# Cardinal Point (optics)

Cardinal Point (optics)

In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of an ideal, rotationally symmetric, focal, optical system. For ideal systems, the basic imaging properties (e.g., image size, location, and orientation) are completely determined by the locations of the cardinal points; in fact only four points are necessary: the focal points and either the principal or nodal points. However, the only ideal system that has been achieved in practice is the plane mirror. Consequently, the practical utility of cardinal points would be very limited. However, the cardinal points are widely used to approximate the behavior of real rotationally symmetric, focal, systems.

The three pairs of cardinal points are:

• The focal points
• The principal points
• The nodal points

Read more about Cardinal Point (optics):  Modeling Optical Systems As Mathematical Transformations, Detailed Explanations

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Cardinal Point (optics) - Detailed Explanations - Nodal Points
... The front and rear nodal pointshave the property that a ray aimed at one of them will be refracted by the lens such that it appears to have come from the other, and ... The nodal pointstherefore do for angles what the principal planes do for transverse distance ... air), then the front and rear nodal pointscoincide with the front and rear principal points respectively ...

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