by alter-ego » Tue Sep 12, 2023 8:31 pm
Chris Peterson wrote: ↑Tue Sep 12, 2023 3:47 am
alter-ego wrote: ↑Tue Sep 12, 2023 1:56 am
Chris Peterson wrote: ↑Tue Sep 12, 2023 1:11 am
Those exposures were so short (on the order of 5 or 6 minutes total, stacked from 10 or 15 second subs), and the field wide enough, that I just let a small, roughly polar aligned mount track the sky. Then I aligned on the comet. You can see that the stars are trailed slightly. Longer exposures at a longer focal length (
https://www.cloudbait.com/c2023p1.php) I actively tracked on the comet (but unguided), then created image pairs, one aligned on the comet and one on the stars, which I combined so that neither was trailed.
Makes sense for the wider FoV. For the longer exposure images I'm missing something. Regarding the image combination technique, how you end up with no trails in the final combination. It seems the comet is muddled slightly when aligned on the stars, and the stars are trailed if aligned on the comet .
Lastly, Are you using your guide scope the track the coma/nucleus?
BTW, your RC is a great upgrade from you're Meade
I use one of two techniques, depending on how much motion I have between subs. One approach simply involves stacking the images with some kind of median pixel rejection. If there is enough movement between frames, the stuff that's moving gets eliminated. I can extend this method by doing several stacks, taking say every three frames so there is more movement. If I do it with RGB filters, that happens automatically.
When there is less movement, I remove the stars from the subs (using one of several star removal tools) and then align on the comet and stack. That gives me a good comet image. Then I align on the stars, remove them (leaving the smeared comet behind) and add the stars into the comet image. Processing comets is quite a bit of work!
I have not had good luck trying to guide on comets. The problem is that they usually are sliding past stars, and those stars sometimes pass through the guide aperture, creating a guiding error. What I do is set the mount to guide on the comet. That is, it adjusts its tracking speed on both axes to match what is calculated from the comet orbital elements. That is open loop, but the tracking is very good so there is not much drift, and it is easily accommodated in post-processing by alignment methods.
Thanks for the additional detail - very helpful. I figured you could easily "erase" open-space stars, but I didn't see how to deal with stars in the comet.
I did suspect you could track the comet good enough by inputting the orbital elements. I've not done it, but my old RCX400 Meade supposedly can track satellites, so I fully expected your setup most likely has that added capability.
I'm thinking you could have used PixInsight somewhere in the process. I really go for powerful image software for analysis purposes (I'm a fair-weather, crude astrophographer
) and considered buying it a year or two ago. Even though it's a one-time expense, I just couldn't justify the cost (yet).
[quote="Chris Peterson" post_id=333724 time=1694490456 user_id=117706]
[quote=alter-ego post_id=333722 time=1694483813 user_id=125299]
[quote="Chris Peterson" post_id=333720 time=1694481112 user_id=117706]
Those exposures were so short (on the order of 5 or 6 minutes total, stacked from 10 or 15 second subs), and the field wide enough, that I just let a small, roughly polar aligned mount track the sky. Then I aligned on the comet. You can see that the stars are trailed slightly. Longer exposures at a longer focal length (https://www.cloudbait.com/c2023p1.php) I actively tracked on the comet (but unguided), then created image pairs, one aligned on the comet and one on the stars, which I combined so that neither was trailed.
[/quote]
Makes sense for the wider FoV. For the longer exposure images I'm missing something. Regarding the image combination technique, how you end up with no trails in the final combination. It seems the comet is muddled slightly when aligned on the stars, and the stars are trailed if aligned on the comet .
Lastly, Are you using your guide scope the track the coma/nucleus?
BTW, your RC is a great upgrade from you're Meade :!: 👍
[/quote]
I use one of two techniques, depending on how much motion I have between subs. One approach simply involves stacking the images with some kind of median pixel rejection. If there is enough movement between frames, the stuff that's moving gets eliminated. I can extend this method by doing several stacks, taking say every three frames so there is more movement. If I do it with RGB filters, that happens automatically.
When there is less movement, I remove the stars from the subs (using one of several star removal tools) and then align on the comet and stack. That gives me a good comet image. Then I align on the stars, remove them (leaving the smeared comet behind) and add the stars into the comet image. Processing comets is quite a bit of work!
I have not had good luck trying to guide on comets. The problem is that they usually are sliding past stars, and those stars sometimes pass through the guide aperture, creating a guiding error. What I do is set the mount to guide on the comet. That is, it adjusts its tracking speed on both axes to match what is calculated from the comet orbital elements. That is open loop, but the tracking is very good so there is not much drift, and it is easily accommodated in post-processing by alignment methods.
[/quote]
Thanks for the additional detail - very helpful. I figured you could easily "erase" open-space stars, but I didn't see how to deal with stars in the comet.
I did suspect you could track the comet good enough by inputting the orbital elements. I've not done it, but my old RCX400 Meade supposedly can track satellites, so I fully expected your setup most likely has that added capability.
I'm thinking you could have used PixInsight somewhere in the process. I really go for powerful image software for analysis purposes (I'm a fair-weather, crude astrophographer :ssmile: ) and considered buying it a year or two ago. Even though it's a one-time expense, I just couldn't justify the cost (yet).