can't use z depth to control blur node

Support Compositing and Post Processing
1

i can’t use z depth to control fast gaussian blur node. in the attachment file, i want the cubes far away from camera blur more.

Attachments

composite problem.blend (424 KB)

2

Try a Defocus node http://wiki.blender.org/index.php/Doc:2.6/Manual/Composite_Nodes/Types/Filter