, Markus Klein, The Principal Axis Theorem for Holomorphic Functions, Proceedings of the American Mathematical Society, Vol. 128, No. 2 (Feb., 2000), pp. 325-335 ...

Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus. Draw a ray which passes from the object ...

C. D. Perrine, THE SUPPORTING AND COUNTERWEIGHTING OF THE PRINCIPAL AXES OF LARGE TELESCOPES, Publications of the Astronomical Society of the Pacific, Vol. 16, No. 95 (April 10, 1904), pp. 97-99 ...

Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus. Draw a ray which passes from the object ...