Understanding Field of View (FOV) and Angular Field of View (AFOV) in Camera Lenses

The Field of View (FOV) of a camera lens refers to the extent of the observable area that can be captured in a single shot, which means the observable area that you can see either through your eyes or an optical device. In camera shooting, FOV solves, “what we are seeing in our image” and “how much of the scene we are seeing.” As light passes through the camera lens, it will converge the light to focus the subject being imaged. Shorter focal lengths converge the light more strongly to focus the subject being imaged.

Conversely, longer focal lengths converge the light less intensely to focus the image. This means the distance of the focal length is determined by how strongly the light is converged by the lens in order to focus the subject being imaged. This, in turn, influences the angle from the horizontal of light that can be captured by the lens. This is known as the angular field of view (AFOV) and is required to determine the overall FOV. The FOV is expressed in either angular or sized terms, with the former being the full angle in degrees and the latter being the length in millimeters or meters.

• Angular Field of View (AFOV) is typically specified as the full angle in degrees, which is the angle between any light captured horizontally, and any light captured at the edge.
• Sized/Length Field of View (object size) is typically specified as the length in millimeters or meters.

The FOV is influenced by the lens focal length and sensor size, with a larger sensor requiring a wider FOV if the lens focal length is fixed. FOV is usually measured horizontally, given that sensors are usually rectangular, and is usually expressed in millimeters. To measure the FOV of UV, visible and infrared cameras, optical tests are commonly used. During the test, light is focused from a black body (an object that absorbs all light that falls on it) onto a test target at the focal place. By using a set of mirrors, a virtual image can be created that is at an infinitely far distance.

Camera FOV (or Camera Coverage)

Note: f is the lens focal length.

Camera FOV vs. Lens FOV

The image below shows the difference between the camera FOV and lens FOV.

Note: the maximum image (circle) diameter of the lens should be equal to or larger than the Sensor diagonal size.