# Wave ratings for mirrors

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.

## Answers and Replies

chroot
Staff Emeritus
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

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

Labguy