Thanks for your suggestion Greg - the PSF tool in pixinsight is reporting FWHM values of 3.5 to 3.7 pixels for all three colour integrations on the same star, and with a bit more careful combination and calibration techniques, there are no longer any halos in the image. I'm actually well chuffed for such a short exposure as a first light test for now.
The other mystery is the absence of any yellow stars. I used to see this with the CLS CCD filter on my DSLR, and it just occurred to me that low pressure sodium is yellow, so I think I'll be leaving this filter off the front of the coma corrector in future!
Latest image...
http://www.astrobin.com/37459/C/
Cheers,
Andrew.
Quote:
Originally Posted by gregbradley
Parfocal is really marketing BS. To be parfocal filters have to be virtually the same thickness. In reality there can be subtle differences in thickness.
Mind you my latest Astrodons are fairly parfocal but others I have had were not but often very close.
Who knows, maybe the seeing was worse or some wind came up when you did your red subs or the scope was lower in the sky where stars will get fatter anyway no matter which filter is being used.
One solution is to do some deconvolution on the red master to get the same FWHM size on the stars before colour combine to match them and prevent this.
Greg.
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