Problem Subs

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h2opolo
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Problem Subs

Post by h2opolo » Tue Sep 12, 2017 9:08 pm

Hey if I have a bunch of Ha subs and 1 or 2 have a little bit of star drag from a bad guide will they really mess up my stars in the stack?

Same question for a bunch of subs where a few are dimmer due to some high clouds that rolled in?

Should pull them out or is it okay to keep them. I hate to lose 30 minute subs but will do it if it's going to have an effect on the final stacked image.
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Re: Problem Subs

Post by Rudeviewer » Tue Sep 12, 2017 9:14 pm

It will affect the image in my opinion. It's not just the stars that are elongated, it's the detail as well.
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Re: Problem Subs

Post by Doug » Wed Sep 13, 2017 8:55 am

If I get subs that have airplane trails in them, I use them. With a sigma clipping stack it will automatically remove the the plane trails.

If you take an image with star trails, it's not only the star trails that are moving, but, the nebula gasses are also moved. So if Sigma Clipping was used, it would then in theory remove the entire star trail sub...so IMO, star trails means it's time to throw it in the bin and do not use it...unless you want to create a star trail image?
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h2opolo
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Re: Problem Subs

Post by h2opolo » Wed Sep 13, 2017 12:03 pm

Yeah I'm probably using the term star trails loosly here. Actually the stars are just out of roundness and more oval shaped in those few subs. If I had actual trails I would toss them but I'm not sure if 1 or 2 oblong star shots will ruin a stack of 24 subs shot at 20-30 minutes.

Sorry for not being clear enough.
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Re: Problem Subs

Post by Rudeviewer » Wed Sep 13, 2017 12:06 pm

Run a HFR on the stack with and without and see what it does....
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h2opolo
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Re: Problem Subs

Post by h2opolo » Wed Sep 13, 2017 6:36 pm

Never thought of that. How do you do that
Carbon ED 127 FCD 100 SERIES, GSO RC-8, WO ED 102, WO GT71 & Zenith Star 61
Losmandy G11G
NEQ6, Ioptron Sky Guider Pro, Lodestar X2,
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Re: Problem Subs

Post by Rudeviewer » Wed Sep 13, 2017 6:44 pm

Just open the images in SGPro and do a star size comparison????? You tell me lol. Isn't there a way to check the HGR of an image?
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Williams Optics GT81
Astro-Tech 8" RC
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Orion Thin Off-Axis Guider

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