What is a focus lock and how to use it?

Focus lock means that after the camera selects focus, hold down the AF lock button on the back of the camera. At this time, the lens is no longer in focus lock. At this time, move the lens, re-compose, press the shutter, and take a picture that the subject is not in the center of the picture. Such photos are more artistic and give people an unusual taste. Practice a few more times and you will be familiar with this second composition. This is a necessary skill for professional photographers. It is also a big advantage of SLR cameras.