Sunday, April 5, 2009

AI Focus vs AI Servo vs One Shot

This is a note to myself. I learned it the hard way, that means I made mistakes to learn this.

AI Focus is for you to focus on something originally stationary, then it starts moving. If you focus on a static subject, and then you move your camera away, the focus will continue to change. There is no focus lock. This mode works very poorly if you are thinking of focusing on a static subject, lock the focus and then point to something else. In the Canon 20D, the focusing points will continue to light up, signalling to you which area is in focus.

AI Servo is for you to focus on something that is ALREADY moving, and you want to continue to focus on that subject. The camera's focusing points won't light up. You will have no idea which point is in focus which is not. The use of this focusing mode can be quite terrible, and many pictures will turn out out of focus. If you use this mode to shoot static subjects, you might kick yourself for not even being able to focus on some simple, static subjects.

One Shot is for you to focus on static subject.

All the above are actually written in the camera manual, just that I don't really understand everything after reading the manual. Nothing is better than practice to learn something, although it may be the hard way.

As I used the wrong mode in a recent shoot, many photos are out of focus, even some simple ones. Sad, sad sad...


  1. Thank you very much for this wonder ful information

    hi my name is Ameya and I am a pastry chef in london. i am very intrested in photography
    I own 2 cameras
    1. sony a200 18-70mm and 70-300mm lense
    2. canon EOS 500D 18-55mm and 70-300mm lense.

    thank you

    ameya purohit

  2. Yes, great post... I'm also learning the hard way and wondering why some of my shots with a Canon EOS 50D/Tamron 17-50 or 70-200 combo are stunningly sharp and some are poo! This explains a lot of it, as the shots I couldn't understand being bad are shots that are low ISO but still looking crappy. Thought it was noise but now I believe it to be a focus issue.