Note from admin - I just ran across this great tutorial showing how to use maxscript and pflow to render fast, simulate dof based on camera focus.
This script will define particle’s scale and transparency depends on camera’s focus. Now you can animate the geometry or the camera and render the particles with scanline. Don’t forget to cache all the particles for viewport/render using the Cache operator.
This setup renders pretty fast as opposed to mental ray’s or vray’s honest dof. And we have fast bokeh effect with the ability to inceract with scene geometry.