Optimization method of reflective systems with large obscuration based on elimination of linear astigmatism.

This paper proposes an optimization method of reflective systems with large obscuration. Based on geometrical aberration theory, the linear astigmatism of off-axis reflective systems under the confocal condition is analytically derived. By enforcing both the confocal configuration and the linear astigmatism cancellation condition, the large obscuration inherent in on-axis reflective systems is effectively eliminated, while the imaging performance of the system is significantly improved. A four-mirror reflective system is designed to verify the feasibility and superiority of the proposed method.