The auto exposure lock (AE-L) function on a DSLR camera lets you physically lock the exposure reading from anywhere in the scene. You can use it on its own or at the point where you focus the image.
Just about all DSLR cameras have an auto exposure lock button. When you press the AE-L button, the current exposure settings are fixed (locked) so that they can’t change as you recompose the shot—even if the level of light alters as you aim the camera elsewhere.
When the shutter is pressed halfway down, the autofocus mechanism is engaged. As it does so, the camera takes a meter reading and sets the exposure. But what if you want to focus and meter from different parts of the scene?
This is where the auto exposure lock function comes in handy. It lets you take an exposure reading independently of where you want to focus.
The AE-L function is best used with spot or partial metering in order to fix the meter reading from a small area in the scene. This is very useful in lighting conditions that may fool the metering system.
For example, if you shoot a scene that has a bright source in part of the image, an evaluative, matrix, or multizone meter can easily force underexposure. To get the right exposure, you need to take a reading away from the bright region.
This can be easily be done by taking a spot or partial meter reading from a mid-tone area of the scene and then locking that reading by pressing the AE-L button and keeping it pressed until you’ve recomposed and taken the shot. On some cameras you don’t need to keep the AE-L button depressed, on others you do.
The AE-L button can be used if the subject or subjects are positioned off-center in the scene. It is also useful when you’re shooting a sequence of images that you want to be stitched together in order to produce a panoramic photograph. The AE-L function makes sure that every shot taken in the sequence has exactly the same exposure settings.
About the Author:
Chris Smith (photography-expert dot com) gives photography tips in his ezine.
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