How does the Lumia Refocus app work on my phone?

When pressing the camera button or the screen, the camera will do a focus sweep, to analyze where the focus is in the scene, then it captures images based on the focus sweep. The focus sweep takes between 1-2 sec and the capturing between 1-1.5 sec, depending on light conditions and how many pictures that will be taken (depending on the analyze form the focus sweep) and device. After capturing the images are analyzed and aligned. Then you can start to change the focus in the image.