汇聚光线,放大图像
凸透镜具有对光的会聚作用
http://www.baidu.com/s?ie=gb2312&bs=%CD%B9%CD%B8%BE%B5%BE%DF%D3%D0%CA%B2%C3%B4%D1%F9%B5%C4%D7%F7%D3%C3&sr=&z=&cl=3&f=8&wd=%CD%B9%CD%B8%BE%B5+%D7%F7%D3%C3&ct=0
聚光,在一定范围内,可使凸透镜另一侧的物象放大