On 08 Oct 2003 02:09:20 GMT, (Rod Mollise) wrote:

Prism diagonals of _any_ kind usually produce poorer images than mirror
diagonals of any kind.

I must respectfully disagree. The statement is true if qualified to
read "when used in short FL instruments." In longer FL 'scopes (F10 &
up), a good prism will be the equal of the many mirror diagonals, and
often will have greater throughput. Their known tendency to introduce
CA is muted by the less steep light cone, and the losses at the
air-to-glass interfaces are less than those of most first-surface
mirrors.

Problem is, its doggone expensive to make a *good* 2" prism, so that's
where the price/performance ratio turns around.

Wayne Hoffman
33° 49" 17' N 117° 56" 41' W
"Don't Look Down"

http://home.pacbell.net/w6wlr/