Astrophysics (Index)About

optical axis

(center line through an optical instrument)

The optical axis of a telescope or other optical instrument is a line through the middle, over which a ray of light will not be refracted or reflected at an angle. This description is generally true of some straight-forward telescopes and instruments, but optical systems may include flat reflectors (e.g., many binoculars) that reflect the optical axis, aiming it, along with all the light, in another direction. Also, some telescopes are be constructed such that their theoretical optical axes are "unused", e.g., a prime focus telescope, or Herschelian telescope.

Further reading:

Referenced by pages:
focal plane tilt
off-axis telescope
spherical aberration