叙述无光焦度补偿组与次镜重合时的全球面双反射系统的设计，给出利用PW法求解初始结构的基本理论，阐述应用无光焦度补偿组来平衡球面反射系统像差的方法。通过改变遮拦比K和焦点伸出量δ进行光线追迹，选择出该类系统K和δ的最佳组合。给出设计实例: 系统工作波段λ=450 nm～700 nm、焦距f′=1 600 mm、相对孔径A=1/8、视场角ω=±0.5°，遮拦比K＝0.35、焦点伸出量δ＝0.1，系统优化后的球差系数 SⅠ=-0.001 207，彗差系数SⅡ=0.000 192，波像差W=0.043 27λ。

The design method of a two-sphere system with an afocal corrector which was on the secondary mirror was described. The basic theory for solving the initial structure by using PW method was analyzed. By changing the obstruction ratio K and the length from primary mirror to focus δ, the ray tracing was realized, the optimized combination of K and δ was obtained. An design example was given: the working band of the system was 450 nm~700 nm, focal length f′ was 1 600 mm, relative aperture A was 1/8, visual field angle ω was ±0.5°, obstruction ratio K was 0.35, and the length from primary mirror to focus δ was 0.1. After the optimization of the system, the coefficient of spherical aberration SⅠ was -0.001 207, the coefficient of comatic aberration SⅡ was 0.000 192, and the wave-front aberration W was 0.043 27λ.