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How Exposure Bracketing Will Make You Love Photography Even More!
So far in this series we've learnt how to create accurate exposures, and control other image characteristics, using the points of the exposure triangle. We then saw how exposure compensation is a really useful little device for helping out in tricky situations. But some situations are really tricky, and it seems that no single exposure is going to produce the result you want. That's when something called "exposure bracketing" comes in. This is one of my favourite techniques, so let's get started...
What is exposure bracketing
Exposure bracketing (just 'bracketing' for short) is simply the process of creating several versions of the same photo with different exposure settings. Instead of just taking one picture, with the exposure meter set to 0, you 'bracket' this shot with overexposed and underexposed versions.
This allows you to either choose the best image from the different exposures, or blend all of the images together in Photoshop to create an image which contains a higher dynamic range (range of different tones). So no burnt out patches or unwanted large shadows. (For a guide to blending different exposures, check out this tutorial on layer masks)
by Daniel Zedda
How does it work?
There are several ways of producing bracketed exposures. It can be done manually, by simply taking several pictures and stopping up/down the exposure between them. Or it can be done through the AEB (automatic exposure bracketing) control on your camera.
The AEB control allows you to set the number of bracketed exposures you want to take and the difference in brightness between them (i.e. 1/3 stop, 2/3 stop, 1 stop). The big advantage of AEB is that, provided you are in continous shooting (or burst) mode, it allows you to hold down the shutter button just once and all the bracketed exposures will be fired off. If you are in single-shot mode, you will need to press the shutter once for each exposure.
This is a great time saver as it prevents you from having to set the exposure controls manually, by which time the photo opportunity would probably have been and gone! Whenever you intend to blend bracketed exposures in Photoshop, using a tripod is advisable so that the images align perfectly.
You can also choose the order in which your bracketed exposures are taken, through the menus in your camera. So, for example, you might like to start with the most underexposed and work towards the brightest. Or begin with the 'correct' exposure and then take the over and underexposed shots.
The control for automatic exposure bracketing on your camera will vary depending on the manufacturer. Nikons tend to feature a button marked "BKT" on the back of the camera, from which settings can be adjusted on the top-plate LCD using the exposure dials.
Meanwhile Canon cameras tend to feature an AEB option in the menus from where the settings can be chosen. To find out exactly how your camera works just Google "bracketing" + "[your camera's name]".
How many shots to take
The minimum number of bracketed exposures that can be taken is, of course, 3: one in the middle and two either side. But it's your choice how many exposures to take. It would normally depend on how challenging the lighting in the scene is. I often find that a simple 3 exposures does the trick, but sometimes that's not enough.
It's also a question of taste, as the more exposures you blend together the greater the dynamic range of the image. When you blend togther lots of exposures an image can begin to take on the appearance of a certain photographic style called HDR (which simply stands for high dynamic range). Actual HDR images have other effects applied to them too, like intense saturation of colours, but blending multiple exposures goes a long way to producing the same effect.
There's a tipping point where blended exposures slip from being clearer, better versions of a normal photo, into hyper-real, stylized HDR creations. By all means have fun experimenting with HDR, you may find you really like it. Personally, I'm not a fan, and find the pictures to have a bit of an odd 'glowing' look. If you are keen to learn how to do HDR well, I highly recommend Trey Radcliffe's awesome site - Stuck In Customs.
Which settings does the camera change?
Often when using automatic exposure bracketing you will want to maintain either a constant aperture size or shutter speed. This can be easily done by selecting either aperture priority mode or shutter priority mode.
Just as with exposure compensation, the camera will adjust whichever setting you have not chosen to manually control to produce the bracketed exposures. Most of the time it is the aperture that we need to remain constant, as depth of field is crucial to the appearance of the final image. So, in aperture priority mode it will be the shutter speed that changes with each bracketed exposure.
Some example uses of automatic exposure bracketing
Finally, let's take a look at a few example situations where bracketing allows us to create better pictures than we otherwise could:
Magic hour landscape: A landscape scene during dawn or sunset is a classic example. The sky is full of light and colour, whilst the foreground and middle-ground are much darker. Any attempt to balance the exposure for the whole scene would invariably burn out parts of the sky, or leave other areas completely black. In this situation I usually find that just three exposures in enough to capture enough dynamic range to show the drama of the whole scene.
Image by h.koppdelaney
Environmental portrait: An environmental portrait is simply a portrait photo where the background to the subject is an important part of the image, and needs to be captured clearly. Very often, the subject will be more brightly lit than the background and so the details in the background end up too dark in a normal photo. Again, I often find that just 3 exposures is enough to capture sufficient dynamic range, but would keep each exposure separated by quite a lot (i.e. 1 full stop of exposure).
Indoor photography: I often find that indoor scenes contain a wide variety of brightness. For example, in a church there may be bright light streaming through a huge window illuminating certain people, whilst other areas are more dimly lit and people tucked away at the back are in complete shadow! The use of flash and additional equipment is handy here, but creating a large number of bracketed exposures (e.g. 7, with 1 at '0' on the exposure meter and 3 either side) can be very effective.
Image by Andrea Costa
So bracketing is a really useful way of ensuring you get the best results in tricky lighting conditions. You can either choose the best of the bracketed exposures, or blend them all togther to create an image that is well exposed in every area. AEB automates the process, adjusting the exposure for you, which saves valuable time when shooting.