title: Geometrical theory of aberrations near the axis in classical off-axis reflecting telescopes.
abstract: A geometrical theory of aberrations for the vicinity of the focus of arbitrary off-axis sections of conic mirrors is derived. It is shown that an off-axis conic mirror introduces linear astigmatism in the image. However, in classical two-mirror telescopes this aberration can be eliminated by tilting the secondary parent mirror axis. It is also shown that the practical geometrical-optics performance of a classical off-axis two-mirror telescope with no linear astigmatism is equivalent to the performance of an on-axis system, proving that both systems have identical third-order coma. To demonstrate the applicability of the theory developed in a practical system, a fast (i.e., f/2), compact, obstruction-free classical off-axis Cassegrain telescope is designed.
authors.affiliation: Department of Electrical Engineering/Electrophysics, University of Southern California, Los Angeles, California 90089-0271, USA. chang@offaxis.co.kr
authors.forename: Seunghyuk
authors.initials: S
authors.lastname: Chang
authors.forename: Aluizio
authors.initials: A
authors.lastname: Prata