Optical axis (optics)

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Beam path on a converging lens. The optical axis is in the middle

The axis of symmetry of a rotationally symmetrical optical system is called the optical axis , OA for short . It depends on the symmetry of the surfaces, not their edges: Even with a crooked mirror , one can speak of an optical axis if the main and secondary mirrors are sections of rotationally symmetrical surfaces with an identical axis.