现在网上的自动对焦资料比较少，这里简单介绍自动对焦功能实现，为大家提供参考！很多年前的资料了，现在把积分调低。

1) Basic concepts of Auto Focus Algorithm 1.1) AF Detection methods There are two focus detection (AF) methods. 1) Distance detection method. 2) Contrast detection method. 1.1.1) Distance detection method The distance detection method is that the camera use AF module for detecting distance for main objects. If the camera is used this AF method, it will not need to use CCD to detect object’s contrast. There are three types of AF modules. 1. Active AF module 2. Passive AF module 3. TTL AF module 1.1.1.1) Active AF module Active AF systems measure distance to the subject independently of the optical system, and subsequently adjust the optical system for correct focus. There are various ways to measure distance, including ultrasonic sound waves and infrared light. In the first case, sound waves are emitted from the camera, and by measuring the delay in their reflection, distance to the subject is calculated. Polaroid cameras were known for successfully applying this system. In the latter case, infrared light is usually used to triangulate the distance to the subject. An exception to the two-step approach is the mechanical autofocus provided in some enlargers, which adjust the lens directly. 1.1.1.2) Passive AF module Passive AF systems determine correct focus by performing passive analysis of the image that is entering the optical system. They generally do not direct any energy, such as ultrasonic sound or infrared light waves, toward the subject. (However, an autofocus assist beam of usually infrared light is required when there is not enough light to take passive measurements.) Passive autofocusing can be achieved by phase detection or contrast measurement.

相机的自动对焦的算法（auto focus），对不同的镜头的对焦算法