Monday, June 25, 2007
Enlighten your photography with the illumination of accessory flash
Compatibility is an issue when selecting an accessory flash. Some work properly with only their own systems, some play nicely with others, and some have features that work with only certain cameras. Before you buy, make sure the flash you want is right for your camera and needs.
The guide number is a representation of how much coverage is provided by a flash to illuminate a subject. Sometimes expressed in feet and sometimes in meters (be sure you know which), it's determined by the distance to the subject, aperture (ƒ-stop) and the light sensitivity (ISO). While most flashes used with their proprietary cameras automatically adjust proper exposure, knowing guide numbers helps you with manual flash photography and also helps you to know when you're going to have "flash falloff"—when there isn't enough light to cover the subject at the distance at which you're shooting.
TTL (through-the-lens) metering capabilities are essential for optimum results, so ideally you'll select a flash that's compatible with your camera's metering system. Most flashes will work to sync automatically with the digital metering of the camera body, and most provide manual options as well. Some flashes also offer extras like AF illumination for autofocus assistance, particularly useful when it's too dark to focus manually. Another convenience is auto-zoom flash, which allows a flash to adjust output based on your lens' current zoom setting.
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