In order to design or to evaluate optical schematics or models or products, optical calculations are needed. The calculations used for these purposes are often based on geometrical optics or on wave optics. Calculations related to optical lenses and physiological optics are based on classic electromagnetic theory. Differences between geometrical optics and wave optics may be seen as differences in the degree to which they approximate Maxwell's equation of electromagnetism. Wavefront optics are useful when both geometrical optics and wave optics must be taken into consideration, such as when calculating diffraction images in situations where there are geometrical aberrations.

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