Back Button Focusing Explained
You hear lots of photographers talking about this but what is it and why should you use it?
Back-button focus will help you focus like a pro and if professionals use it then it must be worth looking at.
What is Back Button Focusing (BBF)
You may not have realised but you camera has several different ways of focussing!
That standard method is to halfway press the shutter button, the camera focuses, and then you press the shutter down the rest of the way to take your image. This is the default setting on cameras and the one most people use. Within this you have two options. AF-C (AF continuous, sometimes called continuous servo) is good use when photographing moving objects. When your camera is set to AF-C and you focus on a moving subject, for example a dog running towards you, the focus will stay on the animal so long as your shutter button is held half way down. In other words, the camera will keep re-focusing as the animal moves. That is, so long as you keep your shutter button held half way down. AF-S (AF single, sometimes called single area AF) mode, is good for photographing subjects that don’t move, such as flowers or portraits etc. It locks the focus on the non moving object that you want to photograph. You can then recompose the shot and take the photograph.
You press the shutter button, the camera takes the shot even if it’s not focused when you press the shutter down. This is not a great idea unless used in conjunction with BBF.
If you use BBF it removes the focus from the shutter button and assigns it to a function to a button on the back of the camera. So when you shoot, you press your back-button to lock focus and then press the shutter to take an image. This can be used in conjunction with option 2 above and may appear to be over complicating things but there are several benefits.
Why use Back Button Focusing
If your subject is in a spot where there is no focus point. In the past, you would have to focus, recompose, shoot and this is further complicated if in AF-C mode as the camera will refocus as you recompose.
The problem here is that after you release the shutter button you will have to focus again. You will end up refocusing, recomposing, shoot, repeat. This process is slow boring and not conducive to fast shooting or fine composition adjustments. With BBF, you focus once, recompose, and shoot until you're done. Unless your subject moves, you don't need to refocus button again.
When using live view it is also much easier to use the BBF option which helps particularly with landscape photography.
With the AF-C or AF-S choice listed above you would find that you could be in the wrong mode for what you are shooting and changing from on to the other is slow. With BBF you can - press the BBF focus release it and recompose same as AF-S mode - press and hold the BBF focus button with the focus point on your subject and you will operate as in AF-C mode
You will find your images are sharper using BBF as you will do more focusing and the camera will compensate for small movements
How to Setup Back Button Focusing
Consult you manual or go online and find a you tube video, but her is a guide but it may not work on all models.
Nikon All Nikons are not the same so this is a typical method. Menu Custom Settings Menu f (Controls) Assign AE-L/AF-L button Press = AF-On and Press + Command dial = OFF From here you select the AF-C focus mode from the AF selection button.
Canon Menu Custom Controls (C.Fn). Remove the AF-ON from the shutter button AE-Lock (*). Select the AF ON button and set it to AF. Set your camera's AF mode to AF-C.
Sony Menu Custom Settings AF w/Shutter = OFF Menu Custom Settings Custom key settings - AE-L Button = AF ON.