[g__day (Matthew)]

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?