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The visual angle is the angle a viewed object subtends at the eye, usually stated in degrees of arc. It also is called the object's angular size. The diagram on the right shows an observer's eye looking at a frontal extent (the vertical arrow) that has a linear size , located in the distance from point . For present purposes, point can represent the eye's nodal points at about the center of the lens, and also represent the center of the eye's entrance pupil that is only a few millimeters in front of the lens. The three lines from object endpoint heading toward the eye indicate the bundle of light rays that pass through the cornea, pupil and lens to form an optical image of endpoint on the retina at point . The central line of the bundle represents the chief ray. Likewise for object point and its retinal image at . The visual angle is the angle between the chief rays for and . ==Measuring and computing== The visual angle can be measured directly using a theodolite placed at point . Or, it can be calculated, in radians, using the formula, . However, for visual angles smaller than about 10 degrees, this simpler formula provides very close approximations: : 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「visual angle」の詳細全文を読む スポンサード リンク
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