For many novice photographers, the term automatic exposure lock (AE-L) is relatively unfamiliar. Some people may have bought a camera and haven’t used it for half a year. In fact, this AE-L button is very easy to use. It can make the camera to maintains an ideal exposure value, allowing you to change the composition at will, now let’s take a look at the usage of this AE-L button!

Camera’s automatic metering system
If you have read the previous post (How to use the light metering mode), you will know that there are roughly three types of metering systems built into the evaluative metering, center-weighted metering and spot metering. In an environment where the light and dark levels are very different, we may need to use center-weighted metering or spot metering if we want the subject to be properly exposed, but if we need to move the central area away from the subject to recompose the image after metering, the system will move according to the movement to re-metering (or the metering value before and after the composition is changed!), so that the previous metering is useless, then in this case we need to use the AE-L button to lock the exposure value!

Several settings of AE-L/AF-L buttons

1. Only lock auto exposure — Only auto exposure locked means that the exposure value will not change after pressing the button, but if the button is released, the auto metering will resume operation.
2. Keep AE locked —Keep AE locked means that the exposure value will remain locked for a period of time after pressing the button (the viewfinder will display the words EL, etc.) until the user presses the AE-L button again to release it.
3. FV lock —FV lock is not actually used to control the exposure, it is used to control the output value of the flash, and its usage is similar to the metering system.