From: Guy Brandenburg 
To: Mark Suchting 
CC:  atm{at}shore.net
Reply-To: Guy Brandenburg 


It's not all that sensitive, though. My 8" f/6 homemade scope looks
absolutely perfect (to me at least) using a ronchi grating at prime focus,
but a star test reveals that it has a little bit of a turned edge
- now that I know what to look for. The ronchi test also doesn't do a
very good job on detecting mis-alignment. Anybody care to differ?
Guy Brandenburg

Mark Suchting wrote:
>
> At 07:31 PM 4/25/2003 -0600, Bill T. wrote:
>
>> In defense of star testing, I have to say that I have seen several "at
>> least acceptable" mirrors made using nothing more than formula
>> polishing techniques augmented with only a few star tests.
>
>
>
> I'd like to add that a Ronchi grating at prime focus on a star is a
> perfectly valid way to final check an F6 or slower mirror before
> aluminising.  Even in the presence of poor seeing, 1/4 wave mirror is
> easy to see and improve upon. More use of a simple test like this may
> give first time foucault test users an independent cross check on their
> mirrors.
>
> ~Mark
>
>
>

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