Visual looming syndrome "fear of pointy objects hitting the eye", "weird sensation behind the eyes", "difficulty in focusing on objects nearby, which are moving and are not operated by the observer, such as windscreen wipers or a pencil someone else is holding". In these studies visual looming syndrome is often referred as sharp edges eye syndrome (SEES). "Looming" is a term used in the study of the perception, as it relates directly to psychology. Looming refers to the rapid expansion in the size of any given image. As the image becomes increasingly large on the perceiver's retina, i.e., when an object "looms", there
Depth of field to object size is independent of focal length, and depends only on the object size and its distance from the subject. This discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the object and image nodal planes, and for which the pupil magnification is unity. Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses. For an asymmetrical lens, the DOF ahead of the subject distance and the DOF beyond the subject distance are given by and where formula_25 is the pupil magnification. Combining