Back Button Focus
So what is back button focus?
Most DSLR cameras set the focus by pressing the shutter button halfway down then fully down to take the picture. Back button focus simply changes the method of focusing by assigning the focus function to another button on the back of your camera. This means that your index finger is now solely responsible for releasing the shutter and taking the picture. Using your thumb to press the button assigned on the rear of the camera to focus.
So, why use it?
When you change the focus button to the rear of the camera you free up your shutter button to to be, well, a shutter button! Whilst this might seem like not much of a ground breaking idea just think about it for a moment and consider photographing a moving subject like sports photography. Within that split second it can take to set focus and then release the shutter your subject would have moved. The result? a blurry and out of focus image.
By moving the focus and shutter functions to work separately you can set focus and get the shot simultaneously. By doing this and saving the split second whilst tracking a fast moving car as shown below allowed me to get a sharp focus on the car as it spun of the track. Using the shutter button to focus and take the shot would have more than likely ensured the car was out of focus and blurry at this point.
Continuous Focus Mode
Using the back button focus mode is great but if you photograph moving subjects a lot you can really take your advantage of using this function in conjunction with Continuous focus mode as well.
Continuous focus mode (AI Servo for Canon and AF-C for Nikon) allows you to constantly track your moving subject and keep it in focus all the time. By continuing to press the focus button your camera will automatically re-adjust its focus as your subject moves.
In the photo below I was able to track the movement of the Breitling Wingwalkers flying towards me by keeping my thumb on the focus button simultaneously as I released the shutter with my index finger. Even though the aircraft were flying towards me and the plane (no pun intended!) of focus was changing by the split second, by using back button focus and continuous focus mode together I was able to achieve great focus on an otherwise difficult shot to track.
Give it a try or are you already using back button focus? I’d love to hear your thoughts and changes you have seen in your photos since making the jump.
If you haven’t already tried this give it a go and let me know how you get on!
It may take some time to get used to the change and focus technique especially as like many others you have probably always shot a DSLR with one button for focus/shutter.