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[ATM] Vignetting in eyepieces

  Looking at the eyepieces provided in the Selby article of ATM 3, I
was having problems making a lot of sense out of quite a few of the
prescriptions.  Some of the key, I think, is the vignetting factor
allowed by Selby.  I finally got the Hastings triplet equivalent of:

    http://users.rcn.com/rflrs/t01-23x.len

This prescription is an exact replication of the values given in the
article (up to the glasses, that is).  However, the last surface is
aperture limited, but allowing for a "liberal" 0.175 mm mounting
surface.  At that limit, the vignetting factor is nearly down to 0.5.

This does make a significant in the gross spot diagram, even if not
as much of difference in the RMS spot size.

-- 

Rick S.

http://users.rcn.com/rflrs


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