What is Auto FP High-Speed Sync?

Indispensable to outdoor photography, Auto FP High-Speed Sync enables action-stopping shutter speeds with fill flash. This function is also important for portraiture, allowing the use of larger apertures for a more pleasing radiant ambient light and soft backgrounds to eliminate distractions. 

If your camera is compatible with Auto FP High-Speed Sync (see camera chart below), it switches on automatically when shutter speeds above 1/250th second are used for flash photography.

Auto FP High-Speed Sync Flash  @ 1/1250 sec, f/8, ISO 400	Auto FP High-Speed Sync Flash  @ 1/1250 sec, f/8, ISO 400

How does Auto FP High-Speed Sync work?
When using normal flash the Speedlight emits one burst of light when the shutter is fully open.

Front shutter curtain opens	Flash sync when shutter is fully open	Rear shutter curtain closes

Auto FP High-Speed Sync provides a series of light pulses that provide consistent and even light as the shutter travels. 

This strobing action takes a large amount of flash power. The amount of light reaching the sensor reduces the faster the shutter speed set. Often the reduction in power does not noticeably affect the image, but when it does, photographers often compensate by either moving closer to their subjects or using more than one Speedlight. 

Cameras compatible with Auto FP High-Speed Sync

^*1 Not all Speedlight’s support Auto FP High-Speed Sync mode, please refer to the Speedlight User Manual for details.
^*2 In i-TTL, AA, A, GN, and M Speedlight modes only. 
^*3 1/8000s on the Nikon Z9, Z8, Z6III and Z f.