Need some help understanding AF Lock...

I've been reading multiple threads, and want to know something...

Generally when I photograph concerts, I have the following settings;

AI Servo
Center point focus
Spot metering

These are all saved under my C1 setting... but I'm interested in taking this further, I shot a show tonight and got a lot of blurry photos, wasn't too happy with it... I went with center point focus (to grab the face) but the lens would hunt after that.. it wouldn't stay attached to the subject... how do you get the camera to permanently lock onto a subject after you've designated the focus point?

In my mind, I'm reading the AF Lock as something that you could focus on that person w/ a center point focus, and then hit the AF Lock and then start panning/following accordingly (with AI Servo) -- thus reducing the chances of misfocusing... Do I need to hold AF Lock the entire time that I'm shooting?

Am I missing something here?

Hmm, let's get this straight!

You are using AI Servo, meaning that you want to focus "on the fly", typically as you are tracking a moving subject. In this mode there is no "AF locking"...

But, at some point if you lock focus then you are no longer using AI Servo...?

Too many threads on blurry focus w AI Servo ...

Use Single Shot Center Point and Spot ... be done with it

Back button focus will help if I am understanding your problem correctly.

http://www.learn.usa.c​anon.com …ckbutton_af_art​icle.shtml

dannequin wrote in post #15694317
I shot a show tonight and got a lot of blurry photos, wasn't too happy with it... I went with center point focus (to grab the face) but the lens would hunt after that.. it wouldn't stay attached to the subject... how do you get the camera to permanently lock onto a subject after you've designated the focus point?

The point of AI servo is that it doesn't lock, it continuously focuses to keep a moving subject in focus. The lens shouldn't hunt particularly though, it should keep the subject in focus.

Are you keeping the focus point on the subject properly? If the focus point moves off the subject the camera will attempt to focus on whatever is now under the AF point. So, if you focus on a face and the camera is moving a little left and right, relative to the face, then the AF point will slip off and the camera attempt to refocus on the background, or whatever else is now under the point.

dannequin wrote in post #15694317
Generally when I photograph concerts, I have the following settings;

AI Servo
Center point focus
Spot metering

...............In my mind, I'm reading the AF Lock as something that you could focus on that person w/ a center point focus, and then hit the AF Lock and then start panning/following accordingly (with AI Servo) -- thus reducing the chances of misfocusing... Do I need to hold AF Lock the entire time that I'm shooting?

Am I missing something here?

You misunderstood AF Lock.
AI Servo is the focus mode you use when shooting moving subjects. It continually refocuses on a moving subject - however you need to make sure that your focus point is over the subject, otherwise the camera will focus on whatever the FP is over, which may be the drums or the back of the stage.

AF lock is basically the opposite of AI Servo. Where AI servo allows you to keep a moving subject in focus, AF Lock locks the focus at the current focal distance, which means it is useless for photographing a moving subject.