Field of View (FOV) is the total angular field captured, viewed, represented or displayed in a perspective image or view of a spatial scene. It describes the extent of space included within a particular visual, optical, graphical or imaging system.
The Perspective Research Centre uses Field of View as the preferred general term. Closely related expressions include Angle of View, Field of Vision, Visual Field, Area of Vision, Cone of Vision, Visual Cone, Pyramid of Vision and Viewing Angle, although some of these terms also possess other meanings and should therefore be distinguished carefully.
Field of view is fundamental to perspective because every view represents only a selected portion of spatial reality. Changing the field of view changes what is included within the image and can also strongly affect its apparent spatial structure, scale relationships, lateral distortion and sense of depth.
Field of View as an Angular Field
A field of view is fundamentally an angular extent measured from a particular viewpoint, eye-point, station point, camera or other perspective centre.
Imagine an observer looking towards a spatial scene. Rays extending towards the outer limits of what can be seen establish the angular boundaries of the view. The angle between these limits defines the field of view.
The field can be measured separately in different directions, particularly as:
- Horizontal Field of View — angular extent from left to right;
- Vertical Field of View — angular extent from top to bottom; and
- Diagonal Field of View — angular extent measured across the diagonal of a rectangular image or viewing field.
These values need not be equal. A rectangular image, camera sensor, cinema screen or visual field may have a considerably wider horizontal than vertical field.
Field of View and Direction of View
Field of View should not be confused with Direction of View or Line of Sight.
The line of sight specifies a single direction from the eye, camera or station point. The field of view specifies the angular extent surrounding that direction.
The Dictionary distinguishes two important uses of the expression Angle of View:
- Angle of View (1): Direction of Vision or Line of Sight.
- Angle of View (2): Field of View — the total angular field captured, represented or displayed.
This distinction is essential. Turning the head or camera changes the direction of view, whereas widening or narrowing the angular extent changes the field of view. Either operation may occur without necessarily producing the other.
Horizontal and Vertical Field of View
The Dictionary specifically distinguishes horizontal and vertical Field of View.
Horizontal FOV measures how much of the scene extends laterally across the view. Vertical FOV measures the corresponding extent above and below the central viewing direction.
This distinction applies to human vision, photography, cinema, optical instruments, perspective drawing, computer graphics and display systems. The proportions of the image surface and the design of the optical or projection system can cause these angular fields to differ substantially.
Field of View in Human Vision
The natural human visual field is much wider than the narrow field commonly represented by traditional rectilinear perspective drawings or photographs.
Volume 1 gives an approximate horizontal field of about 160 degrees for one eye and approximately 200 degrees for binocular vision, with roughly 120 degrees of binocular overlap. The binocular vertical field is approximately 135 degrees.
The Dictionary gives comparable ranges, recognising that measured limits vary with anatomy, testing methods and visual conditions. A monocular horizontal field may be approximately 140–160 degrees, while the combined binocular horizontal field may approach 180–200 degrees.
These figures are approximate rather than rigid universal limits. The important principle is that normal human vision encompasses a very broad angular region extending well beyond the much narrower central region normally employed in traditional graphical perspective.
Monocular Field of View
A monocular field of view is the angular region visible to a single eye when the eye and head occupy a particular position.
Because the nose and facial anatomy restrict vision towards the nasal side more than towards the temporal side, the monocular visual field is not perfectly symmetrical around the central line of sight.
The far lateral region of the total human field is particularly important because portions of the extreme left and right fields are visible to only one eye.
Binocular Field of View
The binocular field of view is formed by the combined fields of the two eyes.
A large central region is visible simultaneously to both eyes. Volume 1 identifies approximately 120 degrees of binocular overlap within a total combined horizontal visual field approaching approximately 200 degrees.
This central overlapping region supports binocular comparison, stereopsis and other binocular aspects of spatial perception. Beyond it lie lateral regions that are seen principally or exclusively by one eye.
Central and Peripheral Visual Fields
The human field of view is not perceptually uniform.
Vision is sharpest around the point of fixation and the central retinal region. As angular distance from the centre of fixation increases, visual acuity progressively decreases.
The peripheral visual field therefore contains much less fine detail than the central field, although it remains extremely important for detecting movement, broad forms, spatial change, contrast and events occurring outside the immediate point of fixation.
A field of view should consequently not be imagined as a uniformly detailed photographic image extending across the entire angular range of human vision.
Fixed-Eye and Moving-Eye Field of View
Volume 1 makes an important distinction between the visual field available to a stationary eye and the larger region explored when the eye moves.
The pyramid or field of sight associated with one eye describes the region visible while that eye remains in a fixed orientation. If the eye rotates while the head remains still, the direction of fixation moves and a different part of the surrounding environment enters the visual field.
The total region explored over successive eye movements can therefore be considerably larger than the visual field available from one fixed direction at any instant.
Movement of the head and body expands the explored spatial field still further. Human visual experience is therefore normally dynamic rather than restricted to one permanently fixed perspective window.
Field of Vision
Field of Vision is commonly used as a synonym for Field of View or Visual Field. The Dictionary nevertheless prefers Field of View as the general term.
In relation to human vision, Field of Vision describes the total angular region visible to the observer at a particular moment, comprising a small central region of high acuity surrounded by a much larger peripheral region of progressively lower acuity.
In graphical perspective, however, the same historical terminology has also been applied more narrowly to the limited field contained within a conventional Cone of Vision. These two meanings should not be confused.
The Conventional Cone of Vision
Traditional linear-perspective teaching often defines a restricted Cone of Vision centred upon the principal direction of view.
A total included angle of approximately 30–60 degrees is commonly recommended for a rectilinear perspective construction, with approximately 60 degrees often treated as an upper practical limit.
This restricted cone should not be mistaken for the total human visual field. It is primarily a practical graphical and viewing region intended to avoid conspicuous lateral stretching and other wide-field effects when a broad angular scene is mapped onto a flat rectilinear picture plane.
The human eye can see considerably farther into the periphery than this conventional perspective cone.
Inside and Outside the Conventional Cone of Vision
The Dictionary distinguishes between a central field inside the conventional Cone of Vision and the wider visual field outside it.
Inside the conventional graphical cone, a flat rectilinear perspective image normally produces less conspicuous lateral stretching.
Outside this restricted region, human peripheral vision continues, but an equivalent wide-angle rectilinear representation can produce increasingly large differences between central and lateral image geometry.
This explains why the approximately 60-degree construction limit found in traditional perspective texts is not a biological boundary of vision. It is a practical limit associated particularly with flat rectilinear representation.
Field of View and the Perspective Window
In traditional graphical perspective, the perspective window establishes the portion of the spatial scene selected for representation.
The artist fixes a station point and a direction of view, while the dimensions and position of the window establish the angular limits of the represented field.
Volume 1 therefore identifies three closely connected elements that must normally be stabilised when constructing a unified central perspective view:
- viewpoint or station point;
- viewing direction or angle; and
- field of view.
Changing any one of these can produce a different perspective image of the same spatial scene.
Field of View and Picture-Plane Size
For a fixed station point, the angular field represented by a flat picture plane depends upon the size and position of the selected picture area relative to that station point.
A larger picture window at the same distance can encompass a wider angular field. A smaller window encompasses a narrower field. Likewise, changing the station-point distance while retaining the same picture dimensions changes the angular extent represented.
Field of view is therefore fundamentally an angular property rather than simply the physical width or height of a drawing, photograph or screen.
Field of View and Viewing Distance
Viewing distance and field of view are closely related in both spatial observation and picture viewing.
Moving closer to a fixed object or picture causes it to occupy a larger angular field. Moving farther away causes the same physical extent to occupy a smaller angular field.
This relationship is particularly significant in perspective representation because an image constructed for one station point and viewing distance has a corresponding intended angular relationship when viewed from that location.
Very short viewing distances can require uncomfortably wide viewing angles and can reveal strong lateral or projection distortions within flat rectilinear images.
Narrow Field of View
A narrow field of view represents a relatively small angular portion of spatial reality.
Traditional linear-perspective drawings, conventional paintings, photographs, television images and cinema images often employ comparatively restricted fields.
Volume 1 notes that perspective pictures with a field around approximately 60 degrees can often tolerate considerable variation in actual viewing position without appearing grossly distorted. Because the represented angular field is relatively limited, the geometrical discrepancy produced by viewing the picture from a different station point may remain visually modest.
This contributes to the familiar fact that a perspective painting or photograph can usually be viewed convincingly from many positions rather than from only its geometrically prescribed station point.
Wide Field of View
A wide field of view incorporates a much larger angular extent of the surrounding scene.
As the field represented upon a flat rectilinear picture plane becomes increasingly wide, lateral regions of the image can undergo progressively large geometrical transformations. Objects far from the central viewing axis can appear stretched, enlarged or strongly altered in shape.
Wide-field representation therefore raises a fundamental perspective problem: how can a large angular field be mapped onto a limited image surface?
Different perspective systems solve this problem in different ways. A rectilinear method preserves straight lines but can produce strong lateral stretching, while curvilinear, cylindrical, spherical and fisheye mappings redistribute the field differently.
Field of View and Lateral Distortion
Field of view is closely connected with the problem of lateral distortion.
In a flat rectilinear projection, image points located at increasingly large angular distances from the central viewing direction must intersect the same flat picture plane. This can cause objects towards the edges of a wide image to become greatly stretched laterally compared with objects close to the centre.
Reducing the field of view reduces this effect. Expanding the field increases it unless another form of picture surface or projection mapping is employed.
The conventional narrow Cone of Vision used in linear perspective is therefore closely connected with the attempt to control such lateral image effects.
Field of View and Curvilinear Perspective
Curvilinear Perspective provides alternative ways of representing large angular fields.
Rather than preserving every straight object-space line as a straight image line, curvilinear systems allow selected directions to bend or curve in order to compress a wider field onto a limited image surface.
Volume 1 identifies fisheye imagery as a familiar optical example. A fisheye lens can compress an extremely wide field — commonly approaching 180 degrees — onto a finite image surface.
The resulting curvature is therefore not necessarily an optical mistake. It can be a direct consequence of the chosen wide-field projection mapping.
Field of View and Cylindrical Perspective
Cylindrical Perspective can extend the represented field horizontally far beyond that of a conventional flat perspective window.
A cylindrical panorama may wrap the horizontal directional field around the observer and can, in principle, represent a complete 360-degree horizontal environment.
This avoids attempting to force the entire horizontal field onto one ordinary flat rectilinear picture plane. The image instead follows a cylindrical geometry more appropriate to the extended field.
Field of View and Spherical Perspective
Spherical Perspective extends the principle further by mapping spatial directions over a spherical or sphere-like image surface or coordinate system.
A spherical representation can encompass directions around, above and below the observer and can therefore represent a far larger proportion of the total surrounding environment than an ordinary flat perspective image.
This makes spherical projection particularly important for panoramic, dome, Virtual Reality and other immersive perspective systems.
Expanding the Field of View
The history of perspective includes a continuing effort to expand the field of view beyond the restricted view provided by conventional flat pictures and ordinary optical instruments.
Methods discussed in the Dictionary and Volume 1 include:
- wide-angle lenses;
- extreme wide-angle and fisheye lenses;
- multiple-camera systems;
- panoramic photography;
- cylindrical representation;
- spherical representation;
- catadioptric systems combining lenses and mirrors;
- wide-field cinema;
- curved and spherical displays;
- Virtual and Augmented Reality; and
- omnidirectional imaging systems.
These methods demonstrate that field of view is not merely a passive characteristic of vision or cameras. It is also a major design variable of perspective systems.
Panoramic and 360-Degree Field of View
A panorama deliberately expands the represented field beyond that normally contained within a single conventional view.
Multiple images can be combined, a camera can rotate around a common centre, or the scene can be rendered directly into cylindrical or spherical coordinates.
A complete horizontal panorama can represent approximately 360 degrees around the observer. A spherical panorama can additionally represent directions above and below, producing an essentially omnidirectional representation of the surrounding scene.
Keyhole Field of View
The Dictionary uses Keyhole Field for an extremely restricted field obtained by looking through a small opening such as a keyhole.
This illustrates that field of view can be limited not only by the eye, camera or image sensor, but also by physical apertures, frames and surrounding structures.
A restricted aperture may exclude much of the surrounding environment while leaving the direction of view itself unchanged.
Area of Vision
The Dictionary treats Area of Vision as another closely related expression for Field of View.
The field can be described in several different ways:
- as horizontal and vertical angular extents;
- as a solid angular field;
- as a projected line representing one dimension of the field;
- as a projected two-dimensional area upon a picture or projection plane; or
- more broadly, as a spatial volume extending into depth.
This distinction is useful because the same field can be described either by its angular extent at the observer or by the physical area it occupies when projected onto another surface.
Cone and Pyramid of Vision
The Cone of Vision and Pyramid of Vision provide geometrical ways of representing the field of view in space.
The eye or station point forms the apex. Rays extending towards the outer limits of the selected visual field form the sides of the cone or pyramid. The spatial scene contained between these boundary rays lies within the selected view.
A circular boundary naturally suggests a cone, while a rectangular picture window produces a pyramidal structure. Both represent the same underlying principle: a finite angular field extending from a viewpoint into spatial reality.
Field Stop
In an optical system, a Field Stop physically restricts the effective field of view.
It determines which off-axis rays or image regions can pass through the instrument and therefore limits the angular extent of the scene that can be observed.
The physical limits imposed by apertures, lens barrels, eyepieces, sensors and other components can therefore determine the usable field even when the surrounding spatial environment extends much farther.
True Field of View
True Field of View (TFOV) is an optical-instrument term describing the actual angular extent of the external scene visible through the instrument.
It represents the angular width of the real-world region encompassed by the optical system rather than the apparent angular size of the image as experienced through the eyepiece.
This distinction is particularly important for binoculars, telescopes and similar instruments.
Apparent Field of View
Apparent Field of View (AFOV) refers to the apparent angular extent of the image as seen through an eyepiece, binocular instrument, headset or similar optical system.
It therefore describes how broad or immersive the presented image appears to the observer rather than directly describing the angular extent of the real-world scene being observed.
The Dictionary notes that the familiar approximation relating true field, apparent field and magnification is useful but not universally exact because eyepiece design and optical distortion can alter the relationship.
Useful Field of View
Useful Field of View (UFOV) has a different meaning again.
In visual science, it describes the region surrounding the current fixation point from which an observer can rapidly detect, identify or locate relevant information without moving the eyes or head.
The useful field is normally smaller than the total anatomical visual field and can vary with:
- attention;
- processing speed;
- visual clutter;
- target contrast; and
- task difficulty.
Useful Field of View should therefore not be confused with either True Field of View or Apparent Field of View in optical instruments.
Working Angle and Field of View
A display or optical system may also possess a working angle or viewing range.
This describes the range of observer positions or directions from which the display or image can be viewed with acceptable brightness, colour, contrast or image quality.
This is not the same as the field of view within the represented image. One concept concerns how much of a depicted or real scene is visible; the other concerns the range of physical positions from which the display itself can be viewed successfully.
Field of View in Photography
In photography, field of view describes the angular extent of the spatial scene captured by the camera.
Volume 1 identifies focal length and sensor size as two important determinants. For a given sensor size, a shorter focal length generally produces a wider field of view, while a longer focal length produces a narrower one.
A smaller sensor records a smaller central portion of the available lens image and therefore produces a narrower field for the same focal length than a larger sensor.
The camera position, however, remains a separate perspective variable. Changing focal length or cropping changes the angular field represented; moving the camera changes the viewpoint and therefore changes the perspective relationships of the scene itself.
Normal, Wide and Extreme Wide-Angle Fields
Volume 1 gives broad photographic examples of different fields:
- Normal: approximately 34–62 degrees;
- Wide Angle: approximately 63–83 degrees;
- Extreme Wide Angle: approximately 84–179 degrees; and
- Fisheye: commonly approaching approximately 180 degrees, with some specialised systems exceeding this.
These ranges illustrate the progression from relatively restricted rectilinear views towards systems designed to capture a much larger portion of the surrounding environment.
Field of View in Cinema and Television
Cinema and television involve at least two different field-of-view relationships.
The first is the depicted or target-space field of view captured by the camera or generated by the rendering system.
The second is the displayed or local-space field of view subtended by the physical screen at the spectator’s viewing position.
These do not necessarily coincide. The camera may capture a wide-angle scene that occupies only a relatively small angular region of the spectator’s actual visual field, or a narrower camera view may be enlarged across a vast cinema or immersive screen.
Field of View in Virtual Reality
Virtual Reality places particular emphasis upon field of view because the represented image attempts to occupy a large proportion of the observer’s natural visual field.
A narrow field can produce the impression of looking through a restricted window into the virtual environment. Expanding the field can increase the sense of surrounding space and immersion.
Virtual environments can also recalculate the directional view continuously as the observer turns or moves, combining a large presented field with a changing viewpoint and direction of gaze.
Viewing Frustum in Computer Graphics
In three-dimensional computer graphics, the viewing frustum defines the region of the modelled world that can appear within the perspective-camera image.
It is the computational equivalent of a bounded perspective field extending from a virtual viewpoint into the modelled scene.
Objects lying outside this field are normally excluded from the rendered camera view, while objects within it are transformed according to the projection system and image geometry.
Field of View in Projection Systems
Field-of-view concepts can also operate in the opposite perspective direction when an image or beam is projected forwards into spatial reality.
An image projector or light source produces a beam with a particular angular extent. This image-beam or light-beam angle determines the physical region covered as the projection expands through space.
The central beam axis defines the principal projection direction, while the beam angle defines its angular spread. As with viewing systems, direction and field are therefore separate concepts.
Represented Field and Displayed Field
A perspective image can therefore involve more than one field of view simultaneously.
The represented field describes the extent of target space depicted within the image. The displayed field describes the angular extent occupied by that image within the observer’s actual visual field when the image is viewed.
This distinction becomes particularly important in cinema, television, immersive displays, Virtual Reality and curved-screen systems, where the same image geometry may be displayed at radically different physical sizes and viewing distances.
Field of View and Image Format
The shape of the image boundary also affects how the overall field is distributed.
A wide rectangular image may prioritise horizontal field; a tall image may include more vertical field; a circular fisheye may represent a large angular region in all radial directions; cylindrical and spherical formats reorganise the relationship still further.
Field of view should therefore always be considered together with the geometry and proportions of the picture or image surface.
Field of View and Perspective Type
Field of view can influence which perspective form is most appropriate for representing a scene.
A relatively narrow field can often be represented effectively by ordinary rectilinear one-, two- or three-point perspective. As the field expands, the limitations and lateral effects of a single flat picture plane become increasingly evident.
Curvilinear, cylindrical, spherical, panoramic and other projection systems provide alternative methods for representing broader directional fields.
Field of view is therefore not merely an incidental camera specification. It is a fundamental factor in determining the geometry and appearance of a perspective image.
Field of View and Spatial Information
Increasing the field of view allows more of the surrounding spatial environment to be represented simultaneously.
This can improve spatial awareness, orientation and contextual understanding, but it also creates representational problems. A larger field must be compressed, transformed, curved, divided or otherwise mapped onto the available image or display structure.
The development of panoramic, wide-field and immersive perspective can consequently be understood as a continuing attempt to balance breadth of view, geometrical consistency, visual clarity and spatial realism.
Common Field-of-View Misconceptions
Several important distinctions should be maintained:
- Field of View is not the same as Line of Sight. The first is an angular extent; the second is a single direction.
- The traditional 60-degree Cone of Vision is not the total human visual field. It is principally a practical limit associated with rectilinear perspective construction and viewing.
- The human field is not uniformly sharp. Central vision has much greater acuity than peripheral vision.
- Monocular and binocular fields are different. The two eyes create a central overlapping binocular region plus lateral monocular regions.
- True Field of View and Apparent Field of View are not identical. One concerns the real-world angular field visible through an instrument; the other concerns the apparent angular extent of the image seen through it.
- Useful Field of View is not simply another name for total visual field. It concerns the region from which visual information can be effectively processed for a particular task.
- Viewing angle or working angle of a display is not necessarily its depicted Field of View.
- A wider field does not automatically produce a more accurate flat image. Different projection geometries distribute wide fields differently.
- Curvature in a wide-field image is not necessarily an error. It can be a consequence of the chosen projection mapping.
- Camera Field of View and physical viewing position are separate variables.
Why Field of View Matters
Field of View is one of the fundamental variables of perspective because every visual, optical or representational system must determine how much of spatial reality is included within a particular view.
It connects the viewpoint with the limits of the visible or represented scene and directly influences picture-plane geometry, apparent object scale, lateral position, image distortion, visual immersion and the choice of projection system.
It is equally important in natural vision and in artificial systems. Human eyes possess central, peripheral, monocular and binocular fields; cameras possess lens- and sensor-dependent fields; linear-perspective drawings employ a selected perspective window; computer graphics use a viewing frustum; and panoramic, cylindrical, spherical and immersive systems deliberately expand the field towards much larger portions of the surrounding environment.
Understanding Field of View therefore provides a foundation for understanding the station point, line of sight, angle of view, picture plane, perspective window, Cone of Vision, Pyramid of Vision, visual field, peripheral vision, viewing distance, focal length, lateral distortion, camera perspective, linear perspective, curvilinear perspective, cylindrical perspective, spherical perspective, panoramic perspective and Virtual Reality.