Re: [ATM] Nasmyth secondary mirror cell ?

[Don Anderson <donanderson@direcway.com>]

----- Original Message ----- 
From: "Jeff Anderson-Lee" <jonah@cs.berkeley.edu>
To: "Don Anderson" <donanderson@direcway.com>
Cc: "The Amateur Telescope Makers List" <atm@atmlist.net>
Sent: Thursday, May 27, 2004 4:27 PM
Subject: Re: [ATM] Nasmyth secondary mirror cell ?


> I'd probably opt for (1) myself.  (2) might introduce some contrast
> reducing diffraction artifacts into the image just as spider vanes do.

Thanks
>
> However, two inches is awfully small for the tertiary on a 22 inch
> mirror.  You will probably never get a 100% illumination field.
> Meanwhile, 8 inches is a large secondary obstruction (36%) which will
> reduce image contrast.
>
> Try sizing the tertiary as if it was a secondary for a standard
> newtonian, then pick a secondary that will give you roughly the same
> size ratio between primary to secondary as secondary to tertiary with
> the tertiary near the expected center of gravity.
>
Your right.  A 22 in. f/6 Newt needs a 2.75 in secondary (my tertiary).
But, the ratios you suggest still require a 7.78 in seconday.


> Finally, I'd consider if some other design might suit your goals better.

This will be a working model/practice run for my 1 meter scope.  Neither are
planned to be mobile.
>
> Jeff
>

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