Optical Aberrations

doi:10.1117/3.2506310.ch8

Optical Aberrations

Book: Geometrical Optics: Lectures in Optics, Volume 2

Author(s): George Asimellis

Published: 2020

https://doi.org/10.1117/3.2506310.ch8

Author Affiliations +

Abstract

If all of the rays from an object meet at a single common point, the formed image is called stigmatic. Stigmatism refers to an assumed image-formation property of an optical system to focus a point source in object space to a single point in image space. The concept that such a proposition is realizable belongs to the realm of geometrical approximation. We have indeed followed this approximation up to now, employing terms such as the image or the focal ‘point.’ A point is a mathematical concept with no dimension, volume, surface area, or length. It is, however, absolutely essential in geometry! As it applies to optics, the concept of the point is used for denoting a very small surface area. Although the focal point is a conceptional point, it has a physical spatial extent, called the blur circle. The ‘point’ at which all rays from an object beam converge may be considered an image point if the corresponding area is very small.