Lens breathing refers to the shifting of the angle of view of a lens when changing the focus over time. Higher end lenses try to minimize this effect, but recreating this effect in your work can make for a more beautiful focal change.

For creating lens brighting effect’s I used Nuke, but you can use any other software to do the same.Literally, it’s zooming the image while the focal change is happening. Don’t zoom your image too much be careful(5%max)