举例说明了一种基于牛顿系统的可见光长焦分档变倍系统的设计方法，并推导、计算了各个光学组元光焦度的分配以及光学初始参数。系统采用了二次成像光学结构形式，引入场镜解决长、短焦系统瞳匹配问题，设置调焦镜组用来补偿因物体距离变化引起的像面移动，通过在长焦系统和探测器焦平面之间切进、切出短焦物镜组实现变倍，在短焦物镜组中设计平行光路以便长焦系统和短焦系统共像面的调整。对光学系统像差进行了优化设计，分别给出了长焦系统和短焦系统不同视场的成像质量优化结果， 0.8视场内光学传递函数在空间频率36 lp/mm时都大于0.4，分析表明设计结果能够很好地满足实际工程需要。

An example is given to explain the design of swith-zoom lens of the long effective focal length working in visible light waveband based on the Newton system. The derivation of the components′ focal power and the calculation of the initial parameters are made. Two times imaging structure is adopted and field lens is used to match the pupil for the sake of making up the focal plane′s changes because of object distance′s differention. Focusing lens is applied and zoom is realized by switching in or out short effective focal length lens between long effective focal length lens and the detector′s focal plane. In order to adjust coplane, a parallel path is set in the short effective focal length lens. The design of optimized aberration is made. The analysis of results at various fields is presented. Within 0.8 field of view, modulation transfer function (MTF) is greater than 0.4. From the results, the conclusion can be drawn that the project is rational and the imaging quality is good.