Focal length refers to the distance (measured in millimeters) between a cameraās lens and its image sensor when the subject is in focus. In surveillance cameras, focal length determines the field of view (FoV) and the level of zoom or detail captured in an image.
Shorter focal lengths, such as 2.8mm or 4mm, provide a wider field of view, ideal for monitoring large areas like parking lots or open rooms. Conversely, longer focal lengthsāsuch as 12mm or moreāoffer a narrower FoV but greater magnification, making them suitable for identifying faces or license plates at a distance.
Surveillance systems often use either fixed, varifocal, or motorized zoom lenses. Fixed lenses have a constant focal length, while varifocal lenses allow manual adjustment. Motorized lenses, often controlled remotely, offer greater flexibility for changing scenes or tracking movement.
Choosing the right focal length is critical to effective video surveillance. It affects not only how much of a scene is captured but also how well specific details can be seen. Matching focal length to the monitoring objective ensures optimal performance and situational awareness.
In summary, understanding focal length helps ensure that a surveillance camera delivers the right balance of coverage and detail for its intended use.