Tips for back-button focusing w/ XSi?

[aliciaqw]

I'm really tyring to get a good grasp on this whole BBF thing. I like being able to lock the focus without using the shutter, but I'm having a heck of a time getting focus when in AI Servo. I read a TON on the subject but every new thing I read just confuses me more. I take a lot of pictures of my almost 6 month old son and he's all over the place. I was under the impression (from reading and more seasoned photogs) that AI Servo would help with this. Unfortunately, I'm getting crap in return.

I'm holding the button down and tracking him as he moves. Should I not be doing this? If I just press and release, focus is locked but obviously that's not going to get me a focused shot since he moves immediately after I lock focus. Soooo, I hold the button down then press the shutter while holdind the * button down. Is this wrong?

And I really apologize if I somewhat covered this topic in another thread of mine. I would loooove some clear advice. I am taking this whole photography thing very slow and know that this is one area (focus) that I need to have down pat before moving on to other areas. Thaaaank you kindly, sirs and madams!

 

[fokker]

Try using AI focus, I never seem to have much luck in AI servo. AI servo locks focus and gives you a confirmation beep and red light flash, but it seems to be slow to pick up on subject movement, when it supposedly automatically switches to AI focus mode instead of one-shot.

If you use AI focus the camera never stops trying to optimise the focus as long as you're holding the focus button. I find this much better when tracking a subject. It will lock on and stay focused as long as you keep the active focus point on the subject, whereas AI servo will sometimes lock and stop searching.

Hope that helps.

 

[Big Mike]

Are you certain that it's a focus issue? If your son is moving, he might just be blurry because of a slower shutter speed.

Post up some examples, along with the EXIF info (shutter speed, aperture, ISO etc.)

 

[stevemunoz]

For shots like these you would just hold down the *(focus button) through the shot. You should also pan through the shot, and not stop when you are about to shoot the shot, this will improve the likelihood of a decent looking shot. Also, make sure your shutter speed is fast enough to freeze the action. I would be shooting at 1/200th and faster to make sure you freeze whatever motion he is making.

Steve