= Coronagraph inner working angle
{title2=$\theta_{\rm IWA}$}
= Inner working angle
{synonym}
The <coronagraph inner working angle> describes how close to the blocked source a specified <coronagraph> can usefully transmit or detect a faint neighbor. It requires a criterion, such as a chosen fraction of the far off-axis <coronagraph throughput>, and is often expressed in units of $\lambda/D$. It is not automatically the <coronagraphic focal plane mask> <radius> or a guarantee of detection. Small separations make useful source transmission and accurate control of <wavefront errors> particularly demanding. https://subarutelescope.org/staff/guyon/04research.web/01adaptiveoptics.web/lowfs.web/content_nomenu.html[Olivier Guyon, Low order aberrations and high performance coronagraphy]{ref}.
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