I first heard about back button focus when Steve Perry, over at Back Country Gallery uploaded this video to YouTube, a couple of years ago.
At the time I thought back button focusing wasn’t possible with my Nikon D3200 and other lower end cameras, as they all lack an AF-ON button on the rear of the camera. However, it turns out you can reassign the AF-E/AF-L button to the autofocus and then decouple the focusing from the traditional button, the shutter release.
After watching the video, I immediately switched the AF button assignment round and started using back button focusing. To start with it was rather strange. I kept forgetting that the shutter button wouldn’t do anything when it was half pressed.
One of the things that bugged me was that I keep protecting images left, right and centre. On the D3200, and other Nikon cameras, the image protect button is the AF-E/AF-L button on the back of the camera. I found hat with image preview on, I kept produced ecting every image I took because I was still holding the focus button when the image popped up on the screen, and I would lock it. This has a simple fix; turn off image preview.
The main benefit I have found from using back button focus is when using my Triggertrap kit for high speed photography. Triggertrap recommend manual focusing you camera and lens, to make sure the cable release doesn’t change the focus when triggering the shutter. (A common problem when the focus is attached to the shutter button.) I often forgot to change the camera or lens to manual, and when I did flick the switch on my lens, I moved the focus ring so slightly that the resulting image wasn’t sharp where it was supposed to be.
The advantage with using back button focus is that you can focus the camera on the target, and then trigger the shutter using Triggertrap mobile, without it changing the focus, or trying to hunt for focus in the dark.