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

[Curtis Spivey <curtis.spivey@gmail.com>]

On 6/14/05, jsgrmfg@gracemfg.com <jsgrmfg@gracemfg.com> wrote:
> 
>  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
> subtle and hard to read.  I read somewhere that if you are testing an F/10
> and can see a definite Foucault "donut", you are already way overcorrected.
> The lateral wire test might be a good solution for the subtle shadow
> problem but building the tester might be more trouble and complication than
> most beginners want.
> 
> Jim Sturtevant
>

So, would it be better to go all the way to say a F/12 and leave it
spherical for simplicities sake?  Or would image quality suffer?
Remember this will mainly be a planetary scope.  I also plan to make
it a truss-style scope on a Dob mount just to be different.  So, a
focal length of 72" (F/12) for a 6" objective would still be
practical.  The eyepiece would still be well within ground level for
viewing.

-- 
Curtis
'03 ST1300 (Hers)
'97 ST1100 (His)
'00 NightHawk (Daughter)
Nampa, Idaho
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