Thank you to those who replied to my testing dilemma. FYI, I have tested my 17" mirror in the scope with a ronchi grating and also performed a foucault test with a razor blade. This was stuck in an eyepiece tube unscrewed from a 2" eyepiece. Doing the foucault test in the telescope proved challenging but showed turned edge with the rest of the mirror going dark grey during that brief moment when everything lined up. When right at the null zone the whole mirror just blanked out. It is a very sensitive test to perform! This is about how it tested inside with my foucault tester setup with TDE showing much the same area. The ronchi test showed straight lines except the outer 1/4" which is the TDE. This is a very easy test to perform so I may just stick to that in future. cheers, Frank
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