Dragging The Shutter: Balancing Fill Flash With Ambient Light
Article from Digital Photography School
Shooting indoors with a flash can challenge the best of photographers. Many times, the goal is simply to create enough light to illuminate your subject, and background be damned. The results, however, tend to be less than pleasing when we allow the flash to be the only light source. Assuming there is some ambient light in the room, adjusting the settings in your camera can help allow that ambient light into your exposure and create more depth in your image.
Most cameras typically sync with a flash at around 1/200 or 1/250 of a second. While this speed is fine for the flash alone, it is generally too fast a shutter speed to allow ambient light to factor into the exposure. This creates images with a brightly lit subject and a very dark background. To allow more ambient light in, you’ll want to slow your shutter down. Putting the camera into Manual mode will allow you to adjust your shutter speed to do this. You can then also open your aperture as wide as it can go to allow as much light as possible into the scene. This technique is typically known as “dragging the shutter”.
The problem with dragging the shutter is that if the shutter speed is too slow, any movement can cause a ghost image, ruining the shot. So you’ll need to keep the shutter speed fast enough to avoid that. This may not allow enough ambient light in, so you have one last option to allow more light in. Adjusting the ISO. By raising the ISO speed, you make the camera’s imaging sensor more sensitive to light, allowing that ambient light to show in the image.
For the image above, the stage lighting for the band created a nice background light, but my flash was too powerful and my shutter speed too fast at the maximum sync speed of 1/250. By slowing down the shutter speed to 1/60, I gained two stops of light sensitivity. I also raised the ISO to 800 to allow the sensor to be even more sensitive. This allowed the flash to illuminate the bride and groom, and the stage lighting to show brightly in the background.
Another way to do this is to change the shooting mode on your camera. For most cameras, shooting in Program or Automatic means the camera will treat the flash as the only light source, and disregard the ambient light for exposure. However, if you change the mode on your camera to Aperture Priority, the camera then sets the exposure based on the ambient lighting, and flash is simply treated as fill. The one caveat with this is that the camera could choose a shutter speed that is too slow to safely hand-hold, creating ghosting or blur in your image. You’ll want to keep an eye on the shutter speed, and if necessary, raise the ISO to give you a faster shutter speed. Many cameras also have a setting, allowing you set a minimum shutter speed when using flash in Aperture Priority mode to help avoid ghosting.