A CCD camera lens is used to focus light from an area of interest onto the ccd sensor in the camera. Simple lenses are constructed of a single element, and an inexpensive one may be made of transparent plastic.
When selecting a ccd camera lens, you must take several factors into consideration, such as how well your scene is illuminated, do you need a wide-angle or not, are you going to remotely control the lens magnification, and other things. In this article I’ll outline a few of the major points here to get you started.
What’s Your Distance?
The most common measure of a lens is its “focal length.” Do you know what it refers to? In photography, focal length indicates the distance from the lens to the spot where it focuses any light that passes through it, or in other words the distance from the glass to the sensor on a CCD security camera.
What does this have to do with anything how our camera works? Well, focal length affects the field of view of the camera, therefore, if you want a wide view (wide angle) you will want to select a lens with a smaller focal length. Focal length is indicated in millimeters.
Exposure and Illumination
The amount of light necessary to get a good image is affected by the f-number value of the lens you select. A smaller f-number indicates a larger opening in the lens, which gets more light to the sensor, so you won’t need as much light as for a lens with a larger f-number.
The depth of field of the lens is affected by the aperture size – a larger f-number gives more depth of field. A pinhole gives practically infinite depth of field, however, it requires a lot of light, or long exposure. For modern CCD cameras, which have an exposure time of 1/60th second, you will need either a lot of light, or a very sensitive (expensive) sensor.
Wide Angle or Narrow?
The scene you are observing will determine the necessary field of view for your camera/lens combination. Viewing angle is given by the focal length of the lens – as discussed above. Viewing angle can be calculated, there are some online calculators available.
Most CCD cameras use a screw mount which allows the lens to thread onto the lens for a more or less permanent mounting. The other popular type of lens is a bayonet mount.
For cameras that don’t have an integral lens, the mount will be either screw-in, or a bayonet type. Screw in is best for a permanent camera, bayonet can be selected when you want to be able to exchange lenses.