CCTV Field of View
Lens Calculation

What is CCTV field of view and why is it important? Field of view is all about what someone will be able to see through the security camera. We will define it in detail and explain how it works and provide some examples to make it easier to understand. If you would prefer to see and listen you can watch our video on CCTV FOV and lens calculations by clicking this link.

The field of view (or FOV) is the total height and width of the view seen through the cctv security camera lens. It can also be referred to as the angle of view or the angular field of view.

Field of View Example

The angular field of view is stated in horizontal and vertical degrees. The question is degrees of what? It is degrees of a circle. If you look at the picture of the circle you will see that the dark blue section could be stated as 43.6 degrees field of view or angle of view. The full circle is 360 degrees.

Angle of View

When we are talking about CCTV Field of View for security cameras we are looking for a linear field of view. Meaning we are looking for the actual measurement in feet and inches. The Horizontal FOV (Field of View) is the width of the view. The Vertical FOV (Field of View) is the height of the view. The overall FOV is a combination of the horizontal FOV and the vertical FOV. You can even measure it diagonally if you want too but its really not necessary to do that.

Below are examples of how the field of view changes with a different lens focal length on the CCTV Security Camera.

The first example is at 65 Feet away with a 22mm Focal Length.

FoV Example 25mm

The next image is still 65 feet away with a 12mm Focal Length.

FoV Example 12mm

Again at 65 feet away with now a 6mm Focal Length.

FoV Example 6mm

And finally with a 3.6mm Focal Length.

FoV Example 3.6mm

Now lets talk about how you actually calculate it. If your good at trigonometry you probably already know how to do this. However, if your not good at it we will show you how it is done.

There are a few key factors that are important to know when calculating the CCTV Field of View.

First you must know the CCD imaging device size in the CCTV Security Camera. If you do not know this you will not have an accurate number in your calculations. See the chart for the various CCD sizes and their corresponding actual dimensions that are used to determine the correct field of view.

Then you need to know at least two of these three items in order to make your calculations.

• The Focal length of the lens – Such as 9mm
• Distance to the object/scene
• Width of the object/scene

Normally what you will know is the distance to the object/scene as well as the approximate width. With that you will be able to calculate the focal length of the lens you will need on your cctv security camera.

To help with this calculation we put together a simple spreadsheet CCTV Field of View Calculator. You can download the calculator from our Google sites by clicking this link here!

The calculator assumes that the CCD size you are using is 1/3rd inch since that is the most common size used. Once you have done that you can enter the example below.

As an example if your distance to the object in the scene is 80 feet. The width of the view that is desired is 10 feet. Enter those numbers into the calculator in the lower section. The resulting focal length of the lens should be 38.4mm. To see how that translates into degrees of view you can enter 38.4 into the upper Focal Length box and you will see the corresponding degree of view in the right circle. It should show 7.15 horizontal degrees of view.

Click here for our Online CCTV Field of View Calculator

The following chart shows a variety of focal lengths and what the degree of view would be for that focal length and the corresponding linear field of view at the given lengths.

Some CCTV installers will carry with them a small circular field of view calculator. That is very handy to have but really its not even necessary. For a quick and easy way to figure out what size of lens you need you can do the following calculation. You will take the distance to the object and divide it by the desired width for the view and then multiply that by the image size. Referring to the CCD image size chart above you will see that the size for a 1/3rd inch sensor (which is the most common) is 4.8mm for the horizontal measurement. So continuing our example you will take the distance (lets say 80 feet again.) divided by the width of 10 feet and multiply by 4.8.

The calculation would look like this. 80/10*4.8 = 38.4

There you have it. A quick easy way to know the focal length needed for your cctv security camera.