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 .

变焦系统的目的不是为了成一个聚焦过的像，而是改变在传感器上成的像的大小，结果就是在传感器上成一个大小改变过的像。

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 .

一种最常见的变焦镜头设计的光学部分分为两块，一块焦距固定的聚焦镜头以及一个由一串固定或可移动镜头组成的焦距无限远的变焦系统。