This chapter is from the book
This chapter is from the book
This chapter is from the book
Balancing Flash and Ambient Light
Previous chapters covered the effect of long exposure to capture a dimly lit scene, and this chapter shifted gears to cover the importance of using flash for illuminating darker subjects with a quick burst of light. Now it’s time to put this dynamic duo together. When done correctly, magical things can happen because the image is captured over two different time planes within the same scene: one very quick and the other slower. The trick is to get the long exposure and flash burst of light to work together in harmony. How you do it is in information you’ll find in the proverbial section on “easier said than done.”
Making these two techniques come together begins with understanding the factors that control each one. Flash exposure is dictated by the aperture setting with little effect from shutter speed. Conversely, ambient exposure (the natural light in the scene) is controlled by shutter speed duration. It has little impact because the flash already produces a quick burst of light, so duration doesn’t play much of a part in affecting exposure.
For example, if you were shooting a portrait that was properly exposed at an aperture setting of f5.6, changing the shutter would just affect the areas not covered by the flash. One exception is if the shutter speed creates “more” exposure than the flash.
Adjusting shutter speed provides a great means for balancing exposure, as shown in Figure 4.10. So, find an aperture setting that works with the flash exposure, and then adjust the shutter duration to expose the ambient (natural light) part of the scene.
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Figure 4.10 Although this image looks natural, this uniquely composed portrait depended on balancing the flash and ambient exposure. Once I established the aperture setting for the flash exposure, I chose a matching shutter speed for the illuminated sign in the background.
Canon 6D • ISO 100 • 1/15 sec. • f/1.8 • Canon 85mm lens • Canon Speedlite 580EX Flash
Get a Good Reading of the Scene
Understanding how to control flash and adjust for ambient light in the scene provides a good start to a successful photograph but still requires a little trial and error. Unfortunately, some situations leave little time to plan. The next time you need to balance flash and long exposure, consider the following suggestions:
- Shoot on Manual: You don’t want any surprises affecting exposure or fluctuations from passing light, or something else that might affect exposure.
- Test flash exposure: Use a middle aperture setting, anywhere from f5.6 to f11, to see if that properly exposes the subject. You don’t want to overexpose with flash. It’s best to have a little less exposure than a little more.
- Adjust ambient exposure: Use the camera as a light meter to measure a middle tone in the scene. Because the aperture is already set for flash, adjust exposure by changing the duration.
- Take a test image: Once you have an idea of the exposure in the scene, take a test exposure and then make adjustments.
Use a Tripod or Not?
Normally, you mount your camera on a tripod to capture a long exposure; doing so and using a flash provides more flexibility. But there’s nothing unusual about handholding the camera when you’re using flash. It’s also possible to handhold a long exposure with flash to create a sense of motion. Usually, anything but a fractional exposure time requires that you mount the camera on a tripod, unless you want to blur motion, either accidentally or intentionally. However, when you want to shoot action scenes, you can use a high shutter speed to freeze the action (along with flash), as shown in Figure 4.11.
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Figure 4.11 When you want to freeze action, using a high shutter speed along with flash produces the scene without any motion blur. Because it was relatively dark and I handheld the camera, I also used a higher ISO setting to capture the diver in midair.
Canon 6D • ISO 1250 • 1/125 sec. • f/11 • Canon 24–70mm lens at 50mm • Canon Speedlite 580EX Flash
Mixing flash and long exposure provides a creative alternative when the camera is handheld, allowing you to create a more exaggerated sense of motion. Of course, if you want the background to be crisp and sharp or maybe rendered as a subtle blur through selective focus, then by all means use a tripod (Figure 4.12).
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Figure 4.12 This family photo mixed flash and long exposure by mounting the camera on a tripod and using the self-timer. Because the ambient portion of the scene needed a longer exposure time, you can see a slight motion blur around the subjects.
Canon 20D • ISO 100 • 2 sec. • f/7.1 • Canon 20–35mm lens at 27mm (equivalent to 43mm) • Pop-up flash
