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Old Apr 5, 2005, 2:04 AM   #1
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I was photographing my nieces today on bicycles, and the AI Focus is supposed to track them (it shifts from the one shot focus to AI Servo, correct?). Well....it didn't. The background wasn't moving, my camera wasn't moving, they were moving, but the camera seemed to have no idea. When I switched to AI Servo it worked the way it is supposed to, but am I doing something wrong? Does anyone have success with the AI Focus mode?
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Old Apr 5, 2005, 2:30 AM   #2
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I use one shot for action...AI servo never gets upto the full speed and it doesn't seem to focus well unless you have the subject covered in the main + of the focus points
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Old Apr 5, 2005, 9:14 AM   #3
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I also use One-shot for action!

Even when tracking birds in flight I use One-shot focus - The AI Servo is supposed to track the subject, but I found it guesses most of the time wrong when the mirror is up - with One-shot I know exactly what I locked on...
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Old Apr 5, 2005, 10:47 AM   #4
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AI Focus has cost me pictures, so I never use it.
AI Servo works fairly well, depending on how the subject is moving (directly towards/away doesn't normally work, more side-to-side does.)

Like NHL I've used One Shot and its worked... ok. If you really care about the expression or fine detail (the head angle, the eye catching the light) then one-shot doesn't work too well 'cause you can't sit and wait until that exact moment occures. I find that by the time one-shot locks focus that moment is gone. But it can work. I've gotten some good shots using it. I've just gotten more using AI Servo.

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Old Apr 5, 2005, 11:41 AM   #5
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Thanx for the info. I will try one shot, never used it, AI Focus in concept seems like it would be the best, butI don't think it works, or maybe mine just doesn't work. If the focusing screen was a bit better I would just manually focus, which is what I wind up doing most of the time, anyway.
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Old Apr 5, 2005, 12:37 PM   #6
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Like Spec3 has said AI servo works best on large objects, like racing cars that can fill a whole frame, so that more than 1 AF sensor can cover the subject under question - It rarely works well when only 1 AF sensor is active

AI Focus is just One-Shot initially and then shift to AI Servo if movement is detected by the camera - The problem with that is it's unpredictable!
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Old Apr 5, 2005, 4:24 PM   #7
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Quite unpredictable, being that it can't sense two kids going about 15mph on bicycles, I don't think I will bother with that mode, but thanks for all of the info, it was quite helpful, and it made me feel better about my camera (I thought it might be defective).
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Old Apr 5, 2005, 11:00 PM   #8
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NHL, I'll have to disagree with you there.

AI Servo works very well with only the center point focus active (but I'm not using an f2.8 lens, so it's no better than the other AF points.) I take pictures of birds in flight all the time with it and it worked very well on the 10D and my 20D it worked ok (but I blame my camera not the model.)

And trust me, none of the birds I photograph are as big as cars.

I completely agree with you about AI Focus. I wish they'd just remove it from the camera. Its never worked well for me. I know what I want (One Shot or AI Servo) and I don't want the camera to try to guess it when I can just set it directly.

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Old Apr 6, 2005, 8:50 AM   #9
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eric s

You said it yourself:
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AI Servo works fairly well, depending on how the subject is moving (directly towards/away doesn't normally work, more side-to-side does.)
-> When the subject is moving sideway - the AF distance really didn't change that much (combined with the larger DOF of not having f/2.8 )... Is this really different from One-Shot AF (with the subject moving sideway)? ie what is the AI-Servo tracking if the distance is relatively constant?
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Old Apr 6, 2005, 9:10 AM   #10
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But nothing is moving perfectly side-to-side. Sure, I don't expect the camera to track even a car (a nice big subject) if it were coming straight at me fast. And to keep the distance really constant, the subject would have to fly a circle around me. Nothing does that.

I can guaranty you that the birds I shoot are often coming at an angle (not straight left/right, forward/back or in a circle) and AI Servo can often track them. While AI Focus should be taken out and shot, AI Servo should stay on the camera as it serves me very well most of the time.

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