Optics for Technicians

Additional RelationsFigure 2.3 identifies additional relations, indicating the locations of the object and image, and the ratio of their heights (magnification) and orientations.Ray 1 enters the lens parallel to the optical axis.Therefore, the point at which it crosses the axis after exiting the lens is the second focal point F 2 .Ray 2 passes through the front focus F 1 and leaves the lens parallel to the optical axis.The two nodal points are special cardinal points because they lie on the optical axis.A ray aiming at N 1 leaves the lens from N 2 in the same direction as it entered the lens, indicated with ray 3.