Category Archives: Autofocus

I want to talk specifically about autofocus when shooting portraits. To start off, let’s go back to the teddy bear portrait studio that I set up recently and look at a couple of example shots.

If you’re like most people, you’ll perceive the second image as being better than the first… the first one will probably seem like it’s not quite right, even if you can’t put your finger on why. Since this is an essay about focus, though, you probably spotted the difference pretty quickly– in the first image, the bear’s eyes are slightly out of focus, while in the second one they’re sharp.

As I mentioned earlier, shooting portraits can be tricky when you’re using your camera’s autofocus. Portraits are often shot with a fairly shallow depth of field, since you want your viewer’s attention to be on your subject and not on the godawful tiger-striped background that you’ve posed them against. (Again, don’t do that.) It’s extremely important that the subject’s eyes be in focus for portraits, because… well, because I said so and because every other photographer does too.

Here are a couple of closeups that illustrate the difference in my bear images.

In the image on the left, the nose is in clear focus, but the eye is blurry. On the right, the eye is in sharp focus but the nose is a little bit soft. Why the difference?

In the first image, I just let the camera pick its own focus point. It naturally gravitated toward the center of the image, found a nose that it could grab onto, and used that as the focus point. That’s great if you happen to have a weird fetish for noses, but it’s not great for portraits. In the second image, I told the camera that I wanted to use a specific autofocus point only, and then plunked that focus point right on the bear’s eye. Voila! I got exactly the shot I wanted.

If you can put a focus point right on one of your subject’s eyes, then do that. Some cameras have only one or a few autofocus points. Others, mostly high-end cameras, have eleventy billion of them scattered across the image. (IF you want to see this carried to an extreme, check out the 61 autofocus points on the Canon 5D Mark III. Also, if you’d like to give me one I will be happy to put each and every one of those autofocus points to good use.) As always, check your camera’s manual to figure out how to choose individual focus points, as the controls can vary quite a bit between manufacturers and even between different cameras from the same manufacturer.

If you can’t find an autofocus point that works, then you’ll just have to resort to manual focus. By now you probably know that it’s not so scary. Just flip the camera into manual focus mode, then turn the dial until you get what you want.

Thus endeth my wisdom about focusing for shooting portraits. I have one other topic to cover before I put autofocus to bed, but I’ll save that for another day.

You’ve framed your image. You’ve pressed the shutter button and taken the shot. You quickly review the image on the camera and find out that your subject is horribly out of focus. What do you do? You have a few different tools at your disposal for showing the camera that you’re the boss of it, and different ones are useful in different situations.

The first thing you can do is switch to manual focus mode. That’s probably really obvious, but if you’re in the habit of relying on autofocus for everything it might not occur to you that you can do it yourself. Flip the lens or camera into manual-focus mode (depending upon your camera), then grab the focus ring and twist it until you get exactly what you want. If you’re using a zoom lens you might find yourself habitually grabbing for the zoom ring rather than the focus ring, but practice a few times and you’ll eventually start getting the right one automatically.

The advantage of manual focus is that you’re in complete control of the focus. The downside is that it’s sometimes hard to tell when your image is precisely in focus. This is especially true with cropped-sensor cameras that have smaller viewfinders. Many cameras will light up a focus point when that part of the image is in focus even when you’re using manual focus, so you might be able to use that as a guide.

If your image is static, you can use the camera’s LCD as an assistant. Focus, take a shot, then view the image on your camera’s LCD screen. Zoom in on it and scroll around to see if the right parts of it are in focus. If not, correct the focus and try again. (In a competition between film and digital, film would lose hard on this point.)

Many lenses have distance scales on the barrel. If you know that your subject is six feet away from the camera then just turn the focusing ring on the lens until it’s focused at a distance of six feet. Voila!

The second thing that you can do is to use autofocus, but give your camera some extra guidance about what to focus on. Almost all cameras will let you choose one specific autofocus point rather than letting the camera pick its own. If you’re shooting a portrait, for example, you could choose an autofocus point that’s right over one of the model’s eyes. If you do that and the camera can find focus, then you’ll probably get the shot that you’re looking for.

Consult your camera’s manual for specifics of how to choose a focus point, since this can vary quite a bit between makes and models.

There’s a third strategy that will work well in some situations, but it’s a little bit tricky and doesn’t always get what you’re looking for. It’s called focus and recompose.

Imagine that you’re shooting an image with your subject in the bottom right corner of the frame, and your camera won’t focus on it naturally. With focus and recompose you point your camera directly at your subject, then press the shutter button halfway down so that the camera focuses on your subject. Keep holding the shutter button down while you move the camera back to the composition that you want, then take the picture.

Sometimes this works. It will probably do OK if you’re using a narrow aperture and therefore have a lot of depth of field. If you’re shooting a portrait, or shooting with the lens wide open, you probably won’t get what you’re looking for. Explaining why this is would require you to remember some of your high school geometry and do some math, so I won’t explain the details here. The short answer is that when you move the camera you’re changing the distance to your subject ever so slightly, and that might be enough to make your subject go out of focus.

And there you go– you now have three tricks that you can use for showing your camera who’s boss when you’re trying to focus. I recommend that you go practice each of them, so that you’ll have them ready to go the next time your camera gets some crazy ideas about what to focus on.

Most of the time, autofocus will do a really good job of getting your subject in focus. Even though I never put my camera in green box mode anymore, I usually leave autofocus on. I keep an eye on it, though, just to make sure that it’s doing what I want. This is especially true in tricky situations where autofocus might not be smart enough to get me the results I’m looking for.

Here are some situations where just blindly autofocusing might not be your best bet.

You’re shooting through a fence or other foreground object. If there’s something in the foreground with strong lines, such as a fence, your camera is likely to focus on the foreground object rather than your chosen subject. In this example I’ve manually focused on the container and blurred the fence, but if I’d left it up to the camera I probably would have had a sharp fence and a fuzzy shipping container.

Macrophotography. Macrophotography is challenging because you have razor-thin depth of field, so you have to pay careful attention to what parts of the image you want to have in focus. If you let the camera pick out what it wants to focus on, it will probably guess wrong. Serious macrophotographers generally use manual focus for everything.

Everything in your image is soft. When everything in your image is cloaked in fog, your camera might not be able to find anything to focus on. This beautiful image from award-winning nature photographer Joe Decker is titled Tree Ballet and Pogonip, and is an excellent illustration of the foggy, soft image. This image is from his series Mono in Winter. See more of Joe’s work at Rock Slide Photography.

Your subject is extremely off-center. Again in Joe’s image, even if the trees hadn’t been shrouded in fog the camera might not be able to focus on them. Autofocus systems tend to be heavily weighted toward the center of the image. If you stick your subject way off in a corner then your camera is probably going to lose this particular game of hide-and-seek.

You’re shooting portraits. Portraits are often shot with shallow depth of field, but the subject’s eyes should always be in focus. It’s OK for the subject’s nose to be a little bit soft, and the ears can be downright blurry, but the eyes had better be crisp. If you let autofocus have its way then it might decide that it really wants the ears or the shirt or the background to be sharp, and leave the eyes shrouded in some of Joe’s mist. In this particular example, the camera got overly enthusiastic about the sharpness of the bear’s nose.

You’re shooting in low light. Autofocus often has a horrible time finding focus if you’re shooting in very low light. If you can’t see very well, your camera probably can’t either.

Those are some of the key situations where just trusting your camera to get the focus right might not be the best idea. In the next lesson we’ll see what we can do about autofocus problems.

In my last article, I posted this photo and asked you to identify what’s wrong with it:

As it turns out, this is actually a really easy question to answer– the background of the photo is in focus, but the bear isn’t. Now, I’ll be the first to admit that teddy bears are supposed to be fuzzy, but this isn’t the kind of fuzziness that most people have in mind. The more interesting question here is why the camera got the wrong thing in focus. In order to do that, we have to learn a little bit about how autofocus works.

Before we do that, let’s try a little mini-exercise. Pick up your camera. Look through the viewfinder, point it at any interesting subject and press the shutter button halfway. You’ll probably see a display with a bunch of black boxes and some red ones. In this image I’ve colored the black focus points green so that you can see them better. Your camera might only have a few little boxes or it might have lots and lots of them. Those little boxes are called autofocus points:

So how does autofocus work? It’s a complicated, highly-technical thing, but here’s the simplified one-paragraph version that will tell you most of what you need to know.

When you use autofocus to take a picture, the camera looks at each of the autofocus points and looks for areas of sharp contrast. The camera then changes the focus on the lens just a little bit and checks those points again to see if the contrast is better or worse. It keeps doing this, adjusting the focus a tiny bit each time, until it thinks it has the best focus. Once it does, it takes the picture. There’s a whole lot of black magic going on behind the scenes to make this happen, but that’s the really simple version.

The camera might choose to use all of the focus points if it can. More often, it will use one or a few of them to find the subject. As you’re looking through the viewfinder, the camera will light up an individual focus point if it’s happy with the focus in that area. If your camera is guessing wrong you can boss it around and tell it exactly which points to use, but that’s a subject for a different lesson.

So that’s it– when you autofocus, the camera looks at the areas in the little black boxes and then changes the focus on the lens until it’s happy with the results. That’s not so hard, is it?