Continuing on the list of questions that I regularly get is “What are the three focus modes on my camera?” This is referring to the One Shot, AI Focus, AI Servo settings and people always wonder what they do and which one to use?
They are as follows:
One shot: When you press the shutter release halfway, the camera will focus and will lock the focus as long as you hold your finger on the shutter button, as soon as you release your finger and press the button again it will refocus.
AI Focus: This is a smart focusing system that is suppose to be able to determine if the subject is moving or not and thereby switch from one shot to AI Servo. Most people that I talk to hate this mode as it is so hit and miss, I have tried it but really do not see a lot of improvement over my usual way of shooting.
AI Servo: Is for tracking subjects that are moving nearer or farther away. You push down the shutter half way and as long as you are pressing the shutter button (you can also use the focus button on the back of your camera) the camera will keep refocusing on the subject. One thing to watch for here is that you have to keep your focus point on the subject, if this point moves off the subject your camera is going to refocus on whatever it is now pointing to.
So what is the right mode to use? That depends on the subject and the photographer. As a general statement:
For subjects that are not moving use One shot.
For moving subjects use AI servo.
There are a lot more things to consider and it would take me a long time to type all the possible shooting situations to consider when selecting the right focus mode for you and your subjects. To learn more on this I strongly recommend one of my photo courses where I can cover off all the points.