hi, i recently attempted to freeze the movement of small birds just as they are about to take off. i have varied results with my new sb700. how should i set this, and my d7000 to freeze the movement of the birds wings? faster shutter, ( i can only seem to go to 1/320th s), or should i reduce flash duration by altering its output, and how?. they are so quick i still usually get motion blur, still one or two lucky shots though.