That said, I see way to many systems sellers who sell only on price, and have no idea what the specifications mean.
This is intended to provide the "first time CCTV shopper" a basic understanding of what the various specifications mean, and hopefully what to look for (or at least what questions to ask) when they begin obtaining quotations.
All cameras are not created
equal. If they were there would be no
need for the vast range of cameras which are available.
For
the most effective solution it is important to specify
the correct camera for the purpose and the
environment in which it will operate. The most expensive solution is the one
which does not operate quite as intended or required.
Cameras – WDR (Wide Dynamic Range) & IR
Wide
Dynamic Range is
important in any area where there may be either reflections (e.g. a window) or
a brighter area behind the main subject to be recorded.
It is special software built into the camera which automatically compensates by increasing the range contrast. Together with BLC (Back Light Compensation) which only filters (darkens) the bright background while brightening the foreground image (and thus reducing the contrast range) it provides the clearest possible image under adverse lighting conditions.
This prevents people being “silhouetted” against a bright background, making them unrecognisable.
It is special software built into the camera which automatically compensates by increasing the range contrast. Together with BLC (Back Light Compensation) which only filters (darkens) the bright background while brightening the foreground image (and thus reducing the contrast range) it provides the clearest possible image under adverse lighting conditions.
This prevents people being “silhouetted” against a bright background, making them unrecognisable.
A variable focal lens is a
non-user-adjustable zoom lens, which is zoomed in or out to provide the exact focal length which provides the
image field of view which best suites the requirements of the client. The lens
is then locked into this focal length setting by the installer.
Often a fixed focal length lens (e.g. 3.6mm, 6mm, 9mm, 12mm etc.) may be a compromise, providing a view which is either too wide or too narrow a viewing angle. A variable focus lens provides the flexibility to set the focal length between that of “standard” lenses.
Often a fixed focal length lens (e.g. 3.6mm, 6mm, 9mm, 12mm etc.) may be a compromise, providing a view which is either too wide or too narrow a viewing angle. A variable focus lens provides the flexibility to set the focal length between that of “standard” lenses.
Field of View (FOV)
You need to know the purpose of your camera, and what it is that you wish to see in the image.
There may be (will be) instances where there are substantial costs involved in locating a camera in the perfect position. This would be related to trenching, conduit, camera poles etc. for outdoor cameras. For indoor cameras it may simply relate to additional labour and cabling costs.
There may be (will be) instances where there are substantial costs involved in locating a camera in the perfect position. This would be related to trenching, conduit, camera poles etc. for outdoor cameras. For indoor cameras it may simply relate to additional labour and cabling costs.
It is possible to position a camera either further away (the usual scenario) or closer than desired to the area you wish to view.
Knowing the field of view you wish to obtain, and selecting the correct lens, will help you to overcome these costs. There are, however, factors which need to be considered, depending on the application of the camera.
The FOV consists of two aspects, namely the horizontal & vertical fields of view.
It is very seldom that any required FOV will match the aspect ratio of your camera image.
When selecting the lens to use, make sure that the minimum required FOV is covered from both a horizontal and a vertical aspect.
It is in this type of scenario that a vari-focal lens is useful. Your calculations may indicate, for example, that a 7.8mm lens is required to provide the necessary FOV. Standard fixed focal length lens options in this range would generally be 6mm or 9mm, which leaves you no option but to select the 6mm lens. This will provide a greater FOV (both horizontally & vertically) with the result that the important area of the image is only the central section.
This results in less detail of the area of importance, as the important area is not filling the image.
Calculating the required focal length is a fairly simple exercise. The formula is as follows to calculate the FOV provided by a specific focal length lens at a specified distance from the subject.
FOV = D (Distance) x SS / FL
Where FOV = resultant Field of View; SS = size in millimeters of the image sensor; FL = the Focal Length in millimeters of the lens used.
Different cameras have different image sensor dimensions, so you need to know this. Using the horizontal size will calculate the Horizontal Field of View, while using the vertical size will calculate the vertical field of view.
It is important to remember that the camera mounting height will alter the distance to the subject. If it cannot be accurately measured a bit of High School Geometry will assist here (and you thought you would never have a use for it?)
Depending on the mounting height and the ground level distance to the subject, you could be out by anything up to 30 percent if you do not take the mounting height into consideration.
I have a simple spreadsheet calculator, designed for analogue cameras, which makes the calculation simple. Anyone is welcome to download it and use it. Click HERE to download.
Understanding ZOOM
The ability of a camera to zoom comes in two "flavours" - optical and digital. This is an and rather than an or, as PTZ ( Pan, Tilt & Zoom) cameras (often referred to as "speed domes") generall have both.
Optical provides the better results, as the focal length of the lens actually alters.
Digital on the other hand relies on software. Essentially it simply crops and enlarges a portion of the image, which effectively reduces the resolution.
What this means is simple. When you use your viewing software to zoom in further on an image captured by a digital zoom lens, the results will be far less satisfactory than if you did so on the same image captured by an optical zoom lens. Why? Because the image captured with the optical zoom lens has a much higher effective resolution to begin with.
To understand this, try the following. Set the camera on your smartphone to the highest possible resolution, and take a photograph. Now change the setting to the lowest (or considerably lower) resoltion and take the same photo. You may not see that much difference on the small viewing screen on the phone. However, zoom in on the caputred image and see how drastically different the results are? That is digital zoom.
The other thing to bear in mind about a zoom, or even a fixed longer focal length lens, is the impact on your FOV.
As you zoom in, either digitally or optically, your angle of view changes to provide a narrower field of view at a further point. This has the effect of making the subject matter appear larger in your image (closer to the camera) but you lose detail of what is between the camera and the subject. It is as if you have walked closer to the subject with the camera, and no camera can see what is behind it.
This is why understanding what the purpose of your camera is, and exactly what you need to see.
In some instances it may be better, and usually cheaper, to utilise two fixed focal lenght cameras than it would be to utilise a PTZ Speed Dome. Match the camera choice(s) to the requirement.
Analogue Cameras
This is something of a misnomer, and something which may confuse new users of CCTV technology.
In still picture cameras we first had cameras using film, and these have now been largely replaced by digital cameras, where images are captured by a sensor. This is usually a CCD (Charge Coupled Device) chip, which reacts to light in much the same way as the film did in the "old" days. However, it does not need to be developed as a negative, and then printed as a positive in order to view the resultant image. The image is captured and processed digitally, and is immediately viewable.
Analogue CCTV Cameras use this same technology, and thus are digital.The main difference between analogue CCTV cameras and their IP or Networked counterparts, for a simple understanding, lies in the nethod of cabling and transmission of the images.
Analogue cameras conventionally utilise co-axial cable, such as RG59, while IP or Networked cameras conventionally utilise CAT5 ethernet cable. The RG59 is connected to the camera by way of a BNC connector, while the ethernet cable is connected to the camera by way of a RJ45 ethernet plug.
Yes, this is simplistic, and the differences extend far beyond that, but that will be the topic of a blog all of its own.
A standard data HDD may save costs,
but it is not ideally suited to the demands of recording and streaming CCTV
footage.
I recommend that you utilise only Video Streaming HDD units in your equipment.
I recommend that you utilise only Video Streaming HDD units in your equipment.
Surge
Protection
Fitted at either end of every camera
line it is designed to protect the expensive camera and recording equipment, as
far as possible, from unexpected power surges. It is far cheaper and easier to
replace a surge protector than to replace a blown camera or recorder.
