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Posted by Robert May on March 31, 2002 02:48:30 UTC

There's all kinds of possibilities with astigmitism (one side of focus the oval goes one way while the other side it goes 90deg. away), especially your're eyes or the secondary. If you don't wear glasses and have never been tested for eye problems you may have a bit of astigmitism and never know it. Rotating the primary and the EP will show astigmitism in those two items. I might also note here that many EPs do have astigmitism in the outer regions of the FOV so you need to do this test in the center of the FOV.
Next comes the lack of a good focus. This could be either the astigmitism or could be parabolization problems. To find this out, have you done the Foucault test on the mirror? You should have a better than 1/4 wave mirror just to make the quality of the mirror adequate. I might also note that focus problems will show up for what they are a lot better with a shorter FL EP as you will be able to see what the problems are a lot better.

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