Photography 101 – Exposure Bracketing
Written by: Tiffany Joyce
The term “exposure bracketing” refers to taking a photograph at a baseline exposure, then “bracketing” that shot with one that is slightly under-exposed, and one that is slightly over-exposed. This method is used to increase the odds that you have captured the shot with the best exposure, which is especially helpful in tricky lighting situations where the light conditions are variable. Exposure bracketing is also used to create High Dynamic Range (HDR) photos.
There are also “white balance bracketing” and “flash bracketing” techniques which I’ll talk about in a later article, but for the purposes of this discussion I’ll be referring to exposure bracketing whenever I use the term “bracketing”.
There are two ways to achieve bracketing – one is manually using a combination of ISO, aperture and shutter speed. The other is automatically, using the Auto Exposure Bracketing capabilities of many current digital camera models.
Here is the manual technique that I usually follow for bracketing:
1. Set the camera to aperture priority mode, and set the aperture to the desired value.
2. Set the ISO to the desired value.
3. Take a photograph of the subject and note the shutter speed. The camera’s automatic metering will baseline the exposure indicator at “0″.
4. Now put the camera on manual mode, and set the ISO, shutter speed, and aperture to those values. Take another shot to ensure they’re set correctly, noting the exposure meter (it should still be at zero).
5. Increase the shutter speed until the exposure indicator is stopped down to the desired level (for the purposes of this demonstration I chose two stops). Increasing the shutter speed decreases the amount of time that light is hitting the sensor, thereby underexposing the photograph. Take the shot:
6. Decrease the shutter speed until the exposure indicator is stopped up to an equal number of stops as it was decreased. Decreasing the shutter speed increases the amount of time the light is hitting the sensor, thereby overexposing the photograph. Take the shot:
Here are three shots that demonstrate this concept (note the changing shutter speed):
Base exposure: ISO 400 | 55mm | f/2.8 | 1/80
Under-exposure: ISO 400 | 55mm | f/2.8 | 1/400
Over-exposure: ISO 400 | 55mm | f/2.8 | 1/25
Auto Exposure Bracketing works similarly in many camera models. Here are two examples (consult your owner’s manual for the technique specific to your camera):
Canon 7D: Press the MENU button and select the Shooting 2 Menu. Choose AEB and press the SET button. Rotate the Main Dial and highlight the number of increments you wish the exposure bracketing range to be. Press the SET button. The next three photos that are taken will be the base exposure, over-exposed and under-exposed increments. You can take three individual photos using shingle shooting mode, set the camera on the timer which will automatically take three photos after the delay, or set the camera on burst mode to take rapid shots in succession (just be careful to count how many shots you capture).
Nikon D300: Press and hold the Fn button and rotate the main command dial to set the number of shots. Then while holding the Fn button rotate the sub-command dial to set the exposure increment. The next number of shots will be at the base exposure, over-exposed and under-exposed. Then to cancel bracketing, hold the Fn button and rotate the main command dial until the number of frames shows 0.
Give exposure bracketing a try this weekend!
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