Re: [ATM] Another Astigmatism question, but at the sphere stage

[Dale Eason <atmpob@yahoo.com>]

Several people believe that you are not measuring
astig using this technique because you cannot put the
mirror back on the stand accurately enough after
turning it.  Perhaps you can test that theory. 
Measure and then rotate the mirror 360 degrees, then
do the test again and see how close the ROC
measurments are to one another. 

I think Jim Burrows once posted about how accurately
the placement must be.  It was very tiny, I think it
was less than a millimeter.  Look through the
archives.

However a good test when you are at a sphere is the
ball bearing test as described in Texerau.

Dale Eason
> At 19:47 8/27/05, J Killea wrote:
> >
> >HOWEVER, I just did three sets of Foucault
> measurements along each 
> >of 2 diameters and Sixtests (set to "Target b=0"
> with variable ROC 
> >calculation) came back with the ROCs of each
> diameter differing by 
> >about 0.5mm.  That's more delta than what I had
> when I thought my 
> >parabola was done the first time.
> >
> >My question is whether it's too early to judge
> astigmatism, since 
> >I'm only at the sphere stage, and whether Sixtests
> with Foucault 
> >data is even a valid way to judge astigmatism.  I
> might just stick 
> >it back in the 'scope
> 



		
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