Depth of field issue with my focus empty target

Hi,

For the first time I would like to add depth of field to make my animation more realistic.
But I think because I set my camera focal lens to 600mm (I know… why? To decrease perspective effect, but I know now is too high) it’s a mess with DOF managment. Or maybe it’s another problem.

First it was impossible to use defocus node directly with z pass, so I tried to use it with a normilize node.
It works fine except that I just find out that moving my empty focus target doesn’t change anything to my DOF.
I can’t change my focal lens because I have to release this animation asap and I rendered all the frames in a render farm (and I’m tired with it).

I thought adding DOF : Rendering all frame at 1 sample to get DOF with Normilize node, and then apply defocus node to all my images. But I realized that I can’t get the focus I want in some parts of my animation because of this focal point issue.

So I think I will give up and produce my animation without DOF, except if someone have an idea???

Thanks for your time,

Jacques