When you first buy a DSLR, you’ll learn the ‘focus and recompose’ technique where you half press the shutter button to lock focus (and exposure), then recompose the scene to how you want it before fully pressing the shutter button to take the picture.
After a while you may well start to think about the peculiarity of this method, which ties together focus and exposure. The next step for many is to investigate the little AE-L/AF-L button to the right of your camera’s viewfinder. Using this button you can separate the two functions of locking focus and exposure, allowing greater control over these two central aspects of photography.
For a long time I used the AE-L/AF-L button to lock exposure. I put it onto the AE-L (hold) mode, where it locks exposure so long as you keep the button pressed. Recently I’ve investigated an alternative that seems popular with many photographers – a method commonly known as back button focus.
To use this method, go to option f2 on your Nikon D5100. Select AF-ON. Then, go to option a1 and choose Release instead of Focus. This prevents the possibility of ‘focus trap’, where the camera won’t let you take a picture.
Now that you’re ready to use the back button focus method, be prepared for a bit of a learning curve where some shots will be out of focus – it’s inevitable that after associating locking focus with pressing the shutter for so long, you’ll intuitively think this is still happening for a while, especially in time-sensitive situations. Instead, the point of back button focus is that you now lock focus with the AF-ON button instead. Once focus is locked, you are free to recompose and take as many pics as you like, knowing that focus remains locked on your subject.
To use back button focus:
1. Point the central focus point of your camera at the subject you want to focus on.
2. Press the AF-ON button to lock focus on this subject
3. Recompose the scene.
4. Press the shutter release button. Alternatively, half-press the shutter release button to lock exposure, then recompose again and fully press the shutter release button.
Commonly cited advantages of this method include:
- You can combine AF-C and AF-S modes. By holding down the AF-ON button in AF-C mode, your camera will track the movement of the focus subject. Yet by just pressing AF-ON once, you will get a normal AF-S focus, even in AF-C mode. Therefore you get the best of both worlds.
- Portraits – lock focus precisely on the eye of your subject after choosing a suitable aperture. Then, feel free to recompose and shoot away to your heart’s content.
- Wildlife/Sports – lock focus on your subject. If something comes between you and your subject, you don’t need to worry about refocusing afterwards, as your focus will remain locked on the original subject.
Many photographers I’ve asked say that they use back button focus, that it takes a while to readjust to this method but that once they have they never go back. Give it a go and see if you like it.