131203

131203 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  TomT, JerryW, TomW, TimC, DmitriiZ, EdK, ChrisU

EdK’s mirror examined again after another 7 hours of home polishing with TomW’s Ronchi tester.  Center is slowing expanding to spherical surface, but TomW thinks more pressure is needed for faster change.  Lighter lapping tool is over mirror as TomW says heavy mirror over tool would be bad for mirror.  Several positions of the tester for curvature of radius were tried.  Using the Ronchi with only one line being used like a knife edge of a Foucault tester shows, per Jerry, two gray areas that have the same radius of curvature, one in the center and one out beyond the 70% area.  Jerry gave EdK a list of the zones that he uses.

TomT loaned his EasyTesters for collimation testing to JerryW.  TomT also showed the Bahtinov mask purchased via Amazon, that helps to find exact focus for a telescope.  The size he had was for 5-8.5” mirror appatures.

TimC continued 320 grit grinding on the donated 8” mirror, while Dmitrii worked on polishing his 12.5” mirror.