How To Use Auto Exposure Bracketing

If you’re ever uncertain of which exposure will produce the best results, then you can always set your digital SLR camera to Auto Exposure Bracketing mode, which is abbreviated AEB. This facility allows you to capture a chain of photographs at slightly different exposures.

All photographers eventually recognize the various kinds of lighting conditions that will usually deceive a camera’s metering system. They will then use techniques such as auto exposure compensation and auto exposure lock.

However, auto exposure bracketing is a rather different technique.

I personally do not use this facility these days because I shoot in RAW mode, and use Photoshop to tweak my images later on. But when I did use auto exposure bracketing in the past, I found the technique to be very useful in capturing at least one well-exposed image, especially when the lighting was a bit tricky.

In days not too long since gone, when film was the only medium you could use to capture images, you had wait to get the film processed to see whether your pictures were well exposed, and if they weren't there was nothing you could do about it. That left you feeling disheartened.

Not so today. All you need to do now is to check your shot on the LCD monitor as soon as you have taken it to see whether you have got the exposure right. If it is not, you can check the histogram, apply exposure compensation, and then retake the shot. However, if you really want to guarantee that you will get a correctly exposed image, you ought to use the bracketing function.

During auto exposure bracketing you take multiple shots of the same scene or subject, but use slightly a different exposure setting in each shot in order to get one that is just right and perfectly exposed. With this method you take one shot using your camera’s recommended meter reading, and then shoot at least one underexposed and one overexposed frame using exposure compensations of plus and minus 1 EV. (Reminder: EV stands for Exposure Value).

That’s the basics anyway, but it may be better to shoot a longer bracketed sequence of up to 9 frames, each taken at 1/3 or 2/3 EV increments and decrements either side of the first setting. You can do this manually if you like, but it’s a pain. Instead, you can use the AEB or BRK function on your D-SLR that will vary the exposure compensation for you. You simply select the number of images you want in the bracketed series and the level of exposure compensation to be used.

With this bracketing technique you can save the best image to your computer later on and delete the others in the series. And it wouldn't have cost you anything. Compare that with doing the same with expensive film!

There’s obviously no need to bracket every shot you take. This technique is only used during difficult lighting conditions, like when the light is changeable, is very bright, or when there are reflections or back-lighting deceiving your camera’s metering.

How to Use Auto Exposure Bracketing

It depends on the make and model of your camera as to how you access the AEB function. Some cameras access it via the menu system whilst others have a dedicated button, which is usually marked BRK, so consult your user manual. Here then is how you use this function:

·       Select the bracketing function.

·       When prompted, set the exposure increment for the bracketed series.

·       Select the number of frames to be shot if this option is available.

·       Mostly, one shot is taken each time you release the shutter, so you’ll shoot several shots to complete the bracketed sequence. However, if you set ‘Continuous’ via the ‘Drive’ menu, the bracketed sequence will be shot in one go, so long as you keep the shutter release button pressed down.

Warning: Never shoot a bracketed sequence in fully automatic exposure mode. This is because the camera will then change the exposure compensations in the bracketed sequence by a combination of aperture and shutter speed, which means that you will have no depth-of-field control. So it is always best to select either shutter or aperture priority mode.

Advanced Auto Exposure Bracketing

You can actually combine AEB with exposure compensation if you need to bias the bracket towards overexposure or underexposure. For example, if you know you need to add exposure but are not sure by how much, you can set the exposure compensation to +1 EV, say, and set the AEB to +/- 1EV. This will generate a sequence of three shots that are taken at the camera’s metered exposure, followed by a shot at +1 EV and one at +2 EV. For underexposures, set the exposure compensation to -1 EV.

As I said before, if you shoot in RAW mode and then tweak your images in photo-editing software, you won’t have to worry about auto exposure bracketing. But at least you now know what auto exposure bracketing is all about.