Pro Talk: Exposure Bracketing

(© Ian Plant) I recently got a question from a reader about whether I use exposure bracketing, and if so, what range of bracketing I typically use. For those of you who are not familiar with exposure bracketing, it is a practice which arose in the days of film to ensure proper exposure. Before digital, photographers did not have the ability to instantly preview their images to check to see if they got exposure right, so while in the field the smart photographer would “bracket” their photographs by taking three (or more) exposures, typically shooting the first photograph at the exposure the photographer believed was correct, then shooting the second and third photographs giving the exposure more and less light. This was like an insurance policy for the photographer: if his exposure calculation was incorrect, then one of the bracket exposures would likely be right on target (or at least closer to the mark).

With digital cameras, however, you know right away whether you got the correct exposure or not, as you can instantly review the image and a histogram on your LCD screen after you have taken the shot. And with most newer cameras, you can preview the image and histogram before you even take the shot, using Live View and exposure simulation. So, is bracketing necessary anymore?

There are still at least two reasons to bracket, at least some of the time. First, if you are working with fast-changing subjects or conditions, you might not have time to review every photograph to check exposure, so bracketing can be a great way to ensure proper exposure (and by setting your camera to auto bracket, bracketing can actually be quite quick and easy). Second, bracketing is necessary for HDR imaging and exposure blending.

Take the image below as an example. I was shooting the sun setting behind clouds and mountains in the Patagonia region of Argentina. The dynamic range of the scene was too much for a single exposure, so I ran a bracket of three exposures (one dark, one in the middle, and one bright) and then hand blended the three exposures in Adobe Photoshop. The techniques for exposure blending are beyond the scope of this post; if you want to learn more, I suggest you download my Creative Digital Processing Videos.

So to answer the first question: Yes, I sometimes bracket my images. Now to the second question: How much should one bracket? If you are merely running an “insurance” bracket, typically bracketing +/- one stop will be sufficient. If you are bracketing for purposes of HDR or exposure blending, the answer to this question will depend on the dynamic range of the scene you are photographing. Basically, you want to be able to capture all of the luminosity tones of the image ranging from the very darkest to the very brightest without clipping your highlights or your shadows. In other words, you want to ensure that no part of your histogram is bunched way up on the right or the left. For the image above, the iceberg-filled lake before me was deep in shadow, whereas parts of the sky were very bright, so accordingly the dynamic range of the scene exceeded the tolerance of my camera's sensor. To ensure that I fully captured the entire dynamic range of the scene, I ran a bracket of three exposures at +/-1.6 stops (Canon cameras allow you to bracket in 1/3 stops). The three undeveloped raw exposures and their accompanying histograms are displayed below.

An example of exposure bracketing

Although the middle exposure captures almost all of the dynamic range of the scene, notice how some of the highlights are clipped on the right side of the histogram. The darker exposure was necessary to ensure that those highlight tones were not overexposed and thus lacking in detail. I probably could have just used the middle and the right exposure for blending purposes, but I decided to also use the bright exposure to the left. Digital noise tends to reside in the left (shadow) side of the histogram, so although the middle image didn't show any clipping of shadow detail, I knew that a lot of my shadow and mid-ranges tones would be a bit noisy with that exposure. The exposure to the left is much brighter, which means less noise in the shadows, which helped me produce a final (blended) image with higher quality than if I had relied only on the two darker exposures.

About the image: "Ice World"—Los Glaciares National Park, Patagonia region of Argentina. Laguna Torre, a glacier-fed lake which sits below the famous triple spires of Cerro Torre, is one of my favorite places to photograph. During my most recent trip there, several days of warm, windless weather helped produce conditions which I have never before seen on the lake. Normally, a few icebergs are drifting in the water, the remnants of ice calving off the glacier, but I have never before seen the lake as I did on this visit: completely filled with icebergs. Sunset is not usually very productive when shooting this scene, as the sun sets right behind the mountain, meaning you don't get any light on the peak. There is, however, one notable exception to this—when low clouds hang over the peak, they can sometimes act as a giant reflector at sunset, bouncing light onto the peaks below them. Lucky for me, this was the case for this image, and at sunset I got a beautiful glow on the east-facing spires. Canon EOS 5D Mark III Digital Camera, Tamron SP 24-70mm f/2.8 DI VC USD Lens for Canon Cameras, ISO 100, f/11, three exposure blend of 0.25, 0.8, and 2.5 seconds.

P.S. Join me in 2014 on my Ultimate Patagonia Photo Tour!


    In your discussion regarding noise, you do mean to say the “left” side of the histogram is the darker part of the image where noise would reside, not the “right” side as stated?

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