It just looks fake. What caught my attention is those sharp borders around objects that are in focus - it's typical for faked dof and doesn't look good. Also, if you have a focal point somewhere in the middle of the scene, then not only should the background objects be blurred, but also the area that is close to the camera. Why not make DOF in Corona? If you want it to be subtle, then it shouldn't render much slower at default settings.