Which function “freezes” the camera’s exposure settings so that if the camera is moved from one area to another, the auto exposure system won’t change aperture/shutter speed values?

Ae lock-there are many situations where this may be useful. a photographer shooting a portrait, for example, might want to place the subject off-center. taking a meter reading off the subject, locking it (along with focus), and then moving the camera to re-compose the subject means that exposure wont shift if the background is lighter or darker than the subject itself. another example might be a shooter taking a sequence of images, panning the camera from one area to another (following a moving subject, for example). if there are differences in the background or lighting, its possible that exposures will vary from one shot to the next. with ae lock active, exposures would be consistent from shot to shot.