By default, pressing the shutter button down half way activates the autofocus feature. It’s handy, quick and can lead to some compositional issues.
Center of the frame syndrome
The autofocus sensors are most accurate at the center of the viewfinder. Because of this, there are a lot of photographs with the subject placed in the exact center of the frame. Usually, a subject in the dead center of the frame is a poor composition. Not to mention that much of the frame is wasted because of the extra room above the subject’s head. Yes, the camera can be focused then, while holding down the shutter release half way, re-frame the shot. Press the rest of the way to make the exposure. Great! Only this has to be done each time a photo is made. There has to be a better way.
Advantages of BBF
Auto servo follow focus activated with a back button keeps Amy in perfect focus throughout her run and jump.
Back button focus (BBF) has a pair of benefits over the standard shutter-release-half-way-down to focus. First once the camera is focused on the subject and the BBF button is no longer pressed, all of the photos made from then on (until the BBF is pressed again) with have the same point of focus. Compositions may be explored. The focus remains the same as long as the distance from the subject to the camera is unchanged. Need to move in closer or farther away? A quick press of the BBF button locks in a new focus point. The second benefit involves servo autofocus. Servo autofocus allows a subject moving toward or away from the camera to be continually in focus. Another name for it is follow focus. While the half pressed shutter release for focus will allow the camera to follow focus, as soon as the photo is made, the servo will stop until the shutter release is press halfway down again. Holding down the BBF button keeps the servo autofocus running all the time no matter how many times the shutter is released. It’s super handy for fashion, sports, no matter if it’s youth soccer or a pro at work on American football. It can’t be beat for motorsports or air shows.
Motorsport Photos courtesy & ©Peter Falkner
Decouple autofocus from the shutter release
Most DSLR and mirrorless cameras offer this feature. I say most because I’m certain there is one or maybe two models in the world that don’t. This is always a custom setting that the photographer has to make to move the focus actuation from the shutter release to a button on the back of the camera. Hence the name, back button focus. Listing all of the popular cameras and how to set back button focusing is not practical. Find out how to set your camera with an Internet search on back button focus. Add your camera make and model to find a tutorial on how to set up this feature.
You’ll like it. It might take a while to remember to press the button you have programmed to handle back button focusing. Once that hurdle is overcome, back button focusing is a powerful technique and a key to better compositions and subjects-in-motion photography.
All photographs ©Kevin Ames unless otherwise noted.