If you’ve ever wondered what AI Servo (if you have a Canon) or Continuous focus (if you have a Canon) is then read on.
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The Nikon term is probably the giveaway as these settings are continuous autofocus systems for your camera. This means that you don’t have to half press your shutter to enable the auto focus or to manually focus on your subject.
When would you use this?
Sport or when there is action in a scene is the best application. If you were photographing a football game and you wanted to track a run down the wing before capturing a beautiful cross into the box then this is ideal.
You could do the same if you had people jumping in the air or swinging from a rope.
Why wouldn’t you use this all the time?
The short answer is that it’s not a perfect technology and its not a accurate as pre-focusing on a subject.
Different cameras and different lenses are better (and quicker) at focusing than others so some experimenting on your part is needed for you to judge what your set-up is capable of.
Experiment time
Find a subject with lots of energy willing to do some running about.
Set your camera to continuous focus on a small aperture to begin with (f11 or something like that).
Set your camera to a high shutter speed to capture movement and a high ISO to allow a correct exposure.
Get your subject to run back and forth in front of you starting off slow and speeding up to sprint.
Track their run with your camera taking shots throughout.
Examine the results. How effective was your camera and lens at focusing on the moving subject?
