Back-Button Focusing is the Swiss-army knife of the various focusing modes. It is easy to setup, use and a time-saver in a wide range of situations.

By default, focus acquisition and shutter release are coupled to a single button – the shutter release. Half-pressing activates and acquires focus, while a full press releases the shutter for the image to be taken.

In contrast, back-button focusing separates these two functions and reassigns focus acquisition – usually – to the AF-ON button.

The benefit of this is [1] to enable single point and continuous focus from a single button. Pressing and releasing AF-ON offers single point focus and pressing and holding AF-ON offers continuous focus. When not set up, the focus mode dial must be toggled to switch between these modes – a fiddly and time-consuming process; and [2] to enable pre-focusing and lock-on to a focus point. Pressing and releasing locks single point focus and makes it possible to take a number of frames at that focus distance without engaging the focus motor – an effective way to capture a series of images without uncertainty about the accuracy of focus.

Set-up (using X-T2 Firmware v4.0)

To set up back-button focus quickly [1] Use or assign the AF-ON button and [2] SETUP > BUTTON/DIAL SETTING > SHUTTER AF OFF

Use it when [1] single point focus and continuous focus are needed interchangeably, [2] distance to the subject is fixed and there is little or no movement, [3] in low light photography with a deep depth of field and [4] for HDR images.

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