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| Hey everyone, I have a question about processing comet images using Siril. I've noticed that after stacking, the comet images appear badly blurred. I'm not sure if this is due to the comet's movement between frames or if it's a common issue in deep-sky stacking software. I've encountered the same problem with Deep Sky Stacker as well. When I tried to process my a3 Tsuchinshan atlas comet sub-frames, the resulting image was not processed well. I'm wondering why stacking and processing comet images seems different from processing deep sky images. Does anyone have an answer to this? |
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Because the comet is moving and you need to align on the comet nucleus, not the stars. The process in Pixinsight is called CometAlignment. |
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Miguel T.: Ah, so it is because it's moved between every frame you took. So, except for every deep sky object, comets aren't stationary objects. When I tried to process them, I got very confused about why I didn't see the comet itself only just the tail that it was producing. |
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Szijártó Áron:Miguel T.: Yes comet move "fast". You would also see the nucleus make a streak and not just a blurry comet tail. Unless both the nucleus and the tail are overexposed, but we didn't see an example image. |
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Siril has a step by step tutorial on how to stack comet fixed and star fixed. Might want to check it out. https://siril.org/tutorials/comet/ Lot's of information on the web and youtube that can be found with simple searches as well |
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The first thing to point is the comet moves fast between the stars, also he's more upclose to the Earth since he is inside de solar system and is much smaller than deep sky objects or even stars. The other thing to point is the DSO's also are moving in the outer space, and also the stars since the Universe is in expansion, but they are so massive and so far away that we don't actually have the ideia of it. Only a photo between decades that that we can glipse just a small movement and within pixels or silver halide prints. Here's an example: check a polar scope in the 90's from an equatorial mount and see where the polaris was put it, and now check an app or a newer polar scope. This is not 100% accurate because we are talking about the Earth's movement (spinning actually like a giroscope), but it also is related with the movement of Polaris. It's a combination of both celestial mechanics. Clear Skies, Cesar |
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| What you're seeing change is precession of the axis of rotation of the Earth. Polaris's proper motion is only 46 arc/sec in 1000 years. The Earth's rotation axis procession is 50 arc/sec per year. |
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Hi! I was struggling a little bit with my comet photos in the last few days. Here is the workflow that worked for me. 1. I took 5 to 30s subs guiding on a star, not on the comet. 2. I stacked my photos with pixinsight, as a normal dso image. I use this stack for the stars. 3. I use the registered images of pixinsight stack process, and I run comet alignment process on them. In pixinsight you have to mark the position of the comet in the first and last photo, and pixinsight will align them for the comet. 4. With starnet or starxterminator I remove the stars from all the comet aligned images. 5. With pixinsight image integration process I integrate all the starless comet images. 6. I process it as a like (stretch, noise reduction etc) 7. I add the stars of the stacked image from the 2. step to the final comet image. It takes sometime if you have many raw images, but like that I could get some decent image of the comet. |
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Tamás Csefkó: That’s my exact workflow in Siril. Works good for me. |
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Miguel T.:Szijártó Áron:Miguel T.: So, how does the comet stacking and processing work in Pixinsight? I'm new to this software, so I'm not familiar with its setup. Do u need to pick all frames or 2 frames only and open them or how? Cause i getting dioriateted with the menus Pixinsight have. |
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| As others have said the comet is moving relative to background stars. DeepSpaceAstro has a great video on how to process comets in Siril - it is a long-winded process (depending on your PC) but produces quite good results. |
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Szijártó Áron:Miguel T.:Szijártó Áron:Miguel T.: This is a rough idea of my comet workflow in PI. The operand section in the Comet Align tool is a powerful way to produce comet only and star only images for processing. The integration step of the comet only images can use some tweeking in the pixel rejection sections to help clean up any errant star streaks left over. 1. Use WBPP to calibrate, align, and integrate each filter. I manually set the alignment frame as the first Lum image I took, which was also the first image of all the filters. 2. Use StarXterminator on each star aligned and integrated master to produce a star only image. 3. Comet align the WBPP registered images using the star only images I just made as the operand image set to star aligned in the subtract section. 4. Integrate each comet aligned and star free image to produce masters of just the comet with no stars. 5. Rerun comet align for each filter but this time use the new comet masters as the operand image set to comet aligned. This produces comet free, star only subs. 6. Integrate the new star only subs to create starless masters. I found this produced a cleaner star field image than the original StarXterminator run. 7. Crop each new master. There will be 8 total, 1 for each filter and then a set with just stars and a set for the comet. Remember though that these are all still aligned with each other so create a dynamic crop instance that you then apply to all 8 to keep them the same geometry. 8. Process and combine the star field and comet only images as you would any regular LRGB deep sky image with DBE, color calibration, background neutralization, stretching, curves, etc. 9. Merge the star field and comet only images. At this point they should still he aligned with each other so use your preferred method here. 10. Do any final tweaks and enjoy! |
