• noun a lens diaphragm that allows the amount of light that reaches film to be regulated
  • noun an opening in a device that allows a specific amount of light or a signal to pass through it
  • The effective light-gathering diameter of a telescope lens or mirror, or other devices used for other wavelengths. The amount of light or other radiation gathered increases with the square of the aperture, in other words with the total area of the light-gathering surface.
  • An opening, such as a hole, gap, slit, vent, port, mouth, outlet, or perforation, through which electrons, light, waves, or any form of radiant energy may pass. Also called orifice (1).
  • The opening by which light enters, or through which it travels, of an optical device or system, such as a telescope or scanner. Such an opening may be in any shape, but is usually circular, rectangular, or elliptical.
  • In an antenna, the opening through which the radiated energy passes.
  • In a speaker, a port in the enclosure which increases and extends the reproduction of low frequencies.

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