Read on to learn about AE-, FE- and AF-lock.
- AE-Lock. AE simply stands for automatic exposure. The button allows users to lock their exposure settings (i.e. aperture and shutter speed). AE-lock can be extremely useful in many situations. For example, if a photographer is taking a series of images for a panoramic photograph and needs identical exposures, such as if you want to stitch together a set of photos to create a panoramic photo, AE-lock can allow you to be certain each photo has the same exposure. AE-lock can also be very useful in difficult lighting situations.
- FE-Lock. FE stands for flash exposure. This button allows users to lock their flash exposure settings. The lock only lasts for 16 seconds or for as long as you keep the shutter button half pressed. On many cameras it's tied together with the AE-lock, but, with more expensive DSLRs, you may find separate buttons. Other cameras allow you to assign FE-lock to a "Custom Function" button. It can be useful to use FE-lock with reflective surfaces, which can fool flash metering, or with photos where the subject is not covered by a focus point.
- AF-Lock. AF stands for autofocus, and AF-lock is the easiest of these lock functions to use. It's also the only one of the three that happens automatically when you take any photo. AF-lock is activated by pressing the shutter button halfway. By keeping your finger on the shutter button as it's pressed halfway, focus is locked. This can be very useful if you want to focus on a subject that is on one side of an image. You can lock the focus on the subject, and then re-compose the image without taking your finger off the shutter button.