Two simple calculating schemes for use in ophthalmic optics--I. Tracing oblique rays through systems including astigmatic surfaces.

A ray tracing scheme using paraxial approximations is described to allow oblique rays to be traced through lenses or optical systems in which some or all of the surfaces may be astigmatic, even at different axes. It is based on consideration of the prismatic effects introduced at each surface. A numerical example reveals some lesser known properties of the circle of least confusion of astigmatic pencils.