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Wave ratings for mirrors

by Artman
Tags: mirrors, ratings, wave
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Sep17-03, 12:34 PM
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I know that a telescope system is supposed to be at least 1/4 wave or less (for both primary and secondary ratings combined), but I am not quite sure what the wave rating refers to. Can someone explain what this is measuring.
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Sep17-03, 08:10 PM
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chroot's Avatar
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A "quarter-wave" mirror is a mirror whose figure is an accurate parabola within one quarter wavelength of a specific color of visible light (green, I believe). In other words, the hills and valleys on the mirror's surface are smaller than about 100 nanometers from the ideal parabolic figure.

- Warren
Sep18-03, 07:31 AM
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Thanks chroot,
I thought it was something like that, but I have never seen it defined.

Sep29-03, 04:31 PM
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Labguy's Avatar
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Wave ratings for mirrors

As chroot said, the measure is usualy in green light, most sensitive to the eye and at a wavelength short enough to be meaningful. A 1/25th wave mirror measured in red light would most likely be a terrible figure for a telescope mirror.

Actually, most wavelength claims are being ignored in favor of an accurate measure of the "Strehl Ratio", which is much more indicative of a mirror's surface accuracy.



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