Flash fires an instantbefore the second (rear) curtain of the focal plane shutter begins to move. Whenslow shutter speeds are used, this feature can create a blur effect from the ambientlight, i.e., a flowing- light patterns following a moving subject with subject movementfrozen at the end of the light flow. (See Front-Curtain Sync .) Most midrange and top flight auto camera models have this feature.mirglossary
Sometimes called second curtain sync, it s a technique in which the flash fires an instant before the second (rear) curtain of the camera s focal plane shutter begins to move.