I understand and have tried some rudimentary light painting, but I'm still not sure how one might achieve something like the photos here: http://www.modelmayhem.com/portfolio/pic/18221422 Is this just a composite of different pictures in post production?
These photos seem to be shot with softened off-camera flash and long shutter time -
- the light trails tell away the long exposure;
- sharp model can be explained by having been lit very briefly during that exposure;
- there is no "deer in headlights" look, so the flash (or flashes) must have been off-camera;
- the shadows have soft boundaries, so there must have been some kind of softening used on flash (a softbox, umbrella, bounce etc).
I would advise against using the second-curtain flash suggested by AJ - flash in the end of exposure means model has more time to shift away from focus, and when you have moved the camera to create some of the painting effects, framing will be off too.
Taking a guess at what you probably were looking at based on your description. I'd hazard that they used a manually focused shot with a long shutter and a second curtain flash. It allows for light painting during the exposure of the frame and then at the end of the exposure, a flash is fired and exposes the rest of the image which freezes an in-focus shot of the subject doing the painting. Best results are obtained when it is possible to make the entire scene very dark (pitch black other than the light source used for painting preferably.
Update: seeing the actual images now, I would use a first curtain flash (flash at the start of the exposure) to expose the subject and then do the light painting. Second curtain is only necessary if the subject is doing the light painting and a natural direction of movement needs to be achieved.
It can be done both ways.
The hard way is to pop the flash at the beginning of a long exposure. IMHO this would be the easiest way if you were shooting film.
The best/easiest way in the digital age is to do as you suggest might have been done- Separate shot of the model (in focus) composited with one or more layers of light trails in Photoshop. It's much easier to control the process this way...