7.1 WAVEFRONTS IN AN OPTICAL SYSTEM

We have seen that an ideal imaging optical system produces a point image of a point light source emitting rays of light in all directions. This is the basic concept in geometrical optics. However, if we recall that light is a wave, we have to think of a point source emitting a spherical wavefront. As defined in Chapter 1, a wavefront is a surface in space where the phase of the light wave is a constant. From another equivalent point of view, a wavefront is a surface in space such that any light ray traveling from the light source to any point in the wavefront travels the same optical path length independently of its trajectory.

We may easily observe ...

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