What Is It About Autofocus That's so Important?

No, it’s not a trick question. I recently asked Fstoppers readers about their absolute must-have in a camera, and the clear winner was autofocus. But there is a lot to autofocus, so I want to examine some of its aspects more deeply.

In a recent article I wrote discussing deal-breakers and new cameras, I asked about the one thing you couldn’t live without and the one thing that you really do need before you're prepared to shell out some serious money for a new body or an upgrade. There was a wide variety of answers and some surprise inclusions on the list such as the tilt screen, ergonomics, dual card slots, buffer speed, and of course, price. But references to autofocus came out on top, which got me thinking about the different facets of autofocus systems that make it so vital to modern photography.

Put simply, autofocus is so important because it provides peace of mind to users. If you know that you’re going to get a high majority of your shots in clear, crisp, perfectly sharp focus, then you can worry about the other things that make a good image, like composition, for example. I mean, there's no more sinking feeling for me than when I look at a shot that has wonderful light or a very pleasingly arranged composition only to zoom in and find that my subject is slightly blurry, or that I haven’t quite nailed focus well enough for a paying client. That moment when you go from “boom baby” to “you gotta be freakin’ kiddin’ me!” is not nice, to say the least. And let me assure you my language is far more colorful than that if I get a well-composed shot that’s not razor sharp.

Sometimes, moments are so fleeting that if you miss the shot, then that light or that composition might not come together again, and the opportunity is gone. So, knowing that you can rely on and trust your autofocus to do its job and provide wonderfully sharp images almost every time is a huge relief and gives you far less to worry about when you’re out in the field.

Frame Coverage

So, what are the different parts of autofocus that make it so important? First, there’s how much coverage you have across the frame. In some modern cameras such as the Sony a9, you get almost total coverage from corner to corner of your frame (93% to be exact), which is extraordinary when I think of the autofocus coverage in my very first Canon Rebel DSLR, which you can see below.

Even now, with my current Canon 5D Mark IV, it has pretty good coverage, but there are times when I really do need a little more, particularly at the top and bottom of the autofocus coverage area, which I've indicated with red arrows in the image below.

Having 93% coverage across the frame like you get with the Sony a9 can make life so much easier and offer up some marvelous opportunities in post-production. For example, if you’re shooting macro and you want to do some focus stacking, it makes it very easy to place the focal point on various parts of the frame quickly and without fuss.

As you can see in this picture of the flower above, there is a lot of the area in the frame that is soft and out of focus. Now, you might like that look and that might be the type of composition that you’re going for, but if you wanted more focus across the frame and different elements of the frame in focus, having an autofocus system that covered the entire frame would make this very, very simple. Say goodbye to focus and recompose forever.

Speed

Another hugely important aspect of autofocus is speed. How fast can your autofocus system lock onto the subject when you press that button? Sometimes, it might only be a fraction of a second delay, but that can often be the difference between nailing the shot and getting a slightly fuzzy image. This is particularly so in scenarios where you might have erratically moving subjects such as surfing or wildlife photography. In cases such as these, you really want to have confidence that your camera’s autofocus system is going to be able to lock on to and keep up with the movements of your subject.

In this shot above (SOOC), I was able to pick up my camera quickly and get my daughter in focus immediately. It’s not often that she runs towards the camera with a smile on her face, as for some reason unbeknownst to mankind, this little diva princess suddenly goes into a shell whenever she sees my camera slung around my neck. So, to have this opportunity and be able to get the shot with one quick press with back-button focus was a testament to the speed of my autofocus system. But it was also a testament to its accuracy, which brings us to our next point.

Accuracy

Of course, there’s a lot of overlap between speed and accuracy, but sometimes, they are separate entities. I’m sure you’ve had an experience where your camera’s autofocus system is telling you that it has locked onto the subject, so you take the shot in good faith, only to then check your shot after the fact and sometimes notice that the focus wasn’t accurate at all. In essence, your camera’s autofocus system lied to you, kind of like telling you it had hit a bullseye on the dartboard when in fact it had barely scraped double twenty.

That’s particularly maddening, because you should be able to trust your camera when it says it has locked on to the subject you have asked it to. Such scenarios might be forgivable if you’re shooting landscapes on a tripod and you can just do it again or even manually focus yourself to get the shot, but in a situation like high-action sports or a wedding where moments are absolutely crucial, then this is unforgivable and perhaps even a deal-breaker.

Different cameras use different autofocus systems. However, regardless of whether they use a phase detection system or a contrast detection system, the accuracy rate should be high if you’re going to use that camera long-term. When I was first learning about autofocus and trying to ensure that my camera could find the subject quickly and accurately, I was always told to look for contrasts in colors or lines in my frame. That way, you give your camera’s autofocus system the best opportunity of locking on to the desired subject. On the other hand, sometimes you might notice when you try to focus on a single solid color that the camera has a lot of trouble, and you hear the lens struggling or you get the flashing light in your viewfinder.

For example, in the picture above, if I were to set my camera on the little dark spot, it would find focus quickly and accurately within the blink of an eye. Conversely, if I tried to focus on the plain white wall, it might struggle a little bit. I can’t speak for any other camera, but I do know that using the 5D Mark IV, it doesn’t handle solid colors like that particularly well. So, in this day and age, when cameras are becoming such extraordinary pieces of technology, you should be able to get an autofocus system that’s fast, accurate, and covers almost all of the screen. That way, you can feel safe in the knowledge that your camera's autofocus system will do its job properly and you can focus on colors, or light, or composition — the things that really separate good images from great images. Autofocus should not be a concern, and that’s why I presume it ranked most highly in Fstoppers’ readers’ responses to my deal-breaker article.

What are your thoughts? I’d love to hear from you in the comments below.