Possible workflow for depth of field:

Maya internal:
cameraShape > Depth of Field (set distance to focus)
or
physical_lens_dof (set plane = distance to focus*-1(reverse)) -> mental ray Lens Shader

Post process:
Maya: zDepth using shader
or
renderLayer preset luminance depth (set surface shader set range old min/old max)
+
Photoshop lens blur using DOF channel
or
Photoshop + DOF pro
or
After Effect (as shown above): effect > compound blur (can be used over animated sequence, keyable blur value)