1. What is CCTV
2. Is it difficult to install CCTV
3. CCTV camera Information
4. CCTV Lens Types & Uses
5. CCTV Cable Information
6. CCTV Monitor Information

1. What is CCTV
Most people think that CCTV is a relatively new invention, but then again, many don't even know what it is ... so first things first, what exactly is Closed Circuit Television? Well the television bit is perhaps self explanatory; it's simply about putting a picture onto a television screen, or 'video monitor' to give it its correct title. Incidentally, very basic video monitors are essentially televisions, but without the additional circuitry needed, to receive and decode the Radio Frequency signals, which are transmitted through the air.

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The 'Closed Circuit' bit is actually quite straightforward. Let's say for example, that you subscribe to Satellite TV. If you watch your favourite television programme, you and perhaps a few million others will be able to receive the transmitted signal through the dish and 'set top box'. As anyone with a correctly tuned 'Telly' can access this signal, we can safely describe this type of arrangement as an 'Open Circuit Television' or 'OCTV' system. If a signal is being linked from any source, whether it's a DVD player, a camcorder, or a surveillance camera, directly to a display device such as a television, this is described as a 'Closed Circuit' simply because it is not available to anyone else.

So you can see that in the early days of developing video camera security systems, the pictures from the cameras were almost always sent to a monitor, or a video recorder, or indeed a sealed Control Room under 'Closed Circuit' conditions, hence the now widely accepted term "Closed Circuit Television".
This extract is by kind permission of www.doktorjon.co.uk

2. Is it difficult to install CCTV ?
Smaller projects are within the scope of a competent DIY'er. The self install approach must be carefully considered. While help and advice can be obtained on equipment and materials it is very difficult to get it right without getting a professional survey completed. Lack of knowledge leads to poor working practice, poor performance, costly materials and in many cases the wrong products being installed. Here is an extract from www.doktorjon.co.uk:

"The truth of the matter is that most CCTV cameras are just not properly set up for their intended purpose, and that’s the main reason why it’s so important to understand the objectives, before installing the system. In the context of Security, their are essentially four main steps to achieving an efficient approach when applying Closed Circuit Television; but it is still worth remembering that in most situations, the general effectiveness of CCTV increases when it is used as part of an overall strategy, involving various other complimentary techniques, (for example, lighting, intruder alarms, access control, etc.).

Step 1 is the Crime Audit (CA)... Before you can address any given problems, you first need to understand the scope and complexity of any criminal behaviour which has so far taken place.
Step 2 The Risk Assessment Survey (RAS) ... is in some respects the key to designing an effective Closed Circuit Television system.
Step 3 Development of the CCTV System Profile (SP)... this is actually the point where the system design begins to get .... just a little bit more interesting.
Step 4 Look closely at the benefits of ‘macro’ profiling... Individual areas of the system are addressed.

That is all the detail that we have room for on this website, go to www.doktorjon.co.ukfor more information. Hopefully now we hade described that CCTV is more than buying a few cameras and chucking them in. Clearly there is a case for a considered approach that, if done carefully and thoughtfully can save money and time.

We refer to the term CCTV loosely as it is the common reference to surveillance cameras but as has been described, surveillance cameras are very often OCTV (Open circuit television).

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3. CCTV Camera Information

What is a CCD sensor?
Most CCTV cameras are now almost exclusively ‘CCD’ sensor type. CCD stands for Charge-Coupled Devices. These are light-sensitive chips, the sensitive area being split into a large number of individual pixels (small dots on the chip). An image from a scene is focused through a lens onto the chip surface and charge is built up in each pixel proportional to the intensity of the light falling on it. Hence an electrical representation of the optical image is formed. Typical active pixel counts for CCD sensors is between 250,000 and 500,000 pixels. Cameras are available in both monochrome and colour types.

Lenses
Note that COP, in common with most other manufacturers, supply cameras without lenses fitted. This is because there are many different types of camera and even more types of lens and so it would be impractical, and very expensive, to stock all possible permutations and combinations to meet each application. Hence - REMEMBER TO QUOTE FOR THE LENS!

Camera performance
The main criteria of a camera’s performance are its sensitivity and resolution. Sensitivity is a measure of the minimum amount of light required by the camera to give a ‘useable' image. Resolution defines the amount of picture detail in the image produced by the camera.

Sensitivity
The CCTV industry has many ways of stating an individual camera’s sensitivity performance. Most common is minimum scene illumination required to give useable picture at a particular lens aperture e.g. 11.4. (This is inherently subjective). Another, more objective definition is the minimum scene illumination required by the camera to give full video output i.e. 1v peak to peak. Few manufacturers use this definition! Most manufactures provide a figure in LUX which is actually a light level (see chart below) the figures quoted are often like this 0.1 LUX. The problem with this is that to get a true representation of the actual sensitivity of the camera the lens apertures must also be compared. Lens apertures, i.e. the size of hole that light can pass through in the lens, must be compared in order to get a true comparison of performance.

• Camera 1 requires a minimum scene illumination of 0.1 lux at a lens aperture of fI .4 to give a useable image.
• Camera 2 requires a minimum scene illumination of 0.05 lux at f 1.0 to give a useable image.

This appears to say that camera 2 is twice as sensitive as camera 1 because it needs half the light to give a useable picture. In fact the cameras have equal sensitivities because the aperture through which light is allowed to fall on the sensor of camera 2 is twice the area of that for camera 1.

Typical sensitivities (defined as minimum scene illumination required for useable picture with lens aperture at fI .4) for current CCD cameras are as follows:

• Medium Performance (General purpose) Monochrome 0.5 - 0.25 lux
• High Performance (Low-Light/Outdoor) Monochrome < 0.20 lux
• Medium Performance (General purpose) Colour 3.0 lux
• High Performance (Low-Light) Colour < 2.5 lux
   

Note that monochrome CCD cameras are still approx. 5 times more sensitive than equivalent colour cameras. Typical light levels are as follows:

• Full Summer Sunlight 50,000 lux
• Dull Daylight 10,000 lux
• Shop/Office environment 500 lux
• Dawn/Dusk 1 - 10 lux
• 1/4 Moonlight 0.1 lux
   

Resolution
Resolution is measured in lines and normally only horizontal resolution is quoted. Vertical resolution of a camera is of little interest because pictures are generally speaking limited by the scanning system used to produce the image. In the UK and Europe this is the CCIR system, which defines that a picture is built-up from 625 lines across the screen. Of more interest in measuring camera performance is horizontal resolution. This is the maximum number of black or white areas that can be identified across the picture. This is always specified per monitor height. A typical general purpose monochrome camera has a horizontal resolution of 380 lines. This means that it should be possible to resolve 380 x 1.33 i.e.. 505 individual actual lines of black, white or grey along any one line of a CCTV picture image. (The factor of 1.33 comes from the fact that a TV picture has an aspect ratio of 4 : 3) Typical resolution performance for CCD cameras are as follows:-

• Medium Performance (General purpose) Monochrome 380 lines
• High Resolution Monochrome 600 lines
• Medium Performance (General purpose) Colour 380 lines
• High Resolution Colour 480 lines.
   

Camera formats
Cameras will be quoted as 1/2", 1/3" or occasionally as 2/3". Newer cameras will be referred to as 1/4". This refers to the format of the camera and defines the size light-sensitive area of the imaging device used in the camera. In itself it gives no measure of a camera’s performance although generally the smaller the format size, the smaller the light gathering area of the sensor. It is provided for information to enable the installer to match the camera to the correct lens. Camera formats are getting smaller in order to reduce the costs of the imaging devices and hence the cameras themselves as well as the lenses put onto them.

IMPORTANT
The format size of a lens must be equal to or greater than the format size of the camera it is being used on. If the lens is of smaller format size than the camera then the corners of the scene being viewed will be cut-off (vignetting).

Camera Lens Mounts
A CCTV lens will be specified as either C or CS mount. Both types of lens look very similar and there is nothing that can be physically measured on a lens. The difference between the two types is the position of the focused image behind the lens. CS lenses focus 12.5mm behind the lens whereas C lenses focus 17.5mm behind.

4. CCTV Lens Types & Uses
There are two main types of lens used in CCTV, these are fixed focal length types and zoom lenses i.e. with variable focal length (vari-focal).The focal length of a lens defines its effective viewing angles both horizontally and vertically. Hence the focal length of a lens determines the size of a particular image on the monitor screen or the area of the scene being covered by the camera.

Fixed Focal Length Lenses
For ½” format lenses on a ½” format camera, the following lens focal lengths are commonly available:

For 1/3” format lenses on a 1/3” format camera, the following lens focal lengths are commonly available:

Note that a 6mm ½” format lens on a ½” camera gives approximately the same angle of view as a 4mm 1/3” format lent on a 1/3 camera

If a ½” format lens is used on a 1/3” format camera then the viewing angles obtained will be 2/3 of those obtained if the lens was used on a ½” format camera.

Lens selection for image size

The choice of focal length of lens fitted to a camera affects how a particular object e.g. a person will appear on the monitor screed or recording from the camera. Obviously the bigger the image appears on the screen, the better the chances of recognizing or identifying a person being viewed or recorded.

Home office recommendations to be incorporated into European standards for CCTV systems specify that in order to be able to recognize a person he or she must occupy at least 50% of the monitor height. Also if necessary to be able to positively identify an unknown person then his or her image must occupy 120% or more of the screens height.

Lens selection for different light conditions

Most CCTV lenses are equipped with an iris that consists of four or six opaque metal vanes which are arranged to give a roughly circular hole or aperture through which light can pass and then fall on the camera sensor surface. The vanes can be driven together to alter the size of the lens aperture to control the amount of light falling on the sensor and hence alter the picture brightness.

Aperture Ratio
The size of the aperture is defined by an aperture ratio or f-number where:

f-number or aperture ratio = focal length of lens

For example, a 6mm lens at f1.0 has an aperture of 6mm in diameter.

The same lens at f1.4 has an aperture of 4.25mm in diameter.

Hence the area has reduced and so has the amount of light allowed to pass through the lens.

Most lenses are marked with f-numbers; with each mark equalling one ‘stop’ i.e. a halving of the area of the aperture through which light can pass.

The smaller the f-number, the larger the lens aperture and so the more light the lens can collect

Control methods for lens iris

Manual Iris Lenses

The simplest type of iris control is termed ‘Manual Iris’. The lens is equipped with a ring on the body that can be turned to alter the aperture directly. In CCTV systems this can only be used generally in fixed lighting conditions or where the camera is readily accessible and it is not inconvenient to have to continually adjust the lens for correct picture brightness.

Auto-Iris Lenses

A far more common arrangement is to use auto-iris lenses where the iris vanes are driven by a galvanometer or servo motor which is controlled by an ‘iris-amplifier’ circuit within the lens, the control input of which is the video signal from the camera itself. Hence an auto-iris lens is used where the lighting level is liable to continuous changes e.g. outdoors where lighting can change from full sunlight down to near total darkness.

Direct-Drive Lenses (FCS)

These are a development on auto-iris lenses where the motor or galvanometer coil moving the iris vanes in the lens is driven directly by the camera, hence ‘Direct-Drive’. There is no active electronics in the lens and therefore they are simpler, smaller and cheaper than an equivalent auto-iris lens. They must be used with a camera capable of driving ‘DD’ lenses and this is normally identified by the presence of the characteristic 4-pin square ‘Hi-Rose’ (Panasonic) plug on the side of the camera.

Direct Drive lenses have no adjustment controls other than focus (and angle of view in the case of Vari-focal lenses).

Picture brightness is now controlled by a level setting on the camera.

DD lenses are slightly less flexible and optimisable for outdoor use.

5. CCTV Cable Information
Video signals used in CCTV systems must be transmitted over 75R ‘low-loss’ coaxial cable in order to give acceptable picture quality at the receiving end. The use of co-axial cable prevents interference to the quite small (1v) peak to peak) video signal from external sources and because the cable is low in capacitance then the high frequency elements of the signal are not attenuated to the same degree as would be the case with say a standard twisted-pair type transmission cable. Distance limitations do have to be set for different types of coaxial cable but these are subjective since different end-users will accept different levels of picture quality and hence levels of signal attenuation. ‘Acceptable’ pictures should be obtainable over the distances as shown for the following common types of cable used in the CCTV industry:

Different Grades within each type of cable exist. These grades define the use to which the cable can be put. ie suitable for direct burial etc. The type (i.e. URM7O) defines the electrical performance. Note that the above distances quoted assume a continuous cable run with a minimum number of joints.

Every well-made joint will add extra signal attenuation equal to approximately 50m of cable, badly made joints considerably more! Coaxial cable is generally supplied either on 100, 200 or 500m drums. Always remember that a video signal is only 1volt in amplitude and is thus very vulnerable to external interference and losses in poor quality cables. Never use aerial down lead type coaxial cable for CCTV signals ! Always keep video signal cables as far away as possible from mains cables and wiring that may carry high-frequency signals.

6. CCTV Monitor Information

Whilst the camera + lens combination is pivotal to providing a decent quality image, it’s down to the humble Video Monitor to actually display a high quality picture.

In terms of monochrome monitors (Black and White), the technology which is based on the good old fashioned Cathode Ray Tube (CRT), has barely changed over the last twenty years. The components may have improved, and production methods become more streamlined, but the resulting picture quality is on average, pretty much the same. It’s only when we look at Colour Monitors, that their's now a noticeable shift starting to take place, towards the latest generation LCD flat panel displays. For much larger displays, particularly in custom built control rooms, Plasma Screens are now creating a bit of a stir.

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The above questions and answers are very basic and by no means a definitive answer as CCTV is a very detailed subject. If you would like us to quote for your requirement please email us the details and we will respond as soon as possible.