Re: [ATM] Astig. due to gravity

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

Actually, most of us test in the horizontal direction where the
astig. isn't a problem with the Foucault test.  As such, just
using the central zone 1 as the reference, you can test the
mirror in several directions andd see if theere is any astig.
which will show up as different readings in the different
directions.
The need to hold a thin mirror in a special fashion is more
related to full mirror tests where all of the mirror is tested as
in interfrometry.  There and in the Ronchi test, you can find the
astig. of the suport as well by rotating the mirror again and
seeing what changes happen.  Test stand astig. will not move
while all of the other defects in the surface willl rotate.
Bob May

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


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