A range differentiator useful for auto-focusing, the range differentiator including an image generator (540, 130, 132) providing an image of a scene at various physical depths, a depth differentiator (132) distinguishing portions of the image at depths below a predetermined threshold, irrespective of a shape of the portions, and providing a depth differentiated image and a focus distance ascertainer (132) ascertaining a focus distance based on the depth differentiated image.