Security cameras with auto iris, have the ability to compensate for large variations in light levels. This is useful for security cameras that need to adjust for changes from bright sunlight to darkness or night. Auto iris circuitry is normally linked to a motorized drive that opens and shuts the iris on the camera lens. Closing a physical iris is a much better way to protect a camera from being damaged by bright sunlight then simply using electronics to reduce the signal strength.
Some DVRs and security cameras have alarm inputs, which can accept input from a sensor device such as a door contact or a passive infra-red motion detection which trigger the camera or DVR to take some action such as to begin recording.
The opening of the CCTV lens. The size of which is controlled by the iris and is measured in F numbers. Generally, the lower the F number, the larger the aperture is and consequently more light can pass through the lens.
Back Light Compensation
This is a feature of security cameras that automatically adjusts the image to compensate for bright light to give more detail on the darker areas of the image. For example, use is to focus on the detail of a face of a person that has the sunlight shining from behind.
A Video Balun enables the transmission of video using unshielded twisted pair wire instead of coaxial cable. The word "balun" comes from combining the terms balanced and unbalanced. The function of a balun is to transform an unbalanced signal into a balanced signal. When video signal is transmitted through coaxial cable, the distance traveled by the signal is limited because the signal is in the form of an unbalanced signal that is susceptible to Radio Frequency Interference or noise. Coax cable incorporates special shielding to minimize noise. Video Baluns transform the video signal into a balanced form in which each wire in the twisted pair transmits an identical signal with opposite polarized magnetic fields. Noise affects each signal equally. When the signals are combined, the noise is cancelled out. By using a designed balun, an unshielded twisted pair wire can transmit video for much longer distances than coax cable and with a lower cable cost.
BNC is a connector for coaxial cable that is most commonly used for CCTV installations.
CCD Charge Coupled Device
Charge Coupled Device, CCD, is one of the two main types of image sensors used in security cameras. When a video is recorded, the CCD is struck by light coming through the camera's lens. Each of the thousands or millions of tiny pixels that make up the CCD converts this light into electrons. The number of electrons, usually described as the pixel's accumulated charge, is measured, and then converted to a digital value. This last step occurs outside the CCD, in a camera component called an analogue-to-digital converter.
C Mount Lens & CS Mount Lens
There are two main types of lenses used in security cameras. The C mount lens has a flange back distance of 17.5mm. The CS mount lens has a flange back distance of 12.5mm. C mount lenses therefore have a longer focal distance. CS mount became widely used, because it its more practical for many of today's more compact cameras. Lenses are often supplied with a 5mm spacer ring (sometimes called a C ring) that allows a C mount lens to be used on a CS camera. Most modern security cameras are CS.
A type of cable typically used in cctv installations that has a central conductor, surrounded by a shield sharing the same axis. The shield can be made from a variety of materials including, braided copper, or lapped foil. There are various standards for specific types of co-axial cable. The cable used for normal CCTV installations is called RG59.
The encoded output of a surveillance camera whereby the red, green, and blue video signals are combined with the synchronizing, blanking, and color burst signals and are transmitted simultaneously down one cable.
Digital video pictures can be compressed with a number of techniques. These include: JPEG and JPEG-2000 (for still images), M-JPEG and MPEG (for moving pictures).
DVR (Digital Video Recorder)
A Digital Video Recorder is a generic term for a device that is similar to a VCR but records television data in digital on a hard drive as opposed to a VCR tape. A DVR looks like a VCR and has all of the same functionality of VCR (recording, playback, fast forwarding, rewinding, and pausing) plus the ability to skip to any part of the program without having to rewind or fast forward the data stream.
Well Time Programming
The length of time a switcher or CCTV multiplexer displays one camera before sequencing to the next. Multiplexers Focal Length
The distance between the center of a lens, or its secondary principal point and the imaging sensor. Lower lengths give a greater field of view and less magnification. Longer lengths give a narrower field of view and greater magnification. The table below gives an approximate value for the angle of the field of view for lenses of various focal lengths and also considering the size of the imaging device (CCD). Most CCTV cameras have one of the 3 sizes of imaging devices listed below, 1/4", 1/3" or 1/2". Almost all of CCTV Camera Pros cameras have 1/3" Sony CCD imaging devices.
Imaging Device Size
Gamma correction controls and adjusts the overall brightness of an image for consistency.
A quality brand of DVR Cards made for Windows based computers. A complete line of Geo-vision DVR Cards can be seen here:Geovision DVR Cards.
The total opposition offered by a device to the flow of an alternating current. Measured in Ohms.
Devices with internal sync have an internal crystal to provide sync pulses without needing reference from any external device.
Low frequency light below the visible spectrum. Infrared is used in surveillance cameras to provide a light source to record images in dark and zero light conditions.
IP Waterproof Rating
IP waterproof ratings are a BSi standard measurement for how waterproof something is. Many security cameras or camera housings are designed for outdoor use need to be waterproof. The IP rating number has two digits, and optional letters after them. E.G IP66 and IP68. The first number defines the protection against ingress of foreign objects. 0 is the lowest rating and means non-protected. 6 is the highest rating and means dust tight and protects against access with a wire. The second number defines the level of protection against ingress of water. 0 is the lowest rating means non-protected. 8 is the highest rating and means protects against continuous immersion in water.
For further information, see the BSi website at www.bsi-global.com or www.bsi.org.uk
The mechanical device that adjusts to vary the amount of light passing through the lens of a camera.
JPEG is a standard for the encoding and compression of images. JPEG is used in the video surveillance systems to compress and store individual frames of video. JPEG was developed by the Joint Photographic Experts Group.
LCD (Liquid Crystal Display)
Technology used for flat screen displays.
Connecting an additional device in parallel with an existing video cable. For example, when driving a video recorder as well as a monitor from the same video signal.
Unit of light illuminable used as a measure of low-light recording capacity in security cameras. Cameras with a Lux rating of 0.2 Lux or less would be considered low-light cameras. It is not possible to get good color definition in low light levels, so in general low light cameras are always black and white. Day/night cameras use electronics to switch from color during the daytime, to black/white during night or low light conditions. Many low light cameras also use infrared, which is useful in zero light conditions. The lower the LUX rating of a camera, the better it will see in low light.
This refers to the part of a video signal that carries the monochrome information. i.e. brightness information.
The Motion Picture Experts Group (MPEG) released MPEG-4 encoding in 1998. The basic idea behind MPEG is that compressed images are compared before being transmitted over the network. The first compressed image is used as a reference and compared to the images that follow it in the video sequence. The first image is transmitted over the network along with the parts of the following images that differ from the initial reference image. The viewing application on the receiving end of the transmission then reconstructs all images based on this information and displays the result. This is a simplified description of how MPEG-4 works.
This is a device that takes inputs from 2 or more video channels and combines them into one signal. This is often done by using time division multiplexing, which interleaves frames from each channel in such a way that they can be split out again. Frequency division multiplexing uses different frequencies to achieve the separation of the signals.
This refers to a camera that is designed to record pictures and transmit them directly over a computer network or Internet connection. Network cameras normally do not have any analogue video outputs. The images are encoded directly in one of the standard compression techniques, such as JPEG or MPEG.
NTSC is an abbreviation for the National Television Standards Committee. The term "NTSC video" refers to the video standard defined by the committee, which has a specifically limited color gamut, is interlaced, and is approximately 720 x 480 pixels, and 30 frames per second (fps). This standard is used in North America.
OSD (On Screen Display)
A method of displaying set-up information and/or instructions on a display monitor.
PAL is an abbreviation for Phase Alternating Line. This is the television display standard that is used mainly in Europe, China, Malaysia, Australia, New Zealand, the Middle East, parts of Africa, and other parts of the world. PAL uses 625 lines per frame and a frame rate of 25 frames per second.
This is a type of lens with a very small aperture. Normally used for covert applications, where it can easily hide behind or within another object.
A device that forwards data packets along networks. Typically when referred to in CCTV installations, a router is used to connect a surveillance DVR and a computer to a single Internet connection. A router can also be used to connect multiple IP based security cameras to a single Internet connection.
A pixel refers to an individual area on the surface of the imaging device, normally a CCD. It is made from photosensitive material which converts light into electrical energy. In the context of a display monitor, a pixel is also referred to as an individual area on the surface of the screen which converts electrical energy to visible light.
RS-232 is a communications standard for serial communications between devices. In CCTV, this can be communication between a controller and a surveillance camera. The RS-232 standard allows for the connection of two devices through a serial link, and is the protocol used for serial connections in computers. RS-485 allows for serial connections between more than 2 devices on a networked system and is defined below.
RS485, also referred to as EIA-485 is a communications standard for serial communication between devices. When talking about surveillance systems, RS-485 is typically used as the protocol to allow computers and remote controllers to control the activity of cameras such as pan, tilt, rotate, and zoom operations. RS485 is an updated version of the original serial protocol, RS-232.
Signal to Noise Ratio (S/N Ratio)
This is the ratio between the signal strength and the noise levels on an audio or video signal.
Television Lines (TVL)
This is a measure of the resolution of a video device. The higher the number, the higher the resolution is. 380 TVL is considered medium resolution. 480 TVL or greater is considered high resolution.
This refers to a type of lens that has the capability to change the focal length. This allows adjustment of the magnification and field of view of the security camera.
WDR Security Cameras
A WDR security camera (Wide Dynamic Range) is used for capturing clear images of objects surrounded by a strong back light, while still keeping the background visible.