Re: ATM stopped down apat. to 18 inches?

["AstroIdiot" <tgooch@arkwest.com>]

To begin with an off-axix Dobsonian would have a parabolic mirror not
sperical. A sperical mirror has sperical aberation in any configuration
unless it employs a corector of some sort (schmidt, wright, maksutov...)
If you want to use a corrector then you should be able to build a usable
sperical mirror telescope. Or you could parabolize the mirror.
The reason a stopped down dob works well is because it is an off-axis
parabola (difficult to make).
----- Original Message -----
From: "Joseph Johnston" <usc@sover.net>
To: "Steve Fejes" <jsfejes@swva.net>; <atm@shore.net>
Sent: Thursday, December 27, 2001 3:13 PM
Subject: Re: ATM stopped down apat. to 18 inches?


>
> Steve
>
>      If what your saying is true, then an actual stopped down 48"er to an
18"er, (NO glass
> being removed at all),  would reveal the same results that OSLO gave you
and thus its
> performance wouldn't be as good as the reports that are given about
stopped down
> apertures, i.e. better contrast, a better planetary scope, etc.. Have I
missed something
> here also?
>
> --
> Joe & the four furry paws of Jenny, the wonder dog,
>        in the Aurora filled skies of northwestern Vermont.
>                Swanton - The Maple Syrup capitol of the WORLD...
>
>
>