An Etymological Dictionary of Astronomy and Astrophysics
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Two apertures where opaque and transparent areas are inverted. If A is an aperture that has some opaque areas and some transparent ones, the complementary pattern A' is the pattern in which exactly the opposite areas are opaque and transparent. Thus, the complimentary screen of a single slit is a wire of the same size, and the complementary screen of a circular opening is a dot. A better term would be → complementary apertures.

→ complementary; → screen.