Geometrical Optics

Geometrical optics refer to light propagation in terms of rays. The ray in geometric optics is an abstraction, or
instrument, useful in approximating the paths along which light propagates in certain classes of circumstances. Geometrical optics is often simpli ed by making the paraxial approximation, or "small angle approximation." The mathematical behavior then becomes linear, allowing optical components and systems to be described by simple matrices. Geometrical optics does not account for certain optical e ects such as di raction and interference.

This simpli cation is useful in practice; it is an excellent approximation when the wavelength is small
compared to the size of structures with which the light interacts. The techniques are particularly useful in
describing geometrical aspects of imaging, including optical aberrations.