**System Information**
Linux and MacOS
**Blender Version**
Broken: 2.69, 2.71
**Short description of error**
Incorrect Z values with enabled Z pass.
**Exact steps for others to reproduce the error**
Camera positioned at (0,0,6) with no rotation and simple plane at the origin. Z pass enabled rendering.
The values in the Image-Editor for the Renderlayer/Depth should be all 6 but they are not. The values change from the center to the border and will even become as large as 6.5. When using the internal Blender renderer the behavior is as expected.