Test setup for AF Fine Tuning of VR80-400 on my D300.
The side of the cigarette pack is parallel to the sensor plane, and the ruler is placed at an angle of 45° to measure the DOF distribution. The barcode is my focussing target.
It would have been better to use a flat ruler instead of this folding ruler.

In my opinion this setup is better than the traditional front/back focus charts,
because it has a focus target parallel to the sensor plane.