# Field of view

360-degree field of view of the Milky Way behind the Very Large Telescope in Chile. Two streams of stars seem to cascade down like waterfalls due to optical effects.[1]

The field of view (also field of vision, abbreviated FOV) is the extent of the observable world that is seen at any given moment.

## Humans and animals

Different animals have different fields of view, depending on the placement of the eyes. Humans have an almost 180-degree forward-facing horizontal field of view, while some birds have a complete or nearly complete 360-degree field of view. In addition, the vertical range of the field of view in humans is typically around 180 degrees.

The range of visual abilities is not uniform across a field of view, and varies from animal to animal. For example, binocular vision, which is important for depth perception, covers only 120 degrees (horizontally) of the field of vision in humans[citation needed]; the remaining peripheral 60 degrees have no binocular vision (because of the lack of overlap in the images from either eye for those parts of the field of view). Some birds have a scant 10 or 20 degrees of binocular vision.

Similarly, color vision and the ability to perceive shape and motion vary across the field of view; in humans the former is concentrated in the center of the visual field, while the latter tends to be much stronger in the periphery. This is due to the much higher concentration of color-sensitive cone cells in the fovea, the central region of the retina, in comparison to the higher concentration of motion-sensitive rod cells in the periphery. Since cone cells require considerably brighter light sources to be activated, the result of this distribution is that peripheral vision is much stronger at night relative to binocular vision.

## Conversions

Many optical instruments, particularly binoculars or spotting scopes, are advertised with their field of view specified in one of two ways: angular field of view, and linear field of view. Angular field of view is typically specified in degrees, while linear field of view is a ratio of lengths. For example, binoculars with a 5.8 degree (angular) field of view might be advertised as having a (linear) field of view of 305 ft per 1000 yd or 102 mm per meter. As long as the FOV is less than about 10 degrees or so, the following approximation formulas allow one to convert between linear and angular field of view. Let $A$ be the angular field of view in degrees. Let $L$ be the linear field of view in feet per 1000 yd. Let $M$ be the linear field of view in millimeters per meter. Then, using the small-angle approximation:

$A \approx {360^{\circ}\over 2 \pi} \cdot {L\over 3000 } \approx 0.0191 \times L$
$A \approx {360^{\circ}\over 2 \pi} \cdot {M\over 1000 } \approx 0.0573 \times M$
$L \approx {2 \pi \cdot 3000 \over 360^{\circ}} \cdot A \approx 52.36 \times A$
$M \approx {2 \pi \cdot 1000 \over 360^{\circ}} \cdot A \approx 17.45 \times A$

## Machine vision

In machine vision the lens focal length sets up the fixed relationship between the field of view and the working distance. Field of view is the area of the inspection captured on the camera’s imager. The size of the field of view and the size of the camera’s imager directly affect the image resolution (one determining factor in accuracy). Working distance is the distance between the back of the lens and the target object.

## Astronomy

In astronomy the field of view is usually expressed as an angular area viewed by the instrument, in square degrees, or for higher magnification instruments, in square arc-minutes. For reference the Wide Field Channel on the Advanced Camera for Surveys on the Hubble Space Telescope has a field of view of 10 sq. arc-minutes, and the High Resolution Channel of the same instrument has a field of view of 0.15 sq. arc-minutes. Ground based survey telescopes have much wider fields of view. The photographic plates used by the UK Schmidt Telescope had a field of view of 30 sq. degrees. The 1.8 m (71 in) Pan-STARRS telescope, with the most advanced digital camera to date has a field of view of 7 sq. degrees. In the near infra-red WFCAM on UKIRT has a field of view of 0.2 sq. degrees and the forthcoming VISTA telescope will have a field of view of 0.6 sq. degrees. Until recently digital cameras could only cover a small field of view compared to photographic plates, although they beat photographic plates in quantum efficiency, linearity and dynamic range, as well as being much easier to process.

## Photography

In photography, the field of view is that part of the world that is visible through the camera at a particular position and orientation in space; objects outside the FOV when the picture is taken are not recorded in the photograph. It is most often expressed as the angular size of the view cone, as an angle of view.

## Video games

The field of view in video games refers to the part you see of a game world, which is dependent on the scaling method used.[2]