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PixInsight Comet Stack

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#1 FiremanDan

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Posted 09 July 2020 - 09:46 AM

I am having a hard time with Comet Stack. I mark the center of the comet in the first and last image (per the video I saw) and the middle subs have the bullseye NOT around the comet, and obviously the resulting stack shows multiple ghost comets.

Is there a way to manually select the comet in each sub?



#2 bobzeq25

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Posted 09 July 2020 - 10:24 AM

Do you have Keller's book?  I found his instructions there worked well.



#3 pfile

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Posted 09 July 2020 - 10:55 AM

you shouldn't have to select the comet in all subs... the script looks at the OBS-DATE keyword of each image and interpolates the position of the comet based on the position in the first and last frames. IDK if it is possible to mark the comet in the wrong frames (which would mess up the interpolation) but you should check that the 2 frames you mark are truly the beginning and the end of the sequence.

 

if the OBS-DATE keywords are missing i guess nothing would work, and i assume the process would complain.

 

i don't think selecting the comet in intermediate frames is even a thing with this process...

 

rob



#4 FiremanDan

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Posted 09 July 2020 - 11:47 AM

I ended up using the first frame and aligning it to the second, then the first to the third, then first to the fourth and so on. It was a pain but it worked. My guess is I bumped the tripod enough to put the comet far enough away from where it expected it to be that it wouldn't align them.



#5 pfile

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Posted 09 July 2020 - 12:46 PM

ah yeah, the script assumes the comet takes a linear path thru the subframes. probably in a widefield image (the one you just posted?) you wouldn't have to run staralignment, but if you bumped the tripod then it won't work.

 

did you run CA on images that came out of StarAlignment though? that is the normal flow for most narrow-field images of comets.

 

rob


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#6 FiremanDan

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Posted 09 July 2020 - 01:09 PM

For the wide field I did star alignment, for the narrow view there weren't enough stars. It was getting pretty bright by that point, and the longer focal length image was the one giving me issues.



#7 Alex McConahay

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Posted 09 July 2020 - 07:55 PM

This might help some. 

Bob Traube from The Astro Imaging Channel a month or so ago..

 

https://youtu.be/iptZ6bj7pnk

 

Alex


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