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Hello, I would appreciate feedback on this image I posted... https://www.astrobin.com/2r3ahb/C/ Thank you! Gowri |
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| I think it's a beauty. Good framing and I like the color. I'm fairly new at this so take my comments with a grain of salt. The black point may be a bit aggressive for my personal taste. Have you tried pixmath to remove magenta color from the stars common in SHO? R = $T[0] G = iif(min($T[0],$T[2])>$T[1],min($T[0],$T[2]),$T[1]) B = $T[2] It's something I do at the very beginning after combining the channels. I also invert and remove green with SCNR. Just fun to try, sometimes pleasing results. did you try the script, DarkStructureEnhance? all subjective. |
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| Thanks John! I appreciate the feedback! I did a lot of the color using Photoshop once I got the details in Pixinsight, and did not use DarkStructureEnhance but will give it a shot. I will also try the Pixelmath formula, thank you for that too! |
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gmadkat: Oh, for removing green with SCNR, I play with 50% to 100% and sometimes use "Minimum Neutral". great fun. |
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| Thanks, I do that too! I found removing green too soon causes signal loss so I do it right at the end as a fine tune mechanism. |
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Hi Gowri, it is already a pretty good image, but that is the nice thing, there is always a bit more what one can do. I can pick any of my images and always see something that I do not like. Hence all my critics shall be seen as such. The black point in the areas outside of the image is not set correctly, blue hue. This is actually one of my pet peeves when I look at images, is the background neutral. Very rarely this is ok, but for that the nebula needs to cover the whole image. I would definitely correct that. It seems to me as well that the noise reduction was overdone, especially the orange parts are very washed out, which is usually a sign of that. I do not know how many hours you spent on this (the information is missing), and maybe this is the reason why you needed to do this harsh noise reduction. With that also the details and structures of some of the interesting parts of the heart are not crisp enough, and there are some interesting ones in there. I think you pulled out the oxygen part very well, which is usually the toughest task. But for some reason the Ha and SII suffered from it. Or maybe just not enough integration time. The surrounding of the heart should shine more (at least for me) and this does not come out well. I remember that my first try a couple of years ago looked very similar, and I believe that the main reason was not enough integration time (so that one can adjust colors better) or the changes to the SHO palette reduced too much the (initial) green part. All in all, it is a very nice image, but I think you can make it better, which is good news 😊😊! Uwe |
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Wonderful feedback Uwe, much appreciated! This is backyard data about 18 hours which I feel is not enough for the Bortle 6 skies I am in. I think what I might do is to add more signal and redo based on your feedback and see how it looks! Much appreciated and thank you again! Gowri |
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Hi Gowri! 18 hours should be enough, but I do not have experience with the Chroma 3nm filters to really judge this, maybe they do need more. I can see that they take away more signal, would make sense. And you imaged it with a TAK, also a fine telescope. And using a reducer! With that said I think your effort taking those images is excellent. How long was your exposure time? It would be interesting to see one of your raw images stretched with STF in PI, if you can add this as a version on your image, that would be great. The Hα most interesting. Uwe |
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With 18 hours of exposure, there is usually enough signal to pull out great detail in a bright nebula like IC1805. As mentioned by others, the noise treatment you have given has washed out some of the structures in the nebula. Let me suggest you try some of these steps in Pixinsight (if you haven't done so already): - MureDenoise script: Very often overlooked, but can make great difference when you have lots of sub-exposures (as I believe you have with your 18hrs). This has to be carried out as the very first step after image integration. This is done instead of any drizzling. - Download EZ processing suite and run the denoise script (still in the linear stage). This script is using John Ristas excellent method for noise reduction and you get a lot of fancy noise treatment for free here. - Boost the detail by applying LRGB combine to the image in the final stages of the processing by checking only L in the LRGBCombine in the meny and use a streched version of the Ha as the Luminance. This will also make the background darker. VisibleDark shows a beautiful example of this technique in the end of this tutorial: https://www.youtube.com/watch?v=j5zsZbHXrFE&t=789s -Martin |
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| A few more hours with this target can indeed help, especially with the Oiii signal, at least in my limited experience. My best image of the Heart so far involved ~24 hours of integration, ~7 of it being Oiii signal, and I wish I had gotten more of that. That's shooting with 3nm filters with a high degree of transparency in the desired band (Antlia Pro filters) from a Bortle 8 zone. Oiii signal under such conditions is always a challenge. |
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Thank you again Uwe, Martin and Greg. Uwe, I only kept my exposures to 120 to 180 secs due to my location, viewing conditions and iffy guiding, I will share a stretched Ha sub later today. Martin, thank you for the denoising tips and the detail boosting, much appreciated, will try them out. Greg, ok to more signal especially with my 3mm filters and location. |
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@Uwe Deutermann here is a 180 second Ha STF'd exposure...  |
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Since I happen to have a similar shot for comparison, here it is. This was shot with an 80mm triplet+reducer at f/3.9, so close to the same aperture and focal length. Please ignore the horrible stars in the corners as my back focus was off by a couple of mm at the time.  This was a 300 second exposure with the same camera (ASI2600MM) using an Antlia Pro 3nm Ha filter. The camera was set to 100 gain and 50 offset, and cooled to 0C. (It was still warm here when I shot this in October.) The ADU of the sub is only 613 out of 65535.  |
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| Thanks for sharing Greg! Fascinating to compare the two images taken with such similar equipment!! |
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| You're welcome. I thought it would be interesting. It's remarkable how similar the 180s and 300s exposures are after stretching. That 2600MM is a great camera! |
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Yes! I see more signal in 300s as expected, but remarkably similar. I really am happy with the 2600 and also noting the two 3mm Ha filters appear to be very comparable. My next project with this setup is the Soul Nebula! Got 4 hours of data so far. |
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Hi Gowri! Thanks for posting the stretched image in Hα, and as others already wrote, the data that you collected look very good! I can only agree from other 2600 users, this camera is really good, you will have a lot of fun with it. With that said, I think you can get a bit more out of your images. Always very difficult to support this, since so many steps play a role. Might be interesting to pass the stacked images to me if you want to, and I might take a look what is possible. I surely do not want to finalize processing, this enjoyment I want to leave to you, nothing is more satisfying 😊. But maybe I can give some hints. Or if you want to try more and you get stuck at some point, please let me know. Uwe |
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| That is really nice of you, Uwe! I can share the masters, much appreciated! |
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Update: Gowri was so nice to pass her stacked images to me (thank you so much Gowri!). A look at them was really revealing a lot, just telling that judging an image is very complicated and that the reason of some of the "insufficiencies" that we try to explain can have many reasons. One of the "insufficiencies" that I was referring to was that the image was too washed out and that some details were not crisp enough, and that this might be caused by applying noise reduction routines too heavily. I believe that I could not have been more wrong. Here the raw stacked image of Gowri's Hα channel compared to the star aligned image taken by me 1.5 months ago.  Both images are just STF Auto Stretched, no other processing done. 2 facts pop up right away: The number of stars and the sharpness of Gowri's image is significantly less. Meaning that the processed image could not be as sharp as I thought it could have been. Yes, one can do some sharpening routines, but those are limited and cannot compete with a sharper image obtained first hand. OIII channel comparison:  Just confirming the seen artifacts of the Hα channel. SII looks identically. What could be the reason? I believe (but cannot be sure without further test images) that the 3nm filters play a role about the signal (which would make sense) compared to my used one of 10/8nm and the different sizes of the telescopes (TAK 76 compared to WO 132). On the other hand: Gowri took 3 min exposures, while I used 2 minutes. Bortle class same as 6. Maybe moon impact? Guiding looked sufficiently good for me, hence I do not think that this could be the reason. All in all, I think Gowri processed her images very well and made a wonderful SHO image out of it! Hope this information helps also others! Uwe |
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Very interesting Uwe. The lack of stars and detail in Gowri's is puzzling. My 5 hours with my 102gt and OSC with Optolong Extreme 7mn, extract Ha in APP in bortle 7 shows similar stars to your image. Gowri used Chroma 3nm filters...should be as good as they get. I didn't star align this crop of stretched stacked Ha.  |
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Thank you Uwe and John! One possibility is the moon effect, I did do some images (unwise on my part but we had so few clear nights, I was tempted to not let it go) when the moon was high and close to full. Do you think that would result in such a dramatic impact? The Chroma 3nm filters I am puzzled about. Not sure what is going on there. Gowri |
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Ha should not be affected that much by the moon. Oiii more so. but it you were within 20 degrees of the moon then that could be a factor. but I'm no expert. john |
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Hi John and all, I did the 3 image comparison and here what it looks like:  Do we see here maybe just the difference of aperture and nothing else? Maybe this is how it is when using less aperture? I remember that my Explore Scientific was not as sharp as I wanted either, and that was 102mm. Maybe it is that simple. Uwe |
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Looks like a pattern 76 vs 102 vs 132. Very good deduction, Uwe! |
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Thanks Gowri! And if this is so I want a 10" refractor now 😂😂😂😂😂. What am I talking .... 15"!! |
