Back focal length

Under the section width s and s ' are understood in optics:

  • The section width of a light beam in a meridional plane in the geometrical optics, the distance of the intersection of the beam and the optical axis from a reference point. As the reference point is chosen usually the peak (center ) of the surface at which the beam was the last broken (see the main plane ).
  • The average length of a lens is the distance of the image from the rearmost optical surface of the lens. The object is thereby normally at an infinite distance. It is the average length of the axis-parallel incident light beam after it has passed through the lens. Strictly speaking, this section length is in paraxial optics, that is, when the height of incidence of the incident beam to zero, with the focal length of the same, otherwise the focal distance of the beam is influenced by the spherical aberration.
  • Paraxial optics
Cardinal point (optics)#Principal planes and points Paraxial approximation
716262
de