field of view (FOV)
What is field of view (FOV)?
Field of view (FOV) is the open, observable area a person can see through their eyes or via an optical device, such as a camera. In the case of optical devices, FOV is the maximum area that the device can capture. In other words, it answers the question: "How much can the device see?"
Field of view explained
FOV is the range of the observable world visible at any given time through the human eye, a camera viewfinder or on a display screen. It refers to the coverage of an entire area rather than a single, fixed focal point. FOV also describes the angle through which a person can see the visible world.
The wider the FOV, the more one can see of the observable world. It is measured horizontally, vertically and diagonally. The camera lens, its focal length and the sensor size all play a part in determining the FOV.
Lens and focal length
The focal length of a lens is the distance between the lens and the focused image on the sensor.
A fixed focal length lens provides a fixed angular FOV (AFOV). AFOV is the angle of light that can be captured by the lens. It is required to calculate the overall FOV. A fixed focal length lens is not the same as a fixed focus lens, which can only be used at a fixed working distance.
The fixed focal length lens can be focused for different working distances to obtain differently sized FOV, even though the viewing angle remains constant. Thus, the lens focal length defines the AFOV and FOV.
For a given sensor size, a shorter focal length gives a wider AFOV and, therefore, a larger FOV and vice versa. Additionally, a shorter working distance is needed to obtain the same FOV compared to a longer focal length lens. However, short focal length lenses are associated with higher distortion, which can influence the FOV and cause variations in the angle with respect to the working distance.
Further, short focal length lenses usually do not provide a high level of performance compared to longer focal length lenses. And shorter lenses may not cover medium-large sensor sizes, which can limit their usability.
With a fixed focal length lens, the FOV can be changed in three ways:
- changing the working distance from the lens to the object -- this requires moving the lens farther away from the object plane;
- replacing the lens with a lens of a different focal length; or
- changing the sensor size.
The FOV can also be changed by using a varifocal lens or zoom lens, both of which enable focal length adjustment and, therefore, FOV adjustment. However, these lenses are larger and more expensive and offer lower performance than fixed focal length lenses.
A larger sensor yields a larger FOV for the same working distance. Changing the sensor size can change the FOV. The sensor size depends on the number of pixels on the sensor and the size of the pixels. Larger sensors enable a better image and higher resolution, while smaller sensors have a smaller depth of field (DOF) -- sharpest point between closest and farthest point of an image -- resolution and pixel size.
Field of view calculation
The relationship among AFOV, focal length and sensor size can be represented by the following equation:
AFOV = 2 x tan-1 (H/2f)
- H = sensor size (horizontal dimension)
- f = focal length of the lens
AFOV = 2 x tan-1 (FOV/2 x working distance)
FOV = 2 x working distance x tan (AFOV/2)
Increasing or decreasing the sensor size changes how much of the lens image is utilized, which alters the FOV.
The human eye and field of view
The human eye is the natural starting point to perceive the FOV. In human vision, the FOV is composed of two monocular FOVs, which the brain stitches together to form one binocular FOV.
Each individual eye has a horizontal FOV of about 135 degrees and a vertical FOV of just over 180 degrees. Stitching together the monocular FOV yields a binocular FOV of around 114 degrees of view horizontally. This FOV is necessary for depth perception.
A person's peripheral vision makes up the remaining 60-70 degrees. However, this version is only monocular because only one eye can see those sections of the visual field. All these FOV measurements assume that the person's eyes are fixed on the observable world.
In addition to monocular and binocular differences in vision, humans also have different FOV for different colors. Color saturation and perception are concentrated in the center of the FOV, so the image becomes more monochromatic on the edges or periphery of a person's vision.
The importance of field of view
FOV is an important foundational concept in optics. Anyone working with optics should be aware of FOV. This includes the following:
- video game designers
- virtual reality (VR) professionals
FOV plays an important part in VR applications. VR glasses with thick and heavy lenses provide a small focal length, which increases the FOV and delivers a more immersive user experience (UX). However, heavier equipment and larger lenses also cause color distortions and chromatic aberrations, so lighter headsets are required to prevent these issues. It can be difficult to achieve this balance. Nonetheless, VR technology is improving, and in the future, we may see lighter equipment and lenses and a larger FOV to deliver enhanced UX.
FOV is also a crucial consideration in computer games. Gamers prefer games that enable FOV adjustment because games without this option are not as natural or immersive as gamers would like. A low FOV may even cause motion sickness.
Finally, FOV calculations matter in drone photography. Drone photographs can capture large swathes of a landscape better with a larger FOV. Extra visibility can also make it easier to see obstacles from a first-person view for better control of the drone.
Field of view in photography and filmmaking
In photography and filmmaking, the FOV refers to what is visible through the camera lens or optical viewfinder. Changing the lens changes the FOV. To increase FOV and capture more of a scene, a wide-angle lens -- which displays a wider field of view than our human vision -- is used. Similarly, to decrease the FOV, a zoom lens can be used. In general, a smaller focal length lens increases the angle and the FOV. Thus, the FOV can be controlled by changing out lenses with varying focal lengths.
A wider FOV makes the viewing experience more realistic. But, regardless of the lens used, the angle is always smaller than the field of vision possible with the human eye. In other words, camera lenses cannot deliver the same kind of immersive viewing experiences possible with human eyesight.
Differences between field of view and depth of field
When a camera lens is focused on a subject, the DOF determines how blurry or sharp the area around the subject is. When the DOF is shallow, only a small area is in focus. But, when the DOF is deep, the lens captures a larger area in focus.
With a small focus area and shallow DOF, the subject is in focus, while the background is blurred. This scenario is required for portrait photographs. When a larger area is in focus with a deeper DOF, everything in the image remains sharp and clear, including the background. This situation is ideal for landscape photography.
The DOF can be adjusted with the camera aperture or by changing the following:
- distance between the camera and the subject;
- lens focal length; and
- size of the camera's sensor.
The main difference between FOV and DOF is that DOF refers to the area of sharpness behind and in front of the subject. FOV is the area that can be seen through a lens or viewfinder at any particular moment. It determines how big the imaged area is. Thus, FOV is about image.
See also: first-person view, imaging, aspect ratio, stereoscopy, Digital Imaging and Communications in Medicine, IP camera, complementary metal-oxide semiconductor sensor and thermal imaging.