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Hi Karl,
Looking at each of your pics, I woulld say that the focal reducer you are using is introducing astigmatism and spherical aberration. The tell-tale sign of astigmatism is those little seagulls that are co-centric to the optical axis. The spherical aberration comes from the comet-like appearance of the stars - it's not coma here. Coma has a similar appearance, but it's not what is being seen.
Alex.
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