So far flash has been mentioned only in passing. It is actually a very important part of photography-for a small flash unit is a portable light, available anytime, anywhere. It can solve many problems, and it can certainly help you to produce a picture under circumstances in which it would otherwise be impossible. But its light can vary in quantity and in quality, just like any other kind of light. Electronic flash is far and away the most common type, except on the very simplest cameras, and if you go out to buy a new camera or flash unit you will almost certainly be offered electronic flash rather than the earlier bulb flash units or cubes. Electronic units designed for amateur use are usually quite small, sometimes no larger than a cigarette packet. Into that small space is cramed the circuitry, batteries, a fluorescent tube and a capacitor. A small unit adequate for indoor portraits and small groups may have a flash duration of 1/2000 second and take about 8 seconds to recycle. But a computer unit will have varying periods of flash duration. Bulb flash and flash cubes work on a different way, and some cameras have a separate flash socket to accommodate these as the synchronization is different too. In this case the bulb must fired just before the shutter is fully open, to allow the light to reach its peak of power.
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