Enter either a Strehl, RMS or Peak-Valley. Press the corresponding button to calculate the other values.
| Strehl = | ||
| RMS = | ||
| Peak-Valley = |
The conversions assume a smooth optical figure.
A Strehl of 1.0 means that all the light is geometrically focused to a point. Because of diffraction caused by the finite aperture, an Airy Disc containing 84% of the light will be formed with 16% of the light being thrown outside this dot in the form of surrounding rings of diminishing brightness. If the light focuses to something less precise, then the Airy Disc will contain less light and the surrounding rings more light. The linear size of this Airy Disk depends on the focal ratio.
A quarter-wave optic has a Strehl of 0.80, an RMS of 1/14 wave and a Peak-Valley of 1/4 wave. The Airy Disk will contain 64% of the light and the surrounding diffractions rings 36% of the light. This is a diffraction limited mirror, though the finest planetary details may be blurred a bit.
A Strehl of 0.9 is a very good mirror, a Strehl of 0.95 is an excellent mirror (PV = 1/8 wave, RMS ~ 1/30 wave).
Sadly, stated Strehls are often exaggerated either through too few of data points used to calculate Strehl (inapproprimately assuming that the mirror is perfect between the points) or through optimistic testing.
See my Rating Mirrors webpage for more. Mel Bartels