Back button focus is used by a lot of professional wildlife and sports photographers. It's just another way to focus and capture an image. It gives you a little more control of what's going on but it is a step that requires two fingers to work together instead of only using one. I have used it and to be honest I did not feel it benefitted me. I actually use a method completely opposite to traditional back button focus and it works much better for me.Back button focus is different than the AF/MF. I have been on a couple of workshops where they talk about BBF for wildlife photography, but using a Nikon. On a Canon I think they call it something else in the camera manual. I am still confused about what it is for.
"Instead, the action of focusing is moved to a button on the back of the camera – usually the AF-On button. Back button focus separates the focus and shutter release functions, moving the former to the AF-On button at the rear of the camera."
I read this off the internet. I guess I need to do more Googling on the subject.
Thanks for trying to help.
To understand back button focus you have to understand the two basic focus modes on cameras. It's beneficial to understand how these modes work for those trying to get better at photography. If your camera is on the wrong mode you will get a lot of out of focus images. Here is a crash course....
There are two basic focus modes on pretty much all cameras. Single focus mode (called one-shot on canon, single-servo [AF-S] on nikon) and continuous focus mode (called AI-servo on canon, continuous servo AF [AF-C] on nikon). Single mode is for landscapes or portraits when nothing in the picture (yourself included) is moving. Continuous mode is for shooting things that can slightly move.
When you press the shutter button half way the camera begins focusing. When in SINGLE focus mode (one-shot or AF-S) the camera will search for focus until it finds it and it will lock it in (usually the camera beeps or your little focus point changes colors). I think most cameras come default in this mode. It works fine for stationary objects but as long as you hold the shutter button half way down the focus will be locked in that one specific spot. If the person or animal moves forwards or backwards they will now be out of focus until you let go of the shutter button and push it halfway down again to refocus.
When you press the shutter half way in CONTINUOUS focus mode (AI servo or AF-C) the camera will acquire focus and constantly adjust it until you take the picture. This way if the person or animal moves further away the AF will adjust for that. Continuous AF is the best mode for anytime you expect the subject or yourself to move. This is the only mode to use for wildlife and sports.
There is one major issue you run into when using continuous focus mode. Say you are using a single AF point in the middle of your viewfinder to focus (you should be). You place it on a bird and push the shutter halfway and the camera focuses on the bird and keeps slightly adjusting the focus to make sure it is accurate. Before you take the picture you want the bird to be on the right side of the screen, not directly in the center where your AF point is. Well if you move a little left and the AF point gets off of the bird the camera will now immediately focus on the background. So the AF point always has to be directly on the bird for the bird to be in focus when using CONTINUOUS AF mode. The only way to make this work is to physically move the AF point to right side of the viewfinder then put it on the bird and take the image. This takes time to adjust and by then the bird might have moved to a different spot. This is where back button focus comes in to play.....
All back button focus does is move the focus button from "halfway holding the shutter release" to an actual button on the back of the camera you operate with your thumb. So pushing the button on the back of the camera is the exact same thing as holding the shutter release button half way down. Here's why it is beneficial. Your AF point is in the middle of your viewfinder and you put it on the bird, then you hold down the back button focus button so it focuses on the bird, then you LET GO of the back focus button. The focus is now locked in position (like if you had switched to single AF mode). Now you can move the camera to the left real quick, press the shutter release to take an image, and get a picture with the bird on the right of the screen.
Back button focus allows you to go from continuously focusing to locking in focus (so you can quickly compose), then go back to continuously focusing without having to go in a menu and change your AF settings. It works and a lot of people use it.
I like the method I use a lot better though. I use the normal shutter button to focus just like everyone else. Hold the shutter release half way down to focus and the camera continually focuses until I take the image. I have my camera set to continuous focus which everyone should if you shoot moving animals. I have a single AF point set in the middle of my viewfinder. What I do different is I set the back button up to disable/lock in focus. So when I see a bird I put the AF point on the bird, press the shutter release half way, the camera focuses on the bird and continuous to slightly adjust focus to keep it right.... then when I want to recompose and move off the bird to put him on the right side I use my thumb and hold down the back button. This locks the focus wherever it was at. While holding the back button I move the AF point off of the bird and push the shutter release all the way to take the image. That's it. So I get to focus the normal way like everyone else the majority of the time without using my thumb, then if I need to compose differently I hold the back button, move a little and shoot. It accomplishes the same goal as traditional back button focus but instead of learning an entirely new way to focus you keep doing it the normal way and whenever you need to you lock focus to recompose you do it with the back button. Pretty simple and it has worked well for me....
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