Camera lenses are an important part of how your security camera will work. The lens collects the light that is reflected from the field of view and focuses the light onto your cameras image sensor. With this tool you will be able to the field of view by entering the distance of the object and the focal length of your lens. Conversely, you may need to know what type of lens you will need for a specific application. Which you would then enter your objects distance and the size of the field of view, and this will let you know what size lens you will need to use.