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Al Servo (1 Viewer)

Hello. Can some one tell me what this Al Servo is? Does it come on every camera such as the Canon EOS 20D? Thank you.

Sam Winslow

Not sure about Nikon, but it is on every Canon dSLR.

There are, basically, two focus modes. With one-shot focus the camera focuses once and stays at that focus until the shutter goes. If you take multiple shots they're all taken at the same focus. This is just what you want if neither the subject or the camera are moving.

If the subject (or the camera) is moving then obviously the focus will need to change as you take a burst of shots. In AI Servo mode the camera tries to measure the motion of the subject and set the focus correct for where it will be when the shutter opens. Highlt useful when shooting things like birds in flight.

There is a third mode on Canon cameras called AI Focus - generally accepted to be useless as it combines all the bad points of the two proper modes.

You'll find a lot of argument about how well particular cameras handle AI Servo, some of it representing real problems, a lot of it representing user error.
 
Its a great feature but needs to be used on a quality lens with a good autofocus system to see the benefits in my experience.Some cheaper lens`AF motors just cant seem to keep up with it IMO.
 
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