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Hi folks. Although I have been taking some photos for a couple of years, I haven't had a lot of time and it's been very sporadic. I am trying to get into this hobby more now and I have had some results in the last couple of weeks I have been pleased with. I took this photo last night of M42 Orion M42 ( GaryLearningAstro ) - AstroBin with a quick edit in Photoshop. I am planning to add more data to this if the skies allow over the next couple of weeks. My question is what is standing between this and the detail in a photo like this one M42 ( Satoshi ) - AstroBin? Is it just integration time? Is it my equipment or filters? Is it post processing? I know the answer might be a mixture of all of the above, but keen to get any tips on improving from where I am now. All feedback and tips welcome! Thanks! Gary |
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Hi Gary, Orion is quite a non-typical target in that it is has very bright areas and also faint dust, as well as a mix of emission nebulae and reflection nebulae. IMO, to capture it well requires a mix of exposure lengths and/or different degrees of stretch, and a mix of broadband and narrowband data. It doesn't need a huge amount of integration time, a few hours can yield good results, although more is better. Processing is key too, the exposures of various lengths and the different filter stacks need to be blended to bring out the stars in the bright core while also exposing the faint dust and the emission nebulae. This can be done in PixInsight, but many people would find this easier to blend the various stacks in photoshop layers. The narrowband filter you are using is Ok for the emission nebulae, e.g. the red bits of the Running Man, but will not yield much of the dust or reflection nebulae. Either no filter or an LP filter such as the L-Pro would be needed for that. A dual band filter with narrower bandwidths would improve the contrast, just avoid moonlit nights with the filter you have as it has a 35nm Oiii/Hb bandwidth. To achieve sharpness in processing you can use deconvolution, but use it sparingly, it is too easy to over-do it and produce strange artefacts that do not exist. As an alternative to deconvolution you can use the new BlurXterminator in PixInsight, this takes much of the pain of doing deconvolution. Here is my attempt from a few years ago, not that it is particularly wonderful: https://www.astrobin.com/fvzdlx/B/ |
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How about your focussing, did you use some kind of autofocus or a bathinov mask? The halos arround bright stars are quite challenging in an area like orion, you could think about doing 30 minutes to one hour RGB stars with a short exposure time of 30-60 seconds and then removing the original stars and blending in the RGB stars. Or, as an alternative, take around 30 minutes of your filtered stars (take the best versions with smallest stars) and stack them seperately and blend them in. Not as good as doing RGB stars but the Halos will be smaller and easier to remove in post processing. |
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Actually the image you are using as a reference has more important defects than yours: The gradients are not well-corrected and the stars have sharpening artifacts. Also there are sharpening artifacts at the nebula itself, probably due to the wrong usage of an "AI" sharpening tool. You did a better job despite the poor focusing which I think is your main issue. I also find your framing to be better. If I were you, I wouldn't be disappointed. I would investigate my focusing issue and I would choose some better images as references. Thankfully we have the top pick nominations/top picks/IOTDs in our avail for good reference images. |
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Michael Ring: I did wonder about my focusing. I used a mask and the diffraction spikes looked good, so not sure what happened. I have been considering getting an AF at some stage. Thanks for the suggestions regarding the layering of the stars, I'll give that a go! |
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Die Launische Diva: Thanks, I appreciate the positive feedback - I'll certainly look into what's wrong with my focusing, as I agree that's a big issue for me here. |
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Roger Nichol: Thanks - this is great feedback and something I hadn't considered re what the filter would be causing me to miss with this particular object. I did take some different exposure lengths too, so I'll look into if I can utilize some of them. |
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I think that your image is pretty good. As others have said M42 is an atypical target especially with respect to dynamic range. One issue might be image scale and sampling ? You don't say what it is in the image description --- but -- for example - if you are sampling at say 1.5 arcsec per pixel then even if the seeing would have permitted resolution at 2 arcsec your set up would not let you see at that level of detail -- and neither would deconvolution or dithering and drizzling get you there. One way to see more detail all the way from the very bright core trapezium area down to the outer fringes of the nebula is to make a high dynamic range composition with very short frames 5-10s used for the core area and an integration of longer frames for the outer parts. HDRC in PixInsight is useful for this. Essentially you flatten down the dynamic range of the image. Another more advanced way to bring out more detail - only really at the core where it is very bright - is to use a semi lucky imaging technique -- take hundreds or even thousands of short exposure images (2-5s) - retain only those with lower FWHM values --lower ellipticity etc (PixInsight subframe selector and Blink tools) to get a sharper image (can be luminance only) of the core part. Don't be afraid to oversample such a bright image as well -- with higher rates of sampling and well selected frames deconvolution tools like BlurExterminator can reallly also really work well. Edit..I agree with most of what Roger Nichol said above and realise that I have repeated some of his points Tim |
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Michael Ring: One more thing you could do is check the weather on that night you were doing your session. When there were high clouds then this would be another explanation for bigger stars and loss of sharpness. You can also check if focus in the first pictures looks different from focus on later images, then there's also a possibility that your focus changed because of temperature changes or the focusser moved a tiny bit because of gravity. |
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Die Launische Diva: I totally agree with the above. Answer to your question "All the above. " Focus being the largest problem. Lynn K. |
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It might be a focusing issue, but if you focused with a Bhatinov mask you should have been good. How long did you allow for your kit to equilibrate with the outside temperature? Note also with a lens as the objective, the lens cools all night due to radiative cooling, so you may need to check focus quite often. I would make sure your kit was outside for at leat 30 to 45 minutes, but even then, if temperature outside is dropping fast, as it does when the sun sets, you might need to refocus after 30 minutes. As it gets later you don't need to refocus as much generally. During acquistion I view the images I am collecting. I use DeepSkyStacker, there I can monitor background and star count (for clouds/haze/dew) and star FWHM (for clouds/haze/dew/seeing/wind). I am tempted to say it is a focusing issue, as maybe there is a donut look to bright stars, but on the other hand small stars are small. The halos around brighter stars seem really strong, to me that suggests the sky may have been very hazy, or you were getting dew. Do you have a dew shield and dew heater. I also thought it odd that the halos are not well centered on the stars, and also stars are better in some directions than others, suggests something is not aligned. Not sure if you have some camera tilt, or perhaps the focuser is not in perfect alignment? Next time you are out compare carefully the images with this night. They may be way better if you happened on a bad night. I use Clear Dark Sky to get an idea of conditions, bad seeing, or poor transparency, or wind, can easily ruin an image. Also, with your focusing mask in place, center a bright star to focus, then put that star at all four edges of your field of view. If you have everything aligned then all 5 points will be in focus with the center. Otherwise you have some tilt to fix. With a refractor it could be in the focuser or camera, otherwise should be okay, there is no collimation for a refractor. Also, your stars are just blobs with little definition, they should show a Gaussian distribution, more intense in the centre and fall off to the edges. Either your stars are overexposed or over stretched. If you load the raw images to your page let me know, Astrobin has an option for that, and I can take a look at what is going on. Finally, even bright targets need probably need at least 5 hours of exposure for really great images, and in fact, even bright targets can gain a lot more if you are in a light polluted area. And hard to judge from one night, even if it seems clear, sky background can vary by a factor of 4, star FWHM can vary by 2X. So only with time and many nights will you have a feel when your system is acting up or when the elements are against you. CS Rick |
