Photographers since the advent of strobes have been balancing it with ambient light to various effects. Faster shutter speeds are used to minimize ambient light, making darker skies or eliminating distracting elements from the backgrounds of flash-lit images. Slower shutter speeds increase the ambient influence on a flash-lit scene, but they also can introduce motion blur to subjects that are moving, or in images made while handholding the camera.
When slow shutter speeds are used deliberately to create subtle motion-blur effects in strobe-lit images, the technique is called "dragging the shutter." Some portrait and fashion photographers (like Douglas Dubler, for example) sometimes do it to create a more interesting and distinctive edge on their subjects—introducing a subtle amount of motion into an otherwise stagnant frame, and creating a softer feel in what may otherwise be a harsh lighting situation. Action photographers may drag the shutter to amp up the feeling of speed or motion, blurring backgrounds while ensuring the subject (illuminated by flash) remains tack sharp.
The fact is there are many instances where dragging the shutter to blend ambient and flash exposures and introduce a bit of motion can be very helpful. Here’s a primer for learning how to drag the shutter.
In order for dragging the shutter to be effective, there must be some ambient illumination in the scene. A dark room, for example, wouldn’t have much effect because there’s no ambient light that creates an ambient exposure to translate into edge blur.
Bicycling down the Las Vegas strip, however, would be an ideal venue for dragging the shutter. A foreground subject would be stopped cold by the flash exposure, while the long shutter speed would allow the bright lights of the background, as well as the moving parts of the cyclist’s body, to blur with the motion—all of which combine to increase the feeling of speed and movement in the still frame.
Dragging the shutter doesn’t just require extreme effects. Portraits, as previously mentioned, can really benefit from a hint of edge blur to separate subject from background. This can introduce a hint of vibrancy to an image that may otherwise feel too stiff, creating the ever-illusive feeling of depth in the two-dimensional photographic image. Douglas Dubler swears by dragging the shutter, though he doesn’t share many of the details. Doing it as well as he does takes time to perfect, but getting the basics right—with any subject—is a relatively simple procedure.
First, choose a location with a bright background. This can be a summer sky, a city skyline at night, or even just a brightly illuminated wall. Next, choose a subject that can be placed in relative shade in front of the bright background. Lastly, use a flash (even a hot-shoe-mounted on-camera flash works fine for understanding the principles of dragging the shutter) and aim it at the subject. (The technique also works when the entire scene is dimly illuminated, but without a recordable amount of light in the background, the distinctive motion blurs won’t be visible.)
Choose the appropriate flash exposure by manually metering and using the flash guide or simply allowing TTL flash metering to do its job. A 60th of a second exposure is a fairly standard starting point, and it will minimize the influence of the background’s ambient exposure—as well as the ability to create motion blur in the frame.
To drag the shutter, simply experiment with slower shutter speeds. Try 1/15th of a second to start, and just keep going slower. In manual mode, you’ll have to adjust the aperture to keep from changing the exposure. Shooting in auto, you’ll need to use Shutter priority so that you can lengthen the duration that the shutter is open. To ensure that your camera isn’t counting on the flash for the lone exposure, consider switching to manual or adjusting exposure compensation.
Hand-holding the camera, coupled with the minute movements of a living, breathing subject, will soon translate into distinctive edges appearing drawn around the subject. That’s the edge-defining appeal of dragging the shutter. The shadowed silhouette of a person against a bright background is due to that person’s slight movement while the shutter was open. The flash only illuminated them for part of the exposure, and during that instant the person’s features are illuminated and should be tack sharp. Longer exposures with moving subjects can make the blurs more dramatic, and accentuate movement of both the subject and the background.
The longer the shutter speed, the more undefined and blurry the edges and background will become. Keep in mind that with the subject illuminated by ambient light too, the blurs will show on the subject as well. With an ambient-shaded subject, however, the edge-enhancing blur can be relatively contained to the brighter background details, leaving the strobe free to concentrate on illuminating the key details of the subject and enhancing the look of motion, depth and dynamism in even the simplest of images.