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Newtons Rings

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Posted by Dave Hawkins/">Dave Hawkins on April 15, 1998 03:21:37 UTC

: Dave, : What test are you doing? Is it a Ronchi test against a flat? : Or is it a Star Test? : Or are you looking through the glass and seeing the far surface? : Remember that a parabolic surface can be produced by a spherical tool. : The final test on convex surfaces has to be done with something that sees the surface. : The easiest testing is probably to assemble the scope and do a double pass test. : As far as deciding which is which, go try to take out one of the error directions and see what it produces. : That is where you are going. : Good Luck with the project. Remember that if concave surface is on top, the radius decreases and viceversa for the other way. : Good Luck and Have Fun. Bob May

Robert. thanks for your reply. I`m trying to establish the radius of curvature of the secondary mirror. I know the radius of curvature of the tool it was ground on. I want to get the convex secondary mirror exactly the same radius, when polished,by looking at Newtons rings when they are placed one on top of the other.At the moment I`ve got two rings just about concentric, If I push anywhere on the discs the rins move towards the center, Does this mean the discs are concave or convex to each other? I`m a bit reluctant to polish further until I know which surface should be on top to get rid of the error, rather than compound it. Hope this explains my problem a little better. cheers for now Dave.

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