The right flash at the right time
It lies in the nature of flash photography to “freeze” all subjects while they are in motion. Instantaneous exposures are usually characterized by a rigid and static atmosphere. However, by synchronizing a moving object that has its own source of light with the second curtain of a focal plane shutter, flash is then able to record this object as “motion” on the exposed frame. The resulting photo creates the impression of dynamics and speed.
Synchronization with the second curtain means that the flash is not fired when the first curtain opens, as is usually the case, but rather a fraction of a second before the second curtain starts to close. When a slow shutter speed (at least 1/30 s) is paired with a corresponding aperture, the light source of the moving object will record “streaks of light” on the film. These streaks of light are trailing behind the moving object to create the impression of movement instead of in front of the object when the flash is synchronized with the first curtain of the focal plane shutter.
We have all seen those fascinating shots of traveling cars trailing bright streaks of light behind them. Since the light is fired just before the end of the exposure time (synchronized with the second shutter curtain), it freezes the subject with the light lines of motion trailing behind the car. Such an exposure is in keeping with the way we perceive motion in a picture, as opposed to light and motion streaks being “pushed” forwards in front of the car. It is advisable to shoot the frame in manual mode as the aperture and shutter speed can then be more precisely adapted to the prevailing photographic situation. A tripod will prove to be useful to avoid camera shake.