Question

define principal focus​

Answer 1

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In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle.❤️

Answer 2

principal focus :when light rays parallel to the principal axis are incident on a convex lens they coverage at a point on the principal axis. this point is called the principal focus