Great question and certainly most wildlife photographers I speak with are still using the default press the shutter button half way down to focus with another full press on the shutter button to shoot method. While a perfectly acceptable method keep reading as you just might discover that back button focus better suits your style of photography. It was explained to me about five years ago and I have not looked back since. So what exactly is back button focus? In simple terms the autofocus (AF) feature that is normally performed by pressing the shutter button half way is stripped away and relegated to a button on the back of the camera.
So what’s the big deal you ask? Below are a few reasons why I think every photographer should consider back button focus, especially wildlife photographers.
- Much easier to lock focus. Let’s say you are out shooting an osprey in its nest and the focal plane remains constant. With back button focus you lock down the focus on your subject by pressing the rear button (AF ON for Nikon) and once in-focus you simply take your thumb off the rear button. Now you may shoot as many pictures as you like and the focus will not change until you press the back button again to refocus. With the shutter button focus if I composed an image and focused then wanted to go off center I had to keep the shutter button pressed half way down to maintain the focus and keep my finger there until I took the shot. Not any more, the camera now makes no effort to re-focus when you press the shutter button half-way down again.
- No override of your manual focus. Ever found yourself out shooting a bird in a busy setting and you needed to manually focus the lens on the bird? Sure you have so you focus manually on the bird but the moment you press the shutter button down half way the AF kicks in and focuses on the trees again, very frustrating. With back button focus activated the shutter no longer controls the focus only the shutter release so your manual focus point is not interrupted. No need to move the AF to MF in this case.
- Timing your shots. I just hated having to hold down the shutter button half way to maintain focus on my subject and then wait for the moment that I wanted to take the shot. In this case of a wildlife photographer this could be a matter of hours not minutes. By using back button focus to pre-focus on the spot where the subject is expected to appear you only need to be concerned with activating the shutter to capture the moment not focus and capture.
- Close up focusing is much easier. If you’re into macro shooting you’re going to love the back button focus method. We all know how hard it can be to get exact focus on a close up subject. With back button focus you can use the AF to get the focus close enough for a first pass by pressing the rear button with your thumb and then taking your thumb off the button again. Now you are free to move a little in one direction or another to get the image sharp. And best of all just like the scenario above the AF is not trying to re-focus every time you touch the shutter button.
So if you’re ready to give it a try here’s the magic setting to disable half-pressed shutter focus per the screen shots below:
Function a5: AF Activation. Default is Shutter/AF-ON, change to AF-ON only
Custom function – C.Fn IV-1 Shutter button/AF-ON button. Default is 0, Metering and AF start. Use 2, Metering start for the shutter button and AF for the button
Give it about a week to get used to as it will take a bit of practice, but once you’re on to it you may just wonder how you ever did without it. Worse case is you revert back to the default and no chalk it up to a failed experiment so what do you have to lose.