Lateral color is the difference in image height between blue and red rays. The figure below shows the chief ray of an
optical system consisting of a simple positive lens and a separate aperture. Because of the change in index with
wavelength, blue light is refracted more strongly than red light, which is why rays intercept the image plane at
different heights. Stated simply, magnification depends on color. Lateral color is very dependent on system stop
location. For many optical systems, the third-order term is all that may be needed to quantify aberrations.
However, in highly corrected systems or in those having large apertures or a large angular field of view,
third-order theory is inadequate. In these cases, exact ray tracing is absolutely essential
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