Types of lenses (according to the application classification) Wide-angle lens: angle of view of more than 90 degrees, the observation of a larger range of near the image is distorted. Standard lens: angle of view of about 30 degrees, the use of a wider range.
Telephoto lens: angle of view within 20 degrees, the focal length can be up to tens of millimeters or hundreds of millimeters. Zoom lens: the lens focal length is continuously variable, the focal length can be changed from wide-angle to telephoto, the longer the focal length, the larger the image.
Pinhole lens: used for covert observation, often installed in places such as ceilings or walls.
The relationship between the size and distance of the subject and the focal length Suppose the width and height of the subject are W. 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 magnitude of the luminous flux passing through the lens, an aperture is set up at the rear of the lens.
Assuming that the effective aperture of the aperture is d, due to the relationship between the refraction of light, the mirror light is actually effective effective aperture D, larger than d, D and the focal length of f is defined as the ratio of the relative aperture A, i.e., A = D / f, the relative aperture of the lens determines the illuminance of being photographed, like the illuminance and the lens of the inverse relative aperture to indicate the size of the lens aperture. The smaller the F value, the larger the aperture, the greater the luminous flux to the CCD chip.
So in the case of the focal length f is the same, the smaller the F value, said the lens is better.
Focal length of the lens 1) fixed focal length: the focal length is fixed, can be divided into two kinds of aperture and no aperture. With aperture: the size of the lens aperture can be adjusted.
According to the changes in the environmental lighting, the size of the aperture should be adjusted accordingly. The size of the aperture can be adjusted manually or automatically, manually adjusted aperture, known as the manual aperture.
The lens comes with a micro-motor to automatically adjust the aperture, known as auto iris. No aperture: i.e. fixed aperture, its flux is fixed.
Mainly used for constant light source or the camera comes with an electronic shutter. 2) Variable Focal Length: The focal length can be adjusted as needed to enlarge or reduce the image of the subject.
Commonly used zoom lens for six times, ten sold zoom. Three-variable and two-variable lenses Three-variable lenses: adjustable focal length, adjustable focus, adjustable aperture.
Two variable lenses: adjustable focus, focus adjustment, automatic aperture.
Two variable lenses: adjustable focus adjustment, focus adjustment, auto iris.
2. Seek basic knowledge of surveillance cameras
In the closed-circuit surveillance system, the camera, also known as the camera or CCD (Charge Coupled Device) that is, charge-coupled device.
Strictly speaking, the camera is a general term for the camera and the lens, but in fact, most of the camera and the lens are purchased separately, the user according to the size of the target object and the distance between the camera and the object, through the calculation to get the focal length of the lens, so each user needs a lens is based on the actual situation, do not think that the camera (head) already have a lens. The main sensing component of the camera is the CCD, which has high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small size, no residual shadow, etc. CCD is an electrically coupled device (Charge Couple Device) for short, which can change light into charge and can be stored and transferred, but also can be taken out of the storage of the charge to make the voltage change, and therefore it is the ideal video recording
It's an ideal component for video recording.
It is a new device to replace the camera tube sensor. The working principle of the CCD is: the object being photographed reflected light, spread to the lens, the lens focus to the CCD chip, the CCD according to the intensity of the light accumulates the corresponding charge, the periodic discharge, resulting in the production of a picture of the picture of the electrical signals, filtering, amplification processing, through the output terminal of the camera to output a standard composite video signal.
This standard video signal with home video recorders, VCD players, home video cameras, the video output is the same, so you can also record or receive a TV set to watch. CCD camera selection and classification CCD chip is like the human retina, is the core of the camera.
At present, our country does not have the ability to manufacture, most of the cameras on the market are used in Japan SONY, SHARP, Panasonic, LG and other companies to produce the chip, and now South Korea also has the ability to produce, but the quality will be a little inferior. Because of the chip production of different levels, each manufacturer to obtain different ways and other reasons, resulting in CCD acquisition effect is also very different.
At the time of purchase, you can take the following methods of detection: Turn on the power, connect the video cable to the monitor, close the lens aperture, look at the image when all black whether there are bright spots, the screen snowflake big or not, these are the detection of the CCD chip is the simplest and most direct method, and does not require other specialized instruments. Then you can open the aperture, look at a still life, if it is a color camera, it is best to ingest a brightly colored object, to see if the image on the monitor is off-color, distorted, color or gray scale is smooth.
A good CCD can well restore the color of the scene, so that the object looks clear and natural; while the image of the defective product will have a bias phenomenon, even if the face of a piece of white paper, the image will show blue or red. Individual CCD due to the dust of the production plant, CCD target surface will have impurities, in general, the impurities will not affect the image, but in low light or microscopic camera, fine dust can also cause adverse consequences, if used for this type of work, be sure to carefully select.
1, according to the imaging color division Color camera: applicable to the scene of fine discrimination, such as identifying the color of clothing or scenery. Black and white camera: for poorly lit areas and areas where lighting can not be installed at night, only to monitor the location or movement of the scene, you can choose black and white camera.
2, according to the resolution of sensitivity and other divisions Image pixels in the 380,000 or less for the general type, especially 250,000 pixels (512 * 492), the resolution of 400 lines of the most common products. The image pixels in more than 380,000 high-resolution type.
Panel type. Pinhole type.
Hemisphere type. 3, divided by the size of the CCD target CCD chip has been developed in a variety of sizes: most of the chips currently used for 1/3 "and 1/4".
In the purchase of the camera, especially on the camera angle has a more stringent requirements, the size of the CCD target surface, CCD and the lens with the situation will directly affect the size of the field of view and the clarity of the image. 1 inch - target surface size of 12.7mm wide * 9.6mm high, 16mm diagonal.
2/3 inch - target surface size of 8.8mm wide * 6.6mm high, 11mm diagonal. 1/2 inch --Target surface measures 6.4mm wide * 4.8mm high, 8mm diagonal.
1/3 inch --Target surface measures 4.8mm wide * 3.6mm high, 6mm diagonal. 1/4 inch. --Target surface size is 3.2mm wide * 2.4mm high, diagonal 4mm.
4, according to the scanning system PAL system. NTSC.
China uses interlaced (PAL) system (black and white for CCIR), the standard is 625 lines, 50 fields, only medical or other professional areas to use some non-standard system. In addition, Japan is NTSC, 525 lines, 60 fields (black and white for EIA).
5, according to the power supply 110VAC (NTSC mostly belong to this kind), 220VAC, 24VAC. 12VDC or 9VDC (microcamera mostly belong to this kind).
6, according to the synchronization method of internal synchronization: using the camera within the synchronization signal generating circuitry generated by the synchronization signal to complete the operation. External synchronization: the use of an external synchronization signal generator, the synchronization signal into the camera's external synchronization input.
Power Sync (linear lock, line lock): Vertical push synchronization is accomplished using the camera's AC power supply. External VD sync: The external VD sync is accomplished by feeding the VD sync pulse from the camera's signal cable.
Multi-camera external synchronization: Fixed external synchronization of multiple cameras, so that each camera can operate under the same conditions, due to the synchronization of the camera, so that even if one of the camera converted to other scenes, synchronized with the camera's picture will not be distorted. 7, in accordance with the degree of division, CCD is divided into: Normal type of illumination required for normal operation 1 ~ 3LUX Moonlight type of illumination required for normal operation 0.1LUX or so Starlight type of illumination required for normal operation 0.01LUX or less Infrared type of infrared illumination, in the absence of light can be imaged in the case of the main technical indicators of the CCD color camera (1) CCD size, that is, the target surface of the camera.
The original more than 1/2 inch, now 1/3 inch has been popularized, 1/4 inch and 1/5 inch has also been commercialized. (2) CCD pixels, is the main performance indicator of the CCD, which determines the degree of clarity of the displayed image, the higher the resolution, the better the performance of the image details.
CCD is composed of surface array photographic elements, each element is called a pixel, the more pixels, the clearer the image. Nowadays, the market is mostly demarcated by 250,000 and 380,000 pixels, and those with more than 380,000 pixels are high-definition camcorders.
(3) horizontal resolution. The typical resolution of color camcorders is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines,.
3. Seek basic knowledge of surveillance cameras
The lens is an essential part of the TV surveillance system, the lens and CCD camera with the CCD camera, can be a long-distance target imaging in the camera's CCD target surface.
There are many types of lenses, from the focal length classification, can be divided into short focal length, medium focal length, and focal length and variable focal length lenses; from the size of the field of view classification, can be divided into wide-angle, standard, telephoto lenses; from the structure of the classification, can also be divided into fixed-aperture fixed-focus lenses, manual-aperture fixed-focus lenses, auto aperture fixed-focus lenses, manual zoom lenses, auto aperture motorized zoom lenses, motorized triple-variable lenses (the aperture, focus, focusing, and so on). Refers to the aperture, focal length, focus all three are variable) and other types. As the lens selection is appropriate or not, directly related to the quality of the camera's strengths and weaknesses, therefore, in practical applications must be reasonable choice of lens.
1, the parameters of the lens The optical characteristics of the lens, including imaging size, focal length, relative aperture and field of view angle and several other parameters, generally in the lens attached to the manual are indicated, the following are introduced. A, imaging size The lens can generally be divided into 25.4mm (lin), 16.9mm (2/3in), 12.7mm (1/2in), 8.47mm (1/3in) and 6.35mm (1/4in) and several other specifications, which correspond to different imaging size, the selection of the lens, the lens should be made to the imaging size and the camera's target size size coincide with the lens.
Table 2
Table 2-1 lists several common CCD chip target surface size, the table in mm. Nominal chip size CCD light-sensitive target surface size 25.4 16.9 12.7 8.47 6.35 Diagonal 16 11 8 6 4.5 Vertical 9.6 6.6 4.8 3.6 2.7 Horizontal 12.7 8.8 6.4 4.8 3.6 Table 2-1 Several common CCD chip target surface size from Table 2-2, the lens should match the size of the camera target size. Chip target surface size As can be seen from Table 2-1, 12. 7mm (1/2in) lens should be matched with 12. 7mm (1/2in) target surface of the camera, when the imaging size of the lens than the size of the camera target surface, will not affect the imaging, but the actual imaging of the field of view than the nominal field of view of the lens is smaller (see Figure 2-2), and when the imaging size of the lens is smaller than the size of the target surface of the camera, it will affect the imaging, as shown in the nominal field of view of the lens (see Figure 2-2). , it will affect the imaging, manifested in the imaging of the screen around the lens barrel obscured, in the screen of the four corners of the black corner.
B, focal length In practice, there are often users of the camera can see how far away from the object or the camera can see how wide the scene and so on, this is actually determined by the focal length of the lens selected, because the focal length determines the size of the image taken, with different focal lengths of the lens on the same position of an object camera, with a long focal length lens with a long lens of the camera taken by the size of the scene on the large, and vice versa, with a short focal length lens, the size of the scene. Large, and vice versa, with a short focal length lens of the camera taken by the scene size is small. Of course, the clarity of the object being photographed with the selected CCD camera resolution and monitor resolution.
Theoretically, any kind of lens can shoot very far away from the object, and in the CCD target surface into a very small image, but by the physical size of the CCD unit (pixel) limitations, as when the image is smaller than the size of a pixel of the CCD sensor, it will no longer be able to form the image of the object being photographed, even if the image is the size of a few pixels, it would be difficult to recognize the image as what. When the known size of the subject and the object to the lens distance, the focal length of the selected lens can be estimated according to the following two formulas: f = hD / H f = vD / V where, D for the center of the lens to the object of the distance; H and V for the object of the horizontal size and vertical size, respectively; v for the height of the target surface imaging; h for the target surface imaging of the horizontal width.
The size of the imaging scene and the size of the imaging object display is contradictory, for example, with the same camera to monitor the same parking lot, the choice of a short focal length lens can be a panoramic view of the entire parking lot to monitor and see the entrances and exits outside of the vehicle in and out, but can not see the license plate number of the vehicle (the car only occupies a very small area on the monitor screen); and the choice of a long focal length lens can see the license plate number (the car only occupies a very small area on the monitor screen). Although the choice of long focal length lens can see the license plate number of the car (the car occupies most of the area on the screen), but can not monitor the entire parking lot of the whole picture. Therefore, when you need to monitor the panoramic view to see the local, generally should be considered with electric two-variable or electric three-variable lens.
Of course, in the selected lens under the premise of selecting high-resolution cameras and monitors can be monitored in the imaging size of the object can also see the local details. C, the relative aperture in order to control the size of the luminous flux through the lens, the rear of the lens are set up in the diaphragm (commonly known as the aperture).
Assuming that the effective aperture of the diaphragm is d, due to the relationship between light refraction, the actual effective aperture of the lens D, D and the focal length of f is defined as the relative aperture A, that is, A = D / f The relative aperture of the lens is determined by the camera's illuminance, such as the illumination of the E and the lens relative aperture squared proportional to the relative aperture is generally customary to use the inverse relative aperture of the lens diaphragm to express the size of the lens, that is, F = f / D. In this case, F is generally referred to as the light bar F, which is generally known as the light bar. In the F is generally known as the light bar F number, labeled in the lens light bar adjustment circle, its standard value of 1. 4, 2, 2. 8, 4, 5. 6, 8, 11, 16, 22 and other sequential values, each of the two adjacent values, the latter value is a multiple of the previous value. Since the image surface illumination is proportional to the square of the light bar, the image surface brightness changes by a factor of two for every change in the light bar.
The smaller the F-value, the larger the light bar, the greater the luminous flux reaching the camera target surface. D, field of view angle The lens has a defined field of view, the lens on the height and width of the field of view of the angle known as the field of view.
The field of view with the focal length of the lens f and the size of the camera target surface (horizontal size h and vertical size v) size, the lens of the horizontal field of view ah and the vertical field of view av can be calculated by the following formula, namely, ah = 2 arctg (h / 2f) av = 2 arctg (v / 2f) from the above two formula can be seen, the lens of the shorter the focal length of the lens f, the greater the angle of its field of view or, the shorter the focal length of the camera target surface. The larger the camera target surface size h or v, the larger its field of view angle. If the field of view of the selected lens is too small, there may be a monitoring dead zone and missed monitoring; and if the selected lens field of view is too large, it may cause the main body of the monitored screen size is too small, difficult to recognize, and the edges of the screen distortion.
Therefore, only according to the specific application environment to choose the appropriate field of view of the lens, in order to ensure that there is no monitoring of the dead zone, but also to enable the subject to be monitored as large and clear picture. Table 2-2 lists the horizontal field of view of several commonly used lenses, the parameters in the table are given as a reference to the Japanese Seiko series of lenses.
Focal length / mm Lens size / in 2.8 3.5 4.0 4.8 6.0 8.0 12.0 16.0 25.0 1/3 86.3 67.4 62.0 52.2 42.3 32.6 22.1 17.1 10.6 1/2 94.6 69.4 57.1 42.6 29.7 22.6 .