FP High Speed Sync
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Feature allowing for flash photography at sync speeds higher than the maximum sync speed of the camera, typically 1/250s, under normal flash use. Accomplished by multiple flash bursts with moderate output, but uniformly on the film or sensor frame as the shutter travels in front of the frame. Recommended for action photography where high shutter speeds are required or for fill-flash images outdoors at wide apertures.
By using FP high speed sync you are getting higher sync speeds at the cost of less light.
With the SB-900, SB-800 and S-600 flashguns auto FP high speed sync support you can sync the flash up to the maximum shutter speed of the camera, typically 1/8000s
