You've done really well with that lens.
I tried using it once on the Pleiades, about 5 years ago, and gave up very, very quickly. Admittedly, the version I was using was the image stabilised version. f/4-f/5.6, non-L series lens.
It has horrible chromatic aberration, in general. I think that's the cause of the magenta stars in your image.
Nicely done -- keep it up.
H
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