To: atm{at}shore.net
From: "James W. Burrows" 
Reply-To: "James W. Burrows" 


At 08:38 2002-12-15 +0000, kwhitefire{at}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-Chr‚tien cass is aplanatic,
but has plenty of field curvature.

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

--- BBBS/NT v4.00 MP