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Old Dec 30, 2004, 11:25 AM   #1
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Pages 64-66 of the User Manual discuss the AF Focus Modes. One Shot is pretty straight-forward. I understand AI Sevo is for moving subjects. The book says AI Focus lets the camera figure out whether the subject is moving and selects whether to use One Shot or AI Servo (continuous focus) mode.

This leads to my question... why would I use anything except AI Focus?

I have noticed that in the Basic Zone (I rarely use anything except Manual or Av) the AF mode changes automatically. In full automatic ("Green Square") the camera selects AI Focus mode and in the sports mode, the camera selects AI Servo mode. I suspect the answer lies in the way the camera selects the focus point(s).

Any ideas?
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Old Dec 30, 2004, 3:47 PM   #2
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My problem with AI Focus is that it seems to switch between One Shot and AI Servo when I don't want it to. I think the focus is right... I keep the shutter 1/2 way down and suddently it shift the focus slightly because well... why? No one (other than Canon engineers) knows why it thinks it needed to switch modes.

To me, the mode is useless because it does things out of my control. If I know my subject isn't moving then I use One Shot (or isn't moving enough that I can control where the DOF is.) The I know exactly what I get. If the subject is moving, I use AI Servo. Trading precise focus placement for focus tracking.

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