FOCUS: One Shot vs. AI Focus vs. AI Servo

Started Jul 18, 2007 | Discussions thread
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FOCUS: One Shot vs. AI Focus vs. AI Servo
Jul 18, 2007

I've been using Canon for many years, but just realized that I had become a bit fuzzy in my understanding of which focus setting is best for which situation.

One Shot: I had always understood that this is for situations in which nothing is moving.

AI Servo: This is for situations in which the subbject is moving, and if it does so in a manner in which the camera is able to predict where it will be when the film (sensor) is exposed, it will be in focus. The camera will immediately shoot as soon as the shutter release is depressed, even if the first shot is not in focus.

AI Focus: The camera starts off in One Shot mode, but if the subject moves, it shifts into AI Servo.

Please correct me if the above is wrong in any way.

My understanding is that this has been so since at least the EOS-3, which is a very long time ago indeed.

1) Won't AI Servo take a decent picture of a still subject? Why do we need One Shot? If it can take pictures of moving subjects, it should be able to take a picture of a still one.

2) What is the advantage of AI Focus over AI Servo? What is the advantage of AI Servo? In which standard outdoor situations would each be preferable.


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