I am trying to reverse the effect of the Defocus node as shown below :
As you can see the Front is being blurred and the back is focused , is it possible for the front to be focused instead?
Add a vector normalize node and a color ramp before the Z input on the defocus node. Playing with the sliders on the color ramp you should be able to find the point where you want to focus.
In camera properties tab alter the focus distance.