On the Parameters rollout, a “Depth Of Field (mental ray)” choice supports the mental ray renderer's depth-of-field effects. To use this, turn on Enable in the camera's Multi-Pass Effect group. Also turn on Depth Of Field on the Camera Effects rollout of the Render Setup dialog.
The mental ray depth-of-field is exclusive of the multi-pass version of the depth-of-field effect. The mental ray renderer also supports motion blur for cameras, but the controls are not on the camera's Parameters rollout: use the Motion Blur toggle on the Object Properties dialog for camera objects. This setting has no effect on the default 3ds Max scanline renderer.
Sets the camera's f-Stop. Increasing the f-Stop value narrows the depth of field, and decreasing the f-Stop value broadens the depth of field. Default=2.0.
The f-Stop can have a value less than 1.0. This is not realistic in terms of an actual camera, but it can help you adjust the depth of field for scenes whose scale does not use realistic units.