On my first attempt with depth of field, Here is an example I got. Attached is the .blend for anyone that wants to take a look and let me know what you think. Very simple but you have to learn somewhere!
You cannot animate this setup but you can if you use the DoF node so, it’s sort of a trade off between focal point or focal plane thickness. I would suggest that you adjust your color ramp so that you have a smoother transition between your focal plane and the background because that’s a fairly harsh transition. Also using FSA rather than OSA will give you exponentially better results when working with depth channels. Finally lower the filter (Gauss in this case) to it’s lowest setting (0.50) for best quality…this is basically the pixel spread between image samples and higher settings result in rougher antialiasing. Note that the filters work backward from their original intent when using FSA as opposed to OSA, i.e. gauss is sharpest while catrom is blurriest.
You can see how all of this is done in the posted screenshot…the SaveBuffers option gives you the FSA option.