As my skill improved as a photographer, there was always one aspect that I struggled to bring up to speed. As my composition and posing improved, I gained ground as a photographer. However, my ability to focus quickly and accurately never seemed to catch up with my other skills... until a photographer friend taught me a few tricks that changed the way I focus. The technique I'll suggest in this article consists of two parts: back button focusing, and focus and recompose.
As the names of the techniques imply, we are using a button on the back of the camera in order to engage the autofocus mechanism of our cameras. Additionally, I am using center point autofocus, and applying a technique called focus and recompose.
Back button focusing
Currently, I'm shooting a Canon 5D Mark II. It is by far the best camera I have ever owned. The image quality and overall "feel" of the images it produces is in my opinion, unmatchable. However, as a recent Nikon convert, it is also my personal opinion (an opinion shared by many others) that the autofocus of this camera has some shortcomings. Using center point focus and recompose as well as back button focus helped me overcome these shortcomings.
Let's first talk about how to setup for this technique. Currently, your camera is probably setup to begin autofocus when pressing the shutter button halfway. I have changed the settings so that the shutter button has nothing to do with the focus process. I like the idea of the shutter button doing only one thing: triggering the shutter.
There are for a number of reasons. I personally prefer that each button do only one thing as often as possible. Furthermore, there are times when covering weddings that I just need to get a shot, whether the focus is perfect or not. If you are using the shutter button to focus as well, your camera may try to hunt and seek focus and you will miss the shot.
The button that engages the focus on the 5D Mark II is on the back of the camera. Nearly every camera has a button on the back of the camera, to the right of the viewfinder window. However, not every camera defaults to this button engaging focus. Often, you will have to tweak a setting to make it behave in this way. Make sure and consult the manual to find how to change it to your liking.
The button on the back labeled "AF-ON" is used for back button autofocus on the 5D Mark II.
This accounts for half of the technique. If this is all that you want to change, that's fine. What this really allows you do to is turn the auto focus off, essentially locking it. If you're using your shutter button to focus, you'll need to depress an AF-Lock button while shooting to achieve this. With rear button focus, you touch the rear button and then just let go of it to lock focus.
If something walks across your frame, just let go so the focus doesn't shift. If you're focused on something and want to change your composition, don't mess with focus points, just let go of the button and recompose. Which brings us to our next point. Frankly, the focus and recompose method is an even bigger part of my focus routine.
Focus and recompose
The focus and recompose method is a somewhat self-explanatory method. As you might know, most camera autofocus systems are based on "points" spread over a grid, visible in the viewfinder. The selected point is the point that the camera focuses on. Depending on the settings of your camera, your camera will range from anywhere between automatically choosing all autofocus settings, and completely manual autofocus. What I choose to do is leave the autofocus point locked in the center of the grid. I then focus on my subject by covering them with that center point, let go of my back button, recompose to utilize the rule of thirds or some other compositional technique, then shoot.
In this example, I placed the subject's eyes in the middle of the frame, focused for them, and then shifted the camera, a technique illustrated further below.
Let's say that I am shooting a portrait. The first step is to position your subject as you want them to appear, and also to have a vision for how you want your photo to appear.
The next step I take is to look down the viewfinder and move my camera so that the center point of the autofocus grid is placed where I want the camera to be focused. For portraits, this point is quite frequently the eye. Then, I engage the focus using the button on the back, and the camera focuses on the point. Next, I shift the camera so that the scene appears as I wish for it to. At this point, I'm not touching the focus button. I click the shutter, and because of my settings, nothing changes in the autofocus system. The shutter button simply shots the scene and the photograph is made.
In the photos above, I have illustrated the shift using a finished photo. On top, I have placed my subject temporarily, focused for the subject's eye. In the second photo, I have shifted the camera for the composition I desire. Note that I let go of the focus button after initially obtaining focus.
Using center point focus doesn't mean that we put our focus point in the center of every photograph - that's where the recompose part comes into play. It sounds like additional steps, but it will soon become second nature. The first few days that I was using it, I wasn't pleased with the results, but it was easy to see the potential that this technique provides.
There is one more setting that I would suggest utilizing. On my camera, I have the shutter button set to lock the metering when being pressed halfway. This comes into great use when using aperture or shutter priority. I have the camera set to spot meter for the face, and while focusing for the eyes, I also freeze the metering by depressing the shutter button halfway. That way, when I recompose, the camera no longer changes the exposure settings.
Advantages of the Technique
As we've discussed above, I switched to this technique and am much happier with my focusing results. I think that back button focus is a great fit for event, sports, and wedding photographers, or anyone that needs to capture fast moving action. You can overcome some of the autofocus shortcomings of your camera.
Although focus and recompose can be a lightning quick technique, while I was in the process of switching to the technique, I noticed my composition greatly improving. I at first concentrated on what I wanted to focus on, then in the recomposing process, I had a better idea of how I wanted to "surround" or portray the focused subject. It made me take my time and give a more conscious thought to what I wanted to do with the photo.
One reason that this technique works is that the center point of the camera's autofocus system is often the most fast and accurate autofocus point. I can say that this is definitely true for my 5D Mark II - the camera's ability to lock focus, particularly in low light, is excellent with the center focus point. Another point that I've already touched on is that I am a huge proponent of disconnecting the shutter button from the focus process. I much prefer using it only to release the shutter and create an exposure.
Finally, this autofocus technique doesn't block you from using continuous focus methods. AI Servo focus, or continuous autofocus, is still possible. The back button autofocus button will continue to drive focus as long as its held. Switching to back button focus and using the focus & recompose method doesn't require us to completely change our autofocus routine, only modify and improve parts of it.
Criticisms of the Technique
In order to cover these alternate techniques fairly, I have to present alternate opinions on this technique. I can say that having shot both methods, I much prefer the methods discussed above. However, a number of recent dissenting opinions have come to my attention lately.
One criticism is that focusing and recomposing can cause some issues with being out of focus when you shift the camera. Basically, the theory is that the angle of the camera to the subject alters as we recompose, and thus the focal plane is no longer aligned with the focus length you just autofocused to. This article provides some background on that opinion as well as a diagram to better illustrate the point being made.
The above article would make it sound as if the majority of shots taken with this technique will suffer in focus. While it may make sense from a mathematical point of view, I think we all know that photography is equal parts science and artistry. I use this technique and the majority of photos are sharper than my eyes can resolve. I've shot with some photographers far more skilled than myself and they use this technique and shoot dozens of weddings each year, so it must be working alright for someone.
The techniques presented above have become an integral part of what I do as a photographer. The ability to quickly lock focus and consistently focusing for the same point were two things that helped my work improve, and helped the camera "get out of the way" and let me do what I do. However, other photographers are perfectly happy with the standard focus methods.
Ultimately, all photography techniques will require a fair amount of experimentation and practice to decide on what you like and what works for you. If you're looking to improve your autofocus results, the above methods are worth the time it takes to experiment.