But the best off-camera lighting conveys shape, dimension, and mood through the interplay of highlight and shadow. You create this kind of lighting wirelessly using masters and slaves. A master (also called a commander) is a controller that attaches to your camera’s hot-shoe and sends signals to an off-camera, accessory flash or flashes (slaves). The master functionality can be built into a flash (even your camera’s pop-up flash, on some models) or a dedicated, flashless adapter, and its commands are sent as pulses of infrared light or radio signals. You can hold a slave flash in your hand, ask a friend to hold it, or mount it on a lightstand.