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Surveillance Systems Basic Guidelines

CCTV Basics

The first thing you should ask yourself before purchasing a security surveillance system is: What do I need this system to do? Do you need detection of an incident only, or do you need to identify the object in question. Keep your answer in mind when reading this document.

The second thing you should ask yourself before purchasing a system is: What is my application? The most common applications are: security applications, safety applications, and management applications.

Many elements must be considered before designing your surveillance system:

• Scene and lighting
• The cameras
• The lens
• Video transmission methods
• The monitor
• Peripheral equipment

Without proper equipment and studying all these variables, you may be deceived on what really is causing poor imaging. For example, what might look like a poor camera, may be a poor monitor. You can't simply take a high resolution camera and expect its high performance to be visible on a poor monitor or display. Each component in the system will affect the overall performance. Your overall quality is only as good as the weakest component in your system.

Scene and Lighting
The scene refers to the objects or area to be observed as well as the environment in which it will be observed. One important aspect that must be considered is the environment. The environment contains multiple colors, materials, reflective surfaces, and varying degrees of light within the picture. To select the proper equipment you must determine the amount of light present during peak times of operation. The amount of light on the scene determines everything from picture clarity to focus. What is the minimum light that will be available? Will it be more cost efficient to go with a better night-view camera or adding more artificial lighting to the scene?

For more detailed information on lighting please click here

The Cameras
A camera's performance largely depends on the amount of light present, as well as the imager used. When the level of light changes dramatically, usually a camera equipped with automatic iris control can help ensure consistent image quality. Auto iris enables a camera to open or close its lens accordingly to the varying levels of light, limiting or increasing the amount of light passing onto the sensor. Cameras are available in several imaging formats expressed as 1/2, 1/3, 1/4 inches. These are the sizes of the imager used. Generally speaking, you should match the camera's format with the len's format (ex. 1/3" sensor with 1/3" lens). It is crucial to understand a camera's format, resolution, and corresponding lens focal length when determining what camera will best suit your needs.

For a more technical discussion of formats, resolution, and pixels please click here

For a discussion on color vs. black/white cameras click here

The Lens
The lens plays a large role in a system's design. The primary function of the lens is to collect light from a scene, focus the image to produce a sharp image on the camera's imager. Selection of a lens is critical. The lens directly affects the size, shape, and sharpness of the image to be displayed on the imager. Factors such as distance to the scene, focal length, desired field of view, lighting, and format affect the size and clarity of the image.

The field of view (FOV) is the actual picture size (height/width) produced by a specific lens. If the view is not suitable, consider a different lens to increase or decrease the field of view.

Camera lenses are divided into two major categories: fixed and varifocal (manual zoom). A fixed lens obviously has a fixed focal length, while a varifocal lens enables the user to change its focal length to produce a zooming effect (narrowing the FOV). Focal length is the distance from the optical center of the lens to the focal point near the back of the lens. This focal length distance is displayed on the lens (in millimeters). A lens with a focal length of 8mm on a 1/3" camera produces a field of view similar to the view produced by the human eye. A wide-angle lens has a short focal length, while a telephoto lens has a long focal length. In order to change the field of view, you must change the lens.

The ability of a lens to gather light depends on the relationship between the lens opening (aperture) and focal length. This relationship is symbolized as the letter F, also know as F-stop. The lower the F-stop number, the larger the aperture, thus the greater ability to pass light through the lens to the camera's imaging device. For example, a lens with an F-stop of F1.2 can gather much more light than a lens with an F-stop of F4.0. A lens with a low F-stop number is sometimes referred as a "fast" lens.

Depth of field is another consideration when determining the proper lens. Depth of field is the area in focus ahead of and behind the main object. When you focus on a particular object there is an amount of area behind the object and in front of the object that will still be in focus, although not as sharp. Depth of field increases or decreases based on the length of the lens, the len's aperture, and distance from the camera to the subject.

Lens length
Shorter lens (ex. wide angle) = longer depth of field
Longer lens (ex. telephoto) = shorter depth of field
Aperture
Wide aperture (low F-stop) = shorter depth of field
Narrow aperture (high F-stop) = longer depth of field
Distance to object
Short distance = shorter depth of field
Long distance = longer depth of field

If depth of field is important consider increasing artificial lighting or install cameras with normal angle lenses.

Camera lenses generally come with a C-mount of CS-mount and must be matched appropriately to the camera's mounting requirements. The difference is the distance from the lens' actual optics and the camera's imaging device. The C-mount lens is 17.5mm from the imaging device, whereas the CS-mount lens is 12.5mm away. A C-mount lens can be used on a CS-mount camera only if a 5mm spacer ring is added (this is why some cameras allow C or CS mount lenses, they just include a spacer). Though, a CS-mount lens cannot be used on any C-mount camera.

For more technical information on lenses, focal length, and field of view click here

Basic Guidelines

Color vs Black and White

Fixed Camera vs PTZ

Lighting Considerations

Resolution and Formats

Lens Information

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We provide lease options for your surveillance system, if the purchase price is over $5k. With a lease, there is generally only a small down payment and all payments are 100% tax deductable. Crest Capital provides our leasing and here is a link to find out if you qualify

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