= Coronagraphic focal plane mask
A <coronagraphic focal plane mask> modifies the <wave amplitude> or <wave phase> in an intermediate <focal plane>. Here it is a perfectly opaque circular disk centered on the bright source. A finite <aperture> produces an extended <point spread function>, so a finite disk blocks only part of the stellar <light>. Its sharp edge also changes the transmitted field and hence the later <diffraction> pattern. The exact model below makes both effects visible.
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