Mirror polished and first test – Foucault

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The mirror is now polished and ready for being tested first time. When I saw the artificial star first time I was very fascinated, alle that work and the little faint star was reflected quite sharp on a white screen at the focal fix point. The radius of curvature was measured to 2370 mm, the focal length is then 1185 mm and the F-number is f:4.7. Pictures of the polishing lap, testbench and the testresults is inserted here:


The scratch up in left corner and the dark area too means I probably have to return to grinding with carbo320. There is a dark area in the center and also just above the center. Near the edge below there is a yellow zone. And the surface have faint schratches. I hope some ATMs with experience will comment these test-pictures.


Here is a picture showing how the mirror is mounted under the test.


The artificial star is placed 291 cm. (twice the estimated focal length) from the surface of the mirror. And moved 5 cm. right to the center of the curvature of radius. I also tried the slitless-method, but it was a little complicated to make the slit sharp enough. When my holidays is over (two weeks yet) I try to make a slitless-tester at work.


This knife-edge-device is a prototype which isn’t finished yet. It is moveable along the center and acros the center of the light-cone. In the background is the artificial star.










The polish lap is made by pitch, wich is melted and formed in a mould. The lap is used with cerium oxide and was very effective. The pitch have to fill out the whole lap, and have to be more uniform and regular.

Category: Astroblog
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