Triangular stars from Star Alignment

[Martin]

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

[georg.viehoever]

Maybe you attach some screenshots to your post.

[Martin]

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

[Juan Conejero]

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.

[Lex]

Hi,

hasn't this something to do with pixel rejection or some sigma clipping? 

[Martin]

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

[Lex]

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?

[Lex]

I assume that it could also be a small blooming issue