Question

Applicatios of aplanatics points
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Answer 1

Explanation:

A spherical refracting surface forms a point image of an axial point object only in the case of paraxial rays. When this condition is not satisfied, the refracted rays will not have a common point of intersection. The image of the axial point object will not be a point image. This departure from the ideal point image is termed as spherical aberration. However, this defect may be overcome by the use of an aplanatic surface. An aplanatic surface, with respect to two conjugate points is such that all the rays originating from one of the two points are reflected or refracted by the surface through the other point. Such a pair of points are termed as aplanatic foci or aplanatic points.