Hello all,
I took subs with LRGB filters with an APO - processed them equally in PI and after combining them as LRGB, many stars show this strange blue halo - which does not exist in the single mono channels - any idea how they came into existence and what to do to get rid of them?
Thanks for your feedback!
Georg
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Are you refocusing between the different filters? Focus is wavelength dependent and if you don't refocus, your different colors will be slightly out of focus depending on the quality of optics you have.
D. Jung · Oct 30, 2025, 10:12 AM
Are you refocusing between the different filters? Focus is wavelength dependent and if you don't refocus, your different colors will be slightly out of focus depending on the quality of optics you have.
Well, just what is necessary to keep the subs well focused - with AF routine in NINA!
Do you think that those blue halos come from subs which had not beed perfectly refocused after filter change - that could be possible, however I am not aware of it. The subs look all pretty good and well focused?
How does the hfr value look like for the different channels?
It's quite possible that you have best focus for all 3 filters, but the optics are not well enough corrected and you just end up with halos.
D. Jung · Oct 30, 2025, 10:30 AM
How does the hfr value look like for the different channels?
It's quite possible that you have best focus for all 3 filters, but the optics are not well enough corrected and you just end up with halos.
The optics is a 12” Truss RC and perfectly corrected
I see, if you have no glass in the optical train at all, that explanation makes no sense. But looking at your screen shot, the star sizes seem to be visually different between the different channels.
D. Jung · Oct 30, 2025, 10:57 AM
I see, if you have no glass in the optical train at all, that explanation makes no sense. But looking at your screen shot, the star sizes seem to be visually different between the different channels.
That I realized just a minute ago as well - I forgot to make “linear fit”….. it resolved the problem totally - everything is OK again!
Thanks a lot for pointing that out!!
CS
Georg
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Georg N. Nyman · Oct 30, 2025, 11:01 AM
D. Jung · Oct 30, 2025, 10:57 AM
I see, if you have no glass in the optical train at all, that explanation makes no sense. But looking at your screen shot, the star sizes seem to be visually different between the different channels.
That I realized just a minute ago as well - I forgot to make “linear fit”….. it resolved the problem totally - everything is OK again!
Thanks a lot for pointing that out!!CS
Georg
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I was just about t make this suggestion. Glad you figured it out.