ABSTRACT
If your camera is precisely aligned and the lens is focused at a specific subject distance, then all objects at precisely this distance are in focus, and strictly speaking, everything else is out of focus. In reality, however, our eyes have a limited optical resolution, and therefore, objects reasonably close to the focus plane also appear perfectly focused in the final print. This creates a zone of still acceptable focus surrounding the focus plane, and objects within this zone are considered to be in focus, while those outside are out of focus. This zone is called the depth of field.
