I have found it a much more responsive approach to getting accurate focus for both action and static situations.
And, more importantly, in static situations that instantly turn into action.
How it works:
Basically, we’re going to disable focus for our shutter release, and switch it exclusively to a button on the back of the camera.This will decouple the shutter release and AF functions, so the ONLY thing your shutter release will do is snap the photo – that’s it. All autofocus will be controlled from a button on the back of your camera. And ONLY from that button. Initially, most people wonder why this is a benefit at all, so let me show you the benefits.
1. Back button focus allows you to easily lock focus
With the standard camera setup where the AF is controlled by the shutter release, every time you take your finger off that button and then put it back on again, it will refocus. You need to keep the shutter button halfway down or you have to use AF-Lock and keep the finger on that button then frame the image. With back button AF, you focus once and when you take your finger off the button, the focus distance stays locked. Now you can recompose your image without worrying that your camera is constantly refocusing in the wrong places or you by accident unlock AF-Lock.
2. Easy to swap between auto and manual focus
All new AF lenses offers full-time manual focus override. It means you can use manual focus at the same time as autofocus. It can become handy for macro or any still image photographers who need or just enjoy to have focus in their hands. Or more often they use autofocus, but time to time they want to adjust / fine-tune focus manually. The problem appears when the shutter release controls the AF at the same time. Pressing the trigger activate the AF and the camera will automatically refocus. Having the back button is the only way how to have manual and autofocus fully under control.
3. Allows you to easily swap between continuous and single autofocus
With back button autofocusing, holding the button down turns on the continuous autofocus. When you don’t need the continuous focus, tapping the button once activate the focus in on still subjects. You don’t need to switch between AF-S/AF-C on camera body anymore. You have it under control by one finger and the time you spend on that button. That means sports, street and even wildlife photographers can shoot the action and the stills without taking their eye off the viewfinder to adjust the focus mode.
Setup your camera
• To set this up for most Nikons, you’ll go under your Custom Functions menu – Autofocus.
• First, make sure your AF-C priority selection is set to one of the “Release” modes and NOT to “Focus”. If it’s set to “Focus,” you won’t be able to use this method in a focus and recompose situation.
• Now, if you have a dedicated AF-On button, scroll down in your autofocus custom functions and look for “AF Activation”. Select AF-On and you’re done. If you DO NOT have a dedicated AF-On button you’ll need to reassign a button. You’ll want to go down to “Controls” in your custom functions menu and look for something that says “AssignAE-L/AF-L lock button”. Under that menu, choose “AF-ON” and you should be all set.