Angle of view (photography)

In photography, angle of view (AOV)[1] describes the angular extent of a given scene that is imaged by a camera.

The image circle (giving the angle of coverage) produced by a lens on a given image plane is typically large enough to completely cover a film or sensor at the plane, possibly including some vignetting toward the edge.

As abovementioned, a camera's angle of view depends not only on the lens, but also on the image sensor or film.

Digital sensors are usually smaller than 35 mm film, and this causes the lens to have a narrower angle of view than with 35 mm film, by a constant factor for each sensor (called the crop factor).

In everyday digital cameras, the crop factor can range from around 1, called full frame (professional digital SLRs where the sensor size is similar to the 35 mm film), to 1.6 (consumer SLR), to 2 (Micro Four Thirds ILC), and to 6 (most compact cameras).

For lenses projecting rectilinear (non-spatially distorted) images of distant objects, the effective focal length and the image format dimensions completely define the angle of view.

Calculations for lenses producing non-rectilinear images are much more complex and, in the end, not very useful in most practical applications.

For a lens projecting a rectilinear image (focused at infinity, see derivation), the angle of view (α) can be calculated from the chosen dimension (d), and effective focal length (f) (f is defined as the distance of the lens with respect to the image plane.

Because this is a trigonometric function, the angle of view does not vary quite linearly with the reciprocal of the focal length.

and thus the angle of view is reduced by 33% compared to focusing on a distant object with the same lens.

Angle of view can also be determined using FOV tables or paper or software lens calculators.

At infinity focus, f = F, the angles of view are: Consider a rectilinear lens in a camera used to photograph an object at a distance

is defined to be the angle-of-view, since it is the angle enclosing the largest object whose image can fit on the film.

Note that the angle of view varies slightly when the focus is not at infinity (See breathing (lens)), given by

The lens asymmetry causes an offset between the nodal plane and pupil positions.

In the optical instrumentation industry the term field of view (FOV) is most often used, though the measurements are still expressed as angles.

[8] Optical tests are commonly used for measuring the FOV of UV, visible, and infrared (wavelengths about 0.1–20 μm in the electromagnetic spectrum) sensors and cameras.

The purpose of this test is to measure the horizontal and vertical FOV of a lens and sensor used in an imaging system, when the lens focal length or sensor size is not known (that is, when the calculation above is not immediately applicable).

[9] The sensed image, which includes the target, is displayed on a monitor, where it can be measured.

This calculation could be a horizontal or a vertical FOV, depending on how the target and image are measured.

Lenses are often referred to by terms that express their angle of view: Zoom lenses are a special case wherein the focal length, and hence angle of view, of the lens can be altered mechanically without removing the lens from the camera.

Another result of using a wide angle lens is a greater apparent perspective distortion when the camera is not aligned perpendicularly to the subject: parallel lines converge at the same rate as with a normal lens, but converge more due to the wider total field.

For example, buildings appear to be falling backwards much more severely when the camera is pointed upward from ground level than they would if photographed with a normal lens at the same distance from the subject, because more of the subject building is visible in the wide-angle shot.

Because different lenses generally require a different camera–subject distance to preserve the size of a subject, changing the angle of view can indirectly distort perspective, changing the apparent relative size of the subject and foreground.

[16] Digital compact cameras sometimes state the focal lengths of their lenses in 35 mm equivalents, which can be used in this table.

For comparison, the human visual system perceives an angle of view of about 140° by 80°.

[17] As noted above, a camera's angle level of view depends not only on the lens, but also on the sensor used.

Digital sensors are usually smaller than 35 mm film, causing the lens to usually behave as a longer focal length lens would behave, and have a narrower angle of view than with 35 mm film, by a constant factor for each sensor (called the crop factor).

Modifying the angle of view over time (known as zooming), is a frequently used cinematic technique, often combined with camera movement to produce a "dolly zoom" effect, made famous by the film Vertigo.

Using a wide angle of view can exaggerate the camera's perceived speed, and is a common technique in tracking shots, phantom rides, and racing video games.

A camera's angle of view can be measured horizontally, vertically, or diagonally.
In 1916, Northey showed how to calculate the angle of view using ordinary carpenter's tools. [ 2 ] The angle that he labels as the angle of view is the half-angle or "the angle that a straight line would take from the extreme outside of the field of view to the center of the lens;" he notes that manufacturers of lenses use twice this angle.
In this simulation, adjusting the angle of view and distance of the camera while keeping the object in frame results in vastly differing images. At distances approaching infinity, the light rays are nearly parallel to each other, resulting in a "flattened" image. At low distances and high angles of view objects appear " foreshortened ".
A geometry explaining how the angle of view can be derived. Red lines are considered as chief rays.
A geometry explaining how the angle of view can be derived. Red lines are considered as chief rays .
Schematic of collimator -based optical apparatus used in measuring the FOV of a camera
Monitor display of sensed image from the camera under test
How focal length affects perspective: Varying focal lengths at identical field size achieved by different camera-subject distances. Notice that the shorter the focal length and the larger the angle of view, perspective distortion and size differences increase.
28 mm lens, 65.5° × 46.4°
50 mm lens, 39.6° × 27.0°
70 mm lens, 28.9° × 19.5°
210 mm lens, 9.8° × 6.5°