Flash photography

Flash photography uses a brief burst of artificial light to illuminate a scene during an exposure. The flash can freeze motion, brighten shadows, or provide the main light source.

Flash synchronization: The coordination of a camera’s exposure with the firing of a flash. The shutter must expose the sensor when the flash illuminates the scene.
Exposure triangle: A model relating aperture, shutter speed, and ISO in determining photographic exposure. Flash exposure depends strongly on aperture and ISO, while shutter speed chiefly affects ambient light.
Bounce flash: A technique that directs flash toward a nearby surface so reflected light illuminates the subject. It creates a larger, softer light source than a bare on-camera flash.
Continuous lighting: Lighting that remains on while a photograph is composed and captured. Unlike flash, it shows shadows and reflections continuously but may require longer exposures.
Shutter speed: The duration for which a camera sensor or film is exposed to light. With conventional flash synchronization, shutter speed controls ambient light while flash duration helps freeze motion.
Inverse-square law: A physical law stating that the intensity from a point source decreases with the square of distance. Moving a flash closer can sharply increase illumination and change brightness differences across a scene.
Fill flash: Flash used to lighten shadows while ambient light remains the principal illumination. It reduces harsh contrast in backlit scenes without replacing the existing light.
Available-light photography: Photography illuminated only by light already present in the scene. It avoids added flash but gives less control over illumination and motion freezing.
Guide number: A measure of a flash’s output used to calculate exposure distance and aperture. It estimates how far a flash can illuminate a subject at a given aperture.
Color temperature: A numerical description of the color appearance of a light source, expressed in kelvins. Flash and ambient sources can have different colors, producing mixed illumination.

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