The camera in your smart phone is a remarkable piece of technology, but it’s not perfect. There are times when you must take control and tell it what to do. One of the easiest ways to do this is by using AF/AE-Lock. While I’ll mostly cover photography, the same points hold true for videographers, too. And, while my examples are from iPhones, Android phone cameras also have AF/AE-L.
What is AE/AF-L?
Auto exposure/auto focus lock (AE/AF-L) is pretty straightforward. You select a point in your composition and the camera calculates the exposure and focus for that spot and then locks it in. You can move your phone around and recompose your shot, but the exposure and focus are locked and won’t change. Essentially, you’re telling your camera to ignore everything else and lock this specific focus distance and exposure setting. If you want a deeper dive into AE/AF-L lock or using it with your DSLR, see my article on auto exposure lock.
You can activate AE/AF-L by placing your finger on the screen at the precise spot on which you want to base your focus and exposure. Hold your finger there until you see both the yellow square and sunburst indicating focus and exposure, and the yellow block confirming AE/AF-L (see image below). If the exposure isn’t to your liking, you can make it lighter or darker by swiping your finger up or down on the screen. (To deactivate AE/AF-L, tap anywhere else on your screen.)
How’s that different from other exposure/focus options?
For many situations, an iPhone camera will do just fine, by itself, without you telling it to do anything. These really are remarkable devices. The camera will select the exposure and focus for you, based on the scene you’re shooting. So long as that scene is in average light, and you want most of the image in sharp focus, you’ll be OK.
But there will be times that the scene you’re recording falls outside those parameters and you’ll need to tell the camera what’s important to you. Maybe there are extremes of lighting and you have to tell it whether to expose for people in the shadows or objects in the highlights. Maybe your subject is in the extreme foreground, like a macro shot of a flower, and you don’t want the background in focus. Maybe you’re going for a silhouette.
Your iPhone camera, like pretty much all cameras, tries to make the exposure close to a mid tone. That’s often fine, but doesn’t work when you’re shooting something really bright, like snow, or really dark, like a bear. The camera will try to make the snow mid tone, resulting in a dingy, gray scene instead of the vibrant white you saw. Or it will render the bear’s fur a dull gray, in an effort to make it mid tone. It may decide it wants to expose for the highlights and let your shadows go black when you really want detail in the shadows. It may decide to expose for the shadows in an evening landscape and blow out all of the colors of sunset.
If you’re interested in learning more about exposure, check out Improve Photography’s free Photography Basics Course and Brenda Petrella’s clear and easy-to-understand introduction to exposure and exposure compensation.
With the native camera app on an iPhone, if it’s giving you an exposure that’s not what you want, you can choose what’s most important. Simply tap the screen where you want the best focus and exposure and the camera will set focus and exposure on that region of the image. That may be OK for many situations, but as soon as you move the camera, everything could change.
And, if you’re shooting video, the camera will be constantly trying to fix focus and exposure as you move around, which results in blurriness and changing lighting. If you’re recording in a situation with pretty stable lighting and can maintain you distance to the subject, AE/AF-L can produce a cleaner video.
When would I use AE/AF-L
There are several common situations where you’d want to consider AE/AF-L. These won’t be the only instances you’d use it, nor would you necessarily use it every time you find yourself facing one of these circumstances. So, consider these examples that can help you get a feel for when you might look at this feature.
1) Something in the scene is moving
If there is movement in your scene, the camera’s focus may try to follow. Imagine trying to focus on a statue in a city park and having your camera’s focus and exposure grab onto a passing pedestrian and follow her across the park, changing as she gets farther away and into a darker area. The camera might pick up a moving vehicle or a plant swaying in the wind. Any of these could potentially cause a blurred and/or badly exposed shot. AE/AF-L can help!
2) There is an extreme range of exposure
Typical of the middle of a sunny day, you can have really bright highlights and really dark shadows. There might be a larger range from brightest to darkest tones than your camera sensor can record. In this situation, one option is to use HDR. Here, the camera takes two exposures—one for the brights and one for the darks—and blends them together. However, if either the brights or the darks aren’t important, you might be better off using AE/AF-L. Imagine shooting a portrait of your spouse under bright gray skies, with no clouds or texture. You might not care about the sky in the background, but you care a lot about a nice image of your husband! Here’s a time you might like to use AE/AF-L, centered on his face, to get him properly exposed and in focus.
You also see this a lot with selfies shot against a bright background. Yes, I could have chosen a more photogenic subject but, sometimes, you just have to work with what you've got. Anyway, the point is that you can get wildly different exposures depending on what region and brightness you choose to base the exposure on. The far right shot is about what the camera wanted to do. As you can see, it make my face a bit too dark and muddy, compared to the center shot. Both blow out the sky. To get the sky, I do AE and AF on the statue, but that makes me too dark (perhaps not a bad thing!) But you'd want your own selfie to be great! So choose the best place to place your AE/AF-L and shoot away! You could also try HDR here.
Three different selfie exposures depending on where I choose to place the AE and AF.
3) Depth of field
The sensor of a smart phone’s camera is small, but very capable. One of the side effects of its diminutive size is that it can render sharp details over a really big depth of field. Almost everything can be in focus, from foreground to distant background. However, something in the extreme foreground won’t be in focus, unless you tell the camera that’s important.
Imagine shooting raindrops or frost on a window from just inside that window. Most cameras won’t automatically focus that close on a transparent object, like a piece of glass. Instead, they’ll focus farther out into the scene, making your frost or water droplets blurry. And, outdoors is generally brighter than indoors so your interior is likely to be underexposed. AE/AF-L to the rescue. You can direct your camera to prioritize what’s happening on and around the window to get the perfect shot.
If you’re trying to create a silhouette, you’ll want to underexpose that person or thing while your camera is trying to properly expose it. You can direct your camera to expose for the sky, by placing your AE/AF-L point in the sky, and letting your subject go into silhouette.
Your phone’s camera can’t really do macro photography, but it can get closer than you’d think. However, in order to get a good bokeh—that creamy, soft background—you’ll have to use AE/AF-L to indicate your priorities to the camera. Try setting the AE/AF-L about where you want your sharpest focus to be. Once that’s set, then move your phone a little closer or farther away, a little left or right, until you see the perfect shot.
6) Your phone’s camera can’t seem to focus
Maybe there isn’t enough contrast along an edge for your phone’s auto focus system to find it. That can happen in soft, low light and with objects lacking clear, sharp edges. Or, perhaps you’re fairly close to the subject and the camera’s having trouble getting enough distance for auto focus. You can try tapping once where you want the focus but, sometimes, that’s not enough. AE/AF-L might solve the problem.
There are many reasons to be familiar with the AE/AF-L function of the camera in your phone, and you’ll find there will be lots of opportunities to use it. Once you’re comfortable with it, and know when to use it and when not to, you’ll find yourself getting better photos and videos from your phone for your Instagram, Facebook, Vero, You Tube or other posts.
And, once you’re used to telling the camera what you want from your shot, you might be interested in taking a look at some of the many camera apps that give you even more control over your phone’s camera. Recent iPhones can record images in RAW, as well as JPG, giving you even more options for shooting and post processing. Check out Brad Goestsch’s review of 14 iOS apps.
Now, get out there and start shooting! And, as a reward for reading to the end, here's a photo of Larry the Superdog and his new cone of shame.