How to Use Autoexposure Lock on Your Nikon D5300
To help ensure a proper exposure, your Nikon D5300 continually meters the light until the moment you depress the shutter button fully. In autoexposure modes, it also keeps adjusting exposure settings as needed to maintain a good exposure.
For most situations, this approach works great, resulting in the right settings for the light that’s striking your subject at the moment you capture the image. But on occasion, you may want to lock in a certain combination of exposure settings. For example, perhaps you want your subject to appear at the far edge of the frame.
If you were to use the normal shooting technique, you’d place the subject under a focus point, press the shutter button halfway to lock focus and set the initial exposure, and then reframe to your desired composition to take the shot. The problem is that exposure is then recalculated based on the new framing, which can leave your subject under- or overexposed.
The easiest way to lock in exposure settings is to switch to M (manual) exposure mode and use the f-stop, shutter speed, and ISO settings that work best for your subject. But if you prefer to stay with an autoexposure mode, you can press the AE-L/AF-L button to lock exposure before you reframe. This feature is known as autoexposure lock, or AE Lock for short.
You can take advantage of AE Lock in any autoexposure mode except Auto or Auto Flash Off.
A few fine points about using this feature:
While AE Lock is in force, the letters AE-L appear in the displays. Look for this indicator at the left end of the viewfinder; next to the Metering mode icon at the bottom of the Live View display; and just beneath the shutter speed setting in the Information display.
By default, focus is also locked when you press the button if you’re using autofocusing. You can change this behavior by customizing the AE-L/AF-L button function.
For the best results, pair this feature with the Spot Metering mode and autofocus settings that enable to you select a single focus point. Then, if you frame your subject under that focus point, exposure is set and locked based on your subject.
Be sure to keep holding the AE-L/AF-L button until you release the shutter button. And if you want to use the same focus and exposure settings for your next shot, just keep the AE-L/AF-L button pressed.