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coma
I read recently that short focal length mirrors always display coma except at the very centre of the field of view.
This would explain why stars in my scope mostly display tails, which no amount of collimation, even with a laser collimator, will fix.
Has anyone any experience of this, and for the future, when I build my 24" reflector, what focal length should I be grinding to avoid this?
Thanx gise.
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