How do you calculate the field of view and focal length? Some installers will use a Lens Selection Wheel. It is a product like a pocket slid ruler that you can use to select a couple of the key options we will discuss below and then it will show the correct lens choice. Others will use some type of spreadsheet calculator or even an online web based calculator that will allow you to enter a couple of the factors and give you a final result. You could also use some basic math to figure out as well.
First you must know the CCD imaging device size in the CCTV Security Camera. If you don't know this you will not have an accurate number in your calculations. For our purposes we will be talking about a sensor that is a 1/3rd inch size sensor. The actual physical horizontal dimension of this sensor is 4.8mm.
Then to determine which lens you will need you need to know the distance to the object/scene and the desired width of the object/scene.Lets see how we would determine the correct lens for a scene where the desired width of the scene is 10 feet wide with a distance from the camera of 80 feet. 80 feet and 10 feet become the two key factors that you could use with a lens selection wheel or online calculator, or we can do some simple math.
The formula for this is (distance/width)*image size = lens focal length.
We will divide that by the width desired of 10 feet. Then we multiply 8 times the image size mentioned above of 4.8mm and get a number of 38.4. That is 38.4mm for the focal length of the lens needed to match our desired field of view for this scene. In other words the horizontal field of view of a 38.4mm lens for a 1/3rd inch image sensor in a security camera would be 10 feet wide at a distance of 80 feet. Now the next big choice is which security camera to use.
First you must know the CCD imaging device size in the CCTV Security Camera. If you don't know this you will not have an accurate number in your calculations. For our purposes we will be talking about a sensor that is a 1/3rd inch size sensor. The actual physical horizontal dimension of this sensor is 4.8mm.
Then to determine which lens you will need you need to know the distance to the object/scene and the desired width of the object/scene.Lets see how we would determine the correct lens for a scene where the desired width of the scene is 10 feet wide with a distance from the camera of 80 feet. 80 feet and 10 feet become the two key factors that you could use with a lens selection wheel or online calculator, or we can do some simple math.
The formula for this is (distance/width)*image size = lens focal length.
We will divide that by the width desired of 10 feet. Then we multiply 8 times the image size mentioned above of 4.8mm and get a number of 38.4. That is 38.4mm for the focal length of the lens needed to match our desired field of view for this scene. In other words the horizontal field of view of a 38.4mm lens for a 1/3rd inch image sensor in a security camera would be 10 feet wide at a distance of 80 feet. Now the next big choice is which security camera to use.
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