Today’s Question: When using back button focus, do you recommend setting the camera to continuous or one shot autofocus?
Tim’s Quick Answer: I absolutely recommend using continuous autofocus in conjunction with back-button focus, so you have maximum flexibility.
More Detail: When you enable back-button autofocus rather than having autofocus connected to the shutter release button, you have a button that is dedicated solely to autofocus. To maximize the flexibility of this approach, I recommend using continuous autofocus rather than one-shot autofocus.
One of the great things about using back-button autofocus is that you are able to exercise better control over when autofocus is activated. When you want to focus, you press the back-button focus button. When you don’t want autofocus, you simply don’t press the button. Metering and capturing a photo are still controlled by the shutter release button.
With back-button focus enabled and your camera configured to continuous autofocus, you can actually switch between the equivalent of continuous autofocus and one-shot autofocus instantly.
If you want continuous autofocus, press and hold the back-button focus button. Naturally you might be tracking a moving subject while holding the back-button focus button for example.
If you want the equivalent of one-shot autofocus, start by pressing and holding the back-button focus button until focus is acquired on the desired subject. Then release the back-button focus button so the camera will discontinue autofocus. This provides the same behavior as one-shot autofocus. Keep in mind, of course, that after setting this one-shot type of autofocus you’ll need to maintain the same distance to your subject to maintain focus, or you’ll need to re-establish focus if you need to move.