What Does Wave Rating Mean in Telescope Mirrors?

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SUMMARY

The wave rating in telescope mirrors refers to the accuracy of the mirror's figure, specifically how closely it approximates a perfect parabola within a quarter wavelength of visible light, typically measured in green light. A "quarter-wave" mirror has surface deviations of less than 100 nanometers from the ideal shape. The discussion highlights that while wave ratings are common, the "Strehl Ratio" is a more reliable metric for assessing a mirror's surface accuracy, as it provides a better indication of optical performance.

PREREQUISITES
  • Understanding of optical physics, particularly wave optics
  • Familiarity with telescope mirror fabrication and design principles
  • Knowledge of the Strehl Ratio and its significance in optics
  • Basic comprehension of light wavelengths, especially in the visible spectrum
NEXT STEPS
  • Research the concept of the Strehl Ratio and its calculation methods
  • Explore the impact of different wavelengths on optical performance in telescopes
  • Learn about the fabrication techniques for achieving high-quality telescope mirrors
  • Investigate the relationship between wave ratings and actual telescope performance
USEFUL FOR

Astronomy enthusiasts, telescope manufacturers, optical engineers, and anyone involved in the design or evaluation of telescope mirrors.

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