Let flash help
Rear-curtain flash results in a blend of sharpness and motion blur when you’re shooting in low light
Modern camera sensors can now have their sensitivity amplified to almost
obscene levels. A D4s, for example, can shoot at a maximum ISO of almost half a million, admittedly at serious cost to image quality. Yet with fast action in low light, this isn’t quite the solution it may be for slower, or completely, static subjects. The reason is that when the action itself becomes the subject, we want more than ever to be able to see these details cleanly and crisply.
This is where flash comes in, even for die-hard flash-phobes like me. Rear-curtain flash (where the flash fires at the end of an exposure rather than at the beginning) is often the way to go if you’re shooting moving subjects in low light, because it works on two levels: by setting a slow shutter speed (to enable a correct exposure in the low, ambient light), you can blur any motion for the duration of the exposure, and then freeze it with a (very fast) burst of flash at the end.
Ordinarily, the flowing movement in the shot below would justify shooting in Continuous mode at its fastest setting. With a good D-SLR you’d get 20-plus frames out of this three-second burst of action. However, an hour after sunset, a shutter speed of 1/30 sec was required for a half-decent exposure at my chosen aperture of f/7, which – without a pop of flash at the end – would have rendered the fisherman as an indistinct blur.
The balance of ambient to flash is key in a shot like this. Here the settings were 1/30 sec and f/7 at ISO400