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| Compared tests | ||
| Here are some
photos of a mirror tested with double pass autocollimation and the same
mirror tested with a Ronchi screen at its center of curvature. This
illustrates the one difference of judging correction using a null test
versus using C of C tests.
The upper photos are the center of curvature tests. The lower photo shows the mirror outside focus (upper) and then inside focus (lower) using the null test.
The mirror is a 10" f/5.4 paraboloid also shown on another page. The null test used a 100 lpi Ronchi grating. For some reason the inside lines are softer than the outside lines when using this spacing. The center of curvature photos used a 150 lpi Ronchi that results in more similar line contrast.
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