Re: [ATM] equatorial platform and best scope for uses

["matt" <electro_optic@bellsouth.net>]

-----Original Message-----
From: Mark Holm <mdholm@telerama.com>
To: atm@atmlist.net <atm@atmlist.net>
Date: Saturday, October 01, 2005 9:34 AM
Subject: Re: [ATM] equatorial platform and best scope for uses



>At f/5, a 25mm eyepiece is going to give 40x which gives an exit pupil
>of 5mm.  By the time you get to be my age (0.05 millenia), it is likely
>your entrance pupil isn't much bigger than this, so any less
>magnification just throws away light.  Boost that to f/6 and you get to
>the same exit pupil at about 32mm eyepiece focal length.
>
>--
>Mark Holm
>mdholm@telerama.com

any less magnification than 40x not only would throw away light but would
make the secondary mirror obstruction more and more visible .
The limit to low power magnification is not due to throwing away light but
due to seeing the secondary shadow like a black spot in the center of the
image .
Not throwing away light would be nice but it's not something that one would
notice by looking through the eyepiece, while the secondary shadow is very
visible .

best regards,
matt tudor

_______________________________________________
ATM mailing list http://www.atmlist.net/