Back Button Focus
“It is during our darkest moments that we must focus to see the light”. Now, I am well aware that this supposed Aristotelian utterance has nothing to do with photography, but it is a strangely accurate description of the landscape photographer’s predicament. As any devotee of the discipline will know, a significant portion of the hard work that leads to a great image takes place in the predawn darkness, and that the two biggest factors influencing the outcome of these dimly lit sorties are “focus” and “seeing the light”.
More often than not, the landscape photographer’s approach to conquering the “light” portion of the Aristotle equation is to sit and wait; patiently watching the highlights and shadows as they dance across the horizon. “Focus”, by contrast, can be a little more of a challenge to overcome, simply because the typical camera is not designed for the “sit and wait” scenario.
By default, cameras are configured such that the shutter button activates three separate subsystems. Half depressing the shutter button simultaneously invokes the camera’s light metering and focus units, and fully depressing it releases the shutter. This configuration is tailormade for run-and-gun photography, which demands the shortest possible time between observing that award-winning scene and capturing it. The faster the camera can meter the light, focus the lens and release the shutter, the better.
Needless to say, run-and-gun is appreciably different from sit-and-wait, an approach that essentially requires that – at the very most – only the metering should change before the shutter is released. When you are patiently waiting for the light, and firing off a shot whenever the composition looks pleasing, the last thing that you want is for the camera to continually refocus before every frame. Not only would the continual refocusing be annoying, but it could also be a real problem if your chosen focal point for the scene does not lineup with one of the camera focal points.
One way of solving this refocusing problem is to switch over to manual focus. There are definite benefits to this approach, including absolute control over the focal point, but I find manually focusing to be clumsy and, in many cases, less accurate than doing so automatically. Another possible solution – which happens to be a bit of a manual-auto compromise – is to focus automatically, and once this function is complete, to then switch to manual focus, effectively locking in the focus for subsequent shots. This approach is perfectly legitimate and one that I have used successfully myself; however, it is still clumsy. The focus mode switch is usually located on the barrel of the lens, and this position suggests that there is at least some risk of bumping the focusing ring while switching between modes. Furthermore, refocusing requires that you switch back to automatic mode, half depress the shutter button to activate the focusing unit, and then return to manual mode for the shot. It’s frustrating for me to write the procedure down, never mind executing it in the field. My preferred solution to the problem is the back-button focus method.
Back-button focusing requires digging deep down into the menu system of the camera and reassigning camera operations to different buttons. The overarching idea is that the shutter button is only allocated two functions instead of its default three. Half depressing the button only activates the light metering unit of the camera, and fully depressing the button releases the shutter. The job of initiating the focusing unit is assigned to a separate button on the back of the camera body; hence the name back-button focus.
The beauty of this arrangement is that once you have established your focus by pressing a button on the back of the camera, it will not change while you shoot. This scenario is precisely the functionality required by landscape photographers; establish the composition, focus using the back-button and then fire away knowing that the focus is precisely as you left it and with the additional advantage of knowing that refocusing is only a button press away.
Now, I am a real fan of this method, but it would be remiss of me not to point out a few obvious problems. First among these is camera capability. I’m not sure how many cameras are supplied with the native ability to have their button operations reassigned. That said, the practice of back-button focusing is reasonably widespread, and so I am comfortable to suggest that most enthusiast-level cameras and above will have the ability to do so.
The second obvious drawback is that the button with the new assignment of activating the focusing unit will have to relinquish its intended task. This problem is further complicated because it is useful to have the new focus button in a location on the camera body, which is ergonomically suited to use when you have your eye pushed up against the eye-piece. Personally, I sacrifice my Automatic Exposure Lock (AE-Lock) button because I rarely use the feature and it is perfectly located for operating using the thumb of my right hand.
The final point to note about back-button focusing is habit. For many, using the shutter button to focus is something that would have been done for several years and training the brain to use a different button can be frustrating. It still astonishes me to note just how often I try to focus my camera with the shutter button and fail, only to then remember that I have moved the focus function elsewhere. I’m sure that a large part of this problem is likely the result of my limited mental capacity, but at least some of the difficulty must be attributable to the adage that “old habits die hard”. Apparently, shutter button focusing is the Bruce Willis of habits.
But, despite these disadvantages and sacrifices, I remain a fervent supporter of the back-button focus system. The technique is not for everybody, but I certainly suggest giving it a go on your next landscape excursion. There is nothing like sampling the benefits to place the costs of the method into perspective and I know one thing for sure; during my darkest moments, I want to “focus to see the light” and not focus on focusing.