focal ratio
焦比；
focal ratio的解释
1. 焦比：即:放大倍数=物镜焦距/目镜口径 =入射瞳孔直径/出射瞳孔直径 ---------------------------------- 焦比(Focal Ratio) 望远镜放大倍数不能无限制的增加,即目镜不能太短;最短约四毫米,主镜焦距亦不能太长,究竟焦距长度如何决定呢?
2. 焦比(焦距/直径)：Focal Length:焦距 | Focal Ratio:焦比(焦距/直径) | Thickness:厚度(应该是主镜镜片厚度)
noun
1. the ratio of the focal length to the diameter of a (camera) lens system
Synonym: f numberstop numberspeed