ATM Re: Spherical mirrors

["Charvell" <charvell@sofnet.com>]

I'm beginning to understand this now. It has nothing to do with f/ratio of
the selected primary but rather the radius of the larger section. I'm then
dealing with a piece of a larger mirror. This is exactly what I was after.
Thanks a bunch.

Herb Watson
Lamar, Mo.

----- Original Message -----

> Date: Thu, 23 Aug 2001 00:54:29 -0700
> From: "John Sherman" <shermj@netzero.net>
> Subject: Re: ATM Spherical mirrors
>
> Herb,
>
> When my uncle Jerry Raths was like 92 years old he tried this for the fun
of it.
> He made a 6" f/12 and tilted it, without your folding mirror (it's a
Herschelian
> telescope). (The flat mirror will require you to tilt your primary even
> farther.)  It didn't work well. A spherical 6" f/12 will work well
on-axis. But
> a tilted 6" f/12 is a section of a 13" f/5.5. Since an f/5.5 has to be
> parabolic, so does the tilted 6" f/12 have to be a section of that
parabola.
> Let's see, a 6" section of a spherical 13" f/12 would need to be ......
too long
> to be practical.
> I believe he then made it into an on-axis and donated it to Grand Canyon
> College.
> Last I heard the McMath Observatory in Michigan was still using the 21"
> off-axis section of parabola he made for them...
>
> John