Flash synchronization

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In photography, flash synchronization or flash sync is the synchronizing the firing of a photographic flash with the opening of the shutter admitting light to photographic film or electronic image sensor.

In cameras with mechanical (clockwork) shutters synchronization is supported by an electrical contact within the shutter mechanism, which closes the circuit at the appropriate moment in the shutter opening process. In electronic digital cameras, the mechanism is usually a programmable electronic timing circuit, which may, in some cameras, take input from a mechanical shutter contact. The flash is connected electrically to the camera either by a cable with a standardized coaxial PC (for Prontor/Compur) 3.5 mm (1/8") connector^[1] (as defined in ISO 519^[2]), or via contacts in an accessory mount (hot shoe) bracket.

Faster shutter speeds are often better when there is significant ambient illumination, and flash is used to flash fill subjects that are backlit without motion blur, or to increase depth of field by using a small aperture. In another creative use, the photographer of a moving subject may deliberately combine a slow shutter speed with flash exposure in order to record motion blur of the ambient-lit regions of the image superimposed on the flash-lit regions.