Tuesday, January 30, 2007
A Flash In The Night
Create dramatic evening images with a touch of artificial light
For even more precise flash exposures, many of today's cameras utilize a series of preflashes which, when combined with the subject's distance from the camera, create an accurate flash exposure. The distance data provided by the lens-focusing system, along with the low-powered preflashes, compensate for subjects that are very dark or very light. Because the camera's software knows what a normal flash output would be at a given distance for a neutral subject, extremes such as white or black subjects that reflect dramatically more or less light, respectively, can be adjusted for. Since most of this is handled invisibly, you don't have to worry much about it. The only thing that's important when using an auxiliary flash unit is to make sure that it's set for TTL mode.
Improving Background Exposure
If you've been shooting images for any period of time, you know what a standard flash photograph looks like: bright foreground and dark background. There's nothing bad about this; often, it's all that you need for photographs taken at an event like a birthday party or an awards ceremony. Yet to reveal more of your background, you don't need a more powerful flash, but rather a slower shutter speed.
This is because the flash exposure is only affected by the aperture when the camera is set for the sync speed or slower. Due to the incredibly short duration of the flash, a shutter speed that's comparatively much slower will have no impact on the accuracy of the flash exposure. By choosing a wider aperture, however, you'll increase the effective range of your flash. But if you want to get an accurate exposure for a cityscape, your flash won't be powerful enough.
Instead, choose a slower shutter speed so that your camera registers more of the ambient light. The easiest way to do this is to select the Slow Sync flash or Night flash mode. Often represented by a lightning bolt symbol and the word "slow," the camera automatically chooses a slower shutter speed to register the ambient light. The result is a balanced image with a good flash exposure and a well-detailed background.
Rear Curtain Sync
Similar to Slow Sync, Rear Curtain Sync takes advantage of shutter speeds that are slower than the flash sync speed. The difference is that the flash is fired at the end of the shutter duration rather than at the beginning. The difference is readily apparent when shooting moving subjects.
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