Choosing a lens for a CCTV camera
To get a high-quality image from a camcorder, every element that is part of the device is important. The lens plays an important role in generating a video stream with a clear, detailed picture. The performance of the equipment depends on the quality of lenses, their fit and assembly, as well as compatibility with the characteristics of the photosensitive matrix. Therefore, when choosing a lens for CCTV cameras, it is important to correctly determine which optics are needed in a particular situation. To do this, you need to know its main characteristics, specifics and scope.
To learn how to choose a CCTV lens, you need to define the tasks that it will perform. Two factors are important here: the installation site, the coverage area and the maximum distance at which the tracking system will work.
How to choose a lens for a CCTV camera by viewing angle
- narrow-angle (3-30 °). Used to control a small sector: corridors, stairs, areas under windows;
- medium-angle (30–70 °). They are used in video surveillance systems at playgrounds or sports grounds, parking lots, small office or warehouse premises;
- wide-angle (up to 95 °). They put on observation of large halls, entrance structures, courtyards of private houses;
- panoramic (360 °). They are used when observing an entire room or outdoor area. Leave no dead spots.
Main characteristics of different types of lenses for CCTV cameras
Each optical system installed in video cameras has a number of characteristics that affect the specifics of its operation. Main settings:
- focal length;
- viewing angle.
What is focal length?
This parameter measures the distance from the light sensor to the lens and accordingly affects the size of the lens. It is measured in millimeters and can be fixed (for monofocal performances) or variable (for varifocal). The focal length affects the angle of view of the camera, the dependence is inversely proportional: the smaller the numerical value, the more area the tracking device will cover. Before deciding which lens for a CCTV camera to choose, you need to think about where the device will be installed. Optics with a small focal length are suitable for covering large areas with low requirements for detail, and a large value of the parameter will be needed in a narrow area with the necessary high image definition.
Types of CCTV camera lenses
By design, there are 4 types of optics:
- Fixed (monofocal). They have one fixed focal length value. Does not require adjustment, cannot change the angle of view of the camera.
- Variofocal. Allows you to manually adjust the focal length within the limits specified by design. Such optics can be adjusted to the object or quickly reconfigured to perform a new task. A universal option when choosing a lens for a CCTV camera.
- Zoom. Equipped with a motor for changing the focal length in automatic mode. Used in PTZ equipment, allows you to change the angle of view, scale the observation area. As a rule, the optics are equipped with an autofocus system for zooming objects.
- Fish-eye. Panoramic optics that give a 360 ° viewing angle. Due to the specifics of image transmission, it requires the use of scanning the picture on a plane. Video captured from the camera is inconvenient to view in its raw form.
How to choose a lens
First of all, you need to clearly define the tasks of video surveillance and the location of the camera. This will allow you to correctly select the focal length, type and angle of view. It should be remembered what the size of the CCTV camera lens affects, how to correctly determine the required viewing angle in a particular situation, and why different types of optics are needed.
CCTV Camera Lenses | Right Lenses For CCTV System | Selection Guide | Bharat Jain
The optimal lens options that are applicable in most situations are fixed and varifocal. Panoramic and zoom lenses perform more highly specialized functions and are much more expensive. You can see the catalog of lenses for video surveillance by the link.
Calculating the focal length of a camcorder lens
Calculation of the focal length of a CCTV camera is necessary for the correct selection of a video camera. Of course, manufacturers indicate the physical size of the matrix, the focal length and sometimes the angle of view in the technical specifications. But for a general understanding, let’s see what affects the choice of focal length, these are:
- At what distance is the object of observation;
- The physical size of the matrix;
- Object size.
So, having the specified technical characteristics of the camera, you can calculate the focal length of the CCTV camera lens using the following formulas:
Figure 1 (at the beginning of the article) shows that objects “1” and “2”, located at the same viewing angle, are displayed on the matrix in the same way, the number of pixels involved per perception of both objects is equal. In other words, the amount of information comes in different, but the closer located object has a smaller amount of data. its detailing is clearer, small details are not “smeared”, do not merge with each other.
In order to increase the resolution and detail of the object, it is necessary to bring the object “2” closer to the lens. This is done by changing the focal length, that is, the camera “zooms in” to the object. But this is applicable only for camcorders with lenses with variable focal length (“floating” lens).
It is possible to equip the receiving device with special software that allows processing the received digital signal in order to increase the detail of the observed object. But this will lead to a significant increase in the cost of the video surveillance system.
Examples of the dependence of the clarity of the picture on the focal length of the lens, angle of view and distance to the object are given in the table:
|Lens focal length, mm||Horizontal viewing angle for matrix = “” 1/3 “, linear degrees||The ability to detect a person, meters (approximate data)||The ability to identify a person, meters (approximate data)||The ability to determine the car number, meters (approximate data)|
When calculating distances, European standards are taken as a basis:
- 20 pixels / meter is the norm for resolution when an object is detected in the field of view;
- 100 pixels / meter is an indicator used for object recognition;
- 250 pixels / meter. identification resolution;
The text contains the determining factors responsible for the angle of view of the camcorder.
But during operation, such factors arise that affect the performance of the device:
- impairment of the lens performance, in the case of the manufacture of the optical component from a polymer material (lens clouding);
- poor-quality fastening of the body to the supporting structure (tremor from gusts of wind or other influences);
- loss of its properties as a lubricating component in the construction of a video camera (the complexity of moving the camera itself or the lens);
- electronic interference affecting the transmitted signal, as well as various other factors;
In addition to theoretical calculations for the viewing angle, important factors are:
- the installation point should provide maximum visibility in the vertical and horizontal planes;
- protection from the effects of climatic or any mechanical influences;
- availability, when performing preventive work on adjusting the video camera and preventive maintenance;
Each object requires an individual approach when determining the viewing angle, the clarity of the picture on the monitor. All this is determined when setting tasks to determine the parameters of the observed territory and is calculated by specialists.
The focal length of a CCTV camera lens is a video camera parameter that we take as a basis when calculating the surveillance area. The angle of view of the lens depends on its size and the physical size of the matrix. Having carried out simple geometric calculations, you can quite accurately determine the area that will fall into the frame of the CCTV camera.
For video surveillance over a wide area, cameras with a wide viewing angle are used. and when viewing objects “clamped”. like a long corridor with a narrow.
An example of calculating focal length and choosing a camera
It is necessary to observe the entrance and passage through the gates to the territory of the enterprise;
Objective of observation: detection of cars and people at the entrance to the territory of the enterprise;
The distance from the camera to the passage is 7 meters;
Camera Proto AHD-1W-EH10F (?) IR, after the letter F the focal length should be indicated. We will calculate it using the above formula:
where 3.2 is the vertical size of the matrix, since The Proto AHD-1W-EH10F (?) IR camera has a 1/4 ”matrix. Since the lenses on the camcorder are made with fixed focal lengths, then we choose the closest smaller one. if you select the nearest larger one, then part of the object will not fall into the camera frame.
Let’s perform another test of the camera for suitability. The control zone is 6 meters wide, the task is to detect. When a person is detected, it is necessary that there is 20-30 pixels of camera resolution per one meter of control. With simple calculations, it can be seen that the Proto AHD-1W-EH10F36IR camera is capable of not only detecting, but also recognizing a person on an object, not to mention cars. In fact, it is still necessary to calculate the vertical focal length, as well as the height and angle of installation of the video camera, but we deliberately omit these calculations, because we do not set ourselves the task of a complete calculation, we wanted to show in this example only the method for calculating the focal length and choosing a camera according to this calculation.
Parameters affecting the viewing angle
As mentioned above, the three parameters of the video camera are interdependent, these are:
- Lens focal length;
- Lens viewing angle;
- Physical size of the video camera matrix.
The longer the focal length of the lens, the smaller the angle of view. Consequently, it is possible to observe objects that are at a relatively large distance from CCTV cameras. Conversely, the shorter the focal length, the larger the angle of view. Accordingly, more objects fall into the camera frame.
The viewing angle also depends on the size of the sensor-matrix. The larger the matrix, the smaller the camera angle of view and vice versa.
Matrix format 1/3 ″
What determines the viewing range of CCTV cameras?
Modern CCTV cameras allow you to get a fairly clear image of objects that are remote from the video camera at long distances.
However, in addition to the visibility of a remote object, video surveillance systems also solve other tasks, such as object detection, recognition and identification.
Therefore, when choosing a CCTV camera, you need to pay attention to the following indicators:
- Detection level. the distance to the object at which the CCTV camera allows the operator to easily and accurately determine whether there is an object (a person or a car) in the frame. For detection, there must be 25 separate pixels for every 1 meter of the observed object.
- Observe. the distance from the camera to the object at which it is possible to describe the specific features of the object, such as the color of clothing and other characteristics. For a given level, there should be 63 pixels for every meter of the object.
- Recognize level. the distance from the camera to the object (person) at which, with a high degree of probability, the operator can recognize a familiar person in the face. To do this, there must be 125 pixels for every meter of the observed object. If we assume that the face of an average person has a height of 20-25 cm, then it should have about 25-30 vertical pixels for confident recognition.
- Identify. the distance from the camera to the object at which the camera image can be easily used to identify a stranger. There should be 250 pixels per meter.
In order to get the pixel / meter value, you need to divide the number of pixels of the video camera horizontally by the width of the video camera’s field of view.
The distance the camera “sees” primarily depends on its lens and resolution. For example, a wide angle lens (2.8mm) will have fewer pixels than a 4, 6, or 12mm lens.
The type of matrix also plays a significant role (distinguish between CMOS. a simple and popular technology, or more modern CCD, Super HAD CCD and Sony Ex-View)
The physical size of the matrix is also of great importance (1/3 is typical for most standard cameras, in more expensive models this value is 1 / 2.8 and in professional, intelligent CCTV cameras up to. 1 / 1.7)
The detection range of the observation object by the video camera is also determined by the focal length. In theory, a video camera can “see” an object at a distance of several hundred meters. In practice, this requires good optics, which are prohibitively expensive.
The focal length of the lens affects the recognition range much more than the resolution. However, it should be noted that the longer the focal length, the smaller the camera’s viewing angles.
But if the angle of view is minimal, then adjusting the position of the view area will cause problems.
In order for the camera to see at a long distance, varifocal or long-focus lenses are often used.
When building a video surveillance system, it is also necessary to take into account the fact that all other components of the system, such as a video recorder, display, cables, connectors, transceivers, can significantly affect the viewing distance of the camera. To avoid this, the resolution of the CCTV display must be greater than or equal to that of the CCTV camera.
For analog formats, the video signal path from the camera to the DVR should not be distorted. To do this, you must use a high-quality TV cable or UTP cable with active video transceivers. On short cables (30-40 m), as a rule, passive broadband baluns are used.
For IP cameras for signal transmission, it is required to install network switches at a distance of 100 meters from each other, which complicates installation and increases the cost of the system.
Therefore, in many cases, it is much easier and cheaper to place conventional CCTV cameras closer to the object, but at the same time choose those that have a longer video transmission range.
A video camera is a mechanical device consisting of a body, a lens and an electronic converter of an optical image into an electronic form of signals:
- The body is the main power element designed for fastening various parts of one product.
- Lens. an optical element consisting of one or more lenses with different diopters. Responsible for creating a virtual or real image in an enlarged or reduced form.
- An electronic converter, or, in other words, a CCD matrix is an integrated microcircuit consisting of photodiodes that convert a light signal (image) into a set of electrical signals for the purpose of their further transmission to a receiver (monitor).
The clarity of the image, or the resolution of surveillance cameras is the ability of the device to confidently record the minimum dimensions of the surveillance object at a certain distance from the camera.
The resolution, and accordingly, the clarity of the image depends on:
- on the quality of the lens and its focal length;
- on the technical characteristics of the CCD (the number and quality of pixels);
- from distance: “lens. observed object”;
If a visual receiving device (monitor) is used, then the following are added:
- the quality of signal conversion in the receiving device (video recorder);
- technical characteristics of the reproducing device (monitor);
For different cameras. analog and IT-technologies (digital) clarity is determined by its characteristics.
Analog video cameras
For this type of cameras, the TVL indicator is used. television lines. Shows how many alternating black and white lines are placed on the measured area in the vertical or horizontal planes.
Analog cameras, according to the degree of resolution, are subdivided into devices:
- with an average image quality: about 500 pixels. corresponds to 380. 420 TVL;
- high degree of resolution: over 750 pixels. over 1000 TVL, respectively;
Many are familiar with this characteristic. this is how the properties of a video camera in a mobile phone are characterized.
HOW TO CHOOSE A CCTV CAMERA
One of the main parameters that is taken into account when choosing a CCTV camera is the degree of image detail.
It depends on the size of the observation object displayed on the monitor and is determined by the tasks facing the system.
It should be noted that the criteria for this choice are not clearly defined. many people use the requirements of the British Ministry of Internal Affairs, there are recommendations of the GUVO of the Ministry of Internal Affairs of Russia, individual manufacturers of CCTV cameras, so the data from various sources may not coincide, which, however, is not critical.
The detail of the image depends on the angle of view of the camera or the focal length of the lens, since these values are interrelated, but the resolution affects this parameter rather indirectly.
Therefore, in order to choose the right CCTV camera, you should be guided by the size of the viewing area in which the observed object should be located (Fig. 1).
The data is given for a horizontal plane and a 1/3 “matrix. One obvious note: the camera will display objects that are also at different distances, but with a different degree of detail.
CHOOSING THE FOCAL LENGTH
Since it is more convenient to choose a camera by the focal length of the lens and the distance to the object, you can use the formula:
f = Rk. Where:
- f. focal length (mm),
- R. distance to object (m),
- k. coefficient for different tasks (shown in the figure).
It should be noted that the given data provide a guaranteed and comfortable solution for the video surveillance operator to solve the problems of detection, identification, identification. In practice, in order to select the desired camera, the given factors can be rounded up to:
- 0.25. human detection,
- 1.recognition of a friend,
- 2.5. identification of a stranger.
For example, to detect a person from a distance of 20 meters, f = 200.25 = 5 mm. and its identification at the same distance requires f = 202.5 = 50 mm. When choosing this parameter, the nearest larger one should be taken from the standard range of values, that is, the focal length of the lens, respectively, should be 6 and 50 millimeters.
SELECTION OF RESOLVING CAPACITY
Now, regarding the choice of the camera resolution. All other things being equal, it determines the minimum distinguishable element of the object of observation. In turn, the vertical size of the identified object must account for at least a certain number of minimally distinguishable elements.
If you choose a camera, guided by the above criteria, then when solving any problem, the resolution of analog video cameras, which is about 400 TVL vertically, is quite enough. IP cameras also provide the required parameter without any problems.
It is advisable to use high-resolution cameras in systems with software image processing (various kinds of video analytics, for example).
The organization of video surveillance at home (in an apartment) or in a country house, as a rule, does not impose excessively stringent requirements on this parameter.
In addition, when choosing video cameras for various operating conditions, you should take into account their other technical characteristics. This is especially true of street surveillance cameras, but more on that in other materials.
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Monofocal, or fixed
Fixed models have a specific focal length and angle of view. You cannot change the parameters. Monofocal devices are easy to use and inexpensive. They are well suited for organizing constant video surveillance, where you do not have to transfer cameras from one place to another.
How to choose a lens for a CCTV camera
All components, without exception, affect the effectiveness of a video surveillance system, even those that at first glance seem insignificant. It’s about a camcorder lens. The clarity and quality of the picture largely depends on this element. Even the most expensive equipment with a bad lens will not cope with the task, the money will be wasted. Carefully study the characteristics of the devices in order to make the right choice.
Transfocal or zoom lenses
The viewing angle and focal length can be adjusted remotely from the remote control. The devices also allow you to zoom the video surveillance area, focus the camera on any object, focus, etc. Transfocal models are used in robotic PTZ cameras (Pan-Tilt-Zoom).
A specific lens is selected for a video camera with a specific matrix. The characteristic affects the actual size of the picture and is indicated in inches. Lenses are selected for a camera with the same or lower parameters, if the mount is suitable. For example, a model with a matrix size of 2/3 is suitable for video cameras 2/3, 1/3.
As mentioned above, the angle of view determines the area of the area that the video camera can cover. Wide-angle lenses allow you to observe large objects with less detail. Narrow-angle models will help you to see individual elements in the frame, but the coverage area will be small. They are well suited for installation above cash registers, ATMs, etc.
- Narrow-angle devices, from 3 to 30 degrees, are chosen for observation in corridors, along fences, on stairs, near the walls of buildings.
- Equipment with an average viewing angle of 30 to 70 degrees is suitable for monitoring medium-sized areas, such as offices, offices, small parking lots.
- Wide-angle models up to 95 degrees are excellent for observing entrance groups, large areas.
The relationship of all the main characteristics (focal length, viewing angle, matrix size) is presented in the table.
|Focal length||dies 1/3 “||dies 1/4 “|
|Viewing angle by||Viewing angle by||Viewing angle by||Viewing angle by|
|horizontal lines||vertical||horizontal lines||vertical|
The characteristic is measured in millimeters and shows the distance from the camera matrix to the lens. The focal length is directly related to the angle of view, that is, to the area of the area that will be visible in the frame. The fewer millimeters specified in the model parameters, the wider the angle will be, and vice versa, a large focal length means covering a small area.
precisely, the characteristic can be determined by the distance of the object of observation. There are two formulas for this:
- F = vS / V, where F is the focal length, S is the distance to the object, V is the vertical size of the object, v is the vertical size of the matrix;
- F = hS / H, where h is the horizontal size of the matrix, H is the width of the object.
The correspondence of inches and the actual dimensions of the matrix can be taken from the table.
For example, it is necessary to install video surveillance of the porch of a building 10 m wide. A video camera with a 1/3 inch matrix is mounted at a distance of 20 m. We obtain the focal length: F = 4.8 x 20/10 = 9.6 mm. It is necessary to choose the closest value of the focal length to the larger side In this case, it is important that the viewing angle is as wide as possible, otherwise in the frame, apart from the main object, nothing around will be visible.
The table below provides indicative data for selecting a device. They can vary up or down from different manufacturers.
|Focal length, mm||Viewing angle||Recognition distance, m|
A table with examples of frames will help you to visually assess the quality of the picture from cameras with different characteristics.
The lens aperture controls the amount of light that travels to the video sensor. In simple models of devices, the diaphragm is fixed. If the degree of illumination on the object changes significantly during the day, then the image quality will be poor: on sunny days the picture will be overexposed, and in the dark, objects in the frame will be indistinguishable.
There are auto iris lenses. A small motor is installed in such devices. It controls the movement of the flaps, narrowing or expanding the lumen depending on the lighting conditions. Auto iris allows you to get a high-quality picture at different times of the day. This is especially important for outdoor video cameras.
Matrix for CCTV cameras. What to look for?
The image quality of a video camera largely depends on the light-sensitive sensor (matrix) used in it. After all, put at least the best processor for digitizing video. if a bad image is obtained on the matrix, it will no longer be good. I will try to popularly explain what should be paid attention to in the characteristics of the sensor of a CCTV camera, so that later it will not be excruciatingly painful when looking at the image. Matrix type
On the Internet, you will probably find information that CCD (CCD, Charge Coupled Device) and CMOS (CMOS, Complementary Metal Oxide Semiconductor) photosensitive matrices are used in CCTV cameras. Forget it! For a long time there was only CMOS, only hardcore.
CCD matrices, with all their advantages (better light sensitivity and color rendering, lower noise level) are practically not used in video surveillance anymore. Because the very principle of their operation of CCD matrices. sequential reading of the charge by cells. is too slow to satisfy the demands of fast modern high-definition video cameras. And most importantly, CCDs are more expensive to manufacture, and in today’s highly competitive environment, every penny counts. That is why all key manufacturers have focused on the release of CMOS sensors.
There are not so many manufacturers left, by the way. The largest, as of the beginning of 2017, are the following companies: ON Semiconductor Corporation (which at one time acquired the well-known profile company Aptina), Omnivision Technologies Inc., Samsung Electronics and Sony Corporation. In addition, matrices for their own needs are produced, for example, by Canon, Hikvision.
Young Chinese chip makers of the “second tier”, such as SOI (Silicon Optronics, Inc.) and others, are trying to create competition for old brands. It is difficult to say whether the young growth will survive when the CMOS sensor market becomes saturated and becomes too crowded. But in any case, in this segment, the emergence of new players and an aggravation of the struggle is not excluded, because setting up the production of CMOS sensors is not too difficult by modern standards.
Large global brands such as Hikvision or Dahua usually prefer to work with first-tier die manufacturers or their own. Local ones behave differently. For example, Tecsar even in inexpensive cameras uses sensors with a good reputation from ON Semiconductor, Omnivision and Sony. In the assortment of other “popular” brands, for example Berger, SOI sensors are widely represented, etc.
How digital camera matrices are made
CMOS technology provides for the placement of electronic components (capacitors, transistors) directly in each pixel of the photosensitive matrix.
This reduces the effective area of the photosensitive element and reduces the sensitivity, plus the active elements increase the level of intrinsic noise of the matrix. But the technology allows converting the charge of the photosensitive element into an electrical signal directly in the matrix and much faster to form a digital image signal, which is critical for video cameras. This is why CMOS is better suited for CCTV cameras where fast frame rates are required.
Plus the ability to randomly read the cells of the CMOS matrix makes it possible to literally “on the fly” change the quality and bitrate of the resulting video, which is impossible for a CCD. And the power consumption of CMOS solutions is lower, which is also important for compact surveillance cameras.
To obtain a color image, the matrix decomposes the luminous flux into its constituent colors: red, green and blue. For this, appropriate light filters are used. Different manufacturers vary the placement and number of light-sensitive elements of different colors, but the essence of this does not change.
The principle of forming an image on a photosensitive matrix:
P. photosensitive element
T. electronic components
You can also watch how the CMOS camera sensor works and works in this video from Canon:
CMOS matrices of all manufacturers are based on the above-described general principles, differing only in the details of the implementation on silicon. For example, in pursuit of cheapness and super-profit, chip makers try to produce matrices as small as possible. Payback for this is inevitable.
The standard size (or in other words, the format) of the matrix is usually measured diagonally in inches and indicated as a fraction, for example, 1/4 “, 1/3”, 2/3 “, 1/2”, etc.
The first rule for choosing the best sensor is quite simple: with the same number of pixels (resolution), the larger the physical dimensions of the sensor, the better. The larger sensor has larger pixels, which means it picks up more light. The pixels of a larger sensor are less closely spaced, which means less interference and less spurious noise, which directly affects the quality of the resulting image. Finally, a larger sensor allows for greater angles of view when using a lens with the same focal length.!
Photosensitive matrix manufactured by ON Semicondactor for CCTV cameras
Photosensitive matrix installed on the video camera board
Alas, large-format matrices in mass surveillance cameras are now practically not used due to the high cost of matrices themselves and lenses for them, which should have larger lenses and, accordingly, dimensions and cost. Today, cameras are mainly installed with 1/2 “- 1/4” matrices (these are the smallest ones). Choosing a camera, you need to clearly understand that buying an ultra-cheap model with a 1/4 “SOI matrix and a tiny lens with plastic lenses of questionable transparency, you will not be able to create a video control system of acceptable quality, on which it would be possible to clearly distinguish small details of captured events, especially when shooting in low light conditions.
Which Security Camera Lens Size Should I Buy?
Choosing a camera with a Sony 1 / 2.8 “matrix, you will a priori get a much better result in video quality, a camera with such a matrix can already be used in a professional video surveillance system. illumination: in bad weather, at dusk, in a semi-dark room, etc. As the resolution increases with the same matrix size, the light sensitivity drops, and this should also be taken into account when choosing. a sensor with a lower resolution and higher sensitivity than an ultra-high resolution camera with a low sensor sensitivity on which, due to noise, nothing can be clearly distinguished.
The light sensitivity of the matrix determines the possibility of its operation in low ambient light conditions. From the point of view of physics, this looks quite commonplace: the less light energy is enough for the matrix to obtain an image, the higher its light sensitivity. But! Let’s be frank, it’s not worth chasing high sensitivity anymore. The fact is that modern CCTV cameras safely switch to day / night modes, with a decrease in illumination, transferring the matrix to a black-and-white image mode with a higher sensitivity. Plus, the automatic inclusion of infrared illumination gives the cameras the ability to shoot perfectly even in complete darkness. For example, in a closed room without windows and with the lights off, when the level of some kind of ambient light is out of the question. Light sensitivity remains critical for cameras without IR illumination, but using such in modern video surveillance is almost bad manners. Although non-backlit box models are still sold, of course.
Comparison of matrices from different manufacturers
In general, the rule is as follows: the higher the illumination, the better the matrix and, accordingly, the camera will shoot. Therefore, it is not recommended to place cameras in semi-dark alleys, even if they have good sensitivity. Keep in mind that camera sensor specifications usually indicate the minimum illumination level at which you can capture at least some image. But no one promises that this image will at least be of acceptable quality! It will be disgusting 100% of the time, it will be difficult to make out anything on it. To achieve at least a satisfactory result, it is recommended to shoot at least with illumination at least 10-20 times higher than the minimum allowable for the matrix.
Manufacturers have come up with a number of technical solutions to improve the sensitivity of CMOS sensors and reduce the loss of light during image capture. For this, one principle is mainly used: to bring the photosensitive element as close as possible to the microlens of the matrix that collects light. First, Sony offered its Exmor technology, which shortened the path of light through the matrix:
Then progressive manufacturers unanimously switched to the use of back-illuminated matrices, which allows not only to shorten the path of light through the matrix, but also to make the effective area of the photosensitive layer larger by placing it above other electronic elements in the cell:
Back-illuminated technology gives the camera maximum sensitivity. Hence the conclusion. “all other things being equal,” it is better to purchase a camera using a matrix with back illumination than without it.
To improve the image in low light conditions for low-sensitivity low-cost sensors, camera manufacturers can use various tricks. For example, the “slow shutter” mode, or more simply. the long exposure mode. However, the “smearing” of the contours of moving objects already at the stage of image fixation by the matrix in this mode does not allow us to talk about the slightest quality of video recording, therefore this approach is completely unacceptable in video surveillance, where details are important.
A definite breakthrough in image quality was the emergence of Starlight technology, which first appeared in Bosch cameras in 2012. This technology, thanks to a combination of a huge matrix light sensitivity (about 0.0001. 0.001 lux) and a very effective noise reduction technology, made it possible to obtain a very high-quality color image from video cameras in low light conditions and even at night.
While the traditional way to overcome low light. using IR illumination. makes it possible to get a clear image only in monochrome (grayscale), cameras with Starlight technology allow you to get a color image that has much more information content. Particularly in low light conditions, a CCTV system with Starlight technology can easily distinguish between the colors of cars, clothing, and other important features.
Here’s a demo of Starlight technology in action:
When choosing a CCTV camera, be sure to pay attention to the characteristics of the matrix, and not just its resolution. After all, the quality of the image will largely depend on this, and therefore the usefulness of the camera. First of all, you should pay attention to a reliable brand, standard size and resolution of the matrix, photosensitivity is fundamental only for cameras without IR illumination.
I highly recommend taking a camera with a matrix, by which you can find a sane datasheet with detailed information, and not buy a pig in a poke. For example, you can easily find specifications for matrices from ON Semiconductor, Omnivision or Sony. But more or less detailed characteristics of SOI matrices cannot be found during the day with a flashlight. There is a suspicion that the manufacturer has something to hide.
And the overall result is this: CMOS matrices unconditionally won in video surveillance devices and are not going to give up any competing technology in the near future.