Re: [ATM] Am I there yet?

[Dale Eason <atmpob@yahoo.com>]

It is hard ( next to impossible) to measure turned
edge using foucault data because the number of samples
across the mirror is too small to see the small tuned
edge.  Making the zones smaller doesn't help however
because then diffraction becomes a problem.  You have
to use other means to determine if there is a turned
edge.  One is ronchi.  However you can also use the
knife as a one line ronchi.  Move the knife inside or
outside ROC just like you do the ronchi then move the
knife accross the mirror so that the shadow is either
1/4 the way across or 3/4 across the mirror.  Look at
the shadow close to the edge.  If it hooks sharply in
or out you have a turned edge.  It will hook the same
as in the ronchi but with out the diffraction lines
caused by the fine line ronchi screen.  This check is
also described in Texerau.

You could try putting masking tape on the bevel if you
think it is causing problems.  


Dale Eason
--- Don Bates <dbates59@yahoo.com> wrote:

> I could use some second opinions on the condition of
> my mirror from some of the seasoned figuring experts
> out there. First, a bit of background:
....
> Here are my questions:
> 4) What is the condition of the edge? When I try the
> Ronchi at 100 lines, it appears to have hooks
> sloping
> outward at the very edge when outside focal plane.
> Is
> this really a turned edge, or just diffraction
> effects
> at the bevel? I can't seem to get rid of these hooks
> no matter what. 
!
> - Don  
> 



		
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