Strobes are the real workhorses in a professional studio, and are basically larger and more powerful versions of your camera's built-in flash. They are cooler than continuous lights mainly because they fire very short bursts of light. These bursts are of such short duration, they also freeze motion. Since they are not on all the time, strobes often have low intensity modeling lights so you can see how the light will fall on the subject. Strobes are great, but cost hundreds, and usually thousands of dollars. They generally have one or more lightweight heads containing the flash tubes that connect by highvoltage cables to a separate power pack that powers and controls the light. However, a version called a monolight has all of the needed circuitry built into the head.

The power of these units is usually specified in watt-seconds. The higher the rating, the more powerful the unit. Another important attribute is the unit's recycle time. The shorter the time, the faster you can get off the next shot.

The power of a flash is important relative to the size of the subject. If you are shooting small objects you don't need anywhere near as much power as you do when shooting large ones. However, the more power you do have, the smaller the aperture you can use to gain increased depth of field— especially important when doing close-ups.

Many digital cameras with fixed lenses have a fairly large minimum aperture of f/11 or so. The camera can't stop down far enough to prevent overexposing an image when used with a powerful strobe. This forces you to move the strobe father from the subject—making the light harder. For this reason, too many watt seconds aren't always good.

Some strobes have zoom heads so you can adjust the cone of light. For consistency, the width of this cone is usually listed in specifications as it would be when 10 feet from the light.