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Terms
  • line of sight (LOS) The line of vision; the optical axis of a telescope or other observation system. The straight line connecting the object and the objective lens of the viewing device.
  • telescope An afocal optical device made up of lenses or mirrors, usually with a magnification greater than unity, that renders distant objects more distinct, by enlarging their images on the retina.
  • terrestrial telescope A telescope that produces an erect image. Erection is achieved either by a lens (for a long instrument) or a prism (for a compact instrument). Very small terrestrial telescopes of low power may be of the Galilean type.
  • Galilean telescope A refracting telescope that yields an erect image by the use of a positive lens for its objective and a negative lens for its eyepiece.  
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