CCD Camera Lens

A CCD camera lens is a device which allows light to pass through it, while causing the light to converge on a point of focus (film, or a CCD sensor array). The most simple lens is a single element, while more complex lenses (compound lens) consist of multiple elements. Optical lenses are usually made of glass or plastic, or a combination of both. A pinhole can also act as a lens, in this case there is no element, just a very small aperture in front of the CCD sensor.

As mentioned, lenses are used to focus light on a surface or object, in the case of a CCD security camera that surface would be the surface of the CCD sensor itself. A lens allows us to focus the camera on a certain distance, and zoom lenses allow us to enlarge a portion of the scene onto the sensor, effectively magnifying the scene for a closer look.

What To Look For When Selecting a Lens For A CCD Camera

Focal Length

Focal length refers to the distance from the centerline of the lens to the point of focus of a beam of light. Note here that we are referring to convex lenses, which is the type commonly used in CCD Camera systems. A lens with a short focal length has more optical power than one with long focal length, since it is bending the light rays more than one with a longer focal length.

Focal length is important when selecting a lens for your CCD camera, because it determines the magnification of objects in the field of view. Focal length is usually denoted in millimeters. A 28 mm lens gives a larger field of view than a 50 mm lens, etc.

F-number

The f-number (which is also called the f-stop, in photography) indicates the diameter of the entrance pupil in terms of the focal length of the lens. It is calculated by dividing the focal length of the lens by the effective aperture diameter. This number has no dimension (it is distance over distance).

The f-number indicates depth of field, which increases as the f-number increases. An image captured using a lens with low f-number will have the subject in focus, while anything else at different distance will be out of focus. Using a lens with higher f-number allows for more of the view to be in focus.

The size of the CCD sensor has an effect on depth of field, in other words, the same lens will provide a different depth of field on different size CCD sensors.

Viewing Angle

The viewing angle of a lens will determine how wide or narrow the field of view of your camera is. Viewing angle is related to the ratio between the focal length of the lens and the size of the sensor. A “normal” lens for a given sensor size is one which has a focal length similar in size to the diagonal measure of the sensor.

Mounting

There are two types of lens mounts in general use today. Bayonet mount allows the lens to be taken off and on the camera easily, and was popularized with the advent of 35mm film cameras. Screw mount is where the lens is threaded into the body of the camera. Adapters are available to go from one to the other type of mount. One thing to consider when using an adapter it what effect it will have on the focusing of the lens.

Zoom Lens

A Zoom lens allows the operator to alter the focal length of the lens. This ability is useful when one wants to observe a large area, and also have the ability to focus in to smaller elements (a face, a car license plate) at other times. Zoom lenses can be remotely controlled to allow an operator at a remote monitoring station to do just that.

Remote Control of a CCD Camera Lens

Lenses with remote control are available for live monitoring situations. These lenses can be zoomed by the operator. Zooming is often combined with the ability to pan and tilt the camera (in other words, aim the camera in different directions) to provide a powerful observation system. A “PTZ” camera can be a very useful tool in your surveillance arsenal.