Design of CCTV System

CCTV system design

Designing a CCTV system is a complex task, requiring at least basic knowledge of all the stages in a system, as well as its components. But more importantly, prior to designing the system, we need to know what the customer expects from it.

Understanding the customer’s requirements

The first and most important preparation before commencing the design is to know and understand the customer’s requirements. Customers can be technically oriented people, and many understand CCTV as well as you do, but most often they are not aware of the latest technical developments and capabilities of each component.

The most important thing to understand is the general concept of the surveillance the customer wants, Constant monitoring of cameras and activities undertaken by 24-hour security personnel, or perhaps just an unattended operation (usually with constant recording), or maybe a mixture of the two. Once you understand their general requirements, it might be a good idea to explain to them what is achievable with the equipment you would be suggesting. This is reasonably easy to accomplish with smaller and simpler systems, but once they grow to a size of more than 10 cameras some of which could be PTZs, a few monitors, more than one control point, a number of alarms, VCRs, and the like, things will get tougher.

Many unknown variables need to be considered: What happens if a number of alarms go off simultaneously? Which monitor should display the alarms? Will the alarms be recorded if the DVR/VCR(s) is/are playing back? What is the level of priority for each operator? And so on.

Those are the variables that define the system complexity and as in mathematics, in order to solve a system with more variables, one needs to know more parameters. They can be specified by the customer, but only after the customer has understood the technical capabilities of the equipment.

Understandably, it is imperative for you, as a CCTV expert, to know the components, hardware, and software you would be offering and to achieve what is required in the best possible way. You can create a favorable impression in the customer’s mind if at the end you give him or her as much as, or even more than, what you have promised. You will prove unsatisfactory if you do not. Remember that if the customer is fully satisfied the first time, chances are he or she will come back to do business with you again. To put it simply: Do not claim the system will do this and that if you are not certain; make sure your system delivers what you say it will.

So, to design a good, functional system, one has to know the components used, their benefits and limitations, how they interconnect, and how the customer wants them to be used. The first few parts are assumed to be fulfilled, since you would not be doing that job unless you knew a few things about CCTV. The last one – what the customer wants – can be determined during the first phone call or meeting.

Usually, the next step is to conduct a site inspection. Here is a short list of questions you should ask your customer prior to designing the system and before or during the site inspection:

• What is the main purpose of the CCTV system?

If it is a deterrent, you need to plan for cameras and monitors that will be displayed to the public.

If it is a concealed surveillance, you will need to pay special attention to the camera type and size, its protection, concealed cabling, and the like, as well as when it is supposed to be installed (after hours perhaps).

• Who will be the operator(s) ?

If a dedicated 24 hour guard is going to use the system, the alarm response needs to be different from that expected when unattended, or a partially attended, system operation.

• Will it be a monochrome or color system ?

The answer to this question will dictate the price, as well as the minimum illumination response.

Consequently, the lighting in the area needs to be looked at. A color picture will give more details about the observed events, but if the intention is to see images in very low light levels, or with infrared lights, there is no other alternative but B/W cameras (unless the customer is prepared to pay for some of the new cameras available on the market that switch between color and monochrome operation).

The price of a color system is dictated not only by the cameras, but also by the monitors, multiplexers, and/or quads (if any). Needless to say, sequential or matrix switchers, as well as time-lapse VCRs, are the same for both B/W and color.

• How many cameras are to be used ?

A small system with up to half a dozen cameras can be easily handled by a switcher or multiplexer, but bigger systems usually need a matrix switcher or a larger number of switchers and multiplexers.

• How many of the cameras will be fixed focal length and how many PTZ ?

There is a big difference in price between the two because if a PTZ camera is used instead of a fixed one, the extra cost is in the zoom lens (as opposed to the fixed one), the pan and tilt head or dome, the site driver, and the control keyboard to control it. But the advantages your customer will get having a PTZ camera will be quadrupled. If on top of this, preset positioning PTZ cameras are used, the system flexibility and efficiency will be too great to be compared with the fixed camera system. A system with only one PTZ camera and half a dozen fixed ones is a choice that may require a matrix switcher for control and will increase the price dramatically (compared to a system with only fixed cameras). Alternatively, single PTZ camera control can be achieved via a special single-camera digital or hard-wired controller, but they would also increase the price considerably. So, if a PTZ camera is required, it would be more economical to have more than one PTZ camera.

• How many monitors and control keyboards are required?

If it is a small system, one monitor and keyboard is the logical proposal, but once you get more operators and/or channels to control and view simultaneously, it becomes harder to plan a practical and efficient system. Then, an inspection of the control room is necessary in order to plan the equipment layout and interconnection.

• Will the system be used for live monitoring (which will require an instant response to alarms), or perhaps recording of the signals for later review and verification ?

This question will define whether you need to use DVR/VCR(s) with multiplexer(s). If you have a matrix switcher, you will still need a multiplexer or two in addition. Have in mind that the time lapse mode you are going to use depends on how often the tapes can be changed, and this defines the update rate of each camera recorded. Choose, whenever possible, a pair of 9-way (or 8-way) multiplexers instead of one 16-way, if you want to minimize the time delay in the recording rate update.

• What transmission media can be used on the premises ?

Usually, a coaxial cable is taken as an unwritten rule and installation should be planned accordingly. Sometimes, however, there is no choice but to use a wireless microwave or even a fiber optics transmission, which will add considerably to the total price. If the premises are subject to regular

lightning activity, you had better propose fiber optics from the beginning and explain to the customer the savings in the long run. So, you have to find out more about the environment in which the system is going, what is physically possible and what is not, and then plan an adequate video and data transmission media.

• Lastly and probably the most important thing to find out, if possible, is what sort of budget is planned for such a CCTV system?

This question will define and clarify some of the previous queries and will force you to narrow down either the type of equipment, the number of cameras, or how the system is expected to work. Although this is one of the most important factors, it should not force you to downgrade the system to something that you know will not operate satisfactorily.

If the budget cannot allow for the desired system, it is still good to go back to the customer with a system proposal that you are convinced will work as per his or her requirements (even if it is over budget) and another one designed within the budget with as many features as the budget will allow for. This will usually force you to narrow down the number of cameras, or change some from PTZ to fixed. The strongest argument you should put forward when suggesting your design is that a CCTV system should be a secure one, which can only be the case if it is done properly. Thus, by having a well-designed system, bigger savings will be made in the long run.

By presenting a fair and detailed explanation of how you think the system should work, the customer will usually accept the proposal.

Site inspections

After the initial conversation with the customer and assuming you have a reasonably good idea of what is desired, you have to make a site inspection where you would usually collect the following information:

• Cameras: type (i.e., B/W or color, fixed or PTZ, Resolution, etc.).

• Lenses: angles of view, zoom magnification ratio for zoom lenses (12.5–75 mm, 8–80 mm, etc.).

• Camera protection: housing type (standard, weatherproof, dome, discrete, etc.) mounting.

• Light: levels, light sources in use (especially when color cameras are to be used), east/west viewing direction. Visualize the sun’s position during various days of the year, both summer and winter. This will be very important for overall picture quality.

• Video receiving equipment: location, control room area, physical space, and the console.

• Monitors: Resolution, size, position, mounting, and the like.

• Power supply: type, size (always consider more amperes than what are required). Is there a need for an uninterruptable power supply (UPS)? (VA rating in that case).

• If pan/tilt heads are to be used: type, size, load rating, control (two wire – digital or multi-core). Is there a need for preset positioning (highly recommended for bigger systems)? Where are they going to be mounted? What type of brackets ?

• Make a rough sketch of the area, with the approximate initial suggestions for the camera positions. Take into account, as much as possible, the installer’s point of view. A small change in the camera’s position, which will not affect the camera’s customer. An unwritten golden rule for a good picture is to try and keep the camera from directly facing light.

• Put down the reference names of areas where the customer wants (or where you have suggested) the cameras to be installed. Also write down the reference names of areas to be monitored because you will need them in your documentation as reference points. Be alert for obvious “no-nos” (in respect to installation), even if the customer wishes something to be done. Sometimes small changes may result in high installation costs or technical difficulties that would be impossible to solve. It is always easier to deter the customer from making changes by explaining why in the initial stage, rather than having to do so later in the course of installation, when additional costs will be unavoidable.
To know more just read Condensed Code BS EN 62676-4 and BS EN 50132-7, BS EN 62676-4 Clause 4.4 & BS EN 62676-4 Clause 4.5.

Designing and quoting a CCTV system

With all of the above information, as well as the product knowledge (which needs constant updating), you need to sit down and think.

Designing a system, like designing anything new, is a form of art. As is true of many artists, your work may not be rewarded immediately, or it may not be accepted for some reason. But think positively and concentrate as if that is to be the best system you can propose. With a little bit of luck you may make it the best, and tomorrow you can proudly show it to your colleagues and customers. Different people will use different methods when designing a system. There is, however, an easy and logical beginning.

Always start with a hand drawing of what you think the system should feature. Draw the monitors, cameras, housings, interconnecting cables, power supplies, and so on. While drawing you will see the physical interconnection and component requirements. Then you will not omit any of the little things

that can sometimes be forgotten, such as camera brackets, types of cable used, and cable length. Making even a rough hand sketch will bring you to some corrections, improvements, or perhaps further inquiries to the customer. You may, for example, have forgotten to check what the maximum distance for the PTZ control is, or how far the operators are to be from the central video processing equipment, power cable distances, voltage drops, and so on.

Once you have made the final hand drawing, you will know what equipment is required, and it is at this point that you can make a listing of the proposed equipment. Then, perhaps, you will come to

the stage of matching camera/lens combinations. Make sure that they will fit in the housings or domes you intend to use. This is another chance to glance through the supplier’s specifications booklet. Do not forget to take into account some trivial things that may make installation difficult, like the coaxial cable space behind the camera (remember, it is always good to have at least 50 mm for BNC terminations), the focusing movement of a zoom lens (as mentioned earlier in the chapter on zoom lenses, in a lot of zoom lenses focusing near makes the front optical element protrude for an additional couple of millimeters), and so on.

The next stage is pricing the equipment – costs, sales tax and duty, installation costs, profit margins and the most important of all (especially for the customer) the total price.

Do not forget to include commissioning costs in there, although a lot of people break that up and show the commissioning figure separately. This is more of a practical matter, since the commissioning cost may vary considerably and it could take longer or shorter than planned. General practical experience shows that it will always take at least three times longer than planned. Also, in the commissioning fees, time should be allocated for the CCTV operator’s training.

After this step has been completed, you need to make a final and more accurate drawing of the system you are proposing. This can be hand drawn, but most CCTV designers these days use computers and CAD programs. It is easier and quicker (once you get used to it), and it looks better.

Also, the hand-calculated price needs to be written in a quotation form, with a basic explanation of how the system will work and what it will achieve. It is important for this to be written in a concise and simple, yet precise form, because quotations and proposals (besides being read by security managers and technical people) are also read by nontechnical people such as purchasing officers and accountants.

Often, spreadsheet programs are used for the purpose of precise calculation, and this is another chance to double-check the equipment listing with your drawing and make sure nothing has been left out. As with any quotation, it is more professional to have a set of brochures enclosed for the components you are proposing.

In the quotation, you should not forget to include your company’s terms and conditions of sale which will protect your legal position.

If the quotation is a response to a tender invitation, you will most likely need to submit a statement of compliance.

This is where you confirm whether your equipment complies or does not comply with the tender requirements. This is where you also have to highlight eventual extra benefits and features your equipment offers. In the tender, you may also be asked to commit yourself to the progress of the work and supply work insurance cover, in which case you will need a little bit of help from your accountant and/or legal advisor.

Many specialized companies only design and supply CCTV equipment, in which case you will need to get a quote from a specialized installer, who, understandably, will need to inspect the site. It is a good practice, at the end, to have all the text, drawings, and brochures bound in a single document, in a few copies, so as to be practical and efficient for reviewing and discussions.

Installation considerations

If you are a CCTV system designer, you do not have to worry about how certain cables will be pulled through a ceiling, raisers, or camera pole mounting; that is the installer’s job. But it would be very helpful and will save a lot of money, if you have some knowledge in that area. If nothing else, it is a good practice, before you prepare the final quotation, to take your preferred installer on site, so that you can take into account his or her comments and suggestions of how the practical installation should be carried out.

First, the most important thing to consider is the type of cable to be used for video, power, and data transmission, their distances and protection from mechanical damage, electromagnetic radiation, ultraviolet protection, rain, salty air, and the like. For this purpose it is handy to know the surrounding area, especially if you have powerful electrical machinery next door, which consumes a lot of current and could possibly affect the video and control signals. Powerful electric motors that start and stop often may produce a very strong electromagnetic field and may even affect the phase stability of the mains. This in turn will affect the camera synchronization (if line-locked cameras are used) as well as the monitor’s picture display.

For example, there might be a radio antenna installed in the vicinity, whose radiation harmonics may influence the highfrequency signals your CCTV system uses.

Mounting considerations are also important at both the camera and monitor end. If poles are to be installed, not only the height, but also the elasticity of the poles is important. Steel poles, for example, are much more elastic than concrete poles. If a PTZ camera is installed, the zoom lens magnification factor will also magnify the pole’s movement which could result from wind, or vibrations from the pan/tilt head movement itself. This magnification factor is the same as the optical magnification (i.e., a zoom lens, when fully zoomed in, may magnify a 1mm movement of the camera due to wind to a 1 m variation at the object plane).

The shape of the pole is also very important

– hexagonal poles are less elastic than round ones of the same height and diameter.

The same logic applies to camera and pan/tilt head mounting brackets. A very cheap bracket of a bad design can cause an unstable and oscillating picture from even the best camera.

If the system needs to be installed in a prestigious hotel or shopping center, the aesthetics are an additional factor to determine the type of brackets and mounting. It is especially important then not to have any cables hanging.

The monitoring end demands attention to all aspects. It needs to be durable (people will be working with the equipment day and night), or aesthetical (it should look good) and practical (easy to see pictures, without getting tired of too much noise and flashing screens).

Since all of the cables used in a system wind up at the monitoring end and in most cases this is the same room where the equipment is located, special attention needs to be paid to cable arrangement and protection.

Often, cables lying around on the floor for a few days (during the installation) are subject to people walking on them, which is enough weight to damage the cable characteristics, especially the coaxial cable impedance. Remember, the impedance depends on the physical relation between the center core, the insulation, and the shield. If a bigger system is in question, it is always a better idea to propose a raised floor, where all the cables are installed freely below the raised floor.

Sometimes, if a raised floor is not possible, many cables can be run over a false ceiling. In such cases special care should be taken to secure the cables as they could become very heavy when bundled together.

Larger installations may want a patch panel for the video signals.

This is usually housed in a 19'' rack cabinet, and its purpose is to break the cables with special coax link connectors so as to be able to reroute them in case of a problem or testing.

Many installers fail to get into the habit of marking the cables properly. Most of them would know all of the cables at the time of installation, but two days later they can easily forget them. Cable marking is especially critical with larger and more complex systems. Insist on proper and permanent cable markings as per your drawings. There are plenty of special cable-marking systems on the market. In addition, listing of all the numbers used on the cables should be prepared and added to the system drawings.

Remember, good installers differ from bad ones in the way they terminate, run, arrange, and mark the cables, as well as how they document their work.

Drawings

There is no standard for drawing CCTV system block diagrams, as there is in electronics or architecture. Any clear drawing should be acceptable as long as you have clearly shown the equipment used (i.e., cameras, monitors, VCRs) and their interconnection.

Many people use technical drawing aids, such as CAD programs, or other PC or Mac-based drawing packages. Depending on the system size, it might be necessary to have two different types of drawings: one of a CCTV block diagram showing the CCTV components’ interconnection and cabling requirements, while the other could be a site layout with the camera positions and coverage area. In smaller installations, just a block diagram may be sufficient.

The CCTV block diagram needs to show the system in its completeness, how the components are interconnected, which part goes where, what type of cable is used, and where it is used.

If the site layout drawing is well prepared, it can later be used as a reference by the installer, as well as by your customer and yourself when reviewing camera locations, reference names, and discussing eventual changes.

When the CCTV system is installed and the job is finished, drawings may need small alterations, depending on the changes made during the installation. After the installation, the drawings are usually enclosed with the final documentation, which should also include manuals, brochures, and other relevant documentation.

Commissioning

Commissioning is the last and most important procedure in a CCTV system design before handing it over to the customer. It involves great knowledge and understanding of both the customer’s requirements and the system’s possibilities. Quite often, CCTV equipment programming and setup are also part of this. It includes video matrix switcher programming, time-lapse VCR programming, camera setup, and so on.

Commissioning is usually conducted in close cooperation with the customer’s system manager and/or operator(s), since a lot of settings and details are made to suit their work environment.

The following is a typical list of what is usually checked when commissioning:

All wiring is correctly terminated.

Supply voltage is correct to all appropriate parts of the system.

Camera type and lens fitted are correct for each position.

Operation of auto irises under various light levels is satisfactory.

If VCRs are fitted, they should be recording in the most efficient time-lapse mode (especially when multiplexed cameras are being recorded).

If DVRs are installed, the pictures per second performance and image quality (compression setting) should be checked .

All system controls are properly functioning (pan/tilt, zoom, focus, etc.)

The setting of all pan and tilt limits is correct.

Preset positioning, if such cameras are used, is correct.

The level of supplementary lighting is satisfactory.

The system must continue to work when the main supply is disconnected, and a check should be made as to how long it does (if UPS is used).

Commissioning larger systems may take a bit longer than the smaller ones. This is an evolution from the system on paper to the real thing, where a lot of small and unplanned things may come up because of new variations in the system concept. Customers, or users, can suggest the way they want things to be done, only when they see the initial system appearance. Commissioning in such cases may therefore take up to a few days.
Commissioning under  BS EN 62676-4 Clause 4.6 & BS EN 62676-4 Clause 13.

Training and manuals

After the initial setup, programming, and commissioning are finished, the operators, or system users, will need some form of training.

For smaller systems this is fairly straightforward and simple. Just a verbal explanation may be sufficient, although every customer deserves a written user’s manual. This can be as simple as a laminated sheet of paper with clearly written instructions.

Every piece of equipment should come with its own User’s Manual, be it a time lapse VCR, a camera, or a switcher, but they have to be put together in a system with all their interconnections and this is what has to be shown to the customer. Every detail should be covered, especially alarm response and the system’s handling in such cases. This is perhaps the most important piece of information to the operators.

For larger systems, it is a good idea to bind all the component manuals, together with the system drawings, wiring details, and operator’s instructions, in a separate folder or a binder. Naturally, for systems of a larger size, training can be a more complex task. It may even require some special presentation with slides and drawings so as to cover all the major aspects.

Good systems are recognized not only by their functionality but also by their documentation.

Handing over

When all is finished and the customer is comfortable with what he or she is getting, it is time to hand over the system. This is an official acceptance of the system as demonstrated and is usually backed by the signing of appropriate documents.

It is at this point in time that the job can be considered finished and the warranty begins to be effective.

From now on, the customer takes over responsibility for the system’s integrity and operation.

If customers are happy with the job, they usually write an official note of thanks. This may be used later, together with your other similar letters, as a reference for future customers.
Documentation consider BS EN 62676-4 Clause 4.8, BS EN 62676-4 Clause 15.3 & BS EN 62676-4 Clause 16.

Preventative maintenance

Effective and regular maintenance of a CCTV surveillance system is essential to ensure that the system remains reliable at all times. It is advisable that maintenance of the CCTV system should be carried out by the company which installed the system. However, the maintenance company should have the means, including necessary spare parts and documentation, to meet the recommendations given here.

Note: This recommendation does not place an obligation upon customers who purchase their systems to have them maintained by the installing company. Maintenance is a matter of agreement between the customer and the installing company or a separate maintenance company. Maintenance comes under BS EN 62676-4 Clause 17 & SC CoP Guiding Principle 10.

The preservation of security within the maintenance company is of paramount importance and steps should be taken to ensure the safe keeping of all customers’ equipment and documentation relating to a particular installation/contract.

Note: BS EN 50132-7 states that “CCTV systems should be maintained in accordance with the schedule supplied by the system designer or supplier”, but does not detail any specific maintenance requirements. These guidelines give specific advice for the maintenance of CCTV surveillance systems, and provide examples of the type of documentation required to be used by the service company.

A maintenance company should ensure that adequate vetting of all employees is carried out. All employees, who visit a customer’s premises, shall carry identification cards which should include a photograph and signature of the bearer, the company’s name, contact details and a date of expiry (maximum of 3 years).

Each service technician employed by the maintenance company should carry a range of tools, test equipment and other equipment to enable them to perform their functions satisfactorily. Specialist tools, test equipment and plant should be available for deeper investigation if necessary.

Note: Disconnections, for whatever reason, should be recorded on a maintenance record and authorised by the client or his representative.

The maintenance company’s organisation should be so staffed as to ensure that the recommendations of this Code of Practice can be met at all times. The following factors should be taken into consideration:

1.       the number of installations to be serviced

2.       the complexity of the installations;

3.       the geographical spread of the installations in relation to the location of the maintenance company, its branches and its service personnel

4.       the method of calling out service personnel outside normal office hours, where applicable.

5.       Service personnel should be adequately trained and training should be updated whenever appropriate.

Maintenance Service is 3 types but scope of work is same.

A.   Preventive Maintenance service.

B.   Corrective Maintenance service.

C.   Performance Maintenance service.

http://arindamcctvaccesscontrol.blogspot.in/2014/09/service-and-maintenance-for-cctv.html

Note: The BS EN standards BS EN 62676-2-X comprising part 1, 2 and 3, provide detailed guidelines to manufacturers as to how they should implement IP video transmission products.

An end user is unlikely to benefit by reading the 62676-2-X standards. They may instead be involved in a buying decision which could place reliance on claims of conformance to the part of the BS EN standard the manufacturer chose to implement. Interoperability of equipment is not solely reliant on the requirements included in the BS EN standards in their current form. There is no guarantee that a product which simply claims BS EN 62676 compliance will provide full compatibility with another claiming the same compliance although it should allow for a minimum level of image transfer. 

Installers, users and specifiers should treat claims of interoperability between manufacturers products with caution. The parts of the BS EN standard which focus on interoperability, are 62676-2-2, which describes the PSIA guidelines for interoperability of IP Video devices, and 62676-2-3, which describes the ONVIF guidelines for interoperability.

ONVIF and PSIA, are at their base level, a common set of commands allowing basic communication between devices but this does not guarantee that the devices will function to the full potential of their design. Issues with product firmware and software should also be considered: a change of firmware / software versions should be tested separately to ensure continued interoperability. Whilst the specifications try to take this into account, the number of products claiming to be conformant currently makes this an impossible task.

Claims by product manufacturers that PSIA or ONVIF compliance means that users do not have to check that the products work together should be treated with great caution. It is strongly recommended that all such products are tested before being deployed.

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!