How to use Depth blur node.

I use Depth blur node found a problem.

As shown, I put the focus of the camera at “Fusion 9” the object,but fuzzy things have appeared in the edge of the objects.It's not in conformity with the real camera.

I saw some of the tutorial, they're made the results of the different with me, I should, how to use Depth blur node？

I hope to be able to get everyone's help, Thank you.