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Comet Wirtanen/46P and the Pleiades (Final)

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#1 james7ca

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Posted 12 January 2019 - 05:34 AM

I managed to get some backing shots of the star field for my image of comet Wirtanen that I captured back on December 15, 2018. This was taken under my typical red/orange zone light pollution which is definitely a hinderance with an object that has such low surface brightness (and the waxing gibbous moon was present in the western sky during about half of these exposures).

 

Anyway, I used a 105mm Nikkor AI-S lens at f/4.6 on a Nikon D5100 (ISO 800) and combined 295 subs that were each exposed for 20 seconds to produce the image of the comet (the 20s exposure is about the maximum given my level of light pollution, total integration time was 295 x 20s ≈ 98 minutes ). Then I took 376 subs using that same setup on two later, mostly moonless nights after the comet moved out of this field of view (to record the comet-less star field and the Pleiades). Note that my original framing on the comet was the same as taken in these later shots, it's just easier to process the star field when there is no comet in the background (and vice versa).

 

Tracking was done with a Celestron AVX mount.

 

Image processing with PixInsight (comet registration tool) and Photoshop CC2017. I had problems with both a light pollution gradient and some uneven image quality falloff from the lens so I ended up spending far too much time trying to make this look presentable. This would have been a LOT easier under dark skies and with a better lens. That said, it's been a while since there was a comet that was even bright enough to attempt from my edge-of-downtown location.

Attached Thumbnails

  • Comet Wirtanen:46P with 105mm Nikkor Lens and Nikon D5100 (Small) .jpg

Edited by james7ca, 12 January 2019 - 08:19 AM.

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#2 mxpwr

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Posted 12 January 2019 - 06:38 AM

Very nice result.
I didn't have a chance to take more than a few pictures of the comet, Swedish winters are extremely cloudy...


Edited by mxpwr, 12 January 2019 - 12:17 PM.


#3 rgsalinger

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Posted 12 January 2019 - 10:06 AM

Great shot!!!! I have tons of comet data that I have to figure out how to process in PI. I am inspired!

Rgrds-Ross



#4 elmiko

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Posted 12 January 2019 - 12:31 PM

Great job James. So how did you add the comet to the star background? Did you integrate the comet subs with each other using linear clipping to get rid of the smeared stars? I have been trying to get a finished photo like yours that has the comet and stars aligned. I took 30 sec subs at 800 fl . 



#5 james7ca

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Posted 12 January 2019 - 09:12 PM

mxpwr, Ross, and elmiko thanks for the notice.

 

As for the processing, I aligned all the subs to the same reference sub that was taken on Dec. 15 and then I integrated just the subs that were taken on the later date that did NOT have the comet (the latter became my star field). Then I took the subs with the comet and used PixInsight's comet registration tool and selected to have the integrated star field subtracted from each of the comet subs and then I completed the comet registration (the subtraction of the star field is an option in the comet registration tool).

 

After the above I integrated the comet registered subs (which had only a few star remnants) to produce a result that had only the comet image. Then I used PixelMath to take the maximum from the star field integration and the comet integration and that produced the final image. You may have to experiment with the rejection parameters when you integrate the comet-aligned subs since there can still be some remnants from the star subtraction.


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#6 elmiko

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Posted 12 January 2019 - 10:17 PM

Thanks James 7ca, I will try your process. Thanks again.

Clear skies Mike



#7 BQ Octantis

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Posted 13 January 2019 - 09:16 AM

Very nice!

 

BQ



#8 james7ca

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Posted 13 January 2019 - 05:59 PM

BQ, thanks for the notice.



#9 BQ Octantis

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Posted 14 January 2019 - 02:40 AM

BQ, thanks for the notice.

No worries, mate. It's a fine exposure with no visible walking noise in the coma (which plagued most of my shots). And being in Adelaide for the Pleiades approach (with none of my equipment), I have to live vicariously through your shot…

 

Cheers,

BQ




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