Photo: A single flash fired with a wireless trigger without modification directly at the biker helped him stand out against the backdrop. The 1/30 sec exposure was slow enough for fast panning to blur the background.
All flash photos are double exposures
The two exposures occur simultaneously, one by the ambient light, the other by the flash illumination. You can vary each of the exposures for a wide variety of different effects: You can make them of equal brightness, a little unequal, or widely unequal; you can give them different color balances; you can even vary shutter effects, with one exposure motion-blurred and the other tack-sharp. This is what makes flash photography so much fun—and so supremely useful.