Excluding diffraction, the CoC for a subject at infinity is the same size as the pinhole.
The reason for this is simple. For a subject at infinity, all light rays from a point on the subject are parallel. The rays that pass through the pinhole keep on going without converging or diverging (because they are parallel) until they hit the film. So they area they expose on the film is the same size and shape as the pinhole.
Last edited by andrew.roos; 04-28-2012 at 12:09 PM. Click to view previous post history.