Infinova: How and Why to Select Megapixel, Network and Analog Security Cameras (Part IV)

A commonsense guide for chief security officers (CSOs), directors and managers on how to maximize the effectiveness of your surveillance solution by selecting the right combination of cameras for the task.

What about the Lens?
The lens is the second most important choice in a security video system after the camera. One of the reasons lenses sometimes are taken for granted is that many video cameras, particularly popular dome cameras, come with a lens already built in.

To determine the right lens, the duo needs to consider how far away and how wide an angle each camera needs to see. But in crucial applications, more appropriate solutions include an integrator's selection of a lens for each camera based on the scene and lighting of the view.

There also is the issue of megapixel lenses for HD or megapixel cameras. Without the correct lens, a megapixel camera may not produce the high resolution images to match the capability of the camera's sensor. The lens bottom line: When selecting a megapixel lens make sure the megapixel resolution power extends across the lens's entire field of view, not just in the center. Some lenses, often lower priced, produce megapixel resolution only in the center of the lens; at the periphery, the resolution can be far less.

There are differences and situation advantages among fixed, varifocal and zoom lenses. Fixed focal lenses have a single millimeter number and can be slightly less expensive than varifocal lenses, which have a range of settings, such as 2.6 to 6 mm (wide angle), 3.5 to 8 mm (medium angle), and 5 to 50 mm (long distance). Even though they cost a little more, varifocal lenses are flexible in most situation except where objects are a long distance away. Motorized zoom and telephoto lenses work with fixed cameras and PTZs. They have longer reach to hone in on a specific of the total image and often are used for specialty scenes and applications.

Aspherical, Standard Lens; Manual, Auto Iris
Aspherical lenses have highly polished, computer-designed convex surfaces that let in more light than standard lenses and hold image focus better from center to edge. The technology is smaller in size, can correct for color aberration and lowers the lens f-stop number for increased light transmission. The iris in a lens is like the iris in the human eye; it opens and closes in response to light. Irises in manual iris lenses are set to one fixed f-stop opening and are best where lighting is relatively constant. Auto iris lenses have an electronically controlled iris that opens and closes as the light changes to maintain a constant video level image.

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