How to Selecting a Video Cable

Selecting Video Cable

There are two factors that govern the selection of cable: the location of cable runs, either indoor or outdoor, and the maximum length of the individual cable runs.

Video coaxial cable is designed to transmit maximum signaling energy from a 75 ohm source to a 75 ohm load with minimum signal loss. Excessive signal loss and reflection occurs if cable rated for other than 75 ohms is used. Cable characteristics are determined by a number of factors (core material, dielectric material and shield construction, among others) and must be carefully matched to the specific application. Moreover, the transmission characteristics of the cable will be influenced by the physical environment through which the cable is run and the method of installation.

Use only high quality cable and be careful to match the cable to the environment (indoor or outdoor). Solid core, bare-copper conductor is best suited to video applications, except where flexing occurs. In locations where the cable must be continuously flexed (i.e., when used with scanners or pan & tilts), use cable intended for such movement. This cable will have a stranded wire core. Use only cable with pure copper stranding. Do not use cable with copper-plated steel stranding because it does not transmit effectively in the frequency range used in CCTV.

The preferred dielectric material is foam polyethylene. Foam polyethylene has better electrical characteristics and offers the best performance over solid polyethylene, but it is more vulnerable to moisture. Use cable with solid polyethylene dielectric in applications subject to moisture.

In the average CCTV installation, with cable lengths of less than 750 feet (228 m),RG59/U cable is a good choice. Having an outside dimension of approximately 0.25 inches, it comes in 500-and 1,000-foot rolls.

For short cable runs, use RG59/U with a 22-gauge center conductor, which has a DC resistance of about 16 ohms per 1,000 feet (304 m). For longer runs, the 20-gauge variety which has a DC resistance of approximately 10 ohms per 1,000 feet will work well. In either case, cables with polyurethane or polyethylene as the dielectric material are readily available.

For installations requiring cable runs between 800 (244 m) and 1,500 feet (457 m),RG6/U is best. Having the same electrical characteristics as RG59/U, its outer dimension also is about equal to that of RG59/U.RG6/U comes in 500-,1000-and 2000-foot rolls, and it may be obtained in a variety of dielectric and outer-jacket materials. Due to its large-diameter center conductor of about 18 gauge,RG6/ U has a DC resistance of approximately 8 ohms per 1,000 feet (304 m) and can deliver a signal farther than RG59/U.

Use RG11/U to exceed the capability of RG6/U. Once again, the electrical characteristics of this cable are basically the same as the others. The center conductor can be ordered in 14-or 18-gauge sizes, producing a DC resistance of approximately 3-8 ohms per 1,000 feet (340 m). Being the largest of the three cables at 0.405 inches, it is more difficult to handle and install.RG11/U cable usually is delivered in 500-,1000-and 2000-foot rolls.

Because of special applications, variations of RG59/U, RG6/U and RG11/U frequently are introduced by manufacturers.

Due to changes in fire and safety regulations throughout the country, Teflon and other fire-retardant materials are becoming more popular as outer-jacket and dielectric materials. In case of a fire, these materials do not give off the same poisonous fumes as PVC-type cables, and therefore, are considered safer.

For underground applications, direct burial cables, made specifically for that purpose are recommended. The outer jacket of this type of cable contains moisture-resisting and other materials that protect the cable, allowing it to be placed directly into a trench.

With numerous choices available, finding the right video cable for each camera application should be easy. After the installation has been properly assessed, read the equipment specifications and complete the appropriate calculations.

Cable Runs

coax cable has built-in losses, the longer and smaller the cable is, the more severe the losses become; and the higher the signal frequency, the more pronounced the losses. Unfortunately this is one of the most common and unnecessary problems currently plaguing CCTV security systems as a whole.

If, for example, your monitor is located 1,000 feet (304 m) from the camera, approximately 37-percent(37%) of the high frequency information will be lost in transmission. The unfortunate aspect of this condition is that it is not obvious. You cannot see information that is not there and may not even realize that information has been deleted. Because many CCTV security systems have cable runs that exceed several thousand feet, unless you are aware of this characteristic of cable, your system may be providing a seriously degraded image.

So, if your cameras and monitors are separated by lengths greater than 750 feet (228 m), you should check to make certain that some provision has been made to guarantee the video signal's transmission strength.

Cable Type* RG59/U = 750 ft.

Cable Type* RG6/U = 1,000 ft.

Cable Type* RG11/U = 1,500 ft.

* = Minimum cable requirements= 75 ohms impedance, All-copper center conductor, All-copper braided shield with 95% braid coverage.

Cable Termination

In video security systems, camera signals must travel from the camera to the monitor. The method of transmission is usually "coax" cable. Proper termination of cables is essential to a system's reliable performance.

Because the characteristic impedance of coax cable ranges from 72 to 75 ohms, it is necessary that the signal travels on a uniform path along any point in the system to prevent any picture distortion and to help ensure proper transfer of the signal from the camera to the monitor. The impedance of the cable must remain constant with a value of 75 ohms. To properly transfer power between two video devices with acceptable losses, the signal output from the camera must match the input impedance of the cable, which in turn must match the input impedance of the monitor. The end point of any video cable run must be terminated in 75 ohms. Usually, the cable run will end at the monitor, which will ensure that this requirement is met.

Usually the video input impedance of the monitor is controlled by a switch located near the looping video (input/output) connectors. This switch allows for either 75 ohm termination if the monitor is the "end point",or Hi-Z for looping to a second monitor. Check equipment specifications and instructions to determine the proper termination requirements. Failure to terminate signals properly usually results in a high contrast, slightly grainy picture. Ghosting and other signal imperfections also may be evident.

It important to note that the BNC connectors , which are usually used for terminating coax cable, are manufactured in two different impedance -75 ohm for video use and 50 ohm for radio use. Most shopkeepers are not a ware of this difference so it is better to check the manufacturer's specification before you buy.

Unsaddled twisted pair (UTP)

UTP cabling is both in expensive and ideal for transmission of video signal up to 1350m. the cabling is run to multiplexer that supports the popular RJ45 connector . Legacy cameras with coax connectors can be retrofit with balun (balanced/unbalanced ) adpters allowing the signal to be converted from the coaxial cable (unbalanced ) to twisted pair (balanced) cable. A typical system consists of a transmitter connected to a coax cable or connector which is then converted to a signal suitable for transmitting over twisted pair cable. On the receiving end of the twisted-pair cable is a receiver that converts the signal back to one suitable for transmission on coax cable.

UTP. Requires only one twisted pair cable to carry power, video and control signals , as opposed to three different proprietary cables with traditional CCTV systems.

While the total cost of UTP cabling can be up to 30% less than traditional CCTV systems over the life of the system, it easily accommodates technological advances such as digital integration IP-based networks and power over Ethernet.

Optical fibre is some times used in this environment where distances would require use of repeaters for signal strength or where EMI. (Elector-Magnetic interference) is an issue.

Fibre Optic Cable

While coaxial cable is the most suitable cable for CCTV signal transmission over short distances it is best to consider other mediums for distances greater than 1 kilometer. The most suitable for these distances is fibre optic.

Fibre optic is a fine strand of glass which is highly transparent. There are two main types referred to single mode and multi-optic fibres. The single mode fibre optic has a high level of efficiency but can transmitting only one mode. Laser transmitters an receivers arousal required for single mode application . Multi -mode fibre optics is thicker and can operate in several modes and can accommodate cheaper forms of transmission media such as infrared . These cables are used main lyover shorter distances while the single mode fibre would be used where distance and performance were critical . The main types of applications for fibre optics are:-

Light Guide fiber-used in instrument panels and lamps it carries visible light only.

Coherent fibre-Normally referred to as coherent bundle because of its construction. This glass fibre will carry an undischarged image of light over a short distance. Its ideal for extending the lens with application in covert surveillance. High performance-For CCTV application we tend to use high performance fibers with a signal transmission media. For CCTV application we have to use the latter , high performance fibers. The glass stransparency quality of the glass is a key factor in its ability to transmit light effectively over distances and this is being improved constantly.

Fiber optic system may consist of a standard camera with the video signal being fed into a fibre optic trasmitter. The transmitter consists of circuits to convert the video signal into a series of modulated pulses . These pulses are then fed to the light source that may either be a laser or light emitting diode (LED) which emits a series of light pulses .these light pulses are focused on to the centre core of the cable which acts as a guide to the light passing along the fibre's lenght. The main light passes straight along the centre of the fibre while a little of the light hits the side of the glass tube. This is reflected back into the centre by the cladding.

This results in very low transmission losses over long distances. Fibre optic cable also has the advantage of not being affected by electromagnetic interference or EMI.

Splitting / Amplifying the Video Signal

Video signal used in CCTV equipment is nominally a one volt peak-to-peak signal and is impedance sensitive to 75 ohms for ideal video reproduction at the monitor. If these parameters are not kept, then the video will degrade.

Distribution Amplification

If the installation of a system requires viewing the video at multiple locations from a single camera, there are a few different ways of accomplishing this. One way is through using a distribution amplifier. This device basically takes the single video signal and reproduces the exact signal into multiple outputs; and in the case of the Pelco DA104DT you would get four identical outputs.

So, if the input signal is a one volt peak-to-peak signal you will get four output signals of the same amplitude. Providing the run distance for the type of coax used is kept within the specified length, no other equipment will be needed to reproduce a nice clear video display on each monitor. Another timesaving feature of the Pelco DA104DT is that there are not adjustments required. Just connect the unit, turn it on, and the installation is complete. If the need arises where more than four signals are required, multiple units can be linked together by simply using one of the output signals as an input signal to the next unit, and so on.

Equalizing Amplification

Due to the many factors that can effect the video signal, it is sometimes necessary to enhance the video signal (as in transmitting a nominal video signal level) directly out of the camera, through RG59 coax to a monitor, while still producing a clear video display across the entire length of the coax. In this case the coax should not exceed 750 feet (228 m).

However, let's say you need to use RG59 because it's more flexible and much easier to work with but the cable length must be 1,500 feet (457 m). The signal at this point is going to be weak and will display a very degraded picture on the monitor. As mentioned, there are many things that can effect signal strength before the signal reaches the monitor. If you find a weak signal, simply pass the weak signal through an equalizing amplifier, make the required adjustments, and once again there will be a good, strong signal that will produce a nice picture.

The Pelco model EA2010 is a post-equalizing amplifier which simply means that this device will be located close to the monitor. There's an advantage to this design in that AC power is usually more readily available at the monitoring location than it is somewhere back up the coax line, and with this type of design it only requires one person to view the monitor display while at the same time making the required adjustments to obtain the nominal signal level.

As mentioned in the example on RG59,the signal strength is good up to nominally 750 feet (228 m). With the Pelco EA2010 amplifying the signal, the same grade of coax can be used in runs of up to 3,000 feet (914 m).

In regard to any equalizing amplification system, there is another type of post-equalizing amplifier that Pelco offers. It is the half-duplex post-equalizing amplifier. This device (as far as the amplification of the video signal is concerned) is exactly like the EA2010.The difference is that the EA2000 was designed specifically for use with any of the Pelco Coaxitron® (up-the-coax) control/transmitter systems. This device enables the video signal requiring amplification to be transmitted over the same coaxial cable over which the control signal is transmitted, whereas if you used the EA2010 it would block the Coaxitron® control signal from being transmitted.

Cabling for IP Cameras

IP convergence means attaching different building and communication systems -- such as data, voice, security cameras and building automation systems -- onto a common network through a common Internet protocol. In the surveillance world, IP convergence means moving from analog to IP cameras.

IP camera technology offers new and expanded features in CCTV surveillance that were previously unavailable on analog cameras. However, performance and scalability can be affected because of poor system infrastructure, as well as product performance.

For organizations to realize the full benefits of IP video surveillance, they must design and build a system that is capable of meeting current and future requirements, which includes allocating sufficient bandwidth to video-carrying traffic that will not congest the network. To do this, they must implement a standards-based structured cabling system that will allow future devices to be added, which will save time and money by providing the biggest return on investment.

Cable selection and bandwidth go hand-in-hand. Considerations when selecting the cable media include number of cameras, type of camera, location of the cameras (environment), distance to the telecom rooms, type of termination equipment and whether PoE will be running through the cable or local power will be provided at the device end. Another factor when selecting cable is the length of time planned to occupy the building.

Today’s TIA standards define cabling types, distances, connectors, cable system architectures, cable performance characteristics, pathways, cable installation requirements and methods of testing installed cable to help system designers and installers select the most efficient cabling for each environment. TIA-recognized structured cabling standards recommend twisted pair copper and fiber-optic cable as the preferred media selection for efficient IP network systems. However, security integrators need to be aware of the range of options available and the pros and cons of each.

Coax Cable

Distances using coax cable can be up to 3,000 feet. This cable is most often found when end users would like to use their installed cable plant, which was installed for analog cameras. However, because an IP camera is equipped with an RJ-45 connection, media converters are needed on each end of the coax cable runs.

Using existing coax cable for running Ethernet to IP cameras is a “band-aid” approach and does not comply with TIA. This is a fast solution, but eventually the cabling system will need to change to a structured cabling system -- through twisted pair or fiber -- especially when higher bandwidth megapixel cameras are required. Running Ethernet over coax is limited to less than 1 GB transmissions. Therefore, as the bandwidth increases on both the camera and the traffic running through the network, coax cable capabilities will be limited.

Twisted Pair

Unshielded or shielded twisted pair cable provides many benefits over coax. Twisted pair, with its RJ connection, allows immediate attachment to the camera. One of the biggest benefits is that twisted pair can provide power over the same cable, eliminating local power at the device end.

There are basically two grades of UTP cable: Cat-5e (100 MHz) and Cat-6 (250 MHz). A Cat-5e cable may be sufficient with its allowable 1 GB/s data rate (depending on the protocol), but Cat-6 operates at a higher data rate (up to 10 GB/s). Because of its improved transmission performance and superior immunity from external noise, systems operating over Cat-6 cabling will have fewer errors than Cat-5e. And, when inducing noise or heat -- such as in PoE and PoE Plus -- Cat-6 has been proven to operate with no latency or fear of dropped packets.

Standards-based twisted pair cabling is limited to 100 meters between the device and the termination point, such as a consolidation point or telecommunications room. The chart on the following page provides cable options for selecting cable based on distance and power. Twisted pair can actually provide a signal farther than 100 meters through active equipment, but this would not meet the TIA standards and therefore would not work if the analog camera is to be replaced with an IP camera.

Fiber-optic Cable

The answer to the distance challenge is fiber-optic cable. Fiber-optic cable can easily operate IP cameras through media conversion, allowing twisted pair patch cords or horizontal UTP cable runs to connect directly to the device and to the terminating equipment in the TR. Even coax-based analog cameras can use fiber-optic cable, but this entails deploying multiplexers in addition to media converters, which can become costly per channel.

Fiber-optic cable’s other advantages include its small diameter and biggest bandwidth carrying capacity. Fiber-optic cable is immune to electrical interference, which makes it ideal for harsh environments such as lightning, power plants and industrial manufacturing. In addition, fiber optic is a more secure signal -- because it is harder to tap into.

Since power cannot run through glass, fiber-optic cable cannot directly carry PoE. But it can be jacketed with copper conductors in the form of a composite cable. Certain cables on the market provide Ethernet to be carried through fiber strands while power runs through stranded copper conductors. Distances up to 3,850 feet can be achieved. Because the cable carries lowvoltage power -- up to 25 watts as defined by PoE Plus and IEEE 802.3at -- this cable is actually defined as a Class 3 copper cable with fiber. The total distance is limited by the media power provided through the active media converter on the termination side, as well as the gauge of the copper. The more power needed, the thicker the gauge.

Challenging Decisions and Changing Standards

Security camera locations vary depending on each installation. When the TIA standards were written, the devices in work areas consisted of telephones, modems, data terminals, fax machines and desktop computers. Although the TIA standards originally applied to data and voice Ethernet applications, mainly in office environments, they were written to be modular, providing scalability for adding IP devices. However, electronic safety and security devices, particularly surveillance equipment, create unique challenges, mainly due to environmental factors.

The BICSI organization, together with ANSI, is currently reviewing the existing standards and has created a standards group to focus solely on physical infrastructure for ESS devices. To be designated “ANSI/BICSI 005” upon completion, this standard will define cabling design and installation requirements, as well as provide recommendations specific to ESS systems, including surveillance, access control, paging, signage, and even fire detection and alarm systems.

The standard also will provide information for access control, intrusion detection and surveillance systems, as well as guidance on other topics, such as meeting the IP needs of fire detection and alarm systems. And as more and more devices find their way to the network, the selection of cabling and physical infrastructure becomes more critical.

Now we are discussed about coaxial cable's Construction

RG59/U, RG6/U and RG11/U is circular. Each has a center conductor surrounded by dielectric insulating material, which in turn is covered by a braid to shield against electromagnetic interference. The outer covering is the jacket.

The coaxial cable's two conductors are separated by a nonconductive or dielectric material. The outer conductor (braid) acts as a shield and helps isolate the center conductor from spurious electromagnetic interference. The outer covering helps physically protect the conductors.

Center Conductor:

For CCTV applications, solid copper conductors are required, which is carrying a video signal. Center conductor comes in varying diameters usually ranging from 14 gauge to 22 gauge. The structure of the center conductor generally is solid copper or copper-clad steel, designated as bare copper weld or BCW. For CCTV applications, solid copper conductors are required. Copper clad, copper weld, or BCW cables have much greater loop resistance at baseband video frequencies and should never be used for CCTV. To determine the type, look at the cut end of the center conductor. Copper clad cable will be silver in the center intead of copper all the way through. Variation in the size of the center conductor has an overall effect on the amount of DC resistance offered by cable. Cables which contain large diameter center conductors have lower resistances than cables with smaller diameters. This decreased resistance of large diameter cable enhances the ability of a cable to carry a video signal over a longer distance with better clarity, but is also more expensive and harder to work with.

For applications where the cable may move up/down or side-to-side, select cable that has a center conductor consisting of many small strands of wire. As the cable moves, these strands flex and resist wear due to fatigue better than a cable with a solid center conductor.

Dielectric Insulating Material

Center conductor is an evenly made dielectric insulating material which is available in some form of either polyurethane or polyethylene. This dielectric insulator helps determine the operating characteristics of coax cable by maintaining uniform spacing between the center conductor and its outer elements over the entire length of the cable. Dielectrics made of cellular polyurethane or foam are less likely to weaken a video signal than those made with solid polyethylene. This lower attenuation is desirable when calculating the loss/length factor of any cable. Foam also gives a cable greater flexibility, which may make an installer's job easier. Although foam dielectric material offers the best performance, it can absorb moisture, which will change its electrical behavior.

Because of its rigid properties, solid polyethylene maintains its shape better than foam and withstands the pressures of accidental pinching or crimping, but, this characteristic also makes it slightly more difficult to handle during installation. In addition, its loss/length attenuation factor is not quite as good as foam, which should be considered in long cable runs.

Braid or Shield

Cables using aluminum foil shielding or foil wrap material are not suitable for CCTV installations. Wrapped around the outside of the dielectric material is a woven copper braid (shield), which acts as a second conductor or ground connection between the camera and the monitor. It also acts as a shield against unwanted external signals commonly called electromagnetic interference or EMI, which may adversely affect a video signal.

The amount of copper or wire strands in the braid deter- mine how much EMI it keeps out. Commercial grade coax cables containing loosely woven copper braid have shielding coverages of approximately 80%. These cables are suitable for general purpose use in applications where electrical interference is known to be low. They also work well when the cable is to be installed in metal conduit or pipe, which also aids in shielding.

If you are not sure of the conditions and are not running pipe to screen out more EMI, use a cable with a "maximum shield" or heavy braid--type cable containing more copper than those of commercial grade coax. This extra copper obtains the higher shielding coverage by having more braid material made in a tighter weave. For CCTV applications, copper conductors are needed.

Cables using aluminum foil shielding or foil wrap material are not suitable for CCTV work. Instead, they usually are intended to transmit radio frequency signals such as those employed in transmitter systems or in master antenna distribution systems.

Aluminum or foil cable may distort a video signal to such a point that signal quality may be far below the level required for proper system operation, especially over long cable runs, and therefore not recommended for CCTV use.

Outer Jacket

The last component comprising a coax cable is the outer jacket. Although other materials are used, polyvinyl chloride, or PVC, is commonly used in its construction. Available in many colors such as black, white, tan, and gray, the jacket lends itself to both indoor and outdoor applications.

Newly developed some Video & Power Combination Cable is there in market.

This combination cable featuring BNC to BNC video connectors and 2.1mm DIN male & female for power supply connection. A BNC to RCA adapter is also included. Also included are two pigtails to allow breakout of power connectors to use with screw terminal power supplies and cameras. This cable is available in 50 foot and 100 foot lengths. Maximum distance for DC power should not exceed 100 feet.

Specials thanks to all of Manufacturers, Suppliers & Exporters to provide the information.

How a Smart Card Reader Works

Smart Card Readers are also known as card programmers (because they can write to a card), card terminals, card acceptance device (CAD) or an interface device (IFD). There is a slight difference between the card reader and the terminal. The term 'reader' is generally used to describe a unit that interfaces with a PC for the majority of its processing requirements. In contrast, a 'terminal' is a self-contained processing device.

Smart cards are portable data cards that must communicate with another device to gain access to a display device or a network. Cards can be plugged into a reader, commonly referred to as a card terminal, or they can operate using radio frequencies (RF).

When the smart card and the card reader come into contact, each identifies itself to the other by sending and receiving information. If the messages exchanged do not match, no further processing takes place. So, unlike ordinary bank cards, smart cards can defend themselves against unauthorized users and uses in innovative security measures.

Communicating with a Smart Card Reader

The reader provides a path for your application to send and receive commands from the card. There are many types of readers available, such as serial, PCCard, and standard keyboard models. Unfortunately, the ISO group was unable to provide a standard for communicating with the readers so there is no one-size-fits-all approach to smart card communication.

Each manufacturer provides a different protocol for communication with the reader.

• First you have to communicate with the reader.

• Second, the reader communicates with the card, acting as the intermediary before sending the data to the card.

• Third, communication with a smart card is based on the APDU format. The card will process the data and return it to the reader, which will then return the data to its originating source.

The following classes are used for communicating with the reader:

• ISO command classes for communicating with 7816 protocol

• Classes for communicating with the reader

• Classes for converting data to a manufacturer-specific format

• An application for testing and using the cards for an intended and specific purpose

Readers come in many forms, factors and capabilities. The easiest way to describe a reader is by the method of its interface to a PC. Smart card readers are available that interface to RS232 serial ports, USB ports, PCMCIA slots, floppy disk slots, parallel ports, infrared IRDA ports and keyboards and keyboard wedge readers. Card readers are used to read data from – and write data to – the smart card. Readers can easily be integrated into a PC utilizing Windows 98/Me, 2000, or XP platforms. However, some computer systems already come equipped with a built-in smart card reader. Some card readers come with advanced security features such as secure PIN entry, secure display and an integrated fingerprint scanners for the next-generation of multi-layer security and three-factor authentication.

Another difference in reader types is on-board intelligence and capabilities. An extensive price and performance difference exists between an industrial strength reader that supports a wide variety of card protocols and the less expensive win-card reader that only works with microprocessor cards and performs all processing of the data in the PC.

The options in terminal choices are just as varied. Most units have their own operating systems and development tools. They typically support other functions such as magnetic-stripe reading, modem functions and transaction printing.

To process a smart card the computer has to be equipped with a smart card reader possessing the following mandatory features:

• Smart Card Interface Standard – ISO 7816 is an international standard that describes the interface requirements for contact-type smart cards. These standards have multiple parts. For instance, part 1, 2 and 3 are applicable to card eaders. Part 1 defines the physical characteristics of the card. Part 2 defines dimension and location of smart card chip contacts. Part 3 defines the electronic signals and transmission protocols of the card. Card readers may be referred to as conforming to ISO 7816 1/2/3, or in its simplified term, ISO 7816.

• Driver – This refers to the software used by the operating system (OS) of a PC for managing a smart card and applicable card reader. To read a smart ID card, the driver of the card reader must be PC/SC compliant which is supported by most card reader products currently available. It should be noted that different OS would require different drivers. In acquiring card readers, the compatibility between the driver and the OS has to be determined and ensured.

Desirable Features in a Smart Card Reader

Card Contact Types refers to how the contact between a card reader and a smart card is physically made. There are two primary types of contact: landing contact and friction contact (also known as sliding or wiping). For card readers featuring friction contact, the contact part is fixed. The contact wipes on the card surface and the chip when a card is inserted. For card readers featuring the landing type, the contact part is movable. The contact "lands" on the chip after a card is wholly inserted. In general, card readers of the landing type provide better protection to the card than that of the friction type.

Smart card readers are also used as smart card programmers to configure and personalize integrated circuit cards. These programmers not only read data, but also put data into the card memory. This means that not only CPU based smart cards, but also simple memory cards can be programmed using a smart card reader. Of course the card reader must support the appropriate protocol such as the asynchronous T=0, T=1 or synchronous I2C protocols.

It won't take long before smart card readers become an integral part of every computer – and, subsequently, the lives of computer users. Computer systems with keyboards that have smart card reader/writer integration are also available.

Smart card readers are also accessible in the form of USB dongle. USB dongles are frequently used with GSM phones, which contain a SIM smart card. Additionally, phone numbers can be edited on a PC using the USB smart card dongle.

Key features and characteristics of smart cards

Cost: Typical costs range from $2.00 to $10.00. Per card cost increases with chips providing higher capacity and more complex capabilities; per card cost decreases as higher volume of cards are ordered.

Reliability: Vendors guarantee 10,000 read/write cycles. Cards claiming to meet International Standards Organization (ISO) specifications must achieve set test results covering drop, flexing, abrasion, concentrated load, temperature, humidity, static electricity, chemical attack, ultra-violet, X-ray, and magnetic field tests.

Error Correction: Current Chip Operating Systems (COS) perform their own error checking. The terminal operating system must check the two-byte status codes returned by the COS (as defined by both ISO 7816 Part 4 and the proprietary commands) after the command issued by the terminal to the card. The terminal then takes any necessary corrective action.

Storage Capacity: EEPROM: 8K - 128K bit. (Note that in smart card terminology, 1K means one thousand bits, not one thousand 8-bit characters. One thousand bits will normally store 128 characters - the rough equivalent of one sentence of text. However, with modern data compression techniques, the amount of data stored on the smart card can be significantly expanded beyond this base data translation.)

Ease of Use: Smart cards are user-friendly for easy interface with the intended application. They are handled like the familiar magnetic stripe bank card, but are a lot more versatile.

Susceptibility: Smart cards are susceptible to chip damage from physical abuse, but more difficult to disrupt or damage than the magnetic stripe card.

Security: Smart cards are highly secure. Information stored on the chip is difficult to duplicate or disrupt, unlike the outside storage used on magnetic stripe cards that can be easily copied. Chip microprocessor and Co-processor supports DES, 3-DES, RSA or ECC standards for encryption, authentication, and digital signature for non-repudiation.

First Time Read Rate: ISO 7816 limits contact cards to 9600 baud transmission rate; some Chip Operating Systems do allow a change in the baud rate after chip power up; a well designed application can often complete a card transaction in one or two seconds. Speed of Recognition Smart cards are fast. Speed is only limited by the current ISO Input/Output speed standards.

Proprietary Features: These include Chip Operating System (COS) and System Development Kits.

Processing Power: Older version cards use an 8-bit micro-controller clockable up to 16 MHz with or without co-processor for high-speed encryption. The current trend is toward customized controllers with a 32-bit RISC processor running at 25 to 32 MHz.

Power Source: 1.8, 3, and 5 volt DC power sources.

Support Equipment Required for Most Host-based Operations: Only a simple Card Acceptance Device (that is, a card reader/writer terminal) with an asynchronous clock, a serial interface, and a 5-volt power source is required. For low volume orders, the per unit cost of such terminals runs about $150. The cost decreases significantly with higher volumes. The more costly Card Acceptance Devices are the hand-held, battery-operated terminals and EFT/POS desktop terminals.

Why consider smart cards?

IF a portable record of one or more applications is necessary or desirable, AND

Records are likely to require updating over time, Records will interface with more than one automated system, Security and confidentiality of records is important

THEN, smart cards are a feasible solution for making data processing and transfer more efficient and secure.

Advantages of Smart Cards:

• The capacity provided by the on-board microprocessor and data capacity for highly secure, off-line processing

• Adherence to international standards, ensuring multiple vendor sources and competitive prices

• Established track record in real world applications

• Durability and long expected life span (guaranteed by vendor for up to 10,000 read/writes before failure)

• Chip Operating Systems that support multiple applications

• Secure independent data storage on one single card

Barriers to Acceptance of Smart Cards:

• Relatively higher cost of smart cards as compared to magnetic stripe cards. (The difference in initial costs between the two technologies, however, decreases significantly when the differences in expected life span and capabilities- particularly in terms of supporting multiple applications and thus affording cost sharing among application providers- are taken into account).

• Present lack of infrastructure to support the smart card, particularly in the U.S., necessitating retrofitting of equipment such as vending machines, ATMs, and telephones.

• Proprietary nature of the Chip Operating System. The consumer must be technically knowledgeable to select the most appropriate card for the target application.

• Lack of standards to ensure interoperability among varying smart card programs.

• Unresolved legal and policy issues related to privacy and confidentiality or consumer protection laws.

Smart Card Applications

Financial Applications

• Electronic Purse to replace coins for small purchases in vending machines and over-the-counter transactions.

• Credit and/or Debit Accounts, replicating what is currently on the magnetic stripe bank card, but in a more secure environment.

• Securing payment across the Internet as part of Electronic Commerce.

Communications Applications

• The secure initiation of calls and identification of caller (for billing purposes) on any Global System for Mobile Communications (GSM) phone.

• Subscriber activation of programming on Pay-TV.

Government Programs

• Electronic Benefits Transfer using smart cards to carry Food Stamp and WIC food benefits in lieu of paper coupons and vouchers.

• Agricultural producer smart marketing card to track quotas.

Information Security

• Employee access cards with secured passwords and the potential to employ biometrics to protect access to computer systems.

Physical Access Control

• Employee access cards with secured ID and the potential to employ biometrics to protect physical access to facilities.

Transportation

• Drivers Licenses.

• Mass Transit Fare Collection Systems.

• Electronic Toll Collection Systems.

Retail and Loyalty

• Consumer reward/redemption tracking on a smart loyalty card, that is marketed to specific consumer profiles and linked to one or more specific retailers serving that profile set.

Health Care

• Consumer health card containing insurance eligibility and emergency medical data.

Student Identification

• All-purpose student ID card (a/k/a campus card), containing a variety of applications such as electronic purse (for vending machines, laundry machines, library card, and meal card).

Optical vs Digital Zoom

After reading the title of this article, you might be asking yourself, “Zooming is just zooming, right?”  Is there really a difference between optical and digital zooming?  You may be surprised to learn that yes, there is definitely a difference.

Optical zoom is considered as true zooming.  In other words, the lens optics on the camera itself are used to zoom in on an object.  This is opposed to digital zooming, in which the camera processes an image internally and focuses on a certain portion of that image.  That certain portion is simply enlarged, thus creating a zoom effect.

One such term is zoom.  Pan-tilt-zoom (PTZ) cameras and some fixed cameras have lenses that zoom in on an object.  In other words, it magnifies the object of the video, such as a car in a parking lot, so that it can be seen in much better detail.

Zoom is a very important feature of video camera lenses.  By making the image larger, it is possible to watch intrusions developing from some distance away from the doors to a building.

In a secure parking lot, for example, if someone bypasses the guard shack, a zoom camera mounted on the side of a building over a hundred feet away should be able to capture easily the progression of the automobile as it gets closer to the building.  This gives time for a security guard to respond before the intruder is leaning over his shoulder with a gun pointed to his head.

This may seem to be an extreme example, but it is one of the things that separates zoom cameras from fixed ones.

When comparing the zoom features of a camera lens, it is absolutely critical to understand the difference between digital zoom and optical zoom.

Digital Zoom

Imagine that you are looking at a Rembrandt in a museum, and you want to get closer to a beautiful pastoral scene to see the master’s details of a country hillside.

Since the guard is paying attention, you have to settle for taking a regular picture of the Rembrandt from a safe distance away.  Then, you have the picture developed and you now hold in your hand the photo you took at the museum.

You have an idea.  Now that you have the picture in hand, you decide to get someone to blow up the picture on a copier so that you can see the hillside better.  At least, that’s what you think you’re going to get.

When you blow the picture up to the same size of the full original painting, you are disappointed.  Now, it just looks like a bad case of psoriasis and you have missed an opportunity to bring Rembrandt home with you.

Digital zoom is very similar to this.  It cuts out a section on a distant image, not actually getting you closer to the object but by magnifying the lack of clarity that already exists.  In other words, if you can’t tell what the details are from a distance, you won’t be able to tell what they are by making it seem closer by digitally manipulating the captured picture.

Digital zoom, while not exactly useless, does not actually help very much when you need to focus on an object as if you are standing much closer to it.

Optical Zoom

Put yourself back in the art museum for a moment.  You are standing in front of the Rembrandt and you really want to get closer to it so you can see the finer details of the hillside.  This time, you don’t have a camera.  Instead, the sleepy-faced guard has his head turned, and you jump over the barriers and put your eyes about six inches away from the painting.

Suddenly, all the details of the hillside are shown.  You see the individual blades of grass, the lines on the outer edges which distinguish an object from its background.  You can see it clearly, and your awe of Rembrandt grows to new heights.

Optical zoom is like standing closer to the object.

In our opening example about the car crashing the guard shack, it would be as if the security guard is only a few feet away from the automobile, allowing him to head off the intruder before he reaches the front door.

The value of optical zoom in video surveillance is priceless.  While it is not quite as good as you will see on television cop shows, it is still a great tool for keeping an eye on your property. 

All about CCTV Lenses

We already discuss about CCTV lenses so, we have the basic idea now we learning in details:

The human eye is an incredibly adaptable device that can focus on distant objects and immediately refocus on something close by. It can look into the distance or at a wide angle nearby. It can see in bright light or at dusk, adjusting automatically as it does so. It also has a long ‘depth of field’; therefore, scenes over a long distance can be in focus simultaneously. It sees colour when there is sufficient light, but switches to monochrome vision when there is not. It is also connected to a brain that has a faster updating and retentive memory than any computer. Therefore, the eyes can swivel from side to side and up and down, retaining a clear picture of what was scanned. The brain accepts all the data and makes an immediate decision to move to a particular image of interest, select the appropriate angle of view and refocus. The eye has another clever trick in that it can view a scene of great contrast and adjust only to the part of it that is of interest.

By contrast, the basic lens of a CCTV camera is an exceptionally crude device. It can only be focused on a single plane, everything before and after this plane becoming progressively out of focus. The angle of view is fixed. At any time, it can only view a specific area that must be predetermined. The iris opening is fixed for a particular scene and is only responsive to global changes in light levels. Even an automatic iris lens can be only be set for the overall light level, although there are compensations for different contrasts within a scene. Another problem is that a lens may be set to see into specific areas of interest when there is much contrast between these and the surrounding areas. However, as the sun and seasons change so do light areas become dark and dark areas become light. The important scene can be ‘whited out’ or too dark to be of any use.

A controversial but important aspect of designing a successful CCTV system is the correct selection of the lens. The problem is that the customer may have a totally different perspective of what a lens can see compared to the reality. This is because most people perceive what they want to view as they see it through their own eyes. Topics such as identification of miscreants or numberplates must be subjects debated frequently between installing companies and customers.

The selection of the most appropriate lens for each camera must frequently be a compromise between the absolute requirements of the user and the practical use of the system. It is just not possible to see the whole of a large loading bay and read all the vehicle number plates with one camera. The solution may be more cameras or viewing just a restricted area of particular interest. A Company putting forward the system proposal should have no hesitation in pointing out the restrictions that may be incurred according to the combination of lens versus the number of cameras. Better this than an unhappy customer who is reluctant to pay the invoice.

Although a lens is crude compared to the human eye, it incorporates a high degree of technology and development. There can be a large variation in the quality between different makes and this should be considered according to the needs of a particular installation. The lens is the first interface between the scene to be viewed and the eventual picture on the monitor. Therefore, the quality of the system will be very much affected by the choice of lens. For general surveillance of, for instance, a small retail shop, it is possible to use a lower quality lens with quite acceptable results. As the demands of the system requirement increase then the use of a premium quality lens must be considered. The difference in cost between a poor quality and a high quality lens will be a very small percentage of the total cost of a large industrial system.

The CCTV Lens Exposure Control
The exposure in a normal photographic camera can be controlled by a combination of shutter speed and iris opening. This is not so with a CCTV camera lens. A standard CCTV camera produces a complete picture every 1/2 of the mains frequency. This is every 1/25 second where the mains frequency is 50 Hz (cycles per second) and every 1/30 second where the mains frequency is 60 Hz. Generally the exposure time is fixed and the only control of the amount of light passing to the imaging device is by adjusting the size of the iris. This is covered in more detail later in this chapter. Most camera tubes and imaging devices have some tolerance of the amount of light passed by the lens to create an acceptable picture. The range of tolerance is generally inversely proportional to the sensitivity of the camera. The more sensitive cameras require greater control of the iris aperture.

Types of Lenses
Lens Formats

Diagram 1 Types of Lens Mounts

Early CCTV lenses were designed for the 1” format tube camera and many of these are still available on the market. The lens screw thread on these cameras is called a C-mount. This is a particular design of thread size and flange length originally used on photographic cameras. In recent years lenses have been developed for the 2/3”, 1/2” and now 1/3” format cameras. Consequently, great care must be exercised when selecting a lens for a particular camera. Just as there are four formats of camera so there are four formats of lenses and they are not compatible in every combination. A lens designed for a larger format camera may be used on a smaller format but not the reverse. In addition, the field of view will not be the same on different size cameras. There is now a further complication in that there is a range of lenses with what is called the CS-mount. The difference between the two types of mount is the flange back length, which is the distance from the back flange of the lens to the face of the sensor. See diagram 4.1. The screw thread and shoulder length for each type of mount is identical. This makes it impossible to see the difference except that the overall size of the CS-mount lens is generally smaller. A C-mount lens may be used on a CS-mount camera with an adapter ring but a CS-mount lens cannot be used on a C-mount camera. The main problem is that either type of lens can be screwed onto both types of camera without apparent damage. The result is that if the wrong type is used it will be impossible to focus the camera. Some C-Mount lenses have a projection at the back that could damage the sensor in a CS-Mount camera.
Below chart is provided at the end of this chapter showing the relationships between different lenses and camera combinations and the associated angle of view. At the time of going to press, most lenses with a focal length of 25mm and above are still designed for 1” cameras. This means that special care must be taken when using this long focal length lens on modern cameras. For instance, a 25mm 1” lens provides the following approximate angles of view on the different formats. Therefore, there would be a significant variation in the expected scene content if this fact were overlooked.
FORMAT 1" -- ANGLE OF VIEW 29°
FORMAT 2/3" -- ANGLE OF VIEW 9.5°
FORMAT 1/2" -- ANGLE OF VIEW 11.4°
FORMAT 1/3" -- ANGLE OF VIEW 9.79°

How to select a Lens
There are two other main factors that must be considered when selecting the most appropriate lens for a particular situation. The focal length and the type of iris control. Within each of these factors, there are other features that will also need to be considered. Lenses may be obtained with all combinations of focal length and iris control. The selection will depend on the site and system requirement.
Focal Length
The focal length of a lens determines the field of view at particular distances. This can either be calculated from the formula given later in this chapter or found from tables provided by most lens suppliers. Most manufacturers also provide simple to use slide or rotary calculators that computes the lens focal length from the scene size and the object distance. The longer the focal length the narrower is the angle of view. Although not strictly correct, lenses with a focal length longer than 25mm are often called zoom lenses. The focal length of the lens requires careful selection to ensure that the correct area is in view and that the degree of detail is acceptable. A rule of thumb is that to ‘see’ a person on a monitor they should represent at least 10% of the screen height. To ‘see’ in this context means to be able to decide that it is a person. For purposes of being able to identify a known person requires them to be at least 50% of the screen height and preferably 60%. An unknown person should occupy at least 120%of the screen height.
Fixed Focal Length
This type of lens is sometimes called a monofocal lens. As the name implies, it is specified when the precise field of view is fixed and will not need to be varied when using the system. The angle of view can be obtained from the supplier’s specification or charts provided. They are generally available in focal lengths from 3.7mm to 75mm. Longer focal lengths may be produced by adding a 2x adapter between the lens and the camera. It should be noted that this would increase the f-number by a factor of two (reducing the amount of light reaching the camera). If focal lengths longer than these are required, it will be necessary to use a zoom lens and set it accordingly.
Except for very wide-angle lenses, other lenses have a ring for adjusting the focus. In addition, cameras include a focusing adjustment that moves the imaging device mechanically relative to the lens position. This is to allow for minor variations in the back focal length of lenses and manufacturing tolerances in assembling the device in the camera. Correct focusing requires setting of both these adjustments. The procedure is to decide the plane of the scene on which the best focus is required and then set the lens focusing ring to the mid position. Then set the camera mechanical adjustment for maximum clarity. Final fine focusing can be carried out using the lens ring.
The mechanical focusing on cameras is often called the back focus, originally because a screw at the back of the camera moved the tube on a rack mechanism. Modern cameras now have many forms of mechanical adjustment. Some have screws on the side or the top, some still at the back. There are cameras that have a combined C/CS-mount on the front that also has the mechanical adjustment and can accept either type of lens format. The longer the focal length of the lens the more critical is the focusing. This is a function of depth of field described later in this chapter.
Manual Zoom Lens
A zoom lens is one in which the focal length can be varied manually over a range. Usually this is by means of a knurled ring on the lens body. It has the connotation of ‘zooming in’ and therefore infers a lens with a longer than normal focal length. (Say more than 25mm.) The zoom ratio is stated as being for instance 6:1, which means that the longest focal length is six times that of the shortest. The usual way of describing a zoom lens is by the format size, zoom ratio and the shortest and longest focal lengths. For example, 2/3”, 6:1, 12.5mm to 75mm. Again, great care must be taken in establishing both the camera and the lens format. The lens just described would have those focal lengths on a 2/3” camera but an equivalent range of 8mm to 48mm on a 1/2” camera.
Variable Focal Length
This is a design of lens that has a limited range of manual focal length adjustment. It is strictly not a zoom lens because it has quite a short focal length. They are usually used in internal situations where a more precise adjustment of the scene in view is required which may fall between two standard lenses. They are also useful where for a small extra cost one lens may be specified for all the cameras in a system. This saves much installation time and the cost of return visits to change lenses if the views are not quite right. For companies involved in many small to medium sized internal installations such as retail shops and offices this can save on stock holding. It makes the standardisation of systems and costing much easier.
Motorised Zoom Lens
Manual zoom lenses are not widely used in CCTV systems because the angle of tilt of the camera often needs to be changed as the lens is zoomed in and out. The most common need for a zoom lens is where used with a pan tilt unit. The lens zoom ring is driven by tiny DC motors and operated from a remote controller.
With the development of ever-smaller cameras and longer focal length lenses the method of mounting the camera/lens combination must be considered. There are many cases where the lens is considerably larger than the camera and it may be necessary to mount the lens rigidly with the camera supported by it. In other cases, it may be necessary to provide rigid supports for both camera and the lens. Always check the relationship between the camera and lens sizes and weights when selecting a housing or mounting. Most manufacturers of housings can provide lens supports as an accessory.
Focussing A Zoom Lens
The most frequent reason for the focus changing when zooming is that the mechanical focus of the camera has not been set correctly. The following is the procedure for setting up the focus on a camera fitted with a zoom lens.
The focusing ring should be marked ‘near’ and ‘far’. Set this to ‘far’ and set the zoom ring to the widest angle of view. Aim the camera at an object about 40 metres away and adjust the camera focus for maximum clarity. Next zoom in to an object nearby and set the lens focus for maximum clarity. It should now be possible to zoom all the way back without the focus changing. Many motorised zoom lenses will be used in external conditions with limited light. If this is the case then it is advisable to fit a neutral density filter in front of the lens to make the iris open fully. A neutral density filter is one that reduces the amount of light that enters the lens, evenly over the whole of the visible spectrum. This will create the shortest depth of field and ensure setting up more accurately for the worst conditions. The depth of field, as explained later, depends on the aperture opening.
Some controllers can override the automatic iris mechanism, usually to open it to see into darker areas. This is often the case when a camera is looking out over open country in bright sunlight and the lens closes because it measures the average light levels. The scene at ground level can be very dark in these conditions, with little detail. This is not a desirable feature to include unless absolutely necessary. This is because the override can be forgotten with resultant poor pictures being recorded if the system is not fully monitored. The better solution is to tilt the camera down until there is less proportion of sky in the picture.
Motorised Zoom Lenses With pre-sets
There are many situations where it is required to pan, tilt, and zoom to a predetermined position within the area being covered. It is possible to obtain motorised lenses with potentiometers fitted to the zoom and focusing mechanisms. These cause the lens to zoom automatically and focus to the setting by measuring the voltage across the potentiometer and comparing it with the signals in the control system. All other functions are as for motorised zoom lenses. Pre-set controls are only possible with telemetry controlled systems. The specification of the telemetry controls should be checked to see whether the pre-set positions are set from the central controller or locally from the telemetry receiver.

Iris Control of Lens
Manual Iris
With this type of lens, the iris opening is set manually by rotating a knurled ring on the lens body. Typically, it will have a range of settings from the maximum to fully closed, although the adjustment will be rather coarse. This type of lens is only suitable for indoor applications where the light levels remain fairly constant. It can also be used indoors with cameras having electronic shutters making a significant cost saving. Care must be exercised in using this camera/lens combination in external applications because the camera may not have adequate control to cover the total light range. In addition, manual iris lenses do not usually have a neutral density spot filter to cope with extremely bright sunlight.
In many indoor situations, the general level of light will vary significantly between summer and winter due to light from windows, skylights, etc. Therefore, it is often necessary to adjust the aperture two or three times a year to maintain optimum clarity of the picture.
Automatic Iris
Due to ongoing development, tubed cameras were becoming more sensitive and their use was spreading to more outdoor applications. They were very limited in the range of light that could be coped with. To overcome this problem manual iris lenses were fitted with motors bolted on to the barrel to drive the iris ring. The motors were connected by way of an amplifier to the video output of the camera. This was monitored to adjust the iris ring according to the voltage of the video signal. The lower the voltage then the more the iris would be opened until the correct video voltage was achieved, and the reverse when the video voltage increased. The early amplifiers suffered from the problem of being too sensitive and responding too quickly to changes in the video signal. This caused ‘hunting’ of the iris opening control and resulted in fluctuating contrast of the picture. To overcome this a delay circuit was introduced in the amplifier but this sometimes caused the reverse problem of the picture changing too slowly.
Modern automatic iris lenses are now completely self-contained units produced by the lens manufacturer and containing very sophisticated electronics and microscopic motors. There are three main types of automatic iris lenses.
Iris Amplifier
This type of lens is sometimes referred to as a servo lens. The most common type contains an amplifier and is connected to the video signal of the camera. It is driven by a dc voltage also provided from the camera. It was mentioned in Chapter 3, that the voltage of the video signal is proportional to the amount of light on the imaging device. The video level falls in proportion to the light level. The amplifier is continuously monitoring this voltage to maintain it at 1-volt peak to peak. As the voltage changes so the iris amplifier opens or closes the iris to maintain a constant 1-volt.
Most cameras that provide an automatic iris drive include a socket on the rear. There are three connections, +v, 0v, video. Unfortunately, there is no current standard for this connector but most cameras are packed with the appropriate plug. This can create problems if one camera is substituted for another make during maintenance or service. It can mean that the service engineer has to change the iris plug on site, which is not an easy job. In recognition of this problem, many cameras are now being produced with screw terminals on the rear.
Sensor Lens
This lens includes a light sensor similar to that in a photographic camera. This measures the light levels and adjusts the iris aperture accordingly. It requires a 12-volt dc supply that may be obtained from any source. This type of lens is not very common now having been introduced for use on Vidicon cameras that did not have a video and 12 volt output. The problem was that the light sensor was pre-set and not responsive to the video level, therefore the correct level was always maintained. The vast majority of cameras now provide an automatic lens connection therefore there will only be rare cases where this lens will be required.
Galvanometric Lens
These are also known as a galvometric or galvano lens. This type of automatic iris lens is driven by a reference voltage produced by an amplifier in the camera. In other words, the amplifier is within the camera instead of being part of the lens. The lens contains a driving motor to open and close the lens and a damping coil to prevent hunting. These lenses have four connections, +ve drive, -ve drive, +ve damping, and -ve damping. The camera specification should be checked to ensure that it contains the circuitry for this type of lens. Galvanometric lenses are usually less expensive than lenses with a built-in amplifier. They are simpler to install but can only be used with a limited range of cameras. Again, for this type of lens many cameras are being produced with screw connectors instead of a socket for the lens connection.

Lens Parameters
Focal Length

Diagram 2. Focal Length of Lenses

The rays from infinitely distant objects are condensed by the lens at a common point on the optical axis. The point where the image sensor of the camera is to be placed is called the focal point. A lens has two focal points, the primary principal point and the secondary principal point. The distance between the secondary principal point and the plane of the image sensor is the focal length of the lens.

Diagram 3. Angle of View

Angle of View of Lenses
This is the angle that the two lines from the secondary principal point make with the edges of the image sensor. The focal length of a lens is fixed whatever the size of the image sensor. The angle of view however varies according the size of the sensor.

The angle of view is given by the following formula:

Diagram 4 Angles of View for Different Sensor Sizes

Diagram 5 Focal Lengths for Different Sensor Sizes

The angle of view for a given focal length lens varies according to the sensor size. This is shown in diagram 4. The corollary of this is that for a given view the required focal length varies according to the sensor size as shown in diagram 4.6. This illustrates that for the same field of view, the smaller the format the shorter is the required focal length.
Field Of View

Diagram 6. Field Of View

The field of view is the ratio of the sensor size to the focal length and the distance to the subject. This is shown in diagram 4.7. The ‘width to height’ ratio of the sensor is 4:3. The horizontal and vertical angles and therefore fields of view are different and must be considered separately.

Sensor Sizes

Diagram 7. Sensor Dimensions

Diagram 7.shows the sensor sizes to be used when calculating fields of view and angles of view.For example, if it were required to view a subject 2.5 M high at a distance of 10M using a 2/3” camera and lens the calculation would be as below.
The nearest standard lens in this case would be a 25mm and the actual height of the subject scene would be 2.64 M. The slightly shorter focal length lens provides a slightly wider angle of view.

Most lens brochures give the horizontal and vertical angles of view. The relevant views can be calculated from the formula as follows:
Where: H is the height of the scene, d is the distance from the camera to the scene. This would give the vertical height of the scene using the vertical angle of view. Similarly, the horizontal width of the scene would be calculated from the horizontal angle of view.
Relationship Between Sensor Size and Lens Size
It can be very confusing to establish the actual field of view that will be obtained from a combination of sensor size and lens specification. Lenses are specified as designed for a particular sensor size. A lens designed for one sensor size may be used on a smaller size but not the reverse. The reason is that the extremities of the scene will be outside the area of the sensor. Many people in the CCTV industry have grown up with the 2/3” camera as the most popular and are familiar with the fields of view produced. However the 1/2” and 1/3” cameras are now being extensively used and therefore there are important factors that must be taken account.

Diagram 8. Effect of Sensor Size on View

Diagram 9. Using a Correctly Matched Camera and Lens Format

Diagram 8. shows the effect of using one lens on two different sizes of sensor. The result of using a larger lens format on a smaller lens format is to create the effect of a longer focal length, which is a narrower angle of view.
Diagram 9. shows the result of using a lens designed for a 1/2” format on a 1/2” sensor. This is an important consideration when deciding the most appropriate lens for a required field of view. The design size of the lens must be related to the size of the sensor being used.
To summarise then:
1. A lens designed for one format may be used on a smaller format camera but will produce a narrower angle of view.
2. A lens designed for one format may not be used on a larger format camera.
3. Assuming a focal length has been assessed based on a particular format of camera and lens, and it is then decided to use a smaller format camera, the same field of view will only be obtained if a shorter focal length lens is used.
4. Always check the angle of view for the particular lens and camera combination it is intended to use.
5. Charts at the end of this chapter provide guidance on the selection of lenses and the relationship between different formats of camera and lenses.

Aperture
The size of the aperture is called the ‘f number’ of the lens, e.g. f1.4, f1.2, etc. This is a mechanical ratio of the lens components and is specified as:
The effective diameter is related to the size of the front lens. Note that this is effective diameter and not the actual diameter. This is a measure of the amount of light that the lens will pass to the imaging device. As stated it is a ratio and does not refer to the quality of the lens. The smaller the number then the larger is the aperture. The figure given in specifications for lenses is the maximum aperture and this value is often followed by the minimum aperture. For instance, f1.4 -- f360, this second value being important if the camera is very sensitive such as an intensified sensor. Intensified cameras often require a minimum aperture as small as f1500. From the formula above it may be calculated that with a 16mm lens having the aperture set to f360 the effective diameter will be only 0.04mm. Even so, this could allow too much light to the sensor of an intensified camera and damage the tube or flare out the picture.

Having said that the f-number is a ratio, this does not imply that a lens with a lower number is better than one with a higher number. There are other factors that affect the light transmission through a lens. However, when comparing the major brands of lenses it is sufficient to use the f-number unless the application is especially demanding, where, for instance, image comparison or ultra fine resolution is necessary.

The efficiency of a lens and the amount of light it can transmit depend on many factors that lens designers must consider. However, ultimately a lens must be a commercial proposition and affordable to the CCTV installer and the customer. Two factors that affect the cost of a lens are the size of the glass elements and the number of elements. Therefore, it is less expensive to produce a 16mm f1.8 lens than it is to produce a 16mm f1.2. Consequently, some manufacturers produce the same focal length lens in two variations of f-number. For indoor conditions with ample light, or outdoor use in daylight only, the cheaper f 1.8 lens would be satisfactory and could represent a saving in cost. Exercise care in selecting the cheaper lens if the application is outdoors with low light conditions. As can be seen from this chapter, this would require nearly three times as much light as the f1.2 lens.

How aperture numbers are calculated
The scale of ‘f’ numbers, 1.4, 2.0, 2.8, 4, 5.6, etc. is such that successive numbers halve the amount of light passed to the sensor. These particular numbers are known as "full stops". This only applies to "full stops"; there are also half stops, which are numbers half way between full stops, and one-third stops In other words, the amount of light is proportional to the cross sectional area of the light rays entering the lens.

It can be shown that the f number,

From this equation the following can be derived;

If the illuminance is defined as ‘E’ lux, the equation can be shortened to;
If reflectance (R) is taken into account, this now becomes,
Another consideration is, how efficient is the lens at passing the maximum amount of light. There are several factors that determine the efficiency of a lens and of course they all cost money. When light passes through a glass/air boundary some is lost through reflection and refraction; this is reduced in the more expensive lenses. In addition, different light frequencies are refracted at different angles; special coatings are used to ensure that all frequencies are transmitted in parallel rays. The factor that measures the efficiency of a lens is known as the transparency ratio, (t) from which is calculated the transmission ratio (T).
The transparency ratio (t) is a function of the lens design and the number of glass elements. This is generally only available from the manufacturer. The transmission ratio (T) is the effective lens stop after adjusting for the transparency ratio (t) and is defined by

The resulting number will always be larger than the specified f-number.

For example, an f-1.4 lens having a transparency ratio (t) of 0.785 would have an effective aperture of f 1.58. This would be the value to use when calculating the light transmitted through a lens rather than the published f-number. All reputable manufacturers should be able to provide information on the transmission ratios for their lenses.
If this is now taken into account, the relationship becomes.

If an example is now worked using;
Transparancy ratio, t=0.785,
Reflectance, R=0.89,
Scene illumination, Escene=15 lux, Lens aperture, f=1.4,
Then, the light required on the sensor

The effect of sensor size
here is yet another factor that affects the efficiency of a camera/lens combination.

As stated in a previous article, light is energy measured in Watts per square Metre. Therefore, if the area of a sensor is known then the resultant power in watts can be calculated. The nominal areas of the sensors in common use are listed in table 2.

Table 2, areas of sensors

The power produced by each individual pixel in the sensor is directly proportional to its area. If three cameras are considered each with the same resolution of say 500 lines then the number of pixels on each sensor must be the same. The result of this is that the pixels on each smaller size of sensor must also be smaller. Therefore, the power produced will be less for the same aperture setting, i.e. the same amount of light energy. It is assumed that the light energy to produce a full 1-volt pp video signal is 5.0 mW/M2
If for the sake of an example, a light source of 1,000 milliwatts per square Metre is passed to the sensor via an f-1.8 aperture lens. The amount of light passed by the lens will be 7.5% = 75 mW/M2. From this, the power output can be calculated for each sensor. This will be the power multiplied by the area of the sensor. The result is shown in table 3.

Table 3-power output of sensors

Therefore the 1/2" and 2/3" sensors will be producing insufficient power for a full video signal. The answer is to use a lens with a larger aperture for these sensors so that more energy is passed to maintain the output power. This is summarised in table 4

Table 4-power output corrected by lens f-stop

This is the reason that many 1/3" cameras have the sensitivity specified with an f-1.0 or sometimes an f 0.9 aperture. Beware though, there are only a limited number of lenses made to the 1/3" format. If the longer focal length lenses must be used they usually have smaller apertures (higher f-numbers) and pass less light energy.
The contra to this argument is that if a sensor of one size has the same size pixels as a larger one, then the light required will be the same. However the total number of pixels will be fewer and the resulting resolution will be proportionally less. There is no such thing as a free lunch!