Wednesday, December 11, 2013

131210 Telescope Workshop notes

131210 Telescope Workshop notes 730-9p Tuesday evening
Attendees:  TomT, JerryW, TimC, EdK, ChrisU, David/MadelineH

JerryW reviewing EdK mirror Foucault photos and describing strokes needed.  EdK has been doing the chordal stroke trying to lower outer surface.  Center seems to be more spherical.  Jerry says matching Ronchi diagram is better than Foucault for determining shape. Later, W stroke (tall in center, tool on top of mirror) will be used for final polishing to parabola.
markers in the photos are at:
            1)  31% = 1.9375  inches
            2)  55% =  3.4375 inches
            3)  70% =  4.375   inches
            4)  84% =  5.25     inches
            5)  95% =  5.9375 inches

TimC suggesting bringing in samples of Telescope Workshop stuff to monthly meetings.  He will bring subject up at planning meeting this Saturday.  He has a 6” donated mirror from Doug? that needs to be refinished if someone will show some interest in attending the telescope workshop.  Tim explaining and showing David and Madeline the grinding of the 8 inch mirror.  TimC continued 320 grit grinding on the donated 8” mirror.

EdK showed us his new Celestron CGEM Pro control module with lots of ports on it. 
He will be mounting this on a Losmandy G11 pedestal? mount.

DavidH brought in the old Celestron German Equatorial Mount.  It was binding so David tried to check out the wormgears.  Seems maybe too much white grease added.  Jerry thinks wormgear shaft needs some spacing Teflon washers to keep it properly in place at the gear to prevent slack when reversing direction.  Also, some 5 pin DIN cables are needed to connect the motors to the controller.  Art Harris may be contacted for his expertise for both situations.

ChrisU brought in his flaming tomato dobsonian telescope and mount. TimC laser collimated the telescope for him.  We checked out the perfection of Mike Farris’s polishing and the aligned unit by looking at the Moon and the straight wall.  The mount worked well.

Saturday, December 7, 2013


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.