= Coronagraph throughput
{title2=$T(\theta)$}
For a specified <photodetector> measurement, <coronagraph throughput> $T(\theta)$ is the fraction of a source's <light> transmitted into that measurement at angular separation $\theta$ from the blocked source, relative to a stated reference configuration. Total transmitted <power> and <power> inside a small image opening can give different fractions; one must specify which is used. Throughput usually depends on <wavelength> and separation. A lower stellar residual is useful only in relation to the retained companion signal and noise. Guyon's worked designs plot transmitted off-axis <light> against separation to expose that tradeoff. https://subarutelescope.org/staff/guyon/04research.web/10coronagraphy.web/60complexApertures.web/content_nomenu.html[Olivier Guyon, High Performance Lyot and PIAA Coronagraphy for Arbitrarily shaped Apertures, §3.4]{ref}.
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