Friday, May 22, 2009

Flash Technique: Ducking the Shutter

Here’s a little tip about a flash technique I call ducking the shutter. It’s a way, when using a flash, to eke out a slightly faster shutter speed than the specifications of your camera would suggest is possible, without resorting to any sort of high speed FP sync mode.

Sometimes you want to use a shutter speed that’s faster than your camera’s flash sync speed so as to reduce the contribution of ambient light to your exposure. If you know the limits of your shutter you can sometimes manage to do just this.

Basically the trick is to compose your photo in such a way that the parts that are to be illuminated by your flash are placed in the area of the frame that will get flash exposure at the shutter speed you’re using.

The easiest way to find out where those areas are is to take some test shots. Here I put my camera in manual mode chose an (unimportant) aperture and then took a shot (with my flash) of a blank background at different shutter speeds. In this case I triggered my flash with a radio trigger and obtained the results shown below.

Shutter Curtain Results

Ignoring the light falloff from right to left (the flash was not aimed perpendicular to the wall) you can see how the shutter curtain begins to obscure the frame as the shutter speed increases. The dark areas in this case are the parts of the frame that were not illuminated by the flash. They are still illuminated by the ambient, it is just that at this particular aperture and shutter speed the ambient was too low to have any noticeable effect.

So even though the official sync speed is 250th as long as I position my (flash) subject in the lower two thirds of the frame I can shoot at 1/400th. It is like I am ducking under the shutter to make the shot. If I duck my subject down to the bottom half of the frame I can even pinch 1/500th of a second.

A perfect example of this technique in action can be seen in the photograph below, a de-fished fisheye close-up of a Ferrari parked at the viaduct. This was 1/400th of a second at f/8 with a wirelessly triggered SB-800 at full power through a Lumiquest softbox.


I was shooting almost straight into the sun. Without a flash there was no way I could get a single exposure for both the car and the sky. But placing the car in the lower part of the frame I was able to sync at 1/400th and still get full flash power onto the car, and thus a good balance between sky and car.

This technique also works in portrait mode. Depending upon which way up you hold the camera you just need to keep your subject to the right or left of the frame.