In Cycles there are two different render passes which seem to give some kind of depth information: the Mist pass and the Z-Buffer pass. I know that the z-buffer gives the actual distance (thus producing values >1) while the mist pass's range is
[0,1]. But even after normalizing the z-buffer pass the two are still not the same, the mist pass is darker.
Here is a comparison (starting with the standard render).
So what is the mathematical difference between a mist pass and a normalized z-buffer?