Ever shoot a moving subject and one shot will be perfectly in focus and the next will be blurry?
Many times a subject can become out of focus because the subject moved out of the area of focus you had set on your camera.
This problem is a sports photographer’s nightmare. With players running every which way, keeping focus can be a difficult task.
Generally, when you set out to take a photograph, no matter what camera you use, you hold the shutter release button halfway down and the camera comes to life by using autofocus points to find areas of focus in whatever your subject matter is. In Canon cameras, this autofocus mode is simply called One Shot.
You hold the shutter release button halfway down and once the camera finds an area of focus it keeps that area in focus. If you or your subject move forward or backward too far, chances are the image will shift from being in focus to drastically out of focus.
There are a few ways to make sure your subject stays in focus while you shoot. You can keep pressing the shutter button halfway down on your camera, forcing the camera to re-autofocus as you shoot. I did this for many years and you get used to it — it’s not impossible, just hard ... especially with fast moving subjects.
You also could increase your aperture value to create a narrower opening for light to travel through in your lens. Doing this creates a larger depth of field and allows for more of an image to be in focus. The only downside to this is you’re losing a lot of light in the process. So, if you’re in a place with limited light you really have to sacrifice your ISO and shutter speed values to make exposure possible. Not good.
Behold, there is an easier way.
Most phones already do this automatically (albeit poorly), but for many Digital Single Lens Reflex (DSLR) camera owners, camera manufacturers have installed a wonderful button that takes care of this problem.
It’s called back-button autofocus.
For Canon users, you simply change your autofocus mode to AI Servo (an autofocus mode that tracks subjects as they move) and hold down the AF-ON button on the back of your camera as you follow your subject with your lens.
It’s a beautiful thing. Your subject moves and the camera moves right along with it by keeping focus on the subject.
Back-button autofocus isn’t perfect, however. You may need to let off the AF-ON button every now and then to get focus back on your subject. Occasionally the camera will still grab the background, but it’s fairly rare these days. Camera technology really has come a long way.
There are a few places where I wouldn’t recommend using back-button autofocus — portrait photography being a primary example. With a subject already sitting still, it’s likely the camera will keep searching for focus and you’ll end up having someone’s face out of focus while their torso is perfectly sharp (provided you’re shooting at wider apertures such as f/2.8).
For times like that, stick to One Shot autofocus. It’ll be a lot easier for you, I promise.
If you’re out shooting wildlife, sports or just your kid on the swingset, give back-button autofocus a try.
It’s a great tool.