Shutter lag refers to the elapsed time between the instant you press the ‘release’ button and the instant the image is captured. This can become an issue with auto-focus cameras, where the time required for the camera to focus can make it difficult to capture moving subjects. Fortunately, most cameras sold today can be forced to focus by applying light pressure (often called a ‘half-press’) and holding the release button. When you press it the rest of the way, the image is captured immediately.