Flash Photography

A flash is a device used in photography producing a flash of artificial light (typically 1/1000 to 1/200 of a second) at a color temperature of about 5500 K to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light. Flash refers either to the flash of light itself or to the electronic flash unit discharging the light. Most current flash units are electronic, having evolved from single-use flashbulbs and flammable powders. Modern cameras often activate flash units automatically.

Flash units are commonly built directly into a camera. Some cameras allow separate flash units to be mounted via a standardized "accessory mount" bracket ( hot shoe ). In professional studio equipment, flashes may be large, standalone units, or studio strobes , powered by special battery packs or connected to mains power. They are either synchronized with the camera using a flash synchronization cable or radio signal, or are light-triggered, meaning that only one flash unit needs to be synchronized with the camera, and in turn triggers the other units.

As well as dedicated studio use, flash may be used as the main light source where ambient light is inadequate, or as a supplementary source in more complex lighting situations. Basic flash lighting produces a hard, frontal light unless modified in some way.Umbrellas and softboxes are commonly used for this purpose (even with small hand-held flash units).

Fill flash or "fill-in flash" describes flash used to supplement ambient light in order to illuminate a subject close to the camera that would otherwise be in shade relative to the rest of the scene. The flash unit is set to expose the subject correctly at a given aperture, while shutter speed is calculated to correctly expose for the background or ambient light at that aperture setting.

Bounce flash is a related technique in which flash is directed onto a reflective surface, for example a white ceiling or a flash umbrella , which then reflects light onto the subject. It can be used as fill-flash or, if used indoors, as ambient lighting for the whole scene.

Bouncing creates softer, less artificial-looking illumination than direct flash, often reducing overall contrast and expanding shadow and highlight detail, and typically requires more flash power than direct lighting.

Part of the bounced light can be also aimed directly on the subject by "bounce cards" attached to the flash unit which increase the efficiency of the flash and illuminate shadows cast by light coming from the ceiling. It's also possible to use one's own palm for that purpose, resulting in warmer tones on the picture, as well as eliminating the need to carry additional accessories.

Also, slave flash units exist that are set up away from the subject and camera, that are triggered by the light from the master flash. This slave flash provides fill or bounce light. Many small flashes and studio monolights have optical slaves built in. Wireless radio transmitters, such as Pocket Wizards are also popular for remote synchronization since the receiver unit can be around a corner, or well over 100 meters away (which would be far to difficult to trigger using an optical sync).

Another method that can be used is strobe. Some high end units can be set to flash a specified number of times at a specified frequency. This allows action to be frozen multiple times in a single exposure.

Colored gels can also be used to change the color of the flash. Correction gels are commonly used, so that the light of the flash would be the same as the tungsten lights (using a CTO gel) or the fluorescent lights.