The Crime Prevention Website


Camera lenses and focal lengths

There are many types of lenses and each with various focal lengths.  The type you need will be determined by the angle of view that is required to include all the detail you want to see on your screen. To capture a useful image of a person standing by your front door or by the till point a 3.6mm or 4mm lens should be sufficient. As the distance between the camera and point of interest becomes greater a lens of longer focal length will be required. 

If you are using the services of an installer they will work out which lens to use based upon your operational requirement.  If you are fitting your own system you should refer to the manufacturer’s tables.  Many cameras are available with varifocal lenses allowing you to adjust the focal length to suit your specific needs.  In the example specification list below the camera is described as ‘2.8-12mm Varifocal with Auto Iris’. 

Types of camera

Here follows a brief and generic description of camera types.  There are literally hundreds of camera models and it is recommended that once you have determined which generic type you require you start comparing one with another using the manufacturers’ specifications. For those of you using the services of an installer make sure that the camera being recommended will fulfil the requirements of your operational requirement.

Here is an example of a camera’s specification

  • Imaging Sensor - The type of CCD being used to capture light*  
  • Total Pixels - E.g. PAL- 752 x 582
  • Resolution - E.g. 700TV Lines Colour – High Res is 500 +
  • Video Out - E.g. 1.0Vp-p/75Ohm CVBS
  • Minimum Illumination - E.g. 0.00001 lux F1.2 (Colour)
  • Day/Night mode - E.g. IR Cut Auto Switching
  • Lens - E.g. 2.8-12mm Varifocal with Auto Iris
  • Power Supply - E.g. DC12V, 3.6W (Max on IR Switching)
  • Operational Temperature - E.g. 10℃ - 50℃
  • Dimensions - E.g. 75mm (Diameter) x 130mm (Length)
  • IP Rating - E.g. IP66
  • Scanning - E.g. 2:1 Interlaced
  • Synchronisation Mode - E.g. Internal
  • Horizontal/Vertical Frequency - E.g. PAL- 15.625kHZ / 50HZ
  • S/N Ratio - E.g. >45dB (AGC Off)
  • Gamma Correction - E.g. 0.45
  • Gain control - E.g. Auto
  • Electronic Shutter - E.g. PAL- 1/50-1/100,000s
  • Operational Humidity - E.g. 20-90Percent RH

*In general, smaller CMOS chips are lower quality than larger CCD ones. 

Box Cameras

As the name suggests this camera is the oblong box shape that we will all be familiar with from seeing them on the corners of supermarket buildings and hanging from masts in car parks.  The smaller ones are used as fixed cameras for domestic installations. They are normally used for long distance viewing, which requires a long lens.  They’re often motorized when they’re known as PTZ (Pan, Tilt and Zoom) and sometimes include lens wipers to keep them clean together with heaters and blowers.  In low light conditions you will see the infrared light version of this camera installed with built-in or separate infrared light source. In commercial installations, when they are installed at low level or where there is a problem of vandalism, they can be installed behind a protective enclosure, such as wire mesh.

Pan Tilt Zoom (PTZ) Cameras

PTZs are generally not used for domestic or small business installations since their purpose is essentially for live monitoring and movement.  They will be found at sports stadiums in shopping centres, town centres and around large commercial buildings and yards and car parks that retain security personnel.   PTZs allow the operator to tilt the camera up and down and pan around (often 360°) and to zoom in and out to a particular point of interest to capture specific detail.  If the monitored building and grounds have residential areas close by the field of view the cameras will be controlled to prevent the operator looking beyond the area intended for monitoring. These cameras can be contained within a dome and have infrared sensitivity.  Various forms of PTZs are available, some of which only have a zoom capability.

In commercial situations PTZs can be pre-programmed to ‘patrol’ a defined area.  They can also be integrated with an alarm system to automatically move to a specified location if the alarm activates.

Next time you’re walking along the shopping streets in your local town or city it is almost certain that you’ll be on a PTZ camera!

Infrared Cameras

These are used to obtain essentially monochrome images when there are very low light conditions.  They are used for domestic installations, especially when viewing long back gardens.  Infrared cameras use the infrared portion of the electromagnetic spectrum and turn the infrared radiation into images (thermal imaging).   The ‘hotter’ the source of the infrared light the brighter it will appear in the image.  Obviously, the quality of the image and the distance a camera can see down the garden are governed by the quality of the camera and its sensitivity to infrared light.  Images can be improved by projecting infrared light into the field of view from the camera position and a lot of cameras do this.  The infrared light is usually delivered using LEDs.  The size of the LEDs and the number of them will determine the range of useful infrared light emitted, which should be checked against the manufacturer’s specifications.

Low Light cameras

As an alternative to an infrared camera you can now purchase low light cameras that will capture images in lux levels much darker than moonlight.  Some switch to black and white images after dark whilst others continue to film in colour. If it’s pitch black you will however need to use an infrared camera or provide a good level of artificial lighting.

Examples of light levels expressed in Lux (Lux is an abbreviation of ‘lumens per square metre’)

  • Very bright sunlight                                  120,000 lux
  • Shade on a very bright day                      20,000 lux
  • Overcast day                                           1,500 lux
  • Sunset and sunrise on a clear day         400 lux
  • Overcast with storm clouds                    200 lux
  • Full Moon on a clear night                       0.25 - 1 lux
  • Quarter moon on a clear night                0.01 lux
  • Moonless night, clear with city glow        0.002 lux
  • Moonless night, clear with no city glow   0.0002 lux
  • Moonless night and overcast                  0.0001 lux

Bullet Cameras

These are small cylindrically shaped cameras, which are much more inconspicuous than box cameras.  They are often used for domestic and small business installations and can capture reasonable short distant images under decent lighting conditions.  Don’t expect them to capture the same quality images obtained by box cameras.

Covert (Spy) Cameras

Covert cameras are designed not to be seen! They have been incorporated into smoke detectors, alarm PIR detectors, cuddly toys (used to spy on babysitters) and door viewers.  Their image quality is limited, but they have their uses.  The ones used in the doors viewers are capable of obtaining and recording ID quality images of callers at the door.

Wireless Cameras

Wireless signalling cameras are used when it is either impractical to run a signalling cable to it or cabling is not appropriate.  Many quality cameras can be fitted with transmitters to convert them to ‘wireless’.  They obviously require a power supply, which can be mains or battery.  A wireless portable camera is useful for monitoring a young child’s or baby’s room. (See also Smart Home Security Systems)

Dome Cameras

Dome cameras are used when the camera is accessible.  You’ll commonly see them in shops and offices where there are low ceilings.  Metal dome cameras tend to be used where there is a danger of vandalism otherwise plastic domes are used.  With the plastic type it is very difficult to see which way the lens is pointing.   Dome cameras can accommodate PTZ and infrared for low light conditions, but their size restricts the lens size.

Motion Detection Cameras

These cameras have a sensor that switches them on when they detect movement.  Some also enable you to digitally block out certain areas in the field of view where natural movement is expected, such as the movement of trees in the wind.  These features can be useful if you want your camera to alarm you. Motion detection will also reduce the amount of footage you’re storing.

IP Cameras

An IP (Internet Protocol) Camera is a type of digital video camera that can send and receive data via a computer network and the Internet.  You will probably be familiar with the term ‘webcam’, which essentially is the same thing, but the term ‘IP’ (and sometimes ‘Netcam’) is normally applied to cameras used for surveillance. You’ll often see them described as IP Megapixel HD cameras. A 1 megapixel camera produces an image containing 1 million pixels.  The resolution of your digital camera and phone camera will be measured in megapixels.

Some IP cameras require a central Network Video Recorder (NVR) to handle the recording, video and alarm management. These are termed ‘centralised’.  A Network Video Recorder contains no dedicated video capture hardware, but is instead a software program that records video in a digital format to a storage device, such as a disk drive, USB flash drive or SD memory card.

The other type of IP camera, (decentralised) does not require a central NVR, and instead has built-in recording and can record directly to a local storage media, such as a flash drive, hard disk or to a network attached storage.

AN NVR is very different from a digital video recorder (DVR) as its input is from a network rather than a direct connection to a video capture card or tuner. Video on a DVR is encoded and processed at the DVR, while video on an NVR is encoded and processed at the camera and then streamed to the NVR for storage or remote viewing.

The majority of NVR home and small business security systems (also termed ‘IP systems’) are fairly easy to install.  They can be accessed, controlled and the images reviewed via a web browser and allow the user to be messaged if an alarm is activated.

For viewing outside of the internal network you will need a mobile connection (3G or 4G). Make sure you have the right data package for the number of minutes that you want to view. In one hour you can use 100mb for 4 average cameras.

(See also Smart Home Security Systems)

Weather and dust resistance considerations

Although external cameras should be weather-resistant you should not locate them in places where they could be soaked by storm water running off the building.

Externally used cameras and or their housings should meet IEC standard 60529 levels IP65 or IP66.  Check the table and explanation below to see what these levels mean. Allowing a loop of cable to fall between the camera and its mounting will form a drip point and will reduce the likelihood of water penetrating the camera housing. 

IP Codes explained

The IP Code (International Protection Marking) sometimes misinterpreted as ‘Ingress Protection Marking’, classifies and rates the degree of protection provided against the intrusion of objects (including body parts such as hands and fingers), dust, accidental contact, and water by mechanical casings and electrical enclosures. It is published by the International Electromechanical Commission (IEC).

The International standard is IEC 60529 (British Standard BS EN 60529:1992)

The numbers that follow the letters ‘IP’ have a specific meaning. The first indicates the degree of protection from moving parts, including hands, fingers and foreign bodies, such as dust. The second number defines the protection level from various forms of moisture, including drips, sprays and from being totally submerged. The table below briefly describes the various levels.  A fuller explanation is available from this link to Wikipedia 

First IP Number


Object Size Protected Against

Effective Against



No protection against contact and ingress of objects


  • 50mm

Any large surface of the body, such as the back of a hand, but no protection against deliberate contact with a body part


  • 12.5mm

Fingers or similar objects


  • 2.5mm

Tools, thick wires, etc.


  • 1mm

Most wires, screws, etc.


Dust Protected

Ingress of dust is not entirely prevented, but it must not enter in sufficient quantity to interfere with the satisfactory operation of the equipment; complete protection against contact (dust proof)


Dust Tight

No ingress of dust; complete protection against contact (dust tight)


Second IP Number


Protected Against

Testing For


Not protected



Dripping water



Dripping water when tilted up to 15°

Vertically dripping water shall have no harmful effect when the enclosure is tilted at an angle up to 15° from its normal position.


Spraying water

Water falling as a spray at any angle up to 60° from the vertical shall have no harmful effect.


Splashing of water

Water splashing against the enclosure from any direction shall have no harmful effect.


Water jets

Water projected by a nozzle (6.3 mm) against enclosure from any direction shall have no harmful effects.


Powerful water jets

Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction shall have no harmful effects.


Powerful water jets with increased pressure

Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction, under elevated pressure, shall have no harmful effects.


Immersion up to 1 metre

Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time (up to 1 m of submersion).


Immersion beyond 1 metre

The equipment is suitable for continuous immersion in water under conditions which shall be specified by the manufacturer. Normally, this will mean that the equipment is hermetically sealed. However, with certain types of equipment, it can mean that water can enter but only in such a manner that it produces no harmful effects.


Powerful high temperature water jets

Protected against close-range high pressure, high temperature spray downs.

Finding an Installer or CCTV cameras and equipment

Please refer to our DIRECTORY for CCTV installers and CCTV product suppliers in the first instance.  For peace of mind and for the best professional service try always to use an installer that is a member of Security Systems & Alarm Inspection Board (SSAIB) or National Security Inspectorate (NSI) 

Updated July 2015