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Introduction

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One thing all digital cameras have in common, from the lowliest supermarket snapshot model up to the top professional SLRs, is a built in flash unit. Even some mobile phones now come with built-in flash. As well as this, many cameras also have the ability to fit an external flash, or even to be connected to a studio flash lighting system.

Flash is essential for taking photos in low light conditions, but few people know how to use it properly, or some of the simple techniques that are possible even with budget-priced equipment that can seriously improve your photography.

How it works
Almost everyone will be familiar with the small built-in flashguns found on every type of compact camera. If you’re not, just turn the camera round and take a picture of your own face. Once your eyes have stopped watering, that bright green blob you’re now trying to blink out of your field of vision is the exact shape of your flashgun, so just look on the front of your camera for a clear window of the same shape. It may take several tries to get this right.

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Almost all flashes work in the same way. They consist of a large capacitor (an electronic component that stores charge and can release it very quickly) connected via a circuit to a glass tube filled with the gas Xenon. When the camera shutter is released, a switch closes the circuit and the capacitor discharges a very high voltage current into the glass tube, causing a large electrical spark in the Xenon gas and emitting a powerful burst of light. The flash is very brief, usually about 1/1000th of a second, but extremely bright. Even the flash on a compact camera can illuminate an area about three metres across as brightly as daylight.

There have been other types of flash used in the past, including rapidly burning magnesium powder which would go off with a bang and a cloud of smoke when ignited, and later flash bulbs, which contained a filament of magnesium wire that could be ignited electrically, but could only be used once. Since Xenon flash bulbs are relatively cheap to manufacture and can be re-used many thousands of times, they have almost entirely supplanted magnesium bulbs for photographic use.

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