Flash Slow Sync

Flash used normally will freeze a moving object, and, if exposure is correct, will evenly illuminate everything within its range. But, as in every aspect of photography, creative rule breaking can produce stunning results; and this is particularly true of the unorthodox technique of slow sync flash. So, what is slow sync flash and how to use slow sync flash?

Most SLR cameras have a mark on the shutter speed dial that synchronizes the flash when the picture is taken. Usually this speed is 1/60 or 1/125 second. If a shutter speed faster than this is used the blinds of the focal plane shutter will not have time to open fully, so that part of the picture comes out unexposed. However, it is possible to use a lower speed such as 1/15 or 1/18 second and still synchronize the flash.
The flash will not last any longer than usual, which means that it will be illuminating the scene for only part of the time the shutter is open.

If a slow shutter speed is used with flash to photograph a moving object when there is a reasonable amount of ambient light, the subject will be marked by a faint trail looking like “speed lines” in cartoons. This can look very effective in an action shot.
 

The important thing is to use a shutter speed compatible with both the ambient light and the desired flash effect. For example, if the ISO is 100, a meter reading of the ambient light says 1/125 at f5.6, in order to get the slow sync effect a shutter speed of 1/15 second is needed. To compensate for the difference the aperture should be reduced to f16. Set the dial on the flashgun to f16 or, if it is a manually controlled one, work out the flash to subject distance that normally requires an aperture of f16. The result should be worth the effort.

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