Question

define principal Axis define principal axis ​

Answer 1

An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light propagates through the system, up to first approximation.

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Answer 2

Answer:

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The principal axis is called a line that passes via the centre of the surface of a spherical mirror or lens and through the centre of curvature of all segments of the mirror or lens.