A fan was photographed backlit using a D3X at 1/60th (recording most if not all of the flash duration)in order to see what is the real life action ability of some of the flashes at my disposal. Flash duration is often an overlooked specification when comes the time to choose a flash system. Manufacturers do not help by specifying the duration in the form of the meaningless
t=0.5 format, while the real life spec should be t=0.1 to be of any use. If not specified, the duration is most likely t=0.5 wich makes specs look impressive, but is deceiving. Divide the unknown spec by 3 and you should be in the ballpark of true flash duration, and therefore of comparable continuous light shutter equivalent. A "1/400th" t=0.5 studio flash has really only a 1/133th t=0.1 duration. Upping the shutter sync speed to 1/250th cuts in the actual duration, lowering overall brightness, but worse, the second curtain travelling while the flash slope is still present produces unevenness, especially visible on seamless backdrops. A leaf shutter only cuts in the brightness.