An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens or microscope..

optical axis

Marginal rays are the light that passes through an optical system that is away from the optical axis.

he points on the optical axis of a centered optical system that can be used to construct the image of an arbitrary point in space for objects in the paraxial region, which is the region around the axis of symmetry of the system where a point is represented by a point, a straight line by a straight line, and a plane by a plane.

optical axis