optical axis
  • The centre line of a telescope or other optical instrument, joining the main mirror or lens to its focal point
  • A line passing through the centers of curvature of a lens or other optical system. light travels along this axis with no deviation. Also called principal axis (2).
  • The axis along which light is transmitted through a doubly-refracting crystal or medium without double refraction. Also called principal axis (3).
  • synonym optic axis

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