Field of view is the area a camera actually covers at a given distance, expressed in degrees or in meters across the scene. It follows from the lens and the sensor, and it sets how large a person or a plate appears in the image, which is what decides whether detail is usable.
Field of view is the practical version of angle of view. It answers the question a site actually asks: how much of the yard does this camera see, and how big is a person at the gate?
Field of view and detail
Spread the same resolution across a wider field of view and each person contains fewer pixels. Identification needs a face at a usable size; overview needs the whole area. Two cameras often do the job better than one wide camera asked to do both.
Measuring it at the site
A lens calculator converts distance, sensor size and focal length into coverage. On site, mark the edges of the view on the ground and check them on the monitor. Adjust aim and zoom before the camera is finally tightened, and record the coverage in the as-built notes.
Related:Commercial security camera systemsGlossary: PTZ camera systems