click the presets button and select luminance depth
click on the shader assigned to the layer if not selected and you should see settings like figure 1
IMPORTANT – You need to Break Connection on old min and old max ( this is so you can adjust the depth, by default it is going to render a pretty flat image, not usuable if you want to use it for detailed DOF )
Select maya software as your renderer and test a render, its going to look flat, go to next step
Adjust the old min and old max numbers, each time testing a render to get a nice even step from white to black. These numbers are dependent on your scene size and camera, so trial and error is the key here. ( figure 2 )
Once your happy with it, set your anti-aliasing to high and render out the final output.
