apertures

Noun

aperture (plural apertures)

1. A small or narrow opening, gap, slit, or hole.
   • an aperture in a wall

   Synonyms:

   chink

2. A hole which restricts the diameter of the lightpath through one plane in an optical system.
   1. The diameter of such a hole which restricts the width of the lightpath through the whole system. For a telescope, this is the diameter of the objective lens.
      • This telescope has a 100 cm aperture.
3. (space flight) The (typically) large-diameter antenna used for receiving and transmitting radio frequency energy containing the data used in communication satellites, especially in the geostationary belt. For a comsat, this is typically a large reflective dish antenna; sometimes called an array.
4. (rare) The maximum angle between the two generatrices.
   • If the generatrix makes an angle θ to the axis, then the aperture is 2θ.