Saving Z-Buffer?

I cannot seem to figure out how to save the Z-buffer in a separate file…

I rendered the scene, and attached a file output node to the Z of the RenderLayer node.
I want the Z-buffer in 32 bit, so I set the format to RAW targa (I cannot read OpenEXR with my external application).
I created an extra ‘check node’ with a normalise and a viewer node, which outputs fine (shows me a recognisable depth map), although I don’t want to normalise the 32 bit z-buffer I’m saving of course!

However, the raw tga file is completely white (in the hex editor it shows only ff’s)! Any idea what I’m doing wrong?

May be the Z information is stored in the alpha channel of Targa, use the gimp of photoshop and check all channels of you image. I remember that one program save the zbuffer in alpha channel.
Also, i don’t know the deep of your scene, but if there is only a object near you the z information of that object will be almost the same to the human eye, increse the contrast or tone map the image to reveal the z information.
hope this help, Agus