Zeno Pelgrims has managed to create a physically accurate Arnold Camera Shader that simulates the multiple layers of glass and their effect on lens bokeh and vignetting. It’s only $10 and is getting me much better results than Nuke’s Zdepth node for those really tight macro shots. Yeah, the AA samples required is pretty high, but it’s a smart solution for special cases.
Check out his website for more information on how ZOIC works and how to purchase the lens shader.