From: J-Engineering 
To: Jeff Baldwin , "atm{at}shore.net"

Reply-To: J-Engineering 


Hi All,

I'm trying to work with what I have which is a knife edge and Ronchi setup.
 I can certainly modify them if I know what helps.

To see any shadows at the knife edge, I need to be within about 0.005
inches from the COC.  Any farther and I can see the knife edge moving in
from the side and the shadows are gone.

So, given these set-ups, is it possible to quantify the surface somehow? 
Will the _very_ slight bends in the Ronchi test tell me something?  The
fact that I can tell they are not perfectly straight must mean that the
surface is ...... what?

Thanks,

Ray

Jeff Baldwin wrote:

> You can still use a couder mask with a sphere.  You can also caustic test a
> sphere.  The best is if you just happen to have a matching convex sphere
> that you can use to fringe test.  The fringe lines will tell you exactly
> what the error altitude is.  The very, very best would be an interferometer.
> JB
>
> Jeff Baldwin
> Stockton  CA
> W121d20.96m N38d01.62m
> bald{at}gotnet.net
> http://bald.gotnet.net/
> ----- Original Message -----
> From: "Ray{at}J-Engineering.com" 
> To: 
> Sent: Sunday, February 09, 2003 4:28 PM
> Subject: ATM Tesing a spheriod?
>
> >
> > Hi All,
> >
> > When testing a spheroid,  how can you quantify the figure?
> >
> > As far as I can tell, the edge is good.  I used an oversized lap which
> > seemed to work rather well.
> >
> > If I set things up just right, I can get the Ronchi lines (grating /
> > grating) to bend just a bit.  Hardly noticeable.  It seems to only work
> > at the few positions where the diffraction images combine or merge just
> > right. How can I tell how far off the surface is?
> >
> > In a slitless knife edge test,  at ROC, I can just eek out a few shadows
> > just before the whole image gets too dark.
> >
> > I'm working on getting a feel for using these tests and trying to
> > associate some kind of number to what I see.
> >
> > (8", f/6.3)
> >
> > Thanks for any help or web links,
> >
> > Ray
> >

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