Using a tape measure, calculate distance between the CCTV camera and the area that you wish to monitor with the CCTV camera. You may have to take help from a friend for this purpose.
Now you need to measure the width of the area that you will be monitoring with the CCTV camera. For instance, if it is the entrance to your home that you want to view, just measure the width of the entrance door and add a few inches to the final reading.
Calculate ratio between width measurement and the distance between the CCTV camera and the area that you wish to monitor. For example, it you want to monitor a 7 feet wide area which is at a distance of 21 feet from the CCTV camera, the answer to your calculation will be 3.
Depending on the camera sensor size, choose a multiplier from the list given below.
- 1 inch sensor multiplier = 12.8
- 2/3-inch sensor multiplier = 8.8
- 1/2-inch sensor multiplier = 6.4
- 1/3-inch sensor multiplier = 4.8
Multiply calculation from Step 3 with the correct value from Step 4. Assuming that the sensor size of you camera is 1 inch, 3 × 12.8 = 38.4. This means that you will need a 38.4mm lens.
To calculate the vertical field-of-view, simply multiply reading from Step 3 (the horizontal field-of-view) with 0.75. This means 3 × 0.75 = 2.25. This is the vertical field-of-view that the CCTV camera will allow.