Wave ratings for mirrors

  1. 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.
     
  2. jcsd
  3. chroot

    chroot 10,426
    Staff Emeritus
    Science Advisor
    Gold Member

    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
     
  4. Thanks chroot,
    I thought it was something like that, but I have never seen it defined.
     
  5. Labguy

    Labguy 733
    Science Advisor

    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.

    See:
    http://www.rfroyce.com/standards.htm

    Labguy
     
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