I've chatted about depth of field, here's how to see it calculated -
Check out "Photo Tools"
Note, I've used the focal length value from Brian at AnandTech.
In this example, I've imagined a snapshot of someone about 5' away that I've focused on. Closer than 3' and further than 18', things will be blurred. From about 7' to 18', things will be equally focused (loose definition for starters).
Apologies to my cousins using the metric system.