Lens type (classified by application) Wide-angle lens: the viewing angle is greater than 90 degrees, the observation range is large, and the close-up image is distorted. Standard lens: the viewing angle is about 30 degrees, and it has a wide range of use.
Telephoto lens: The viewing angle is less than 20 degrees, and the focal length can reach tens or hundreds of millimeters. Zoom lens: the focal length of the lens is continuously variable, and the focal length can be changed from wide angle to telephoto. The longer the focal length, the larger the imaging.
Pinhole lens: used for hidden observation, often installed on the ceiling or wall. 2。
The relationship between the size, distance and focal length of an object assumes that the width and height of the object are w respectively. H, the distance between the subject and the lens is l, and the focal length of the lens is f.
3。 Relative aperture In order to control the luminous flux passing through the lens, an aperture is set behind the lens.
Assuming that the effective aperture of the aperture is D, the actual effective aperture of mirror light is D, which is greater than D. The ratio of D to focal length F is defined as the relative aperture A, that is, A = D/F. The relative aperture of the lens determines the illumination of shooting, and the reciprocal of the illumination of the image and the relative aperture of the lens represents the size of the lens aperture. The smaller the f value, the larger the aperture and the greater the luminous flux reaching the CCD chip.
Therefore, in the case of the same focal length f, the smaller the value of f, the better the lens. 4。
The focal length of the lens is 1) fixed focal length: the focal length is fixed and can be divided into two types: aperture and non-aperture. Aperture: The aperture of the lens can be adjusted.
According to the change of environment, the aperture should be adjusted accordingly. The aperture can be adjusted manually or automatically. If you adjust the aperture manually, it is called manual aperture.
If the lens comes with a micro-motor to automatically adjust the aperture, it is called automatic aperture. No aperture: that is, fixed aperture, and its luminous flux is fixed.
It is mainly used when the light source is constant or the camera has its own electronic shutter. 2) Zoom: The focal length can be adjusted as required to enlarge or reduce the image of the subject.
Commonly used zoom lenses include six-fold zoom and ten-fold zoom. Three-variable lens and two-variable lens: adjustable focal length, adjustable focal length and adjustable aperture.
Variable lens: adjustable focal length, adjustable focal length, automatic aperture. .
2. Seek the basic knowledge of surveillance cameras.
In closed-circuit monitoring system, camera is also called camera or CCD (Charge Coupled Device).
Strictly speaking, a camera is a general term for cameras and lenses. In fact, most cameras and lenses are purchased separately. Users can calculate the focal length of the lens according to the size of the target object and the distance between the camera and the object, so the lens needed by each user depends on the actual situation. Don't think that there is a lens on the camera (head). The main sensitive element of the camera is CCD, which has the characteristics of high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small size and no afterimage. CCD is the abbreviation of charge coupled device, which can convert light into charge, store and transfer the charge, and also take out the stored charge to change the voltage, so it is an ideal camera element.
It is a new device to replace the camera tube sensor. The working principle of CCD is that the light reflected by the photographed object propagates to the lens and is focused on the CCD chip through the lens. CCD accumulates corresponding charges according to the intensity of light, and generates electrical signals representing pictures after periodic discharge. After filtering and amplification, the standard composite video signal is output through the output end of the camera.
This standard video signal is the same as the video output of home video recorder, VCD player and home video camera, so it can also be recorded or connected to TV to watch. Selection and classification of CCD camera CCD chip, like human retina, is the core of camera.
At present, China has no manufacturing capacity. Most cameras on the market use chips produced by Japanese companies, such as Sony, Sharp, Panasonic, LG and so on. Now South Korea also has the ability to produce, but the quality will be slightly inferior. Due to the different grades produced in chip production and the different ways obtained by various manufacturers, the acquisition effect of CCD is also very different.
When buying, you can take the following methods to detect: turn on the power supply, connect the video cable to the display, close the lens aperture, and see if there are bright spots when the image is completely black, and whether the snow on the screen is big or not. These are the simplest and most direct methods to detect CCD chips, and no other special instruments are needed. Then you can open the aperture and look at the still life. If it's a color camera, you'd better take a brightly colored object to see if the image on the display is color cast, distorted, smooth or gray.
Good CCD can restore the color of the scene well and make the object look clear and natural; However, the image of defective products will have a color cast, and even if it faces a blank sheet of paper, the image will display blue or red. Due to the dust in the production workshop, there will be impurities on the target surface of individual CCD. In general, impurities will not affect the image, but in low light or micrography, fine dust will also cause adverse consequences. If it is used in this kind of work, it must be carefully selected.
1. Color camera divided by imaging color: suitable for distinguishing scene details, such as distinguishing the color of clothes or scenery. Black-and-white camera: suitable for areas with insufficient light and areas where lighting equipment cannot be installed at night. When monitoring only the position or motion of the scene, you can choose a black-and-white camera.
2. According to the resolution sensitivity, the image pixels below 380,000 are classified into general types, especially the products with 250,000 pixels (565,438+02 * 492) and 400 line resolution are the most common. A high-resolution image with more than 380,000 pixels.
Machine board type. Pinhole type.
Hemisphere type. 3. According to the size of CCD target surface, CCD chips have developed various sizes: most of the chips used at present are 1/3 "and 1/4".
When choosing a camera, especially when the camera angle is strictly required, the size of the CCD target surface and the cooperation between CCD and lens will directly affect the size of the field of view angle and the clarity of the image. 1 inch-the target size is12.7mm * 9.6mm high,16mm diagonal.
2/3 inch-target size is 8.8 mm * width * 6.6 mm high, diagonal line is 1 1 mm .. 1/2 inch-target size is 6.4 mm * width * 4.8 mm high, diagonal line is 8 mm.
1/3 inch-the target size is 4.8 mm * width * 3.6 mm height, and the diagonal is 6 mm. 1/4 inch-the target size is 3.2 mm * width * 2.4 mm height and 4 mm diagonal.
4.PAL system is divided according to scanning system. NTSC system
China adopts interlaced scanning (PAL) system (black and white CCIR), and the standard is 625 lines and 50 fields. Only medical or other professional fields use some non-standard systems. In addition, Japan is NTSC, with 525 lines and 60 games (EIA black and white).
5. According to the power supply mode, it is divided into 1 10VAC(NTSC system mostly belongs to this category), 220VAC and 24VAC. 12VDC or 9VDC (miniature cameras mostly fall into this category).
6. Internal synchronization according to synchronization mode: use the synchronization signal generated by the synchronization signal generation circuit in the camera to complete the operation. External synchronization: The external synchronization signal generator is used to send synchronization signals to the external synchronization input of the camera.
Power synchronization (line lock): use the AC power of the camera to complete the vertical push synchronization. External VD synchronization: input VD synchronization pulse on the camera signal line to complete external VD synchronization.
Multi-camera external synchronization: External synchronization is fixed for multiple cameras, so that each camera can work under the same conditions. Because the cameras are synchronized, even if one of the cameras switches to other scenes, the picture of the synchronized camera will not be distorted. 7.CCD can be divided into:1~ 3 lux for normal operation; The illumination required for normal operation of moonlight type is about 0.1lux; The illumination required for normal operation of starlight type is below 0.0 1LUX; The infrared type is illuminated by infrared lamp, and the main technical index of CCD color camera (1) is dull imaging.
Originally 1/2 inch, now 1/3 inch has been popularized, and 1/4 inch and 1/5 inch have also been commercialized. (2)CCD pixel is the main performance index of CCD, which determines the clarity of the displayed image. The higher the resolution, the better the image details.
CCD consists of array photosensitive elements, and each element is called a pixel. The more pixels, the clearer the image. At present, most of the markets are demarcated by 250,000 and 380,000 pixels, and more than 380,000 pixels are high-definition cameras.
(3) Horizontal resolution. The typical resolution of color cameras is between 320 and 500 TV lines, mainly including 330 lines, 380 lines, 420 lines and 460 lines.
3. Seek the basic knowledge of surveillance cameras.
Lens is an important part of TV monitoring system. With the cooperation of the lens and CCD camera, the long-distance target can be imaged on the CCD target surface of the camera.
There are many kinds of lenses, which can be divided into short focal length, medium focal length, focal length and zoom lens. According to the size of field of view, it can be divided into wide-angle, standard and telephoto lenses; Structurally, it can also be divided into fixed aperture fixed focus lens, manual aperture fixed focus lens, automatic aperture fixed focus lens, manual zoom lens, automatic aperture electric zoom lens and electric three-variable lens (that is, aperture, focal length and focus are all variable). Because the choice of lens is directly related to the quality of shooting, it is necessary to choose the lens reasonably in practical application.
1, lens parameters The optical characteristics of a lens include imaging size, focal length, relative aperture, field of view and other parameters, which are generally indicated in the manual attached to the lens. The following are introduced separately. A, imaging lens size can be generally divided into 25.4mm (forest), 16.9mm(2/3 inches),12.7 mm (12 inches), 8.47 mm (13 inches), 6.35 mm (.
Table 2- 1 lists the target sizes of several common CCD chips. The unit in the table is mm. The nominal chip size CCD photosensitive target size is 25.416.912.7 8.47 6.35 diagonal161864.5 vertical 9.6 4.8 3.6 2.7 horizontal10. 7mm( 1/2in) should be equipped with 12 camera. 7 mm (1/2 inches) target surface. When the lens imaging size is larger than the camera target size, but the actual imaging field of view angle is smaller than the lens nominal field of view angle (see Figure 2-2), when the lens imaging size is smaller than the camera target size, it will affect the imaging, showing that the imaging picture is blocked by the lens barrel and black corners appear at the four corners of the picture.
B. Focal length In practical application, users often ask how far the camera can see objects or how wide the scene can be, which is actually determined by the focal length of the selected lens, because the focal length determines the size of the shot image. When shooting an object in the same position with lenses with different focal lengths, the size of the scene shot by a camera with a long focal length is large, and vice versa. Of course, the clarity of object imaging is also related to the resolution of CCD camera and monitor.
Theoretically, any kind of lens can shoot distant objects and form small images on the CCD target surface. However, limited by the physical size of the CCD unit (pixel), when the image is smaller than one pixel of the CCD sensor, it can no longer form an image of the object being photographed. Even if the image is several pixels in size, it is difficult to identify what it is. When the size of the subject and the distance from the subject to the lens are known, the focal length of the selected lens can be estimated according to the following two formulas: f=hD/H f=vD/V, where d is the distance from the lens center to the subject; H and v are the horizontal and vertical dimensions of the main body respectively; V is the imaging height of the target surface; H is the horizontal width of target imaging.
The size of the imaging scene is contradictory to the display size of the imaging object. For example, using the same camera to monitor the same parking lot, you can monitor the whole parking lot with a short-focus lens, and you can see the vehicles outside the entrance and exit, but you can't see the license plate number of the car clearly (the car only occupies a small area on the monitoring screen); The telephoto lens can clearly see the license plate number of the car (the car occupies most of the screen), but it can't monitor the whole parking lot. Therefore, when it is necessary to monitor the panorama to see the parts clearly, it is generally necessary to consider using the electric two-variable or three-variable lens.
Of course, under the premise of choosing a lens, we can also see the local details clearly by choosing a high-resolution camera and monitor when the imaging size of the monitored object is small. C. Relative aperture In order to control the luminous flux passing through the lens, an aperture (commonly known as aperture) is set behind the lens.
Assuming that the effective aperture of the aperture is D, the actual effective aperture of the lens is D due to the refraction of light, and the ratio of D to focal length F is defined as the relative aperture A, that is, A = D/F. The relative aperture of the lens depends on the illumination of the lens, and the illumination E of the image is proportional to the square of the relative aperture of the lens. The size of the lens aperture is generally expressed by the reciprocal of the relative aperture, that is, in the formula F=f/D, f is generally called the f number of the aperture. It is marked on the lens aperture adjusting ring, and the marked value is 1 and other series values. 4, 2, 2.8, 4, 5.6, 8, 1 1, 16, 22 and so on. In every two adjacent values, the latter value is twice as large as the previous one. Because the illumination of the image surface is proportional to the square of the aperture, the brightness of the image surface will double every time the aperture changes.
The smaller the f value, the larger the aperture and the greater the luminous flux reaching the camera target surface. D. the viewing angle lens has a definite field of view, and the opening angle of the lens to the height and width of this field of view is called the viewing angle.
The angle of view is related to the focal length f of the lens and the size of the camera target surface (horizontal dimension H and vertical dimension V). The horizontal view angle ah and vertical view angle av of the lens can be calculated by the following formulas, namely, ah=2arctg(h/2f) av=2arctg(v/2f). According to the above two formulas, the shorter the focal length f of the lens, the larger the angle of view, or the larger the size of the camera target surface H or V. If the field of view of the selected lens is too small, it may be missed because of the monitoring dead angle; However, if the field of view angle of the selected lens is too large, the size of the monitored main picture may be too small to be recognized, and the edge of the picture will be distorted.
Therefore, only by choosing a lens with a suitable field of view according to the specific application environment can we ensure that there is no monitoring dead angle and the monitored subject picture is as large and clear as possible. Table 2-2 lists the horizontal field of view angles of several commonly used lenses, and the parameters in the table are given with reference to Seiko series lenses in Japan.
Focal length /mm lens size/in2.83.54.06.08.012.016.025.01/386.367.462.052.242.332.622.11.