How to choose a CCTV camera: focal length, angle of view, distance to the object
When choosing a CCTV camera, several criteria must be considered:
- Place of installation of the video camera;
- Observation area dimensions;
- Matrix format;
- And finally, the ability to change the camera’s field of view.
First you need to decide where the camera will be installed. outdoors or indoors. Usually, outdoor camcorders use an auto iris, i.e. She herself adjusts the level of the incoming light flux. In rooms, there is either no diaphragm at all, or it is manually adjustable.
Matrices can be 1/2 “, 1/3”, 1/4 “and other values. Accordingly, a 1/3” camera can work with 1/2 “and 1/3” lenses, and a 1/2 “camera only with the same lens.
Table 1. Dimensions of the video camera matrix
| Vertical, mm | 4.8 | 3.6 | 2.4 |
| Horizontal, mm | 6.4 | 4.8 | 3.2 |
The size of the observation area is necessary to determine the focal length of the camera. It is calculated using the following formula: f = vS / V or f = hS / H, where:
- F. focal length;
- V is the vertical size of the matrix;
- V is the vertical size of the object;
- S is the distance to the object;
- H is the horizontal size of the matrix;
- H- horizontal size of the object.
Of course, all this has already been calculated, therefore, below are tables that will help you to stay on a particular camera.
And the last parameter. the need to change the viewing angle. We are talking about varifocal cameras. The operator can change the viewing angle from a distance, thus bringing the picture closer or further away, and not losing quality. Such camcorders are more expensive than conventional ones.
Table 2. Viewing angles of CCTV cameras
| 2.5 | 90 | 120 | 150 | 2 | 0.7 |
| 2.9 | 78 | 104 | 130 | 3 | 1,2 |
| 3.4 | 70 | 94 | 110 | 3.4 | 1.4 |
| 3.5 | 63 | 79 | 98 | ||
| 3.6 | 54 | 72 | 92 | 3.5 | 1.5 |
| 3.7 | 52 | 70 | 90 | 3.8 | 1.6 |
| 4 | 48 | 65 | 75 | ||
| 4,3 | 47 | 62 | 73 | 4 | 1.8 |
| 5.5 | 40 | 55 | 70 | five | 2 |
| 6 | 32 | 42 | 53 | 6 | 2,3 |
| eight | 24 | 32 | 40 | eight | 3 |
| 12 | 17 | 22 | 28 | 12 | 4 |
| sixteen | 12 | 17 | 21 | sixteen | 6 |
| 25 | eight | eleven | fourteen | 25 | ten |
| 50 | 4 | 5.5 | 7 | 50 | 20 |
| 75 | 2.8 | 3.7 | 4.6 | 70 | thirty |
The values given are approximate and given for informational purposes only.
Table 3. Dependence of the horizontal viewing angle on the focal length
| f (mm) / CCD | 2.45 | 2.96 | 3.6 | 4.0 | 6.0 | 8.0 | 12.0 | 16.0 | 36.0 | 72.0 |
| 1/3 | 93 º | 86º | 72º | 62º | 43.5º | 35.6º | 22º | 18º | 7.8º | 3.6º |
Table 4. Dependence of the object size (in meters) on the focal length (1/3 “)
| 3m | 6 × 4.5 | 5 × 3.75 | 4 × 3 | 3.8 × 2.85 | 2.4 × 1.8 | 1.8 × 1.35 | 1.2 × 0.9 | 0.9 x 0.67 | ||
| 5 m | 10 × 7.5 | 8.4 × 6.3 | 6.6 x 4.5 | 6 × 4.5 | 4 × 3 | 3 × 2.25 | 2 × 1.5 | 1.5 × 1.12 | 0.66 × 0.5 | |
| 10 m | 20 × 15 | 17 × 12.8 | 13 × 10 | 12 × 9 | 8 × 6 | 6 × 4.5 | 4 × 3 | 3 × 2.2 | 1.3 × 0.97 | 0.66 × 0.5 |
| 20 m | 40 × 30 | 34 × 25 | 26 × 20 | 22 × 16.5 | 16 × 12 | 12 × 9 | 8 × 6 | 6 × 4.5 | 2.7 × 2 | 1.3 × 0.97 |
| 30 m | 60 × 45 | 50 × 37 | 40 × 30 | 36 × 16.5 | 24 × 18 | 18 × 13.5 | 12 × 9 | 9 × 6.7 | 4 × 3 | 2 × 1.5 |
| 40 m | 80 × 60 | 65 × 49 | 53 × 40 | 48 × 36 | 34 × 25 | 24 × 18 | 16 × 12 | 12 × 9 | 5.4 x 4.1 | 2.7 × 2 |
| 50 m | 95 × 71 | 40 × 30 | 30 × 22 | 20 × 15 | 15 × 11.2 | 6.6 × 4.9 | 3.4 x 2.5 | |||
| 80 m | 64 × 48 | 48 × 36 | 32 × 24 | 24 × 18 | 11 × 8.2 | 5.4 × 4 | ||||
| 100 m | 60 × 45 | 40 × 30 | 30 × 22 | 13.5 × 10 | 6.6 × 4.9 | |||||
| 150 m | 60 × 45 | 45 × 34 | 20 × 15 | 9.5 × 7.1 |
Which camera for a video surveillance system to choose. analog or digital? And in general, how can they be compared, given that their quality is measured in different indicators? TVL. these are television vertical lines. In other words, the more TVL, the clearer the image. Pixels. these are the minimal elements of digital two-dimensional raster graphics, from which the entire image is built.
These indicators are quite difficult to compare, however, we have compiled an approximate table of correspondences between analog and IP video cameras, which will help you determine.
TVL pixels Megapixels 380 640 × 480 0.3 420 720 × 576 0.36 480 800 × 600 0.5 560 933 × 700 0.65 600 1024 × 756 0.75 800 1280 × 960 1.23 1000 1600 × 1200 1.92
Camera resolution and detail of small details. Camera resolution and detailing of small details in the frame. mutually Unrelated things?
Choosing a high resolution camera does NOT guarantee excellent detail on small objects in the frame. In this article, we’ll explain why. And at the same time advise how to successfully solve this problem.
Problem
Many users, after purchasing a high-end CCTV camera, complain: they say, we bought a fancy camera with the “highest resolution” and hoped that with its help, for example, it would be possible to distinguish the license plates of employees from a distance of 15 meters. But it turned out. on the image there is an illegible “mess” instead of Clear details! What went wrong? Did we buy a bad camera? The sellers promised us the best, but here is # @%. You see, the point is that the resolution of the camera and the distinguishability of small objects in the frame are very specific and indirectly related. The lens has a huge impact on this matter.!
Objective view
High resolution matrix. It is very cool. But! For solving specific problems, the correct pairing of the matrix lens is very important. It is quite simple to achieve the required image detail with the help of the correct selection of the lens: after all, it is the optics that are responsible for the image, which ultimately ends up on the camera’s light-sensitive matrix. Of course, in some cases you can try to solve the issue of detail with a large matrix (good approach) or digital zoom (wrong approach), but, as practice shows, the most optimal solution. This is exactly the selection of the right optics.
The shorter the focal length of the lens, the larger the area in front of the camera will fit into the frame (larger angles of view). But, alas, the worse small details become visible.
The longer the focal length, the more the lens “brings” objects closer and the better the fine details are seen. In other words, the longer the focal length of the lens, the visually closer the subject will be located (it will be larger in the frame) and the better all its features will be visible. Here is a visual illustration of the dependence of the camera’s field of view and detail of objects in the frame on the focal length of the lens:
It can be seen that in this case, with a 3.6 mm or 4 mm lens, it is almost impossible to distinguish small image details in the background, but with a 12 mm and 16 mm lens. no problem at all.
Where to use the knowledge gained
Short focal length lenses are used when you need to observe a large area: for photographing streets, buildings, parking lots, checkpoints, large premises and large groups of people. That is, when the widest possible coverage of the territory is important, while the detailing of small objects is not critical.
A lens with a long focal length should be used in cases where greater detail and the greatest possible clarity of certain objects in the frame are needed: human faces, license plates, items in the shop window, bills at the checkout, etc. That is, at the entrance, at the entrance, near cash registers, etc. It is necessary to use cameras with a long focal length. Using a camera at times of lower resolution and a properly selected lens, you can easily get many times better detail and distinguishability of small objects of interest in the video than when using a high-resolution camera with an improperly selected lens!
For example, a Full HD camera with a 6 mm lens mounted at a distance of 5-10 m from the entrance will allow better face recognition near the entrance than a 4K camera with a 2.8 mm lens mounted at the same distance. In the latter case, you can, of course, try to programmatically enlarge a fragment of the image (use digital zoom), but this will not give a good result. after all, as NOT increasing the “mess” of blurry pixels, you still DO NOT get a clear picture. If you are at a loss to determine exactly what lens focal length you will need for optimal performance before purchasing a camera. choose a camera model with a varifocal lens. This lens allows you to change the focal length at the place of installation of the camera. However, even cameras with a fixed lens often allow replacing the lens with a version with a different focal length in order to optimize the video surveillance area. If the camera is a fixed lens, please make sure it has lens upgrade capability.
How a Varifocal Lens Works:
You can evaluate the change in detail in the frame with the configuration of the focal length (the so-called zoom) of the camera lens on this
Lens zoom ratio (degree of image enlargement). it is the ratio of the maximum focal length of the lens to the minimum. Typically cameras are 2.8. 12mm, which means approximately 4x optical zoom is provided. (Digital can be safely neglected.) Thus, the visibility of small details in the video can be improved, roughly speaking, by 4 times. This is clearly demonstrated in the above video.
The most expensive, but also a win-win option. this is the use of controlled PTZ cameras with a zoom lens. Such cameras allow “on the fly” to zoom in on objects and improve the details of the required objects at times (just beware of using little useful digital zoom here). Plus, these cameras make it possible to rotate the lens in any desired direction, and even provide such useful functions as automatic patrolling, etc.
How a PTZ-controlled video camera works and how it will allow you to see even small details in the image, you can watch this
When choosing a video surveillance camera, first of all decide on the area of video surveillance and the required detail. Then, it is quite possible that you will not have to spend money on an expensive ultra-high resolution camera, but you will be able to do with an inexpensive model with an optimally selected lens.
The viewing angle of the CCTV camera and its calculation formula. 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;
- The physical size of the video camera matrix.
The longer the focal length of the lens, the smaller the angle of view. Therefore, you can observe objects that are located at a great 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 array. The larger the matrix, the smaller the camera angle of view and vice versa.
Matrix size
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.
Focal length
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 viewing angle, that is, with the area of the site 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 long focal length means covering a small area.
precisely, the characteristic can be determined by the distance of the observation object. There are two formulas for this:
- F = vS / V, where F. focal length, S. distance to the object, V. vertical size of the object, v. vertical size of the matrix;
- F = hS / H, where h. horizontal matrix size, H. object width.
The correspondence of inches and the actual dimensions of the matrix can be taken from the table.
| Format | 1 “ | ½ “ | 1/3 “ | ¼ “ |
| Height, mm | 9.6 | 4.8 | 3.6 | 2.4 |
| Width, mm | 12.8 | 6.4 | 4.8 | 3.2 |
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, except for the main object, nothing around will be visible.
The table below shows approximate data for selecting a device. They can vary up or down in different manufacturers.
| Focal length, mm | viewing angle | Recognition distance, g. | |
| Vertically | horizontally | ||
| 2.8 | 90 | 120 | 2 |
| 3.5 | 63 | 79 | 3.4 |
| 4.0 | 48 | 65 | 3.8 |
| 5.5 | 40 | 55 | 6 |
| 6.0 | 32 | 42 | 6 |
| 8.0 | 24 | 32 | eight |
| 12.0 | 17 | 22 | 12 |
| 25.0 | eight | eleven | 25 |
| 50.0 | 4 | 5.5 | 50 |
A table with examples of frames will help to visually assess the quality of the picture from cameras with different characteristics.
Viewing angle
As mentioned above, the viewing angle determines the area of the site 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.
A few precise recommendations:
- Narrow-angle devices, from 3 to 30 degrees, are chosen for observation in corridors, along fences, on stairs, near walls of buildings.
- Equipment with an average viewing angle of 30 to 70 degrees is suitable for monitoring medium-sized areas, such as offices, office, small parking lots.
- Wide-angle models up to 95 degrees are excellent for observing Entrances, large areas.
The relationship of all main characteristics (focal length, viewing angle, matrix size) is presented in the table.
| Focal length | 1/3 “dies | 1/4 “dies | ||
| Viewing angle by | Viewing angle by | Viewing angle by | Viewing angle by | |
| horizontal lines | vertical | horizontal lines | vertical | |
| 2.8 mm | 82 | 65 | 65 | 52 |
| 2.9 mm | 80 | 63 | 63 | 50 |
| 3 mm | 77 | 62 | 62 | 48 |
| 3.5 mm | 69 | 55 | 55 | 42 |
| 3.6 mm | 67 | 53 | 53 | 41 |
| 3.7 mm | 66 | 52 | 52 | 40 |
| 3.8 mm | 65 | 51 | 51 | 38 |
| 4 mm | 62 | 48 | 48 | 37 |
| 4.2 mm | 60 | 46 | 46 | 36 |
| 4.4 MM | 57 | 45 | 45 | 34 |
| 4.5 MM | 56 | 44 | 44 | 33 |
| 5 mm | 51 | 40 | 39 | thirty |
| 6 mm | 43 | 33 | 33 | 25 |
| 7 mm | 38 | 29 | 29 | 22 |
| 8 mm | 34 | 25 | 25 | nineteen |
| 8.8 mm | 31 | 23 | 23 | 17.5 |
| 10 mm | 27 | 20 | 20.5 | 15.4 |
| 12 mm | 22.6 | 17 | 17 | 12.8 |
| 15 mm | 18.2 | 13.7 | 13.7 | 10.3 |
| 16 mm | 17.1 | 12.8 | 12.8 | 9.6 |
| 25 mm | eight | eleven | 7.3 | 5.5 |
| 50 mm | 4 | 5.5 | 2.7 | 2.8 |
How to choose the focal length of a CCTV camera
So, the focal length and viewing angle of the video camera. this is an important parameter that will determine the area captured by the objective lens. It affects the image quality of the area being viewed, showing the object in detail. Correctly selected focal length allows you to distinguish the desired objects at the required distance. It is worth remembering that long focal length lenses are recommended when you need to observe objects far from the camera. How to choose the focal length of a CCTV camera?
Correct calculation is required to select the focal length. Despite the fact that all manufacturers indicate both the size of the matrix and other industrial properties. But for understanding it is necessary to take into account the following nuances:
- The distance at which the Observed Object will be located;
- Matrix and object size.
From the above, it becomes clear that for different areas it is best to choose a camera, which viewing angle to cover the entire room, or if required. part of the territory. Today the standard focal length of a camcorder. 3.6mm. On a standard 1 / 2.8 “FullHD sensor, this provides an 80-degree viewing angle. This is an average value that is suitable for most tasks. Such camera parameters allow viewing faces and license plates at a distance of up to 15 meters.
The focal length of telephoto cameras and cameras with variable focal length (varifocal) is usually 12mm. If the Observed Object is far away, then it is recommended to use just such a device. This camera provides a detailed image at a distance of up to 40 meters.
For example, if a person is at a distance of 12 meters, then a camera with a focal length of 12 meters and a viewing angle of 21 degrees can clearly distinguish him. Therefore, it will NOT be superfluous to remind you that in each case, you should individually select the camera so that it performs the tasks that the owner assigns to it.
Wide panoramic video cameras
This device has a viewing angle of 120 degrees and more. Such a device gives a whole panorama of what is happening. The camera is able to detect the face of a person who is NOT more than 3 meters from the camera. That is why such a device should be chosen in order to control large open spaces. One camera will do its job, and there is no need to install additional devices. However, it is impractical to use a wide-angle camera to monitor a long narrow corridor.
Narrow-format devices
Cameras with a viewing angle of 20 degrees, transmit the picture in detail at a distance of 50 meters. The purpose of installing such a video camera should also be taken into account here. Most owners opt for devices with a viewing angle of 60-70 degrees, which allows observation from 10 meters and get a guaranteed clear picture.
Those who first set up a surveillance system on their own make various mistakes. Thinking that I bought a camera with the highest resolution matrix, in which the lens is wide-angle, will cover a huge observation area. At the same time, they count on a high-quality picture. It is important to choose cameras with a focal length that suits your specific needs. As we noted above, 3.6mm cameras are suitable for most objects. For a wider overview. 2.8mm. If you find it difficult to choose the required video surveillance camera, please contact our specialists and we will help you make a choice!
Lens view
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.
Varifocal
The main characteristics of the lens can be changed by adjusting the clarity of the image. The manufacturers indicate the adjustment range for each device, for example, 3.6-8.0 mm. There are models with auto and manual focus. With their help, you can “cut off” all unnecessary from the picture, defining the most important area, or vice versa, covering the entire area in front of the video camera. Varifocal models are very convenient to use, but they are more expensive than fixed ones.
Transfocal or zoom lenses
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, sharpen, etc. Transfocal models are used in robotic PTZ cameras (Pan-Tilt-Zoom).
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 given technical characteristics of the camera, you can calculate the focal length of the CCTV camera lens using the following formulas:
F = hS / H or F = vS / V
Where h. horizontal size of the matrix;
S. distance to the object of video surveillance;
H. horizontal size of the object;
V. vertical size of the matrix;
V. vertical dimension of the object.
The dimensions of the sides of the CCTV camera matrix are given in the table:
| Matrix size | 1/4 “ | 1/3 “ | 1/2 “ |
| Horizontal, mm | 3.2 | 4.8 | 6.4 |
| Vertical, mm | 2.4 | 3.6 | 4.8 |
An example of calculating the 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 surveillance: detection of cars and people at the entrance to the territory of the enterprise;
The width of the passage and the gate is 6 meters;
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 according to the above formula:
Where 3.2 is the vertical size of the matrix, because. In the Proto AHD-1W-EH10F (?) IR camera, a 1/4 “matrix is installed. Since the lenses on the camcorder are made with a fixed focal length, we select the closest smaller T. K. If you select the nearest larger one, then part of the object is not will 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 for one meter of control there are 20-30 pixels of camera resolution. 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, it does not speak about 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, since K. 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 for this calculation.
What else needs to be considered
Everything described above applies to cameras with fixed phased array. Sometimes it is difficult to determine the size of the site over which you need to establish control. There is also another situation: the area of the observation zone changes, then increasing, then decreasing. Here we recommend a device with a varifocal lens. Here you can customize the overview. In a separate category, devices are distinguished in which you can change the FG and the viewing angle (varies up to 360 ° in the horizontal plane and up to 180 ° in the vertical).
The AF range typically ranges from 2.8 to 50 mm. In some models, it is higher. When using varifocal optics, the image quality does NOT deteriorate when zooming in / out. This is possible thanks to the optical zoom of the lens.
If the angle needs to be changed, it is better to choose a camera with a motorized lens, such as are usually used in PTZ cameras, it also eliminates the need to physically transfer the camera.
Tips for choosing
The choice of the angle of view is determined by the tasks that are assigned to the camera. If you need to monitor a large area, and not highlight a specific object, a device with a 2.8-3.6 mm lens will do. The optimal angle is considered to be in the range from 70 to 140 °.
The 60 ° angle is close to the viewing angle of the human eye. This value is considered average. Devices can transmit a detailed picture when the object is located at a distance of up to 10 m.
A long-focus lens with a view of up to 30 ° is suitable for observing objects that are distant from the control point by 20-70 m.
Knowing the size of the matrix, the lens FH is calculated using the following formulas:
CCTV camera lens view angle
One of the fundamental characteristics that must be taken into account before purchasing a CCTV camera is the angle of view of the lens. This value directly depends on what area of the observed area falls into the field of view of the camera. For example, to get a general view of an area or a tight room, you need to choose cameras with a wide viewing angle, and if you need to focus on any specific object. with a thin.
These are the parameters that the viewing angle depends on.?
The viewing angle of a lens depends on two parameters that determine it:
- The focal length that the lens has;
- Sensor size (matrix).
It should be remembered that the larger the FR a lens has, the smaller its angle of view will be, therefore long-focus lenses have the ability to observe objects that are far from the camera, while wide-angle lenses allow coverage of a large area of a territory or room.
The dependence of the viewing angle of the CCTV camera on the physical size of the matrix also takes place. So, the larger the matrix, the larger the viewing angle, for example:
- A matrix with a diagonal of ¼ will have a 64 ° angle of view at a focal length of 2.8;
- In this case, the matrix with a diagonal of ½ will have a viewing angle of 96 °.
These calculations are valid for the designation of the horizontal viewing angle; to find the vertical angle, it is necessary to take into account the ratio of the vertical and horizontal sides of the matrix.
Determine the required focal length
In almost all cases, it becomes necessary to choose the optimal viewing angle of the camera, which can be determined by calculating the PH of the lens. In fact, the angle of view is dependent on the focal length. It may differ for each specific case, and directly depends on:
- Distances to the object of observation;
- Matrix size;
- Observed object size.
So, for example, a viewing angle of 100 ° is well suited for small confined spaces, but will not be suitable for observing objects that are several tens of meters away. when viewed on the recording, it will simply be impossible to distinguish the details of the object. As the focal length increases, the viewing angle narrows and it becomes possible to observe distant objects.
Knowing several parameters of the CCTV camera and some data about the object of observation, it is not difficult to determine what is necessary in each particular case of the FG lens.
The optimal FG of the lens is calculated by the formula:
F = hS / H or F = vS / V, where
H. size of the horizontal side of the matrix;
S. distance to the tracking object;
H. horizontal size of the object of observation;
V. size of the vertical side of the matrix;
V. vertical size of the object of observation.
You can find out the size of the vertical and horizontal sides of the camera sensor from this table:
For example, let’s calculate a simple problem. Given: it is necessary to observe the front side of a small garage, 4 meters wide, the distance to the object. 10 meters. Matrix size. ½ inch. Calculate a suitable FH of the camera lens. For the solution Let’s use the formula, and Substitute all the necessary values:
Having calculated the formula, we got that the FH of the lens should be 16, but there is one more nuance. It is very important that the angle of view of the camera is more calculated, otherwise, apart from the object of observation, nothing else will be visible. Therefore, in this case, the optimal focal length of the camera lens will be 8-10 mm. The viewing angle at such values will be about 35 °, and is quite suitable for video surveillance of the garage at a distance of 10 meters. Below is a detailed table with camera viewing angles with different focal length parameters and matrix sizes.
If you need to change the angle of view from time to time, or in any difficult situations when it is difficult to determine the focal length before buying a camera, it is worth purchasing cameras with a varifocal lens, which allow you to adjust the angle of view manually. The range of FH of such cameras is usually in the range of 2.8-12 mm. When using varifocal lenses, you can zoom in or out without loss of quality thanks to the optical zoom of the lens.
Which viewing angle to choose?
The answer to this question depends on the specific task, because each situation is individual. For example, for video surveillance of a large area without the need to select a specific object, cameras with a wide-angle lens 2.8-3.6 mm and a viewing angle of 70-140 ° are used.
The 60 ° field of view is similar to that of the human eye and is an average value. Cameras with such an angle are capable of transmitting a detailed image with a range of up to 10 m to the object of observation.
Cameras with a long-focus lens and a thin viewing angle (10-30 °) are used to observe distant objects, the distance to which can vary from 20 to 70 meters, and depends on the FR of the lens.
There is one interesting feature that allows you to determine the distance of confident recognition of an object, and can serve as a kind of cheat sheet when choosing a camera. It consists in approximately equality of the focal length, expressed in millimeters, with the confident recognition distance in meters. For example, a camera with a 1/3-inch sensor and a 12 mm focal length lens will be able to recognize a human figure at a distance of 12 meters. At this distance, the size of the observed zone will be 3 meters high and 4 meters wide, which will allow for a fairly confident identification of a person.
Focal length of CCTV cameras
In the description of video cameras, you can see such an important parameter as focal length. What does it affect? Let’s take a look at this article. The focal length of the CCTV camera directly affects the angle of view of the video camera. At the same time, it depends on the format of the camera matrix. And in order to determine the required parameters, it is necessary to take into account some rules. For instance:
The higher the focal length of the CCTV camera lens, the narrower the viewing angle.
With the same focus of the video camera, a device with a large matrix size will have a large viewing angle.
In a word, the focal length of a CCTV camera. it is a key parameter when calculating the controlled area. Quite simple calculations help to precisely establish the zone that will appear in the field of view of the video camera. In order to monitor a wide area, a camera with a much wider viewing angle is required than when monitoring a long narrow corridor.
That is, the selection of the focusing distance of the CCTV camera depends on how much more or less the Objects are removed. And the more correct this choice, the more objects appear in the frame. So, before buying a video camera, you need to pay attention to the settings and parameters, especially the viewing angle, on which the range of the controlled area depends.
How to choose the focal length of a CCTV camera
So, the focal length and viewing angle of the video camera. This is an important parameter that will determine the area captured by the objective lens. It affects the image quality of the area being viewed, showing the object in detail. Correctly selected focal length allows you to distinguish the desired objects at the required distance. It is worth remembering that long focal length lenses are recommended when you need to observe objects far from the camera. How to choose the focal length of a CCTV camera?
Correct calculation is required to select the focal length. Despite the fact that all manufacturers indicate both the size of the matrix and other industrial properties. But for understanding it is necessary to take into account the following nuances:
- The distance at which the Observed Object will be located;
- Matrix and object size.
From the above, it becomes clear that for different areas it is best to choose a camera, which viewing angle to cover the entire room, or if required. Part of the territory. Today the standard focal length of a camcorder. 3.6mm. On a standard 1 / 2.8 “FullHD sensor, this provides an 80-degree viewing angle. This is an average value that is suitable for most tasks. Such camera parameters allow viewing faces and license plates at a distance of up to 15 meters.
The focal length of telephoto cameras and cameras with variable focal length (varifocal) is usually 12mm. If the Observed Object is far away, then it is recommended to use just such a device. This camera provides a detailed image at a distance of up to 40 meters.
For example, if a person is at a distance of 12 meters, then a camera with a focal length of 12 meters and a viewing angle of 21 degrees can clearly distinguish him. Therefore, it will NOT be superfluous to remind you that in each case, you should individually select the camera so that it performs the tasks that the owner assigns to it.
Wide panoramic video cameras
This device has a viewing angle of 120 degrees and more. Such a device gives a whole panorama of what is happening. The camera is able to detect the face of a person who is NOT more than 3 meters from the camera. That is why such a device should be chosen in order to control large open spaces. One camera will do its job, and there is no need to install additional devices. However, it is impractical to use a wide-angle camera to monitor a long narrow corridor.
Narrow-format devices
Cameras with a viewing angle of 20 degrees, transmit the picture in detail at a distance of 50 meters. The purpose of installing such a video camera should also be taken into account here. Most owners opt for devices with a viewing angle of 60-70 degrees, which allows observation from 10 meters and get a guaranteed clear picture.
Those who first set up a surveillance system on their own make various mistakes. Thinking that I bought a camera with the highest resolution matrix, in which the lens is wide-angle, will cover a huge observation area. At the same time, they count on a high-quality picture. It is important to choose cameras with a focal length that suits your specific needs. As we noted above, 3.6mm cameras are suitable for most objects. For a wider overview. 2.8mm. If you find it difficult to choose the required video surveillance camera, please contact our specialists and we will help you make a choice!
CCTV camera focal length
The calculation of the optimal structure of the security system for an apartment, office or a local area is based on taking into account a set of correlating parameters. One of them is the focal length of the CCTV camera, which determines the device’s ability to see the area from a thin or wide angle of view. To view corridors or tunnels, you will need a narrow one, in order to control the yard or stadium it will need to be increased.
What is it?
System architecture calculations require knowledge of several device parameters. Focal length. this is also its characteristic, which is taken as the base when determining its viewing angle. The device can be aimed at a small area, or it can cover an area of the entire yard. The amount of visual information that gets into the lens depends on its quality, detail, clarity and the likelihood of effective framing and enlargement. You can calculate the viewing angle yourself; this requires only basic knowledge of geometry. This characteristic is measured in millimeters.
Payment
Even without Special knowledge, you can find the required viewing angle yourself. Calculation Based on a combination of two parameters:
- The most focal length;
- Metric matrix sizes.
The proportion in this case is straight. The larger the focal length or the physical size of the matrix, the smaller the viewing angle the user can expect. Chinese and European factories indicate all three significant parameters in the manuals for their device, but when purchasing a camera, you need to understand exactly how to choose the necessary values so that the device works well in the area intended for it.
For the calculation, it is necessary to determine and record 3 parameters:
- The physical size of the matrix;
- Distance to the intended object of observation (if we are talking about the territory. To its border)
- Dimensions of the object itself (it is supposed to observe a person in the office or the maneuvers of a locomotive).
With knowledge of THESE parameters, they can be substituted into the following formula: F = MGRG / RO or, the second option, F = MVRG / PO
In this this formula:
- F. focal length;
- MG. the size of the matrix in the horizontal dimension;
- RG. distance to the object or border of the territory;
- RO. dimensions of the object, also horizontally. the length of the car, the width of the yard or staircase;
- MV. vertical physical size of the matrix;
- IN. the vertical size of the object itself.
By substituting the data into the formulas, you can find out the required focal length.
The physical dimensions of the matrix can be found based on the following parameters:
- If it has parameters 1/2 “, then the horizontal size will be 6.4 mm, vertical. 4.8 mm;
- If it has parameters 1/3 “, then the horizontal size will be 4.8 mm, vertical. 3.6 mm;
- If it has 1/4 “parameters, then the horizontal size will be 3.2 mm, vertical. 2.4 mm.
These figures will remain the same for all camera models of all manufacturers.
Calculation example
For orientation in a specific situation, the following calculation example can be given: the camera is installed in the courtyard of the office and its task will be to recognize the face of a person entering the scrotum or a car passing through the gate. Gate width (horizontal parameters of the object). 6 m, length up to them. 7 m.
The user has a camera with a 1/4 “matrix. Thus, F (focal length) = 3.27 / 6 = 3.7 mm. The size 3.2 characterizes the horizontal dimensions of the matrix of this type. 3.7 mm. Is a value, which will give a viewing angle between 60-70 degrees.
High-quality face recognition at this distance will NOT work with a camera with this focal length. She can only offer his signs. height, gender, color and type of clothing. Calculations can be made not manually, there are calculator programs that will do this automatically.
How to choose a focal length?
The choice of standards set by the owner of the protected area depends on the tasks assigned to a particular device. It is necessary to proceed from the following factors:
- Wide angle cameras have a viewing angle of over 100 °. They are designed to control large areas. A human face with this format will be distinguishable at a distance of NOT more than 3 meters, and it will NOT work to enlarge it. But for control around the perimeter, movements around it and penetration behind it, it will be the best solution.
- Narrow-format video cameras that can provide a viewing angle of about 20 °. They will offer the observer a very detailed picture that can be easily enlarged and cropped at a distance of 30-50 m.
- Medium format devices make up about 80% of the total supply on the market. They are multifunctional, their viewing angle ranges from 50-70 °. This makes it possible to easily conduct surveillance over large areas, and individual objects, for example, a person in a parking lot, will be discernible in detail at a distance of about 10 m. But the user should note that this transmission quality may not be enough to recognize a license plate or a person’s appearance. with the introduction of professional software for this.
The correct choice of the focal length will allow the eye of the device entirely in such a way as to receive the required amount of operational information in what is happening in the controlled space in an acceptable quality.