Aside from exposure compensation, focus lock is perhaps my favorite feature on my camera. This feature can be found on almost every digital camera that has been made within the past few years. I use it ALL. THE. TIME. There is a time and place for changing focal points on a camera, and I will cover that in another post, but most of the time focus lock is all I need.
Focus lock allows your camera to quickly focus on a subject that you don't necessarily want to appear directly in the center of your photograph.
For example, I didn't want these leaves to appear directly in the center of my photo. I looked through my viewfinder and positioned the center focus point directly over the object I wanted most sharply in focus, the uppermost leaves in the foreground. I held my shutter button down half way until I heard a beep. Once I heard the beep, I knew my camera understood the exact point I wanted it to stay focused on.
Keeping my shutter button held down half way, I moved my camera down and to the left a bit until I liked where the leaves were positioned in my viewfinder. I pressed the shutter button the rest of the way down to capture this picture.
The leaves remained sharply in focus and they didn't have to reside directly in the center of my photo.
Keep in mind that this only works if both the camera and the subject do not change depths/planes. If I would have taken even a tiny step forward or backward after I had pressed the shutter button down half way, the leaves would not have remained in focus. I would have had to release my shutter button completely and start over.
Here is another example where I held my shutter button down half way after center-focusing on the big tree you see on the left and then moving my camera over to the right and snapping the photo. The tree trunk remains in focus, but it is not in the center of my photograph.
Getting to know this feature on your camera will allow you to view your subject, and the composition of your entire photograph, in a whole new way. It is fun to stray from the belief that everything you take a photograph of must remain directly in the center of your photograph.