TalenFlash: Stroboscopic flash
Current Speedlite models offer a stroboscopic flash function. This fires a rapid burst of low-power flashes to capture a sequence of images of a moving subject in a single frame.
Here are a few terms you need to be familiar with:
Hertz (Hz) A Hertz is the unit of frequency. It tells you how many times something happens in one second. For example, 1Hz means that something happens once a second while 10Hz means it happens 10 times a second. So, the higher the Hz value, the more flashes you get per second. You can set the frequency on your Speedlite, but not all Speedlites have the same frequency range − it varies between 1 and 10Hz, and 1 and 199Hz on current models.
Flash count The total number of times the flash will fire at the set frequency. Not all the Speedlites give you the option to set this. However, this is not a problem as you can use the shutter speed to determine the flash count. You must set a shutter speed that will give the Speedlite enough time to fire the flash count you choose. This shutter speed must not be shorter than the flash count divided by the firing frequency (Hz). For example, if the flash count is 10 and the firing frequency is 5Hz, the shutter speed must be at least two seconds.
Flash power The brightness of flash from a Speedlite is always the same. The amount of illumination is not controlled by its brightness, but by the duration of the flash. The longer the flash, the greater the power.
These three factors are intimately linked. The more times you set the Speedlite to fire each second, the shorter the duration of the flash and the lower the power.
Also, the faster you set the flash to fire, the less time it has to recycle and the lower its output will be. You may need to reduce the flash-to-subject distance − sometimes to a metre or less − to stay within the working range of the Speedlite.
Exposure values for strobe flash have to be set manually − you can’t use E-TTL autoflash. A table in the Speedlite instruction manual tells you the power output you need for a given combination of firing count and firing frequency. A second table gives you the guide number of the flash at that power output. Divide the guide number by the subject distance (in metres) to obtain the aperture needed for the exposure. Guide numbers are given for an ISO of 100. You will need to alter the aperture for other speeds.
Stroboscopic flash allows you to capture multiple images of a moving subject on a single frame. It is best to shoot against a dark background to avoid overexposure of the background. Shooting outdoors at night can be effective.
