Re: ATM null for sphere

["Bob May" <bobmay@nethere.com>]

Not only does the test check for flatness (moderate accuracy here) but it
checks for something more important with refractive optics - the internal
homogenity and refractive index changes which will seriously affect anything
that you may want to do with the glass.
Don't forget to do the test with the glass in several different orientations
so you can see errors at an angle other than vertical or horizontal.
I might note that early refractive optics were often modified after the
inital polishing to get rid of internal refractive problems with changes of
the surface shape.
Bob May
http://nav.to/bobmay
bobmay@nethere.com