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That's a very striking image Paul.
The star halos aren't that noticeable to me.
It may be you didn't feather at some point the star selection so it has a harsh edge.
It could be your blue stars have larger FWHM than the red and green.
You could go back to your master red, green and blue and measure the FWHM of the same stars in CCDstack (double click on a star) and see if the FWHM values are much worse in blue (they often are).
Then try deconvolution/positive contraint -say 40 iterations, increase the radius a tad and pick that same star as a reference. Run decon and remeasure. When you get blue FWHM on that star the same as red and green then try a new colour combine and see if that handles it.
Jase had a fairly complex way of handling halos. Its in the processing tips area. I have a copy of it if you need it.
Photoshop actions reduce small violet halos can work but it really just desaturates the blue halo. Its not bad.
Reflection halos around bright stars I would guess are reflections off your reducer and CCD window. Roland Christen has commented on the single layer anitreflection coating of the QSI CCD window causing reflections on the AP group. Perhaps it only happens with faster F ratios with different light angles.
Only thing I can think of to try to stop that is a black cardboard mask with a cutout for only the CCD chip put over the CCD window to reduce stray light getting in and causing unwanted reflections. Short of that check for any shiny bits in adapters for the reducer or the reducer itself.
Greg.
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