What is Exposure Bracketing?
Exposure bracketing is the technique of taking several shots of the same subject, at varying exposures (brightness). The images are then blended to create an overall balanced exposure of the subject which combines the lowlights of the brightest image, the highlights of the darkest image, together with the mid-tones of the middle exposure. This is aslo referred to as HDR or ‘High Dynamic Range’ photography.
Why use this technique?
Often, photographers are presented with a shot which contains two very different levels of exposure within the frame – sometimes referred to as a ‘high contrast scene’. An example of this would be a sunset on a beach or perhaps the front of a building, in shadow, with bright sunlight in the background.
In this photograph (right), when in ‘evaluative metering’ mode, the camera tries to adjust the exposure to strike the best balance between the bright sky and the dark building. However, this will nearly always lead to the sky being slightly over-exposed and the building being too dark.
Similarly, if you were to meter for just the sky or just the building, you will leave to other area completely under or over exposed. What we want is a shot where the sky and building are both correctly exposed. This is where we use Exposure Bracketing.
How It’s Done
Firstly, you’re going to need a tripod and a remote shutter release (or use the self timer function) to ensure all shots are perfectly aligned and pin-sharp, as you’re going to layer them together later on. You take a number of photos (normally 3, but you can take 5, 7 or more) of your subject, varying the exposure level between each one. For example, if using the three shot method, you’d perhaps take one shot at normal exposure, one shot at -2 stops and a third shot at +2 stops (denoted as -2 / 0 / +2 from here-on). If using the five shot method, you’d potentially take shots at -2 / -1 / 0 / +1 / +2 stops of exposure. The more shots you take, the better the overall result will be. Most DSLRs, however, only take three shots when using their automatic exposure bracketing (AEB) function.
Furthermore, the more extreme the contrast is in the scene you’re photographing (ie, the bigger the difference between the brightest and darkest areas), the further apart you’ll want your highest and lowest exposure shots to be – perhaps closer to -3 / 0 / +3 stops. When shooting a scene with a more subtle difference in contrast, such as an interior room, you may find exposure settings of -1 / 0 / +1 more suitable.
Automatic Exposure Bracketing (AEB)
Because I’m a Canon user, I’m going to describe how to set up automatic exposure bracketing (AEB) on Canon DSLRs. Specifically the Canon 60D. Nikon users should still be able to follow these steps despite the slight differences in your camera’s interface.
- Move your ISO setting away from Auto and on to 100. This way you’re ensuring your camera doesn’t increase your ISO to achieve different exposures and introduce noise in to your images.
- Ideally you want your camera in Aperture Priority (AV) mode. You can shoot AEB in Shutter Priority (TV) mode, but the camera will change your aperture in order to achieve different levels of exposure. This will affect your depth of field between the shots. Not something you want. Similarly, you can shoot exposure bracketing in Manual (M) mode. Most Canon DSLRs will only change the shutter speed when bracketing in Manual mode. However, other cameras may perform differently. Personally, I always use Aperture Priority mode and my ISO set to 100.
- Set your camera to high speed continuous shooting – under ‘Drive’, indicated by an ‘H’.
- Next, access your camera’s exposure level meter (also labelled as AEB Setting – or BKT on Nikon cameras). This should resemble something like this (pic right).
- Use your camera’s jog wheel (for canon users, this is normally next to your shutter button) and turn it clockwise. You will see that two smaller markers appear which spread further from the central marker. The numbers they align with represent stops of exposure. +1 being twice a bright as at zero for example. You can even shift all three markers along the exposure bar by turning your main jog dial on the back of your DSLR. Once the three markers align with the low, mid and high exposure levels you want, press ‘Set’. You are now ready to shoot.
- Using your tripod and a remote shutter release / self timer, frame and focus your subject. Then press and hold the shutter button. Keep the button held and your camera will shoot three images in quick succession. Release the button. If you choose Single Shot mode rather than Continuous, you will need to press the shutter button three times to take the three different exposure shots.
- Preview your three images and you should see the same shot but at three different exposures.
In this example, the -2 stops image shows the correct exposure of the sky, while the +2 exposure has the correct exposure for the church.
Combining the Images
The final stage is to combine all three images. Previously, I used Photomatix Pro by HDRsoft, which is an excellent piece of software which automatically blends your three (five, seven or more) photographs together and offers you a number of preset effects including extreme HDR effects. The downside is that it isn’t free. However, there are a number of free programs out there which achieve much the same results, without any financial outlay. As an Abobe Creative Cloud user, I use the built-in HDR merge feature present in the latest version of Lightroom – which renders very pleasing results.
Combining the above three images produces the following final shot (right).
Some minor adjustments to saturation and contrast and suddenly you’re left with a photo which is streets ahead of anything you could achieve with just a single shot.
All areas of the photo are perfectly exposed, creating the perfect shot. This method may seem long-winded and somewhat intimidating at first, but with a little practice, using auto exposure bracketing will soon become your default option when faced with a scene of varying exposure levels.
Author – Oliver Pohlmann