Re: ATM Newtonian with a Tilted Secondary

[Anthony Stillman <atmer@flash.net>]

>...a Newtonian with a
>secondary that is tilted at an angle other than 45 degrees.  Specifically,
>I want to reduce eyepiece height...


Mike,

This is my current plan for the 30 inch.  I intend to follow Bob Pfaff's 24
inch design.  Bob's design can be seen at
<http://www.rtmc-inc.org/RDS/RTMC96.html>.  For observational convience he
uses a star diagonal at his waist high focusor.

Clearly there are two issues to overcome.  Concern about the effect of the
size of the obstruction on light loss and on contrast.  My plan calls for a
secondary diameter right around 35 percent of aperture.  About the same as
a Mak.  At ten percent, the light loss is negligible and concerning myself
with contrast loss is pointless.  Even assuming the final system is tenth
wave the odds of a thirty inch diameter tenth wave window appearing in the
atmosphere over the mirror while I'm using it are at best small.  On the
other hand falling off a 12 foot ladder at two in the morning seems all too
real.

I do intend to address scatter issues by having the secondary and star
diagonal (assuming its a mirror) overcoated with MgF.


Anthony