the only time i've had a problem was when shooting a model under street lights with a 3-10 second exposure (getting the cars streaming in the background)
the orange light on the white shirt wasnt overpowered by the strobe, and the wind caused ever so slight halo's on the edges where the clothing was flapping in the breeze.
a shorter exposure fixed it..
basically.. donrt expose for ambient...ignore your in-camera meter and stick to iso100 and your max sync speed.
its easy from there
