The camera “sees” more than the human eye
The human eye is unable to follow rapid movements. It is unable to follow the precise successive phases of a motion, for instance every hundredth of a second of a sports action. But this is not a problem for the camera. In stroboscopic mode several overlapping images of a moving object appear in the same picture by firing several flashes in rapid succession. The resulting partial light outputs produce a precise record of the individual phases of a motion on the film.
The actual number of flashes you wish to use in the exposure depends upon the required resolution at which the course of the motion is to be divided up. For instance between 2 and 50 flashes can be selected on the Metz mecablitz 58AF-2 digital. The flash frequency (number of flashes per second), i.e. the time within which the flashes are to be fired, is then set on the flash unit.
Let us assume that you wish to record a tennis serve in 10 sequences. It is first necessary to establish how much time the player requires to complete the serve, e.g. 2 seconds. The required flash frequency is then calculated with the following formula:
Flash frequency= Number of sequences: Duration of motion= 10 : 2 = 5 flashes/sec.
Ensure that the camera’s shutter speed is sufficiently slow for the intended stroboscopic exposure. The relevant table contained in the flash unit user guide shows the correct speeds.
If you are using a Metz mecablitz 58 AF-2 digital or Metz mecablitz 76 MZ-5 digital, you will find the applicable distance for the adjusted data in the LC display. Should the indicated distance deviate from the actual distance of the subject, then either adjust the partial light output or the aperture. Set the required f/stop on the lens.
The stationary background must either be very dark or far behind the moving object to ensure that it is not overexposed. The best results are achieved at the lowest levels of ambient light.