These controls let you add depth of field to the rendering. Depth of field is available only when you render a Camera or Perspective view.

MAXScript Language Reference
3ds Max Objects
RendererClass
Quicksilver_Hardware_Renderer : RendererClass.
When on, the rendering generates depth of field. Default=off.
When From Camera (the default) is chosen, the Quicksilver renderer uses the camera's Target Distance and f-Stop settings to generate depth of field.
When Override Camera is chosen, you can choose values for generating depth of field that differ from the Camera settings.