From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


Ah, not realizing the effects of the optical system, are you Martin? Here's
the thing.  If your eyes are astigmatic (it soulnds like yours aren't) the
larger the exit pupil, the more the light hits the edges of the 7mm
(standard by definition of measuring a lot of eyes when fully dialated by
the dark) eye and that is where the astigmatism comes from, more than in
the center of the eye's lens.
Now, this is different than the astigmatism from the optical train of the
telescope where the various surfaces of the telescope and eyepiece can
cause the optical error.  This will be seen by all observers to the same
degree as it is from the optics external to the eye.  On a Newt., the
astigmatism will be done by the eyepiece.  I'll note that some designs are
noted for having that problem to a large degree and I have seen some EPs
that the problem is quite apparent.
Bob May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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