The DOF calaculator will give you the answer. At 400mm and f5.6 you can get from 3300' to infinity in focus. At 400mm and f16 you can get from 1500' to infinity.
Jim 'Carnac' Carnahan
|Spring evening by Kaappo|
from Landscape #1
|Bringing Home the Bacon by Domenick Creaco|
from My Best Photo of the Week