Re: ATM X-Mailer: Juno Webmail Version 1.0

["James W. Burrows" <burrjaw@earthlink.net>]

At 08:38 2002-12-15 +0000, kwhitefire@juno.com wrote:

>Aplanats are telescopes with flat focal planes.  This is a difficult 
>situation with mirrors.  Add mirror #3 and the focal plane becomes 
>flattened more easily than with two mirrors.

THE Bible (Born & Wolf, "Principles of Optics") says an aplanatic system is 
one which is free of spherical aberration and coma - nothing about 
curvature of field.  The Ritchey-Chrétien cass is aplanatic, but has plenty 
of field curvature.

         -- Jim Burrows
         --              mailto:burrjaw@earthlink.net
         --              http://home.earthlink.net/~burrjaw
         -- Seattle      N47.47233, W122.36620 (WGS84)