If AF-ON only is selected for Custom Setting a7 (AF activation), the camera will focus only when the AF-ON button is pressed, freeing you to concentrate on the shutter-release button during portrait or sports photography and in other situations where you focus using AF-C.
The camera focuses while the AF-ON button is pressed and pauses when the button is released. If you press the shutter-release button while focus is paused, the camera will not focus again but will only release the shutter. If you use the sub-selector for focus-point selection and the AF-ON button to focus, you can quickly compose shots using only small motions of your right thumb.
