In-Depth Introduction to the FOV of Security Cameras

In our previous article,<How to Select the Focal Length and Field of View Parameters for an IP Security Camera>， we focused on the relationship between the Field of View (FOV) and focal length, as well as how to select the appropriate camera based on actual usage scenarios and requirements. Today, we will delve deeper into the FOV. What exactly is FOV, and how can we understand and learn about the FOV concept more professionally from the perspectives of physics and applied engineering technology?

For those who read our last article, we know that FOV stands for Field of View. According to the principles of physical imaging, the imaging width of each optical LENS is fixed. For different focal lengths, the value of the field of view angle α varies. The relationship is as follows: the longer the focal length, the smaller the FOV; the shorter the focal length, the larger the FOV; the longer the focal length, the further the range of view, and the shorter the focal length, the closer the range of view. See the diagram below:

Today, we will continue to introduce FOV in depth. Based on the basic principles of physical optics, objects are three-dimensional in the actual imaging process. From the perspective of optical engineering, we further subdivide FOV into horizontal, vertical, and diagonal dimensions, namely HFOV, VFOV, and DFOV.

HFOV: Corresponds to the Horizontal Field of View, as shown by the angle β between lines 2 and 3 in the diagram below.

VFOV: Refers to the Vertical Field of View, as shown by the angle α between lines 1 and 2 in the diagram below.

DFOV: Refers to the Diagonal Field of View, as shown by the angle γ between lines 1 and 3 in the diagram below. See the diagram:

From the diagram, we can conclude that the horizontal field of view HFOV is determined by the focal length and the width of the imaging area; the vertical field of view VFOV is determined by the focal length and the height of the imaging area; the diagonal field of view DFOV is determined by the width and height of the imaging area. For convenience in communication, the FOV we usually refer to is HFOV, which is the horizontal field of view.

Therefore, in the industrial camera field, cameras are conventionally classified according to the size of the FOV:

Standard lenses： Have a field of view of 45° and are widely used, such as in security cameras for home, indoor baby monitors, security camera doorbell etc..

Telephoto lenses or Long-focus lenses: Have a field of view typically within 30° or smaller, allowing for imaging at long distances. Such as in security camera mount, security camera with monitor for car park etc..

Wide-angle lenses: Have a field of view exceeding 60°, offering a broader observation range, but with some degree of distortion in close-up images.

Fisheye lenses: Have a field of view exceeding 120°, even up to 160°, resembling the protruding eyes of a small fish. Compared to wide-angle lenses, the distortion in close-up images is more pronounced. However, due to the large field of view and broader range of vision, these lenses are extensively used in areas such as security camera 360 degree coverage in vehicles and bus security cameras.

Of course, the above introduction mainly pertains to the FOV of fixed focal length optical lenses. For zoom cameras, as introduced above, it is easy to understand that the FOV of zoom cameras also changes with the focal length.

Has the above content given you a deeper understanding of the field of view parameter concept? When purchasing an IP security camera in the future, will you be more targeted and confident in finding the camera that suits your needs?

The End.