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Old Jan 25, 2009, 8:45 PM   #1
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I just got my new XSI and have been trying to learn all of the features. I've been playing around with the focus modes and have a question about the AI Servo mode.

When in this mode, how do I know what focus point is being followed? Unlike in the other modes, no focus point turns red, so although I hear the lens refocusing, I don't know what I'm actually focused on.

Is it always using the center point in Servo mode, or does it select one and just no tell me which one? If I manually pick the AF point, will it use the one I choose?
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Old Jan 26, 2009, 6:06 AM   #2
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In AI Servo if you select automaticAF point selection the camera starts off with thecenter AF point first and if the subject moves off this point AF will continue as long as the subject is covered by another AF point. The focus confirmation light blinks when you have no AF and goes off when you do (focus confirmation light works like this on my 1D MKII N and i presume it works the same on your XSI).

With a manualy selected focus point the camera uses this point only and it should be lit up, the focus confirmation light works the same as above.
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Old Jan 26, 2009, 10:28 AM   #3
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dannox02 wrote:
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Is it always using the center point in Servo mode, or does it select one and just no tell me which one? If I manually pick the AF point, will it use the one I choose?
One of the reason the AF points do not light up is because the camera can also predict a 1/2 way point between two AF sensors as the subject moves across or anticipate the subject location as the mirror is flipped up after the few milliseconds where the last AF point was sampled (i.e. the focus does not have to be on any particular sensor...)

On a 1D it's easier as you can expand the center point to the other AF sensors around it when you manually pick the center AF
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