It works because the human eye, and camera lenses
has a very narrow range of focus when looking at small things close up.
By narrowing the depth of field (the distance from the subject where things are in focus) using selective blurring on an image, you trick the eye into thinking it is doing the same thing.
(
chenobble rocking his explorer beard on, Thu 27 Nov 2008, 12:16,
Reply)