You need to find an area of open shade to position your subject on the edge of so that it falls to darkness behind them – an opening to a wooded area is perfect or a doorway would work well, too. You do need some sun to reflect on to your subject’s face, but overcast days are more flexible. Place them at the edge of the light where no shadows fall across their face.
2 Find your exposure
Your first step is to find your ambient exposure and then deliberately underexpose it. You can do this in manual mode by dialling in your flash sync speed (check your camera’s manual), the lowest ISO rating and a mid-aperture (f/5.6-f/11). It’s a fine balancing act between underexposing the background and getting a good exposure of your subject, so trial and error is necessary.
3 Light your subject
The further away your background is from the subject the easier it will fall into darkness as you expose for your subject’s skin tone. On bright days, try to place your subject just behind the edge of the shade and angle a reflector towards them to bounce a little sunlight on their face. Placing a reflector underneath them, too, can help bounce up a little light to fill in any shadows under their chin.
4 Flash power
Once you’ve found your optimal exposure, revealing a well lit subject against a dark background, set your flashgun to half-power and fire a test shot. You’re wanting a full halo of light that, ideally, will also reach the reflector to be bounced back on to your subject’s face. If the hair light is too weak, increase the flash power; you’ll likely need to wait longer for the flash to recycle between frames.
5 Position your flash
Both these images are shot at 1/200sec at f/7.1 but show a massive difference – the position of the flash. The further the flashgun is set away from the subject and the head is tilted upwards, the more it’s going to illuminate the surroundings. Position the flashgun on a stand or the floor with the head angled 45° and pointing towards the back of your subject’s head.
6 Edit your image
To get your background dark in-camera, you may have to underexpose the subject’s skin slightly and lift it in post-production. Using a Levels or Curves adjustment layer, you can easily brighten the skin tone a stop or two and/or darken the background to minimise distractions. The Clone Stamp Tool will also help with removing any nearby foliage that has been illuminated by the flash.