Field of view

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FOV both eyes FOV both eyes.svg
FOV both eyes
Vertical FOV Vertical FOV.svg
Vertical FOV
Angle of view can be measured horizontally, vertically, or diagonally. Angle of view.svg
Angle of view can be measured horizontally, vertically, or diagonally.
A 360-degree panorama of the Milky Way at the Very Large Telescope. Such a panorama shows the entire field of view (FOV) of the telescope in a single image. In the image, the Milky Way appears like an arc of stars spanning horizon to horizon with two streams of stars seemingly cascading down like waterfalls. Cascading Milky Way.jpg
A 360-degree panorama of the Milky Way at the Very Large Telescope. Such a panorama shows the entire field of view (FOV) of the telescope in a single image. In the image, the Milky Way appears like an arc of stars spanning horizon to horizon with two streams of stars seemingly cascading down like waterfalls.

The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.

Contents

Humans and animals

In the context of human and primate vision, the term "field of view" is typically only used in the sense of a restriction to what is visible by external apparatus, like when wearing spectacles [2] or virtual reality goggles. Note that eye movements are allowed in the definition but do not change the field of view.

If the analogy of the eye's retina working as a sensor is drawn upon, the corresponding concept in human (and much of animal vision) is the visual field. [3] It is defined as "the number of degrees of visual angle during stable fixation of the eyes". [4] Note that eye movements are excluded in the definition. Different animals have different visual fields, depending, among others, on the placement of the eyes. Humans have a slightly over 210-degree forward-facing horizontal arc of their visual field (i.e. without eye movements), [5] [6] (with eye movements included it is slightly larger, as you can try for yourself by wiggling a finger on the side), while some birds have a complete or nearly complete 360-degree visual field. The vertical range of the visual field in humans is around 150 degrees. [5]

The range of visual abilities is not uniform across the visual field, and by implication the FoV, and varies between species. For example, binocular vision, which is the basis for stereopsis and is important for depth perception, covers 114 degrees (horizontally) of the visual field in humans; [7] the remaining peripheral 40 degrees on each side have no binocular vision (because only one eye can see those parts of the visual field). Some birds have a scant 10 to 20 degrees of binocular vision.

Similarly, color vision and the ability to perceive shape and motion vary across the visual field; in humans color vision and form perception are concentrated in the center of the visual field, while motion perception is only slightly reduced in the periphery and thus has a relative advantage there. The physiological basis for that is the much higher concentration of color-sensitive cone cells and color-sensitive parvocellular retinal ganglion cells in the fovea – the central region of the retina, together with a larger representation in the visual cortex – in comparison to the higher concentration of color-insensitive rod cells and motion-sensitive magnocellular retinal ganglion cells in the visual periphery, and smaller cortical representation. Since rod cells require considerably less light to be activated, the result of this distribution is further that peripheral vision is much more sensitive at night relative to foveal vision (sensitivity is highest at around 20 deg eccentricity). [3]

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 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 be the angular field of view in degrees. Let be the linear field of view in millimeters per meter. Then, using the small-angle approximation:

Machine vision

In machine vision the lens focal length and image sensor size 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.

Tomography

In computed tomography (abdominal CT pictured), the field of view (FOV) multiplied by scan range creates a volume of voxels. Abdominal CT with scan range and field of view, with box and text.jpg
In computed tomography (abdominal CT pictured), the field of view (FOV) multiplied by scan range creates a volume of voxels.

In tomography, the field of view is the area of each tomogram. In for example computed tomography, a volume of voxels can be created from such tomograms by merging multiple slices along the scan range.

Remote sensing

In remote sensing, the solid angle through which a detector element (a pixel sensor) is sensitive to electromagnetic radiation at any one time, is called instantaneous field of view or IFOV. A measure of the spatial resolution of a remote sensing imaging system, it is often expressed as dimensions of visible ground area, for some known sensor altitude. [8] [9] Single pixel IFOV is closely related to concept of resolved pixel size, ground resolved distance, ground sample distance and modulation transfer function.

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 VISTA telescope has 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. For a normal lens, the diagonal field of view can be calculated as:

where is the focal length.

Microscopy

Field of view diameter in microscopy Field of view diameter in microscopy.jpg
Field of view diameter in microscopy

In microscopy, the field of view in high power (usually a 400-fold magnification when referenced in scientific papers) is called a high-power field, and is used as a reference point for various classification schemes.

For an objective with magnification , the FOV is related to the Field Number (FN) by

,

if other magnifying lenses are used in the system (in addition to the objective), the total for the projection is used.

Video games

The field of view in video games refers to the field of view of the camera looking at the game world, which is dependent on the scaling method used. [10]

See also

Related Research Articles

Optics Branch of physics that studies light

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light. A system with a shorter focal length bends the rays more sharply, bringing them to a focus in a shorter distance or diverging them more quickly. For the special case of a thin lens in air, a positive focal length is the distance over which initially collimated (parallel) rays are brought to a focus, or alternatively a negative focal length indicates how far in front of the lens a point source must be located to form a collimated beam. For more general optical systems, the focal length has no intuitive meaning; it is simply the inverse of the system's optical power.

Binoculars Pair of telescopes mounted side-by-side

Binoculars or field glasses are two telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal mounted military models.

Angle of view Angular extent of given scene imaged by camera

The angle of view is the decisive variable for the visual perception of the size or projection of the size of an object.

Dolly zoom in-camera effect that appears to undermine normal visual perception

A dolly zoom is an in-camera effect that appears to undermine normal visual perception.

Monocular

A monocular is a modified refracting telescope used to magnify the images of distant objects by passing light through a series of lenses and usually prisms, the application of prisms resulting in a lightweight, compact telescope. The typical volume and weight of a monocular are less than half of a pair of binoculars having similar optical properties, making a monocular easier to carry, and also proportionally less expensive. This is due to the fact that monoculars typically only have half the optics of binoculars, as they only process 1 image as opposed to 2. Monoculars produce 2-dimensional images, while binoculars add perception of depth, assuming one has normal binocular vision.

Optical telescope Telescope for observations with visible light

An optical telescope is a telescope that gathers and focuses light, mainly from the visible part of the electromagnetic spectrum, to create a magnified image for direct view, or to make a photograph, or to collect data through electronic image sensors.

Depth perception Visual ability to perceive the world in 3D

Depth perception is the visual ability to perceive the world in three dimensions (3D) and the distance of an object. Depth sensation is the corresponding term for animals, since although it is known that animals can sense the distance of an object, it is not known whether they perceive it in the same subjective way that humans do.

Peripheral vision Area of ones field of vision outside of the point of fixation

Peripheral vision, or indirect vision, is vision as it occurs outside the point of fixation, i.e. away from the center of gaze or, when viewed at large angles, in the "corner of one's eye". The vast majority of the area in the visual field is included in the notion of peripheral vision. "Far peripheral" vision refers to the area at the edges of the visual field, "mid-peripheral" vision refers to medium eccentricities, and "near-peripheral", sometimes referred to as "para-central" vision, exists adjacent to the center of gaze.

Magnification

Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in size, sometimes called minification or de-magnification.

Visual acuity Clarity of vision

Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an examinee's ability to recognize small details with precision. Visual acuity is dependent on optical and neural factors, i.e. (1) the sharpness of the retinal image within the eye, (2) the health and functioning of the retina, and (3) the sensitivity of the interpretative faculty of the brain.

Eyepiece Type of lens attached to a variety of optical devices such as telescopes and microscopes

An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.

The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is the angular aperture. The angular diameter can alternatively be thought of as the angular displacement through which an eye or camera must rotate to look from one side of an apparent circle to the opposite side. Angular radius equals half of the angular diameter.

The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point.

Visual angle

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.

Cortical magnification describes how many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size, as a function of visual field location. In the center of the visual field, corresponding to the center of the fovea of the retina, a very large number of neurons process information from a small region of the visual field. If the same stimulus is seen in the periphery of the visual field, it would be processed by a much smaller number of neurons. The reduction of the number of neurons per visual field area from foveal to peripheral representations is achieved in several steps along the visual pathway, starting already in the retina.

Telecentric lens

A telecentric lens is a compound lens that has its entrance or exit pupil at infinity; in the prior case, this produces an orthographic view of the subject. This means that the chief rays are parallel to the optical axis in front of or behind the system, respectively. The simplest way to make a lens telecentric is to put the aperture stop at one of the lens's focal points.

Defocus aberration Quality of an image being out of focus

In optics, defocus is the aberration in which an image is simply out of focus. This aberration is familiar to anyone who has used a camera, videocamera, microscope, telescope, or binoculars. Optically, defocus refers to a translation of the focus along the optical axis away from the detection surface. In general, defocus reduces the sharpness and contrast of the image. What should be sharp, high-contrast edges in a scene become gradual transitions. Fine detail in the scene is blurred or even becomes invisible. Nearly all image-forming optical devices incorporate some form of focus adjustment to minimize defocus and maximize image quality.

In human visual perception, the visual angle, denoted θ, subtended by a viewed object sometimes looks larger or smaller than its actual value. One approach to this phenomenon posits a subjective correlate to the visual angle: the perceived visual angle or perceived angular size. An optical illusion where the physical and subjective angles differ is then called a visual angle illusion or angular size illusion.

Peripheral Head-Mounted Display (PHMD)

A Peripheral Head-Mounted Display (PHMD) describes a visual display mounted to the user's head that is in the peripheral of the user's field of view (FOV) / Peripheral Vision. Whereby the actual position of the mounting is considered to be irrelevant as long as it does not cover the entire FOV. While a PHMD provide an additional, always-available visual output channel, it does not limit the user performing real world tasks.

References

  1. "Cascading Milky Way". ESO Picture of the Week. Retrieved 11 June 2012.
  2. Alfano, P.L.; Michel, G.F. (1990). "Restricting the field of view: Perceptual and performance effects". Perceptual and Motor Skills. 70 (1): 35–45. doi:10.2466/pms.1990.70.1.35. PMID   2326136. S2CID   44599479.
  3. 1 2 Strasburger, Hans; Rentschler, Ingo; Jüttner, Martin (2011). "Peripheral vision and pattern recognition: a review". Journal of Vision. 11 (5): 1–82. doi: 10.1167/11.5.13 . PMID   22207654.
  4. Strasburger, Hans; Pöppel, Ernst (2002). Visual Field. In G. Adelman & B.H. Smith (Eds): Encyclopedia of Neuroscience; 3rd edition, on CD-ROM. Elsevier Science B.V., Amsterdam, New York.
  5. 1 2 Traquair, Harry Moss (1938). An Introduction to Clinical Perimetry, Chpt. 1. London: Henry Kimpton. pp. 4–5.
  6. Strasburger, Hans (2020). "Seven myths on crowding and peripheral vision". i-Perception. 11 (2): 1–45.
  7. Howard, Ian P.; Rogers, Brian J. (1995). Binocular vision and stereopsis. New York: Oxford University Press. p. 32. ISBN   0-19-508476-4 . Retrieved 3 June 2014.
  8. Oxford Reference. "Quick Reference: instantaneous field of view". Oxford University Press. Retrieved 13 December 2013.
  9. Wynne, James B. Campbell, Randolph H. (2011). Introduction to remote sensing (5th ed.). New York: Guilford Press. p. 261. ISBN   978-1609181765.
  10. Feng Zhu School of Design – Field of View in Games