简析光学系统自动调焦的方法

自动调焦技术已经广泛应用于各种光学仪器中。常见的调焦方法，从基本原理上可分成基于物方测距的主动式和基于像检测法的被动式两大类。主动、被动式自动对焦方式各有千秋，主动式由系统主动发出光波，可以在低反差、弱光线下对焦，但当被摄体能吸收或反射光或波时对焦困难。被动式直接接收来自景物自身的反光，对具有一定亮度的被摄体能理想地自动对焦，自身不要发射系统，耗能少，有利于小型化。被动法中的以数字图像处理作为调焦检测函数的方法，理想的评价函数要求无偏性、单峰性、能反映离焦的极性、对噪声敏感度低等。为提高效率，往往还希望计算量尽可能地小。文章介绍了目前应用于光学系统的几种基于光电测试和图像处理的自动调焦方法。

On auto-focusing technology of optical system

Auto-focusing technology is widely used in all kinds of optical apparatus.The commonly used auto-focusing methods can be divided into two kinds according to the basic principle: one is active mode based on object distance measuring,the other is passive mode based on the image examining.Each one has its advantages and drawbacks.In the active mode,the system emits light wave actively,can realize focusing under low contrast and dark condition,but it is difficult for focusing when the object can absorb or reflect the light/wave.In the passive mode,the system receives directly the light reflected from the object,can realize ideally auto-focusing for the object with a certain degree of brightness;transmitting system is unneeded,the whole system is low energy-consumptive and easily miniaturized.For the method taking digital image processing as auto-focusing examining function in the passive mode,ideal merit function is non-deflection,single-peak,the off-focus direction reflected,low sensitivity to the noise,computing cost as less as possible for improving the efficiency,etc.Several auto-focusing technologies based on the photoelectric test and digital image processing currently used in optical systems are introduced.