初中物理教材介绍的透镜分为凸透镜和凹透镜．凸透镜对光线有会聚作用，凹透镜对光线有发散作用．具体作图时应抓住三条特殊光线．（1）平行于主光轴的光线经透镜折射后，折射光线或其反向延长线通过焦点．如图1所示．（2）通过光心的光线经透镜后传播方向不发生改变．如图2所 The lenses introduced in junior high school physics textbooks are classified into convex lenses and concave lenses. The convex lens converges on the light, and the concave lens has a divergent effect on the light. 3. Three special rays should be captured during specific drawings. (1) After the light parallel to the main optical axis is refracted by the lens, the refracted light or its reverse extension line passes through the focus. As shown in Figure 1. (2) The propagation direction of the light passing through the optical center does not change after passing through the lens. As shown in Figure 2