Slow sync flash is when you fire your flash either at the beginning or end of an exposure that’s slower than normal, for example 1/8 of a second. Anyone with experience behind a camera knows that it’s very hard to hold the camera steady enough for a sharp exposure at this sort of speed, and that’s where the flash comes in. By firing the flash, you freeze the motion and collect light trails in the remaining time, creating this rather cool effect, like in the photos inside.

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