A focal plane shutter exposes a given point on the film for a shorter time. In operation, when the shutter is activated, the "first" curtain starts to move across the film opening. At a given time, the "second" curtain follows. That is not necessarily "faster". As the "slit" (actually the area separating the first and second curtains ) moves across the film, of necessity, there must be some distortion of the form of a fast moving subject. There is a specific time when the second curtain starts its movement only when the first curtain has uncovered the entire frame ... that is called the "mechanical" shutter speed, and it is the only speed where the light from a very fast "electronic" flash will reach the entire frame.Originally Posted by Max Power
With a leaf shutter, electronic flash is suitable - synchronized - at any speed.