Lenses for network video cameras

Matching lens and sensor

It is important to use a correctly sized lens for the camera’s image sensor. If the lens is intended for a smaller image sensor than the one actually in the camera, the image will have black corners (see the illustration to the left below).

If the lens is intended for a larger sensor than the one in the camera, the field of view will be smaller than the lens’ capability, as part of the information will be lost outside the image sensor (see the illustration to the right below). This situation creates a telephoto effect as it makes everything look zoomed in.

The effects of different lenses on a 1/3” image sensor.

Figure 4: The effects of different lenses on a 1/3” image sensor.

Standards for lens mounting

There are three main mounting standards for interchangeable network camera lenses: S-mount, C-mount, and CS-mount.

S-mount (also known as M12-mount) is common in covert cameras and fixed mini domes. The distance between the lens and sensor is not fixed, so focusing may be required. An S-lens lacks iris control (see below).

C-mount and CS-mount look identical, both having a 1-inch thread and 32 threads per inch (TPI). The CS-mount is an update to the C-mount standard. The difference between these mounts is in the distance from the lens to the image sensor:

  • CS-mount. The distance between the sensor and the lens is 12.5 mm.
  • C-mount. The distance between the sensor and the lens is 17.526 mm.
C-mount and CS-mount lenses.

Figure 5:  C-mount and CS-mount lenses.