Re: ATM 11.2" F/2 Primary testing questions :)

["Dennis Nikitin" <ndenis@sarkor.com>]

----- Original Message -----
From: James Lerch <jlerch1@tampabay.rr.com>
To: <atm@shore.net>
Sent: Monday, December 31, 2001 1:39 AM
Subject: ATM 11.2" F/2 Primary testing questions :)

>>>
Construction has began on my 11.2" F/2 Dedicated CCD scope (CCD chip resides
where secondary mirror would normally be)  I plan on stopping the primary
down to F/2.5ish (most-likely) if coma becomes a problem.
<<<

Hi, James
Don't warry about coma. You can stop down the aperture at the point of
curvature radius just like in Schmidt camera. It will kill coma +
astigmatizm. You will get a strange Schmidt with no corrector and with
parabolic primary. Anyway f/2 mirror has big field curvature. I don't know
what is the resolution of your CCD chip but it seems that you will have to
include Piazzi-Smith lens.

>>>
I'm just looking for some guidance on which might be best/easiest ;)
<<<

Focault test is hopeles for f/2 parabola. Wire test will work but its
sencitivity and acuracy won't be satisfactory. For my  RC cassegrian with
f/3 primary I used Spherical Null Test. SNT gives a lot of fun while testing
such a fast paraboloid. I'm sure that it will work with f/2 as well.


Happy New Year!!!
Dennis Nikitin