So you want to install security cameras at your house or business and decide to go online and research but all you see is a list of cameras but you are not sure on what exactly what all those terms mean or what would you need. Before diving into this pool of options you have to identify your needs:

At what distance from the subject are you going to install the cameras?
How far do you need to monitor the scene?
Do you need to change the monitored distance at times?
Is the camera going to be installed outdoors or indoors?
Is the camera going to be used in an environment with good lighting?
How sharp do you need the image to be? Sharp enough to see the characters of a license plate?


Now that you have all your needs clarified, lets get technical:

1. What is a CCD imager?

CCD (Charged Couple Device) image sensors are electronic devices that use a variety of technologies to transform an image (light pattern) into an electric image (electronic charge pattern) In the process of reading the value in the image , CCD sensors create high-quality, low-noise images.

What is the size of a CCD imager?

Expect 1/3″, 1/2″, rarely 2/3″.

If the CCD imager is 1/3″ you need a 1/3″ lens (1/2″ and 2/3″ will work).

If the CCD imager is 1/2″ you need a 1/2″ lens (2/3″ will work).

If the CCD imager is 2/3″ you need a 2/3″ lens.

2. Should you use a manual iris or an auto iris lens?

You can save money by using a manual iris lens when the scene illumination never changes, for example, an illuminated store, office or inside a warehouse.

An auto iris lens is always a better choice, especially when there is outside light or direct light where the camera is pointing.

3. What focal length lens do you need?

The smaller focal length number, the wider the field of view. If you have a camera in an office or warehouse and you want to see as much as you can, you should use a 2.9mm or 4mm lens (wide, somewhat distant view). If you want to observe a limited area, like an entrance, or if you want to see detail close up, use an 8mm or 12mm lens (narrower view and objects are closer).

The rule: use varifocal lenses for flexibility and the best field of view.

Definitions

Auto Iris Lens: a lens in which the iris aperture automatically opens or closes to maintain proper light levels on the faceplate of the camera pickup device.


Video Type Auto Iris Lens:an auto-iris lens with internal circuit which receives voltage and a video signal from the camera to adjust the iris.


DC Type Auto Iris Lens: an auto-iris lens without an internal circuit to control the iris. All iris control voltages come from a circuit located within the camera.


Manual Iris Lens: a lens with a manual adjustment to set the iris opening (f-stop) in a fixed position. Generally used for fixed lighting applications.


Angle of View: the angular range that can be focused within the image size. Small focal lengths give a wide angle of view, and large focal lengths give a narrow field of view.


F-Stop: a term used to indicate the speed of a lens. The smaller the f-number, the greater is the amount of light passing through the lens.

By: Monica Martin

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