It used to be common for nearly all serious photographers to practice exposure bracketing at least once in a while. With the advent of digital however, this practice is not so widely done anymore which is a shame, as it can still provide a lot of benefit and additional options for the photographer. Exposure bracketing is useful in challenging lighting situations or in preparation for photographs of high dynamic range.
When your camera’s meter reads a scene and decides on what settings to use, it sometimes gets it wrong. You can minimize the likelihood of this happening but using the appropriate metering mode but there are still situations where the meter may be fooled. An example would be where the subject is (relatively) small and dark while the background is large and bright. Or vice versa.
Automatic exposure bracketing (AEB) can help in these situations. You typically set it to firstly take the shot as defined by the meter, then take a shot slightly underexposed and a third slightly underexposed. Some cameras allow you to set it so that more than three frames are taking, but for simplicity’s sake, we’ll use three in this post.
Say your camera’s meter gives a reading of f8 1/125 at ISO100. AEB will adjust the shutter speed if you’re in Av or the aperture if you’re in Tv to allow the under and over exposed images to be taken. If we choose a one stop bracket, then the above situation will see exposures at 1/250 and 1/60 if you’re shooting in aperture priority (in shutter priority, you’ll get f11 and f5.6). You usually have a choice of setting the AEB amount in 1/3 stops or ½ stops.
You might be tempted to check the LCD screen and delete 2 of the 3 frames afterwards. That would be a mistake, IMHO, unless you are seriously running out of memory card space and don’t have any spares. Keeping them and loading all three onto your computer is a much better practice. If you have the right skills in Photoshop, you could load them all onto separate layers and erase or mask various parts of each layer to end up with a perfectly exposed image that’s been put together from all three exposures.
Taking things a step further, with the camera secured to a sturdy tripod, you could take 5 images one stop apart. If your camera allows it, you can set 5 in the menu, otherwise set it to shoot 3 and then use some exposure compensation in conjunction with the bracketing to get 5 frames. These can all be processed as HDR type imagery, which I’ll take a look at in a future post.
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