RE: [ATM] what to do next Part 2

["Michael Warne" <mwarne@network2000-hi.com>]

Hi David,

>I've got a foucault tester and need to know how to use it.  
>>looked like my mirror was spherical.  We could see a doughnut image in
the tester.

When you have a spherical surface, the entire mirror surface will darken
equally as the knife cuts into the light cone at radius of curvature.
What I mean to say is that you should not see a 'doughnut' shape for a
spherical surface. You have some other figure... Not a spherical
surface.  Do you have a ronchi grating?  Ronchi lines will appear
perfectly straight for a spherical surface. 
David Harbor has a nice article with pictures to help with understanding
focault.
http://www.atmsite.org/contrib/Harbour/Foucault.html

For the Ronchi test:
http://www.atm-workshop.com/ronchi-test.html


Also a 20 inch, by 1 inch is rather thin.  A thin mirror needs proper
support both in the telescope, and maybe even while testing (Others on
this list will have better advice for you on this topic).

Mel Bartels has a Thin Mirror page..
http://www.efn.org/~mbartels/tm/largthin.html

Sounds like a challenging project!
Keep us posted on how you're doing..

Mike Warne.

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