Re: [ATM] Re:(ATM) F/10 or F/8?

["Richard Schwartz" <richas@earthlink.net>]

Instead of a 6" f/10, you should have a 9" f/6.66.   The tube length would
be the same.  The magnification would be the same.  Diffraction would be
less.   There would be a lot more photons for photography.   The satanic
f-ratio would be the same as the palomar 200, if I remember correctly.

----- Original Message ----- 
From: "Michael Peck" <mpeck1@ix.netcom.com>
To: <atm@atmlist.net>
Sent: Tuesday, June 14, 2005 7:48 AM
Subject: Re: [ATM] Re:(ATM) F/10 or F/8?


> At 08:44 6/14/05, jsgrmfg@gracemfg.com wrote:
>
>
>
>
> > >Can anyone tell me if there would be any advantage in making a mirror
> > >in an F/10 vs. a F/8?  Seems like everything is a an F8.  This will be
> > >for a 6" mirror for primary use in a planetary scope.
> >
> >   F/8 is common and often recommended because it is the longest focal
ratio
> >that can be tested easily by a beginner.  An F/10 is too short to leave
> >spherical but so close to a sphere that the Foucault shadows are very
>
> A 6" f/10 sphere is diffraction limited by any reasonable criterion. A 6"
> f/8 sphere falls just short of satisfying the Marechal criterion, and also
> fails by varying amounts on other, older criteria.
>
> Mike Peck
>
>
> ------
> Michael Peck
> mpeck1@ix.netcom.com
>
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