Auto electronic shutter (AES). Feature of a camera to adjust for light changes without the use of an auto-iris lens.
Auto iris. A special camera lens with the ability to open or close its iris automatically in response to changing light levels.
Back-light compensation (BLC). The ability of a digital security camera to adjust for bright background lighting that would normally cause the subject to appear too dark.
C-mount. A type of camera lens mount that enables different lenses to be swapped out and used on a security camera.
CCD. The light-sensitive imaging microchip found in digital security cameras.
Digital video recorder (DVR). A special computer that converts analog computer images to digital images, compresses the images, and then stores them for later viewing. A DVR replaces the time-lapse VCR, multiplexor and switch found in analog CCTV surveillance systems.
Duplex. An electronic device used to record and display camera images at the same time. A full-duplex DVR can record camera images while displaying images from a different camera at the same time.
Housing. Protective enclosure that a camera can be placed in to protect it from outside weather conditions.
Lux. Unit of measure of light sensitivity for a camera. Sensitive cameras can operate with low levels of lux.
Multiplexer. An analog device found in older CCTV systems that allows multiple cameras to be displayed simultaneously on a single monitor. Multiplexers can also be used to transmit multiple camera images at once over a single cable.
Pinhole camera. A spy camera with a lens that can see through a tiny hole. These camera are usually hidden.
Power-over-Ethernet (POE). Device that allows one to transmit power to a security power through an Ethernet network cable.
PTZ. Stands for pan-tilt-zoom. PTZ cameras have motors that allow them to be remotely moved up-down, side-to-side, and the camera lens zoomed in or out.
Quad. Analog CCTV equipment used to display 4 camera images simultaneously on a single monitor.
Real-time recording. For digital video, 30 frames-per-second per camera allows no jerkiness in the video.
Remote surveillance. The ability to view a camera image that is located remotely, where the video image is transmitted over a phone line or the Internet.
RG-59. A type of coaxial cable used in CCTV systems.
Signal-to-Noise Ratio (SNR). The ratio of video signal to noise. This is a measure of how much signal noise the camera can withstand and still present a good image. The higher this number is, the better the picture quality.
Switch. An analog device found in older CCTV systems that takes multiple camera inputs and displays them on a monitor one at a time (unlike a quad).
Time-lapse VCR. A special VCR found in analog CCTV systems designed to slow down the recording rate in order to store many hours of video footage on a single videotape.
Varifocal lens. A camera lens in which the focus is not fixed and that can be adjusted either manually or automatically.
Video gain. Also called video amplification, this is the increase in video signal power by an amplifier.
Watch-dog timer. The automatic reboot of a DVR system whenever a problem is detected.
All About CCTV
Bullet cameras are shaped like cylinders, and get their name from the fact that they resemble bullet cartridges. Bullet cameras are often used outdoors in CCTV systems and come with weatherproof housings.
Most bullet cameras have a fixed 4mm lens. A 4mm camera lens lets you to see facial features out to approximately 35 feet. A 4mm lens allows provides about a 70Â° viewing angle, which is the widest angle you can have without suffering picture distortion.
Day-Night Security Cameras
Day-night cameras, also called low-level cameras, employ a very sensitive digital chip that can capture scenes in very low-level lighting conditions. During the day, the camera takes images in color while at night it automatically switches to black-and-white mode when the light level drops a certain amount. These cameras do need some light in order to take images, even if it is the light of the moon or stars.
Some people confuse day-night cameras with infrared cameras but they are not the same. The latter use infrared illumination for their operation to see without any light at all.
Dome cameras gets their name from the plastic dome housing that the camera is enclosed in. They are most often seen in retail businesses and office buildings. Often the dome is dark tinted making it hard to see where the camera is pointing.
Dome security cameras are very tough and some models come with high-impact polycarbonate housings that will withstand heavy blows, making them ideal for locations with high-potential vandalism.
Hidden Spy Cameras
Hidden cameras, also called spy cameras or covert cameras, are designed to be very small and either hidden from view, concealed in everyday objects, or disguised.
Most hidden camera are pinhole cameras, which feature a small lens that can see through a tiny pinhole opening, such as behind a wall.
Infrared cameras, also called night-vision cameras, use an infrared light source near the camera lens to illuminate the area with infrared light, which people cannot see. This allows the infrared camera to see in conditions with no light at all, such as inside dark offices at night. With just a slight amount of normal light, an infrared camera can take a picture that looks as good as that in daytime. Most infrared cameras take pictures in black-and-white.
One problem that infrared security cameras can experience when placed in outdoor housings is light reflection from the front glass cover of the housing. By placing the camera lens flush with the housing, this problem can be minimized.
Some people confuse infrared cameras with day-night cameras but they are not the same. The latter do not use infrared illumination for their operation.
Outdoor Security Cameras
Outdoor security cameras are housed in special weatherproof enclosures or housings that protect them from tough weather and temperature conditions such as rain, snow, wind and the sun. Some enclosures utilize electric strip heaters and fans. The strip heaters help keep the humidity down for the electronics, prevent condensation from forming on the housing cover and camera lens, and provide heat in cold environments.
Other security cameras meant to be placed in high-crime or high-vandalism areas feature tough “armored” enclosures that can withstand heavy blows.
Pan-Tilt-Zoom (PTZ) Security Cameras
PTZ security cameras feature a motorized mount that allows the camera to be moved remotely up-down and side-by-side. In addition, the camera has a motorized zoom lens that can be moved in or out.
Digital Video Recorders (DVR)
Digital video recorders (DVRs) have replaced older analog CCTV system equipment such as multiplexers, quads, time-lapse VCRs and videotapes over the last few years.
A digital video recorder allows live camera images or previously-recorded video images to be viewed on your computer over a computer network or over the Internet. All digital video recorder equipment can be setup to record only images where motion is detected on the camera field of view. This saves you from having to play back hours of video footage that doesn’t change. Digital video recorders for video surveillance are available with 4, 6, 8, 10 and 16 video camera inputs.
A DVR can be connected to a CD or DVD burner, computer hard drive, or other mass storage device. PC-based DVRs are also available – these consist of a PCI card that is installed in the computer along with software. DVRs can be set to email you or even call you on your cell phone if a motion is detected one of the cameras.
Other features of a digital video recorder surveillance system include motion sensing, selectable alarm triggers and pan-tilt-zoom camera support. All video, audio, alarm and control signals are sent over the Internet.
Selecting the Right Security Camera
Application. Ask yourself for what purpose you intend to use a security camera or camera system for: real-time viewing, store surveillance (which means recording and storing video footage), one room of a house, access doors for an office building, etc.
Color vs. B&W. How important is it to have camera images in color? Black-and-white security cameras generally have greater sensitivity at low light levels and thus are cheaper than an equivalent color cameras.
Indoor vs. Outdoor. If the camera is mounted outdoors, be sure and get an appropriate enclosure for the environmental conditions likely to be encountered. This can include rain, snow, heat, cold, sun glare, humidity and corrosive atmosphere.
Fixed lens vs. zoom lens. Fixed-lens cameras are much cheaper than zoom lenses. Ask yourself how important it is to be able to remotely zoom in or out a scene.
Fixed mount vs. pan-tilt camera mount. Similar to the lens issue, ask yourself how important it is to be able to move the camera up, down, or side to side.
Note: One pan-tilt-zoom (PTZ) camera can replace the job of several fixed mount, fixed lens security cameras.
Open vs. hidden camera. Do you care if the security camera is visible or is covert operation of the camera important?
Real-time vs. later viewing. Do you need to be able to view camera images in real-time or is storing images on a video recorder for later viewing acceptable?
Local viewing vs. remote viewing. Do you want to be able to view images from anywhere? This would mean getting a network IP camera that can be accessed over the Internet.
Lens Selection Guide
The focal length of the lens is measured in mm and directly relates to the angle of view that will be achieved. Short focal lengths provide wide angles of view and long focal lengths become telephoto, with narrow angles of view. A “normal” angle of view is similar to what we see with our own eye, and has a relative focal length equal to the pick up device. Our online lens calculator is a simple to use device for estimating focal length, object dimension, and angles of view.
The lens usually has two measurements of F stop or aperture, the maximum aperture (minimum F stop) when the lens is fully open, and the minimum aperture (maximum F stop) just before the lens completely closes. The F stop has a number of effects upon the final image. A low minimum F stop will mean the lens can pass more light in dark conditions, allowing the camera to produce a better image at night. A maximum F stop may be necessary where there is a very high level of light or reflection, as this will prevent the camera from “whiting out”, and help maintain a constant video level. All auto iris lenses are supplied with Neutral Density spot filters to increase the maximum F stop. The F stop also directly affects the depth of field.
C or CS MOUNT
Modern cameras and lenses are generally CS mount. With CS mount cameras, both types of lenses can be used, but the C mount lens requires a 5mm ring to be fitted between the camera and lens to achieve a focused image. With C mount cameras it is not possible to use CS mount lenses.
DEPTH OF FIELD
The depth of field refers to the area within the field of view which is in focus. A large depth of field means that a large percentage of the field of view is in focus, from objects close to the lens often to infinity. A shallow depth of field has only a small section of the field of view in focus. The depth of field is influenced by several factors. A wide angle lens generally has a larger depth of field than a telephoto lens, and a higher F stop setting typically has a larger depth of field than a lower setting. With auto iris lenses, the automatic adjustment of the aperture also means constant variation of depth of field. The small depth of field is most apparent at night when the lens is fully open and the depth of field is at its minimum. Objects that were in focus during the day may become out of focus at night.
AUTO or MANUAL IRIS
Generally we tend to use auto iris lenses externally where there are variations in the lighting levels. Manual iris lenses are used normally for internal applications where the light level remains constant. However, with the introduction of electronic iris cameras it is now possible to use manual iris lenses in varying light conditions and the camera should electronically compensate. There are several considerations to this option though: the setting of the F stop becomes critical; if the iris is opened fully to allow the camera to work at night, the depth of field will be very small and it may be more difficult to achieve sharp focus even during the day. The camera can maintain normal video levels, but it cannot affect the depth of field. If the iris is closed to increase the depth of field, the low light performance of the camera will be reduced.
VIDEO DRIVE or DIRECT DRIVE
With auto iris lenses it is necessary to control the operation of the iris to maintain perfect picture levels. Video driven lenses contain amplifier circuitry to convert the video signal from the camera into iris motor control. With direct drive lenses, the camera must contain the amplifier circuitry, and the lens now only contains the galvanometric iris motor making it less expensive. The deciding factor depends on the auto iris output of the camera. Most now have both types.