's a scope issue OR a flattener issue. What else is there to do other than a monochrome camera with different focus points for each channel? Lol, is THAT even a solution? |
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Chris Barthel: Well, for starters I would try and find the culprit. My money is on the scope but the only way to know for sure is shooting without the reducer. Just a trial shot would do (say 5 min worth of exposure). That is enough to establish which is which. If indeed is the scope and you can't return it I'd suggest a good minus-violet filter will make things right. Just get one with IR cut as clip on filter for the Canon. I'm using a Baader Semi-APO but is probably excessive in in a Bortle 4 sky. As for the present situation you can still improve things in processing, as shown below. This time I used EZ Suite to denoise it (just remove the MedianTransform at the end as it is too heavy on the details) and then processed as described in my previous post. At the very end I used the usual star reduction tecnique to bring down emphasis on the stars and consequently on their halos. The full image is available to you (just need a place to post it to).  |
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Chris Barthel:Andy Wray: It might be worth checking that LocalNormalisation isn't exaggerating the halos a bit. That said, I would follow the advice of more experienced people on here to isolate if the chromatic aberration is more the scope or the flattener. |
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Chris Barthel: It might be worth checking that LocalNormalisation isn't exaggerating the halos a bit. That said, I would follow the advice of more experienced people on here to isolate if the chromatic aberration is more the scope or the flattener. |
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And here is the final elaboration full field, removing a bit of the green cast. |
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Andy Wray:Chris Barthel: I'll certainly give that a try. Thank you very much for the help. |
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andrea tasselli: That looks better. I'll definitely keep working at it. It seems this might just be, as was mentioned, an optics issue in the flattener or scope. I'll work on figuring out which one it is and then go from there. Also, thank you very much for the help. |
