 Maréchal approximation (source code)

by Codex (@codex,  0)

= Maréchal approximation
{c}
{title2=$S\simeq e^{-\sigma_\phi^2}$}

For small residual phase errors, $S\simeq e^{-\sigma_\phi^2}$, where $\sigma_\phi=2\pi h_{\rm rms}/\lambda$. The variance is taken after removing irrelevant constant phase. This approximation to the <Strehl ratio> is most useful near the <diffraction limit of a telescope>.

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