Wierd doughnut glow on bright objects?
I have noticed this recently when I image bright stars for a moderate duration - it looks like a glow on some internal surface - anyone guess what it is (I suppose something needs cleaning and / or alignment)
Here is an shot of Jupiter for 30 secs that clearly shows the problem.
Imaging train is Celestron SCT -> Lumicon OAG with focal reducer lens -> Hutech LPS filter -> Canon 400D
Many thanks
Matthew
PS
What's it telling me that the doughnut is not dead centre of the image - that the focal reducer is not perfectly seated parallel to the Canon imaging chip? Maybe this is the source of coma in my shots?
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