If you’ve attempted the above but are still having problems, here are some ideas and tips that may help:
1. Autofocus works by moving the camera’s lens in or out, depending on the distance of the object. If you have activated the focus lock and then proceed to move closer or further away from your subject or you get your subject to move closer or away from the camera, the subject will then be out of focus. Be sure to zoom in (or out) before pressing the shutter button half way down. If your subject moves and alters the distance after you’ve initiated the focus lock, simply release the shutter button and try again.
2. What happens when you hold a book too close to your face? Try as you might - cross you eyes, wrinkle your forehead - the only way to make those words come into focus is by moving the book further from your eyes. If your camera refuses to cooperate when you try using focus lock, it could be because you are too close to your subject resulting in the camera being unable to focus. Try zooming out or taking a step back and give it another shot.