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Security Cameras: Understanding Field of View (FOV)

Field of View (FOV) is the maximum observable area that is seen at any given moment through an optical device such as a camera lens. The coverage of the area can be measured using the horizontal and vertical distances to find the diagonal of the area in degrees. Mathematically, the FOV is calculated using the horizontal dimension of the sensor (h) and the Focal Length (F).

You can find the camera’s Field of View details in the Specifications sheet. Click here for additional support content including security camera documentation.

FOV Diagram

The Camera Lens, Sensor and Focal Length

Focal length (F) is the distance between the center of a lens and its sensor. The size of the lens is the aperture size.

These factors affect field of view. A narrower focal length captures more of the scene and displays a larger field of view. A wider focal length magnifies a scene and decreases the field of view. The higher the focal length value the lower the FOV.

Focal Length Diagram

Focal Length Result

Types of Camera Lenses

Fixed: a fixed camera focal length provides an Angular FOV which is permanently set and cannot be adjusted by the user. Varifocal: the camera focal length can be manually adjusted by the user. Generally, this is done manually with screws or dials. At Lorex we have motorized varifocal cameras that allow you to digitally zoom using your phone or NVR without losing details. These lenses provide flexibility and customization for your camera image needs.

The importance of Field of View

A wide angle lens or smaller lenses produce a greater field of view and captures more objects in a scene enhancing your ability to cover larger and wider areas such as foyers, parking lots or warehouses.

A narrow angle lens or larger lenses produce a smaller field of view; capturing a limited area, but the camera quality image improves in detail. These are designed to monitor a specific object, such as cash registers, entrances/exits, hallways or objects of value.

How to Calculate the FOV

To calculate the FOV requires the sensor size and the focal length of the lens: h = Sensor Size F = Focal Length of the Lens

FOV is represented by this equation: FOV = 2tan-1(h) / 2F

Example: h = 4.7mm F = 6mm FOV = 2tan-1(h) / 2F = 2tan-1(4.7)(12) = 2tan-1(0.39) = 2(21.4°) = 42.8°

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