
The angular extent of the sky that an instrument can observe at one time.For the human eye, the field of view is about 130 degrees vertically and 200 degrees horizontally (including peripheral vision), but only a small central region, the fovea, provides high acuity. This is why we move our eyes and head to scan a scene. In photography and videography, the field of view is determined by the lens focal length and the sensor size; a wide-angle lens has a large field of view, while a telephoto lens has a narrow one. In virtual reality and augmented reality, the field of view is a key factor in immersion, with wider fields providing a more convincing sense of presence.
The concept of field of view has been understood since the early days of optics, with Galileo and Kepler designing telescopes with specific fields of view. The term became more formalized in the 19th century with the development of photographic astronomy. Modern wide-field surveys began in the 20th century with Schmidt cameras, which were designed specifically to provide large fields of view for sky surveys.
The field of view is determined by the geometry of the optical system. For a simple lens, the field of view is given by the angle subtended by the image sensor (or film) at the lens's nodal point. Mathematically, it is approximately 2 * arctan(d / (2f)), where d is the sensor dimension and f is the focal length. A shorter focal length or a larger sensor increases the field of view. In telescopes, the field of view is also affected by the eyepiece or camera attached to the focal plane. For wide-field surveys, telescopes are designed with short focal ratios (fast optics) and large detectors, sometimes using multiple CCDs arranged in a mosaic to cover a larger area.
Field of view is used in designing telescopes for astronomical surveys, cameras for surveillance and photography, and optical systems for autonomous vehicles. In medicine, endoscopes and surgical microscopes are designed with specific fields of view to balance visualization and maneuverability.
The human eye's field of view is about 200 degrees horizontally, but if you hold your thumb at arm's length, it covers about 2 degrees—the same angular size as the full Moon.





