Flash is a device that produces a brief burst of light. It can freeze motion, fill in shadows, and provide the main light source when none exists. On-camera flash is convenient but produces flat, harsh light and a distinctive shadow behind the subject. Off-camera flash is more versatile. It can be bounced off a ceiling or wall, diffused through a softbox, or positioned to create dramatic side lighting. Flash power is measured in guide numbers or watt-seconds, and it can be adjusted manually or automatically through through-the-lens metering.

Flash has a maximum sync speed, the fastest shutter speed at which the entire sensor is exposed at once. Above that speed, the shutter curtains block part of the frame. High-speed sync overcomes this by pulsing the flash multiple times during a single exposure. Flash can also be used as fill light, reducing shadows without becoming the dominant source. This is common in outdoor portraits, where the sun creates harsh shadows under the eyes and nose. Flash is a tool. Used well, it is invisible. Used poorly, it is obvious.

Flash techniques

• Fill flash. Softens shadows in bright light.
• Bounce flash. Reflects light off a ceiling or wall.
• Off-camera flash. Creates directional lighting.
• High-speed sync. Allows flash at fast shutter speeds.

Flash is not just for dark places. It is for controlling light anywhere.