Takayuki NAKANO and Yasuhisa TAMAGAWA

Information Technology R&D Center, Mitsubishi Electric Corporation, Kamakura, Kanagawa 247-8501, Japan

(Received February 1, 2007; Accepted August 29, 2007)

All-reflective optical systems have theoretically no chromatic aberration and are suitable for wide spectral application, but co-axial reflective systems are difficult to design as low F-number optical systems. In this paper, the aberration of plane-symmetric optical systems with low F-number is analyzed based on the wavefront derived from optical path length. Up to third-order aberrations are classified into three categories by their characteristics. The reduction method of the dominant aberration, astigmatism-like aberration, is proposed. In the method, the Gauss image plane is modeled by means of a simplified mirror surface with third-order approximation. Because the system is plane-symmetric, symmetric cross section and asymmetric cross section are modelled differently. The design example of a three-mirror system with F/2 is shown.

Key words: design method, reflective system, off-axis, plane-symmetry, aberration, perturbation, astigmatism