The scope of the human field of vision is extensive, covering the width, height and depth of the spectacle being viewed, but at
broad
angles sight is indistinct. In order to see details we must focus on a small, specific area. The amazing flexibility of the eye
lens
which can alter both depth and length of focus, enables the eye to quickly scan the spectacle being viewed, and to focus on one detail or another. Thus the eye can scan both close and distant planes of vision.
A basic tenet of focusing is that it is impossible to simultaneously focus on two objects at different distances from the eye. When you focus on an object close to you, the background becomes blurred, and vice versa .
We tend to organize the field of vision, and the details within it, so that we can identify the limits of each object, classify the object, and incorporate it into our conceptual world. Focusing is for the most part done unconsciously, but it can be controlled by the attention mechanism. Without this being conscious or deliberate, the eye skims through the field of vision and focuses on objects according to a certain sequence of stimuli: light objects will be focused upon before dark ones, asymmetric before symmetric, moving before stationary, colorful before monochromatic and so on .
