Author Topic: NB Alignment Problems - Ha and OIII data  (Read 139 times)

Offline Rastaban

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NB Alignment Problems - Ha and OIII data
« on: 2018 August 12 20:00:08 »
Hi all,

I've been diligently making my way through the Warren Keller book as well as the Light Vortex tutorials and have been learning a lot about PixInsight. Recently I captured two hours each of Ha and OIII on the Eagle Nebula. I decided to try my hand at the Light Vortex tutorial on Narrowband Bicolour Palette Combination. Everything has gone well all up until the Pixel Math portion of the workflow. As you can see on the attached image, I'm getting mis-aligned stars. However, when I overlay the Ha and OIII images they line up properly. Any ideas as to why this is happening? For reference, here the the link to the tutorial.

Thanks,

Daniel
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“The thing’s hollow—it goes on forever—and—oh my God!—it’s full of stars!”

? Arthur C. Clarke, 2001: A Space Odyssey

Daniel

Offline pfile

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Re: NB Alignment Problems - Ha and OIII data
« Reply #1 on: 2018 August 12 22:07:42 »
well i havent read the tutorial but it would seem that you didn't use a common reference frame when you did the staralignment step. you should choose the same subframe, no matter what filter it is, when aligning all the subs.

rob

Offline armyortho

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Re: NB Alignment Problems - Ha and OIII data
« Reply #2 on: 2018 August 12 23:01:28 »
This has happened to me.  Your subs for Ha were likely all registered to an Ha, and your subs for OIII were all registered to an OIII image (like the tutorial says).

You have to then register your resulting Ha to the OIII to get them to align.  Or, as pfile points out, simply use the same Ha file for the reference file for all your subs (Ha and OIII).

Just open Star Alignment again, pick your colsolidated Ha stack as your reference, and drag it onto your consolidated OIII file.  Then Color Combine the resulting *_r images and you're in like Flynn.

Offline Rastaban

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Re: NB Alignment Problems - Ha and OIII data
« Reply #3 on: 2018 August 13 02:03:32 »
This has happened to me.  Your subs for Ha were likely all registered to an Ha, and your subs for OIII were all registered to an OIII image (like the tutorial says).

You have to then register your resulting Ha to the OIII to get them to align.  Or, as pfile points out, simply use the same Ha file for the reference file for all your subs (Ha and OIII).

Just open Star Alignment again, pick your colsolidated Ha stack as your reference, and drag it onto your consolidated OIII file.  Then Color Combine the resulting *_r images and you're in like Flynn.

Booyah! That worked, thank you!
“The thing’s hollow—it goes on forever—and—oh my God!—it’s full of stars!”

? Arthur C. Clarke, 2001: A Space Odyssey

Daniel

Offline pfile

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Re: NB Alignment Problems - Ha and OIII data
« Reply #4 on: 2018 August 13 04:56:27 »
that's good - but note that you've done a double interpolation on the ha master. while it works OK it is sub-optimal... next time thru it's better to use a common reference frame for the staralignment processes (or just run SA once against all subs from all filters, that is perfectly fine.)

rob

Offline Rastaban

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Re: NB Alignment Problems - Ha and OIII data
« Reply #5 on: 2018 August 13 15:35:09 »
that's good - but note that you've done a double interpolation on the ha master. while it works OK it is sub-optimal... next time thru it's better to use a common reference frame for the staralignment processes (or just run SA once against all subs from all filters, that is perfectly fine.)

rob

Noted. Next time around I'll make sure to properly align first.
“The thing’s hollow—it goes on forever—and—oh my God!—it’s full of stars!”

? Arthur C. Clarke, 2001: A Space Odyssey

Daniel