Flash (photography)
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In photography, a flash is a device that produces an instantaneous flash of light (typically around 1/1000 of a second) at a Color temperature of about 5500K to help illuminate a scene. While flashes can be used for a variety of reasons (e.g. capturing quickly moving objects, creating a different temperature light than the ambient light) they are mostly used to illuminate scenes that do not have enough available light to adequately expose the photograph. The term flash can either refer to the flash of light itself, or as a colloquialism for the electronic flash unit which discharges the flash of light. The vast majority of flash units today are electronic, having evolved from single-use flash-bulbs and flammable powders.
In lower-end commercial photography, flash units are commonly built directly into the camera, while higher-end cameras allow separate flash units to be mounted via a standardized accessory mount bracket. In professional studio photography, flashes often take the form of large, standalone units, or studio strobes, that are powered by special battery packs and synchronized with the camera from either a flash synchronization cable, radio transmitter, or are light-triggered, meaning that only one flash unit needs to be synchronized with the camera, which in turn triggers the other units.
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[edit] Types of flashes
[edit] Flash bulbs
The earliest flashes consisted of a quantity of magnesium powder that was ignited by hand. Later, magnesium filaments were contained in flash bulbs, and electrically ignited by a contact in the camera shutter; such a bulb could only be used once, and was too hot to handle immediately after use, but the confinement of what would otherwise have amounted to a small explosion was an important advance. A later innovation was coating flashbulbs with a plastic coating to improve spectral quality as well as providing protection from the rare occasion when a flashbulb would crack during a flash. One of the most widely used flash bulbs up through the 1960s was the number 25. This is the large (approximately 1 inch (25mm) in diameter) flash bulb often showed used by newspapermen in period movies, usually attached to a medium format bellows camera.
[edit] Flashcubes, Magicubes and Flipflash
In the late 1960s, Kodak improved their Instamatic camera line by replacing the individual flashbulb technology (used on early Instamatics) with the Flashcube. Flashcubes consisted of four electrically fired flashbulbs with an integral reflector in a cube-shaped arrangement that allowed taking four images in a row. The flashcube automatically rotated 90 degrees to a fresh bulb upon advancing the film to the next exposure.
The later Magicube retained the four-bulb format, and was superficially similar to the original Flashcube. However, in the Magicube each bulb was set off by a plastic pin in the cube mount that released a cocked spring within the bulb. This in turn struck a piezoelectric element in the flash that ignited the magnesium filament, so that a battery was not required. Magicubes could also be set off by inserting a thin object, such as a key or paper clip, into one of the slots in the bottom of the cube.
Another common flashbulb-based device was the Flipflash which included ten or so bulbs in a single unit. The name derived from the fact that once five flashes had been used up, the unit had to be flipped and re-inserted to use the remaining five.
[edit] Modern flash technology
Today's flash units are often electronic xenon flash lamps. An electronic flash contains a tube filled with xenon gas, where electricity of high voltage is discharged to generate an electrical arc that emits a short flash of light. (A typical duration of the light impulse is 1/1000 second.) As of 2003, the majority of cameras targeted for consumer use have an electronic flash unit built in.
Another type of flash unit are microflashes, which are special, high-voltage flash units designed to discharge a flash of light with an exceptionally quick, sub-microsecond duration. These are commonly used by scientists or engineers for examining extremely fast moving objects or reactions, famous for producing images of bullets tearing through objects like lightbulbs or balloons (see Harold Eugene Edgerton).
[edit] Technique
A flash is commonly used indoors as the main light source, because there is not enough other light for a desired shutter speed. A fill flash is a low powered flash mixed with ambient light, and is often used to illuminate shadows on the side of a subject facing the camera. Another technique, bouncing a flash, involves pointing a flash upwards off of a surface, often a white celling, where it is reflected back onto the subject. Bouncing creates a more natural light effect and lessens shadows and glare but requires more flash power than a direct flash.
Part of the bounced light can be also aimed directly on the subject by "bounce cards" attached to the flash unit. That increases the efficiency of the flash and compensates shadows caused 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.
[edit] Pitfalls
- A typical problem with amateur cameras is the low intensity of the flash, as the light will often not suffice for good pictures at distances of over 3 meters (10 ft.) or so. Dark, murky pictures with excessive image noise or "grain" will result. In order to get good flash pictures with simple cameras, it is important not to exceed the recommended distance for flash pictures.
- The "Red-eye effect" is another problem - since the retina of the human eye reflects red light straight back in the direction it came from, pictures taken from straight in front of a face often exhibit this effect. It can be somewhat reduced by using the "red eye reduction" found on many cameras (a pre-flash that makes the subject's irises contract). However, really good results can be obtained only with a flash unit that is separated from the camera, sufficiently far from the optical axis, or by using bounce flash, where the flash head is angled to bounce light of a wall, ceiling or reflector.
