The difference between single AF (one SHOT), Ai Autofocus (ai focus), AI Servo AF (AI SERVO)

 

Single AF (one shot) is the most common. The working process of this mode is initiated by a half-press of the shutter, and the focus process continues until the focus is not accurate.

Once the processor considers the focus to be accurate, it completes the shooting process as soon as the shutter is completely pressed, while the AF system stops working.

The focus is automatically locked after the focus is finished, so it's easy to re-frame without changing the focus, as long as the shutter is not released.


One-shot autofocus is suitable for capturing stationary objects such as still life, landscapes, macro, static portraits, etc. If a single focus is completed and a focal point appears, the subject is moved again before the shutter is pressed, and a single-shot focus is likely to get a picture with a focus.

Because a single autofocus mode does not "track" the object in motion, it also produces a continuous autofocus. Unlike a single AF, the AF system continues to work and the focus is not locked when the processor determines that the focus is accurate. The aim is that when the subject is moved, the AF system can drive the lens motor to focus continuously in real time according to the change of focus, thus keeping the object in a clear state.  

Of course, the camera's focus frame is also continuously aligned to the subject, so that when the shutter is completely pressed, it is not necessary to worry about the problem of the object focusing. Continuous autofocus is used for shooting objects in motion, such as shooting athletes in sports competitions, children in play, shooting spokespersons in press conferences, and capturing the wonderful moments of animals in motion.

And, combined with the high-speed burst function, it's easy to take a set of dynamic photos. Continuous autofocus for continuous tracking of moving body theoretically speaking, since there are two ways of single AF and continuous autofocus, it should be able to meet the needs of different shooting scenes. However, there are still some problems in the process, such as the large power consumption of long-time continuous AF.

In addition, when photographing an object that may be converted from a stationary state to a moving state at any time, or vice versa, neither of these modes seems appropriate. 
 
Intelligent autofocus is a camera automatically selects the focus mode according to the state of the subject (stationary or motion), which combines single-shot AF and continuous autofocus to resolve the above mentioned problems, thus making it more suitable for use in situations where the object is stationary. It should be noted that the first two mentioned autofocus methods are the most common, most commonly used, the camera manufacturers are basically named after the above name. The third type of approach, regardless of the name of the family, works essentially the same.


Canon, known as "AI Servo focus", referred to as "the recent subject of dynamic Autofocus", Sony and Danone known as "automatic switching Focus", the name of a variety of, in fact, is one thing. If you have no confidence in your focus control, it is recommended to choose a third option. As long as you focus and half press the shutter, the lensAlways focus on automatic tracking of your chosen focal point. Even if the focus moves a little bit, you will feel the lens is turning, which is automatically chasing the Coke.

If your lens is using an ultrasonic motor, the focus speed is quite fast. Smart autofocus automatically selects the focus mode based on the state of the subject (stationary or motion)