BBF - Back Button Focusing

This week I saw a post on Facebook where a friend was talking about seriously starting to use Back Button Focusing. I know there are lots of opinions and articles on this topic but one more will not hurt. Please note, this has nothing to do with back focusing. Before we go to far into the BBF stuff let’s get familiar with camera focusing. Most modern DSLR Cameras have the ability to manually focus on your subject or automatically focus.  Some lenses do limit you to manual focusing as they have no motors and electronics to drive the focusing elements.Automatic or Auto Focus has a few modes, One Shot, AI Focus and AI Servo in Canon speak and AF-S and AF-C in Nikon speak. There really should be some ISO standards for this kind of stuff.One Shot and AF-S basically means the camera will trigger the lens to auto focus on the subject, lock the focus for you to capture the image.AI- Servo and AF-C means the camera will trigger the lens to auto focus on the subject and then do its best to keep the focus on the subject while the subject is in motion.Canon has AI-Focus which is supposed to intelligently detect motion and trigger the appropriate auto focus mode, one shot of AI-Servo. This can be problematic so let’s leave it out of this article.No lets understand how we get this to work. By default your camera is set to focus and read the exposure when you half press the shutter button. Fully depressing the shutter button takes the picture. Not a bad way to do your photography.So what is the problem?  If you have a static subject, and use center auto focusing point (it is the most sensitive AF sensor) you would half depress the shutter button.  This action will initiate the auto-focus and then you will see or hear focus confirmation, now you can depress the shutter all the way and capture your image. Optionally, keeping the shutter button half depressed you can recompose and then press the shutter button all the way and take your image. This system works great for static subjects. Now you are trying to photograph moving subjects. You can’t half depress the shutter and lock focus and then take the shot because your subject will have moved and no longer in focus.You switch your camera to AI-Servo (canon) or AF-C (Nikon). You are capturing great action images and you notice a great subject that is static. You point your camera, focus and recompose – Oh! NO! you lost focus and more Oh! No! the opportunity is gone. What could you have done? You could have switched the camera back to One-Shot or AF-S or switched your lens to manual focus after getting focus and then pressing the shutter to grab the shot. This would definitely be too late.To overcome this issue you need to separate the focus initiation from your shutter release. Now you need to assign focusing to some other button. Typically this is one of the buttons on the back of your camera and hence the term Back Button Focusing or BBF.Using your custom functions or menu functions set your shutter to meter only, assign the AF-On button to initiate focus. Now you will use your thumb to depress the AF-On button to initiate focus and then use the shutter button to capture the image. There are two steps but well worth it.One of the greatest benefits is when you want to lock focus, you simply release the AF-On button.  The lens will not refocus till you depress the AF-On button again. So for any action photography you can be ready for any motion and yet be in a position to lock focus when you need to.A huge benefit, you can leave your camera in AI-Servo or AF-C mode and never have to switch to One Shot or AI-S mode. When you use BBF, as long as the AF-on button is depressed the focusing system will remain active in follow focus mode tracking your subject (AI-Servo or AF-C), release the button and focus stays locked. So for stationary subjects, all you need to do is to tap the AF-ON button and focus system will focus and lock.  Remember to release the AF-On or the camera will continue to try and refocus.Now once you set BBF you need to be aware that this will take some getting used to.  Your fingers and brain need a major reset.  You will miss a few good shots but once you are used to this system you will wonder why you have been wasting so may good opportunities.Warning for Nikon users: The back button focusing button AF-ON will not trigger the lens vibration reduction “VR”. The shutter button must be half depressed to trigger VR.