Re: [ATM] [ ] making Foucault tester

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

Sounds like you understand the Foucault test with the Couder Mask
perfectly!
The test isn't a test of a parabola but, as you have said, a test
of the ROC of different zones.  When you reduce that data, you
can tell if the mirror is a paraboloid shape and, if the slopes
between the zones are smooth, you have a paraboloid surface.  You
can make a mirror for a mask of any particular mask and hav it
not be a good mirror but it will test well with that mask because
the zone readings are good.  The problem that would be in the
mirror is that each zone would be a spherical surfacce and there
would be a jump in ROC hidden by the mask.  Use another mask with
zzones in a diffeerent spot and you will then be able to spot the
error out.  This is the problem that I have with a Cassegrain
secondary from a commercial maker of telescope optics and it is
an interesting thing to see when doing a Ronchi test on a star.
Nothing like seeing the lines jump from one angle to the next as
you go out towards the edge of the image!
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


_______________________________________________
ATM mailing list http://www.atmlist.net/