Author Topic: Triangular stars from Star Alignment  (Read 2932 times)

Offline Martin

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Triangular stars from Star Alignment
« on: 2012 April 15 04:40:45 »
Hello
I am trying to register image data taken with an FSQ106/STL11K, which has a resolution of 3.5 arcsecs/pixel - undersampled.

The problem I am finding is that the result of the alignment from PI is triangular stars.  I have 'blinked' the original data and the aligned data to confirm this.  I have used both the defaults, and various algorithims in the 'interpolation' dialogue box to no avail.

So what values do I need to adjust to overcome this? Otherwise,PI does a great job of alignment, but is distorting the result.

thanks
Martin

Offline georg.viehoever

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Re: Triangular stars from Star Alignment
« Reply #1 on: 2012 April 15 04:45:45 »
Maybe you attach some screenshots to your post.
Georg (6 inch Newton, unmodified Canon EOS40D+80D, unguided EQ5 mount)

Offline Martin

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Re: Triangular stars from Star Alignment
« Reply #2 on: 2012 April 15 06:05:49 »
Sure, two files attached.  The file was aligned used the defaults in StarAlignment, but all of the parameters I have changed so far, has a similar result.

thanks
Martin

Offline Juan Conejero

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Re: Triangular stars from Star Alignment
« Reply #3 on: 2012 April 17 04:33:31 »
Hi Martin,

I can't say anything from these screenshots. Could you please upload the images (the whole set you are registering)? I really need the images to know what's happening.
Juan Conejero
PixInsight Development Team
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Offline Lex

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Re: Triangular stars from Star Alignment
« Reply #4 on: 2012 April 21 16:24:19 »
Hi,

hasn't this something to do with pixel rejection or some sigma clipping?  ::)
Clear Skies!!

Lex

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HADSO (Hagen Deep Sky Observatory)20 km W of Luxemburg City

Offline Martin

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Re: Triangular stars from Star Alignment
« Reply #5 on: 2012 April 25 05:15:48 »
Hi Juan
wish I could upload the entire set of images, but the full frame FITS files are 21Mb each and there are dozens of them.

I think Lex might have a point...what parameters in the star alignment process affect pixel rejection?

Otherwise, If you could please indicate some parameters I can try - quite simply, the data is undersampled, stars are quite blocky, and the alignment takes these blocky stars and turns them into diamond shaped stars.

thanks!
Martin

Offline Lex

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Re: Triangular stars from Star Alignment
« Reply #6 on: 2012 April 25 14:54:45 »
Hi,

It is kind of difficult to figure out what has to be done; perhaps try some noise reduction with applied inverted starmask in order to cut of the external misshapes of the stars?
Clear Skies!!

Lex

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HADSO (Hagen Deep Sky Observatory)20 km W of Luxemburg City

Offline Lex

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Re: Triangular stars from Star Alignment
« Reply #7 on: 2012 April 25 14:56:02 »
I assume that it could also be a small blooming issue  ???
Clear Skies!!

Lex

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AZEQ6 GT, TS UNC 10" f5, ASI1600mm-c

HADSO (Hagen Deep Sky Observatory)20 km W of Luxemburg City