A simple zoom lens system . The three lenses of the afocal system are l1 , l2 , l3 ( from left ) .
一个简单的变焦系统，从左到右的三块透镜分别是l1、l2、l3。
The afocal system 's purpose isn 't to create a focused image but to simply change the size of the image hitting the detector . The result is a focused image that changes size on the detector .
One of the most common zoom lens designs divides the optical assembly into two sections , a fixed focal length focusing lens and an afocal zoom system consisting of a series of fixed and movable lenses .
