I usually do a custom depth map that I export as a alpha channel for PS. Then I use PS blur.
Here is the very simple way I prepare the map (it's usable in animations too): I assign to every object in the scene the same shader whose only parameter is a gradient in the luminosity. The gradient goes from white to black using 'object distance' as parameter; the object is a null in the scene that basically represents my 'in focus' point, so I can move it where I want or even animate it. No lights are used in the scene. The result is a render where objects fade from black to white depending on the distance from the null. I load the normal render in PS than I load this BW render as alpha channel and I play with PS blur reaching the best quality in a fraction of time used by standard DoF or Digital Confusion. Hope this helps
