机械补偿式变焦距镜头以其自身的优点受到了广泛的关注和应用。介绍机械补偿式三组元连续变焦系统的基本工作原理及组成，根据实际使用要求，设计出保证变倍过程中变倍组和补偿组按一定函数规律运动的圆柱凸轮结构、导向机构及相应的加工工艺，从变倍运动方程和设计的变焦结构形式出发，分析变焦过程中焦距实时输出的实现方法和存在的问题，并提出相应的解决措施，对焦距值实时输出精度的提高以及变焦距镜头的设计和装调具有借鉴作用。

Zoom optical systems with mechanical compensation are widely used in all kinds of optical instruments due to its unique advantages. The structures and principle of mechanical compensation zoom optical systems with 3-unit were briefly described. Cam mechanism and guide mechanism to improve the image quality of zoom optical system were discussed. Actual focal length output with changing focal length was analyzed, including implementation of focal length output and some problems. It is shown that proposed methods are feasible for improving the design and adjustment of zoom optical lens, in addition, the accuracy of actual focal length output at different focal length is improved significantly.

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