Briefly describe the types and characteristics of autofocus.

Choose the focusing mode on the lens There are two main focusing modes on the camera lens: autofocus (AF) and manual focusing (MF), among which autofocus is divided into single autofocus (S) and continuous autofocus (C), which are the three most commonly used focusing modes of the camera. Mastering and controlling these focusing modes is very important for obtaining clear photos. With the continuous progress of electronic technology, AF technology is first applied to small cameras. At present, AF focusing function has become the standard configuration of 135 SLR cameras. The world's major camera manufacturers gradually give up the traditional manual focus camera and develop a highly electronic autofocus camera. Auto-focus is generally represented by AF(Automatic Focus), which is a built-in function of the camera. It automatically focuses on the subject through electronic and mechanical equipment to make the image clear. The main characteristics of autofocus are high focusing accuracy and convenient operation, especially for the focus of the subject, autofocus has more advantages. In addition, because manual focusing operation can be omitted during shooting, it is also beneficial for the photographer to focus more on the shot picture and concentrate on capturing the moment of the subject. Auto focus can be divided into active auto focus and passive auto focus. Active autofocus mainly measures the distance of an object by emitting infrared rays or ultrasonic waves, and the autofocus system drives the lens to adjust the image distance according to the obtained distance data, thus completing autofocus. At present, most digital SLR cameras adopt passive autofocus: that is, directly receive and analyze the reflection from the subject itself, and use the principle of phase difference to autofocus. The advantage of this autofocus method is that it does not need the transmission system itself, so it consumes less energy and is conducive to the miniaturization design of the camera. Auto-focus is very suitable for subjects with certain brightness and contrast, and it can also focus well under backlight, and can focus through transparent obstacles such as glass. The AF focus area has one or more autofocus frames in the center of the camera viewfinder. When shooting, you should aim at the subject, otherwise the focus will be inaccurate and the image will be blurred.