It is a mode on the flash that allows you to use the flash at rates higher than the max-sync rate by changing the way the flash works. In normal mode, the flash fires a single fast pulse of light that falls within the period when the shutter is fully open. Since the shutters are not fully open above the max sync speed, FP (or for Canon HS Sync), changes that pulse to a bunch of smaller pulses so light is applied over a longer period of time, i.e., the full shutter period. This means two things: 1) You lose power 2) The motion-stopping feature of the flash is lost since flash-period == shutter speed now.
Look in your flash manual for the FP Sync mode.
Can you clarify what you mean by "you lose power"? Do you mean it drains the batteries faster or that you can't fire the flash with as great an intensity (or both)?
Also, unless you're shooting a bullet going through a watermelon or something like that, won't the shutter speed be enough to freeze the motion at speeds above 1/320 (speed at which D300 begins using the FP feature)?
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i tried , but no luck
i guess i will have to live with 1/200 max
[ until D3x becomes affordable
/ɯoɔ˙ƃnɯƃnɯs˙ʇlɟsɐq//:dʇʇɥ
Also, unless you're shooting a bullet going through a watermelon or something like that, won't the shutter speed be enough to freeze the motion at speeds above 1/320 (speed at which D300 begins using the FP feature)?
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the same flash is distributed over several smaller , weaker flashes
hail instead of bullet
/ɯoɔ˙ƃnɯƃnɯs˙ʇlɟsɐq//:dʇʇɥ