When I began taking photographs, there was no instant feedback from an LCD screen or histogram to tell me if I’d chosen wisely with my exposure settings. It was a matter of relying on the camera’s light meter (or an external light meter) and then crossing my fingers until the film was processed and I could view the printed result. Most of the time things turned out okay, but if I’d misjudged the situation, as is easy to do in tricky lighting conditions, there was no going back – a badly overexposed or underexposed image went straight into the bin.
One of the safeguards against this was to bracket exposures. This simply meant taking several shots of a scene using different exposure settings in the hope that at least one of them would give a good result. This could be done manually or, with later film cameras, the camera could be programmed to do it automatically. That’s all well and good, except that rolls of film usually came in 12, 24 or 36 exposures, so you would quickly fill a roll if you bracketed all or most of your exposures – not to mention the extra cost of processing duplicate images, some of which would inevitably be discarded.
The rise of digital photography has made it a lot more practical to take multiple images of a scene and then just discard the ones you don’t want. Wasted images cost nothing these days, and even cheap memory cards will hold far more than 36 images. Also, we can simply check the histogram or LCD screen as soon as we’ve captured an image, and if it is overexposed or underexposed, delete it and reshoot the scene immediately. So given this, is there any point in bracketing exposures on a digital camera? Actually, yes, there are several very good reasons.
The sensor in a digital camera has a very limited dynamic range compared to the human eye. Whereas we can see detail both in bright clouds and in dark shadows within a single scene, few digital cameras can discern both in a single frame – either the clouds will come out overexposed and washed out, or the shadows will be underexposed and black. One of the ways of dealing with this is to take bracketed exposures of the scene and then blend the ‘correctly’ exposed parts of each image together in software, to create a final image that is closer to what our eyes see.
This approach has become known as HDR (high dynamic range) photography, and various software packages have been developed to carry out the process automatically. I’m not a fan of automated HDR processing, but I often manually blend together multiple exposures of a scene using layers and masks in Photoshop. It is still important to think about your exposures and check them after taking a shot, but the HDR process allows you to spread the exposure information across several images rather than trying to squeeze it into one.
Most dSLRs these days have an auto-bracketing function that allows you to set how many images of a scene you want to capture and how far apart (in terms of f-stops) you want them to be. A simple example that most modern cameras can handle is to take a sequence of three shots spaced 1 f-stop apart – that means one image at the exposure determined by your camera, one image overexposed by 1 stop, and one image underexposed by 1 stop. You can reduce the interval between exposures to fractions of a stop or increase it to multiple stops, and some newer cameras allow you to take a sequence of five or more bracketed images.
I commonly take a series of three bracketed shots to make sure I cover the full dynamic range of the scene I’m photographing. In contrasty situations, such as shooting towards the sun, an exposure interval of at least 2 stops is often required, and in more even lighting, 1 stop is usually adequate. You should always check your exposures as soon as you’ve taken a series of bracketed shots and before you move your tripod. A quick look at the histogram or the blinking highlight alert will let you know if you’ve captured the full dynamic range of the scene – if not, it’s a simple task to capture an additional exposure or two at a brighter or darker setting as required.
A drawback of bracketing most or all of your images like this is that you will end up with quite a few duplicate images that you don’t need. To counter this, your post-capture workflow should begin with a ruthless culling of images so your photo folders don’t get cluttered up with unwanted files.
Another good reason to bracket exposures arises when you are shooting sports, wildlife or other moving subjects. Unlike with landscapes, it is often not possible to check your exposures after capture and re-shoot if you’re not happy as the critical moment will have passed. Exposure bracketing becomes your insurance policy against missing an unrepeatable image because of poor exposure.
Exposure bracketing isn’t always necessary, and lots of people can’t be bothered with it. But if you really value the images you capture and want to make sure they are well exposed, it is worth learning how and when to use this simple technique.