Attendees: EdK, TomT, DmitriiZ, TimC, TomW, JoeD, NathanF, JerryW
EdK- 1968 pyrex 12.5” f/5 mirror: TomW showed EdK how to polish out the raised center with a 6” tool (TomW made for EdK) and center only motion. TomW set up the Ronchi tester, with the diffraction grating, to check the mirror progress after 30 minutes and again after 15 minutes of polishing. I think the mirror was improving a bit. EdK had a price list for a barn door type telescope mounting base ( http://www.equatorialplatforms.com/ ).
TimC-continued his work on donated 8” mirror grinding to f/5 but skipping to 220 grit from 80 grit since 120 grit was not available. TimC let TomT and ChrisU practice the grinding cycle/motions (1/3 over centers) with the mirror. TimC explained that once the needed depth of sagitta (curvature) of the mirror blank is reached by larger grit grinding, then the mirror glass blank and the tool need to switch bottom/top positions about every 3 grinding cycles around (or when the grit wears smooth?), so that the center and edges of the mirror wear down evenly. At the end, TimC showed us the cleaned off surface of the mirror glass showing some imperfections from the unfinished grinding process.
DmitriiZ-working on his 12.5”, polishing the center down, DZ used TomW idea to form the pitch against mirror with a “washer of paper” at the edge, so the pitch extends a fraction more out in the center. Later tested on TomW Ronchi tester, it was still high in center and TomW/JerryW giving ideas on how to polish out the center.
JerrryW talking a long time to NathanF & TomT about astrophotography, and types of camera sensors, noting that human eyes are most sensitive to green light. NF is looking to take good photo of M31 for one. ChrisU asked JW about finding a finished 8” mirror that he can construct a telescope around and JW checked CloudyNights.
More photos and videos: http://www.flickr.com/photos/27241501@N03/sets/72157635376717258/
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