Color me befuddled. Flash set to second curtain. Seems not to matter TTL or manual ... Set the widget swinging from left to right - snap at the bottom of the arc for maximum speed. Want to see a slight motion blur trailing. So what the heck is the leading blur from? Only thing I can come up with is a delay between the flash firing (long decay tail?) and the 2nd curtain actually closes. Tried three flashes all get the same effect (FL-300R, YN560 & Vivitar 3700).