Many cameras will allow you to trigger your flash at the beginning of an exposure or at the end. For a short exposure, this doesn’t matter much, but if you choose a long exposure you can have an action-blur in front of or behind your subject.
In the Front version of this shot, the sparklers continue in front of the subject because I used the front curtain sync which triggered the strobes at the beginning of the shot. In the Rear version of the shot, the flash went off at the end of the exposure and so the light from the sparklers leads to the subject.
Front Curtain Sync - (c) John Siskin
Rear Curtain Sync - (c) John Siskin
NOTE: John Siskin teaches three excellent online photography courses here at BetterPhoto.com:
- An Introduction to Photographic Lighting
- Getting Started in Commercial Photography
- Portrait Photography Lighting on Location and in the Studio.