After you've taken a photograph of two people have you looked at the image and noticed the camera has focused on the background, between their heads instead of them? Well, you're not the first. By raising the camera, putting the people in the middle of the picture and clicking the shutter button you'd think the camera would know to focus on the people but until Face Detection started appearing, they didn't and this is where focal lock came in useful. Even though you can take sharp portraits with Face Detection now there's still times when focus lock will come in handy. For example, if you're taking a photo with the subject off-centre, so some of the background can be seen the camera can adjust to focus on the background instead of your subject. As a result you'll have a lovely shot of your background but your main subject will be blurred.
Here's how you use focus lock:
Point your camera at your subject, making sure they are in the position you want them to be and half press the shutter button to activate the focus lock function. This tells the camera this is what you want to focus on and as long as you don't let go of the button or fully press it, the focus will remain locked.
Next, move your camera to frame the shot however you want then press the shutter button fully to take your photograph.
Make sure your subject doesn't move as if they change position, even slightly, it'll mean they're no longer in focus and you'll have to start the process again.
Move the slider in the image to the right to see how using focus lock to change the point of focus can alter the look of an image.
Use focus lock for close up work
You can also use the focus lock to ensure the camera has focused on exactly the right point of the subject. This is important for close up photography where it may not be possible to get the whole of an insect or flower in focus. In such cases, pick the area that's most important and focus there.
Photo by Peter Bargh.