Quote:
Originally Posted by Stonius
This is a sub from my Luminance Data.
Just looking at the non-symmetrical halo around Alnitak.
Is its asymmetry caused by being positioned in the top left of the image? Or should I look to my collimation?
I did check it on the night using the tube reflections method and it seemed spot on.
Cheers
Markus
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It could be lens flare/reflection caused by an off axis light source or a refection from filters or even from the sensor itself. There appear to be multiple faint haloes around the star, displaced ever so slightly along a line towards the image centre, which is typical of lens/optical system flare. When these
ever so slightly displaced haloes appear on top of one another they appear as an ovalish shape as a whole and I can certainly see how they could blend together to form the
IMPRESSION of a collimation issue (whilst not actually being one). See attached (exaggerated) diagram.
I recall reading of an issue with reflection artifacts with the ASI1600 caused by a lack of/type of anti-reflective coating on the sensor window. I also recall the image had faint diffraction type spikes in a 4/8 spoke pattern, which are also present and similar to those in your image, but I'm not sure. The spikes may have been caused by a diffraction/reflection from the prism of an off-axis guider. Did your image also use an OAG?
To try to verify the cause, perhaps a different type of filter could be trialled, with a different antireflective multicoating. Perhaps a photographic filter
Best
JA