Quick guide to exposure bracketing

The photography phrase ‘bracketing’ refers to a simple technique where you capture a number of frames of the same scene, but each image has an intentional technical difference, writes Andrew James and Jon Adams.

The most obvious thing to bracket is the exposure. You’d do this to shoot frames that are both overexposed and underexposed, as well ‘correctly’ exposed. Correctly in this case means the metered exposure given by the camera. So, for example a three frame exposure bracket could be  -1 stop, 0, +1. The term ‘bracket’ is most likely derived from its ‘military’ use. In this sense it is known as the distance between two shots fired either side of the target to establish range, and this is similar to what you are doing when using exposure bracketing – hedging your bets as to which of the exposures will give you the BEST result.

If you are new to photography, you might understandably assume that when taking a sequence of three bracketed shots at one stop underexposed (-1), the metered exposure (0) and one stop overexposed (+1), that the metered exposure would always be the best one. However, this isn’t always the case, especially in tricky lighting situations, such as shooting directly into the sun. Plus of course, since High Dynamic Range (HDR) images have been popular, exposure bracketing has been a way to capture all the dynamic range within a scene from the brightest to the darkest points. The different exposures are then merged to create one HDR photograph, as shown below.

To capture a series of bracketed exposures, you can either work manually, altering the shutter speed for each shot in the sequence, or better still, especially if you intend to shoot while handholding the camera, set up Auto Exposure Bracketing (AEB) on your camera, so for each shot that’s taken in the sequence, the camera adjusts the shutter speed by the amount you’ve set. Once AEB is active you will have to fire each shot one at a time, unless you have selected continuous shooting drive mode, where it will fire each bracketed shot one after the other, as long as you keep the shutter button pressed down. This is definitely the way to go – whether you are handholding or working from a tripod.

You can dial in the exposure variance in third or half stops, as well as whole stop increments, as well as change the number of images that are taken in a sequence. Typically, this will range from 2 to 7 frames but you don’t want to overdo it and shoot a load of unnecessary extra frames, as this will run up your shutter count and clog up your memory card with shots you won’t even need.

Because of the flexibility we have in editing RAW files, subtle bracketing involving 1/3 or 1/2 stop differences is pretty pointless – save this for tweaks in exposure compensation when trying to perfect a single frame, as opposed to a bracketed sequence. This is because you can make these kinds of small changes with Lightroom’s Exposure control without any noticeable detriment to image quality, so you’re wasting frames and card space by shooting them.

The minimum difference you should use for a bracketed sequence is 1 stop, so a 3-shot sequence of -1, 0, +1 would be a standard set up if the scene is not too contrasty, and doesn’t have a huge change in brightness between the shadows and the highlights. The image below shows a three stop bracket. Taken at midday when the sun was high, there was a lot of variance between the brighter beach and the shaded cliff. This is very much a hedge your bets style of bracket because, as you can see there is very little to choose between the Shadows lift on the ‘0’ exposure, and the HDR version. In truth, although the scene looked tricky, we could have relied on one exposure and a minor tweak in Lightroom but to be on the safe side, we fired off a three one-stop bracket sequence.

In situations where there IS a massive range of brightness – say when you’re shooting into the light, or have a bright light source in shot, then it makes sense to still shoot 3 frames, but extend the difference between them to 2 stops. In this situation, you’d shoot -2, 0, +2. By doing this you keep things economical in term of shutter count and card space, but extend the possibilities for the dynamic range in the scene. You can see this in the image below. Here, because of the extreme tonal range, we really did need to merge the three frames for the best result.

In a nutshell, use a 3-frame bracket all the time, but use 1 stop when the difference isn’t too great, and use 2 stops when it’s more extreme. Once these frames are blended together into a new DNG file, you’ll have all the variance you need to further tweak the look of your HDR.