会聚和发散作用分别是凸透镜和凹透镜的重要光学性质。那么 ,什么是会聚和发散作用呢 ?会聚和发散作用如何判断 ?这些问题在课本中未曾说明 ,现在此加以讨论。光束分为平行光束、会聚光束和发散光束三种。光线平行的光束称平行光束 ,光线的正向延长线相交于一点的光束称会聚光 Convergence and divergence are important optical properties of the convex and concave lenses, respectively. So, what is convergence and divergence? How to judge convergence and divergence? These problems were not described in textbooks and are discussed here. The beam is divided into parallel beam, converging beam and divergent beam. A beam with parallel rays is called a parallel beam, and a beam with a positive extension line of rays intersects at a point is called a convergent beam.