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Originally Posted by janoskiss
I see your point. I have no direct experience of how that looks in practice. I certainly cannot see anything wrong with star images at the edge of a 70 degree FOV of 10mm XW eyepiece at f/5, or even at f/4. Looking at Al Nagler's graphs (above), I should. I remain curious to try a Paracorr.
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Depends on many things, mainly on how critical the observer is. Some eyepieces may in fact reduce visible aberrations (some well known examples are Pretoria + paraboloid or Plossl + Jones-Bird). Unfortunately, I don't have any experiences with 10mm XW, but I'll keep an eye on it.
Naglers definitely show coma of an f/4 paraboloid, compared to a much better corrected scope like my homemade f/4 Wright. But difference is indeed rather small compared to say astigmatism of 'ordinary' eyepieces.
Bratislav
PS '101' as in elementary principles, not some ideal cases that don't apply to real life