CCTV Box Camera is that the lens can be changed. If you need to see further than 35 or 40 ft then you’ll need a Box camera with a special lens.

An example of where you might use a fixed 4mm lens is in a small office, or at home to focus on your driveway. A higher millimeter lens will provide further distance, but narrows the field of view.

Cctv C-Mount lenses are available from 4mm to 50mm. A 4mm lens provides facial detail and a 70-degree angle of view focused up to about 35 ft. An example of where you might use a fixed 4mm lens is in a small office, or at home to focus on your driveway.

A higher millimeter lens will provide further distance, but narrows the field of view. So, a 16mm lens would provide about a 15 to 20-degree angle of view at a focus distance of about 35 ft (or a 70-degree angle of view at about 140 feet).

In general, an 8mm lens is like a 4mm lens zoomed in 2 times. Similarly, a 16mm lens is like a 4mm lens zoomed in 4 times. Many times, the best option is to use a varifocal lens. This will allow you to vary the focus from 5 to 50mm.

So when you install the camera you can fine-tune the focal distance and angle of view. An example of where you might use a varifocal lens is outside (or inside) a large commercial building where you need more distance than 35 ft. and the varifocal lens will allow you to adjust the focal distance to your preference.