Camera Field of View and Lens Size

The Field of View produced by a camera is the area that the camera can see. It is an important factor to consider when planning for a security system, because it determines not just what the camera can see, but also the level of detail that is visible at a given distance.

The size of the camera lens, or focal length, is the main factor that determines the Field of View. Cameras with a smaller lens, also known as a wide-angle lens, produce a greater Field of View than cameras with a larger lens. This means that the camera can see a large area, but that objects will appear smaller within the scene area. This is useful if you want to monitor an entire room or a yard.

Cameras with a larger lenses, also known as narrow-angle, have a smaller Field of View. They can only see a limited area, but objects will appear larger within the scene area. This is useful if you want to monitor a specific target, such as cash register or doorway. An example of the difference between two cameras with different lens sizes is shown below.

The photo on the left is from a camera with a 6mm lens, and the photo on the right is from a camera with a 3.6mm wide-angle lens. Both pictures are taken at the same distance. The 3.6mm lens shows much more of the scene but with less detail of the hotel than the 6mm lens. The image below provides a simulation of different lens and Field of View combinations to give you an idea of the scene area you can expect in a typical surveillance application.

Field of View comparisons

NOTE: The Field of View for Lorex cameras is measured by the angle created between the camera and the diagonal corners of the image. When purchasing cameras, it is more important to consider the actual Field of View than the lens size, as the camera sensor and other factors also affect the Field of View. The image shown assumes that the same camera sensor is used for each example.

Fixed Lens vs. Varifocal

A Fixed Lens is one where the camera's focal length is permanently set and cannot be adjusted by the user. This means that the Field of View is permantently set, so it is important to select the correct Field of View (i.e. wide angle or narrow) for your application.

A Varifocal Lens allows the user to manually adjust the camera lens, generally using adjustment screws or knobs. Varifocal cameras are typically more expensive than the equivelent fixed lens model, but they allow for greater flexibility to optimize the camera picture for your specific needs. The focus settings on a camera with a varifocal lens may need to be adjusted from time to time.

Zoom and focus adjustment knobs on a Lorex Varifocal Bullet Camera