So, what is BBF?  Well, it’s exactly what it implies: it’s using a button on the back of your camera to autofocus.  The default for most dSLR cameras is to press the shutter button halfway down to lock focus and exposure, then to fully press to actuate the shutter and capture the image.  However, using the default can be a little unreliable because if you lift up ever-so-slightly on the shutter button, you might accidentally lose your focus lock and end up focusing on something you didn’t intend to.  BBF solves this problem by separating the focus from the shutter, so once you lock focus, it’s locked until you choose to refocus again.

I’ll run you through setting up BBF on either your Nikon or your Canon, but if you have a different make or even the same make but different model, just refer to your User Manual.

We’ll start with the Nikon D300 pictured above.  You’ll see the AF-ON button is circled.  This is the button you’ll use to BBF. So, to set this let’s open the Menu and go to Custom Settings as pictured below.

Hit your OK button with Autofocus highlighted on the screen and then scroll down and choose ‘a5.‘ This will give you two options.  Select AF-ON only.  Hit your OK button again and exit the menu.  You’re done!  If you have another Nikon model, just look into the User Manual to see where the option is located and it’ll direct you where you need to go.

Alright Canon users, we’ll use the 40D for you.  You’ll see your AF-ON button circled below.

Alright, so now go into your menu and scroll over to the Custom Functions options.  Turn your dial to highlight C. Fn I – IV and press SET.  Turn the dial again to highlight C. Fn IV-1 and press SET.  Turn the dial again to set the value to ’3 – AE lock/Metering + AF start’ and press SET one last time.  Then you can exit your menu.

Again, if you have another Canon model, just look into the User Manual to see where the option is located and it’ll direct you where you need to go.

Note: depending on how comfortable or easy it is for your thumb to reach the AF-ON button, you might find it beneficial to switch the operations of the AF-ON button and the ‘*‘ button to the right of it.  To do this, just set your C.Fn II button to value ’1′ and you’ll use the ‘*‘ button to BBF instead of the AF-ON button.  It’s just a matter of preference, but don’t let it confuse you.

Alright, now that you have your camera set to use BBF, you need to practice a little bit.  The way I suggest doing this is to set your camera to use a focus mode of AF-S for Nikon or Single Shot for Canon and set your focus point to the center of the screen so that it doesn’t move.  This is just suggested for the practice exercise, so if you prefer AI Focus over Single Shot, then feel free to do what you like; do set the focus point to the center though.

Note: If you’re not used to this technique and have good lenses that are fast and quiet when they focus, you might not have confidence that the BBF is actually working.  Don’t worry, it is.

Choose your fastest lens (your nifty fifty will be perfect for this) and set it to its largest aperture.  Place a few things (3-4 small objects like coffee mugs will work) at different places on an uncluttered table.  Vary the distance of the objects to you and your camera, but be sure to place them so that they’ll all fit in your camera viewfinder.  The next steps describe the focus/recompose technique so if you’re already familiar, get to it.

Get as close as you can to your minimum focusing distance and center the closest object  in your frame.  Press the back button to focus on it.  Use the shutter button to activate your meter and dial in proper exposure, but don’t take the picture yet.  Once that’s done, recompose the image so that one of the other objects is centered in your viewfinder, but make sure that the original object is still in the frame.  Don’t refocus! Now, take the picture.

The object that you originally focused on should still have the main focus even though it wasn’t the object in the center of the frame when you pressed the shutter button.

It will take some time to get used to using BBF, but once you do, you’ll wonder how you ever took pictures without it.