Attendees: EdK, TomT, TomW, JerryW, DmitriiZ, ChrisU
EdK- Was polishing his 12.5” mirror at home for 90min with the 9” pitched tool made by TomW. So, started tonight with testing with TomW’s Ronchi setup. TomW says 75% of mirror is spherical, but outer area TomW says is turned down still. Plus laser check of mirror surface by TomW shows outer area is still not specular; the light at the outer area is very wide compared to the inner area of the mirror. TomW took on more polishing and Ronchi tested the mirror at the end again, edges still turned down and other little things going on, but mirror surface is more polished out.
Dmitrii set his tool and continued his polishing. Noticing the slower polishing rate used by TomW on EdK’s mirror, TomT raised the question about speed of polishing motion. TomW says about 1 stroke per second across and one second back. JerryW says going too fast can cause microripples that show up in Ronchi test as soft lines. At the end of the evening, Dmitrii’s mirror was put on for Ronchi test…very interesting dual alien eyes, very curvy (see video on Flickr site below).
TomW brought in the book “Principles of Physical Optics”, by Bennett, used by junior/seniors at Westmont. ChrisU showed up with five astronomy books that were for sale cheap at the SBCC library, at least one was owned by Fred Marshak and a 2004 “Cosmos” book co-written by Alex Filippenko was also picked up in teacher/student versions.
EdK showed pictures of his Foucault test and polishing stand using a barrel at home. He had a picture of a heavy duty mount with large bearings made in Michigan that he was interested in.
More pics/vids at Flickr: http://www.flickr.com/photos/27241501@N03/sets/72157636608824126/
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