The Ins and Outs of Autofocus



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This shot was deliberately focused on the guest, leaving the wedding party out of focus in the distance.  I had to make the AF ignore the bigger part of the scene.

This shot was deliberately focused on the guest, leaving the wedding party out of focus in the distance. I had to make the AF ignore the bigger part of the scene.

I remember when the first autofocus cameras came out, it was a topic of some ridicule and professional snobbery in the early days. Some of the real early systems were based on IR or sound which could be fooled by rain or anything moving in the field of view. All of the early autofocus systems were slow. Push the button, then watch as the focus system started hunting around, eventually settling on something that seemed about right. In the late 70s and 80s came the lenses with in-lens focusing motors so big they left an obvious lump in the lens contour. We called those “goiter” lenses.

Fortunately for all of us today camera manufacturers ignored our laughing and taunting and kept improving autofocus systems until it became one more thing that your camera does better than you. Although some of us still use manual focus and don’t shy away from manual lenses, most professional shooting is done with AF lenses today. Even at that, focus is another artistic element in a photograph and while your camera may focus faster than your eyes can adjust, it still doesn’t mean the camera is going to make the right artistic decision. That’s where you come in. Let’s look at the different focusing modes and when you should step in and take over.

Thanks One Shot Autofocus! Let's just ignore that big train taking up most of the frame and focus on the crappy tree branch hanging down.

Thanks One Shot Autofocus! Let’s just ignore that big train taking up most of the frame and focus on the crappy tree branch way off to one side.

One Shot Focusing

This is the default for most cameras and basically means every time you press the shutter button, the camera is working out the focus for the shot. It’s also called “Single” on some camera models. This great for slow-moving subjects, not so good for fast-paced environments.

One shot is great for portraits, landscapes and probably for 90 percent of the pictures you’ll ever take. Where it falls down is when subjects are moving fast and you want to take a sequence of shots.

One shot or single focusing is the most thrifty with your battery power because running those focusing motors burns a lot of electrons. On the plus side, with one shot you can focus on one part of the frame, hold the shutter button half-way down while recomposing and then take the shot.

Continuous Focusing

Continuous autofocus is a big selling point for many cameras and there are times it’s the right choice, just be aware that it tends to be a power hog. In this focus setting depress the shutter button and your camera will keep a moving subject in continuous focus. A few cameras even have this feature in video mode, which is great for backyard movies but would horrify filmmakers who use DSLRs in production shots. For moving subjects you’ll get much better results, again at the cost of electrons. Canon calls their continuous focusing AI Servo. There’s also AI Focus, which is supposed to be a hybrid but in my experience using it I’m never exactly certain which mode it’s in, so I stick with One Shot or AI Servo.

Manual Focus

Lenses like this Bower 35mm at B&H Photo are all manual focus and priced hundreds less than their autofocus peers.

Lenses like this Bower 35mm at B&H Photo are all manual focus and priced hundreds less than their autofocus peers.

It seems crazy anyone would want to manually focus a shot in these days of contrast autofocus and high speed precision focusing motors but you’d be surprised. For those of us growing up in the days of manual focus lenses, it’s nearly automatic anyway. But the real bonus is lens manufacturers can put all their focus into lens elements and produce some really fantastic lenses that cost hundreds less than their more sophisticated cousins.

Other times to switch to manual focus are shots with low contrast backgrounds when your camera’s autofocus doesn’t have a defined subject to lock onto. Some cameras won’t take the shot if the autofocus is hunting around and it can be very frustrating to hit the shutter button and nothing happens!

Automatic Focus

You can go the other way and let the camera decide your focus point and the focusing mode. Automatic settings on camera systems all work a little differently, there are even differences between camera models made by the same company. Most of the time, when you’re in full Auto mode, the camera is making all the decisions, including which type of focusing is appropriate to the scene.

DSLR Video

When your camera is in video mode, you’ll definitely want to use manual focus. The last thing you want in a scene is to have your camera hunting for focus. That’s why video shooters using a DSLR will likely either have manual focus lenses or have the AF, along with almost every other automatic function, switched off.

Don’t be afraid to experiment with different focusing options on your camera and I encourage you to practice manual focusing. The times you’re most likely to need manual focus are times when it’s least convenient to learn the process. Those will be difficult focusing situations, which almost always involve poor lighting. Trying to learn manual focus while bumbling around in the dark is not a great idea. Practice in the light for the times when you don’t have it.