BACK-BUTTON AUTOFOCUS, THE RATIONALE
[Editor’s Note: This post explaining back-button autofocus has been one of the most popular ever written here on The Discerning Photographer. It’s accounted for thousands of page views over the past few years as people look for information on this incredibly powerful and easy-to-use technique. I remember when I first started using back-button autofocus and how difficult it was the first couple of weeks. But after that, I would never go without back-button autofocus–it’s just that superior. Here’s the entire post for you to consider. Read through it once straight through, then read through it again slower, maybe while having your camera in hand.–/DiscerningPhotog]
Does your camera have back-button autofocus? Is it an option on your DSLR to switch between shutter-driven autofocus and thumb-driven back button? If you grew up on shutter-driven autofocus and never bothered to relearn, you’re selling yourself short. Here’s why….
I remember when Canon first came out with the back-button autofocus option, early in their roll-out of their clearly-superior autofocus film cameras. It was 1989, and I was a Nikon shooter at the time. Nikon went through all sorts of contortions to try and explain away Canon’s innovation…which Canon had a patent on. It took Nikon several years to figure out a way to make their own back-button autofocus option without violating that Canon patent, but in the meantime, we Nikon shooters watched our Canon counterparts with envy.
Why? Well, as a newspaper photographer who has shot a whole lot of action-driven events (sports and news, mostly), you come to quickly see the genius of the back-button autofocus approach: it separates the focus function from the exposure function! This is critical! Let’s say you’re shooting a hockey fight. You autofocus with your thumb while shooting away with your index finger….now other players skate into view between you and the fight….you remove your thumb from the focus button, in effect locking the focus on the fight, while you continue to shoot with your index finger. Separating these two distinct functions allows you to have much greater control over your focus/exposure relationship!
Contrast this with the same situation but with focus and exposure both tied into the shutter release button. Shooting the same fight, you’ll have far more trouble keeping what you want to focus on in focus…things will be jumping around…you’ll be missing photos!
It also comes in handy every time you want to focus on something on one side of your frame, then recompose without refocusing and shoot the photo. This happens a lot with wide angle compositions. Instead of having to switch your focus point over t0 the left or right side of the viewfinder, with back button, you simply focus on the point you want in focus, then recompose and shoot your frame.
So do yourself a favor. If your camera has the back-button autofocus option, learn to use it! You probably will need to dig around in the Custom Settings for your camera to figure out how to set this up, but it will be worth it. At first this will feel incredibly awkward—you’ll be uncomfortable as you start making the change. (Sort of like rubbing your stomach and patting your head—I never was much good at that!) But keep at it. Soon back-button autofocus will become second nature and you’ll find your percentage of in-focus photographs going up!
Hi, I’m Andrew Boyd, a.k.a. The Discerning Photographer, and I hope this post has been interesting and informative. Please leave me a comment about it, let me know what you’d like to see more of on the site! You can also sign up for email delivery of all future articles or my RSS feed. Or subscribe to our Facebook page ,Google+ pageor our Twitter feed. Thanks!–DiscerningPhotog