| Selection and the main parameters of the lens |
| Camera lens is the most critical equipment video surveillance system , its quality ( indicators ) directly affect the overall index surveillance cameras , so the camera lens selection is appropriate both to the quality system , and related to the project cost. The lens of the human eye 's lens , if there is no lens , people watch anything ; If no lens , the image output from the camera is the white one , there is no clear image output, which our home surveillance cameras and camera the principle is the same. When the muscles of the human eye lens can not be stretched to its normal position, that is, myopia , commonly known as the scene in front becomes blurred ; camera and lens with a similar phenomenon , when the picture becomes clear can adjust the back focus of the camera, and the camera changes from the reference plane of the CCD chip ( equivalent to adjust the position of the eye lens ) can be blurred image becomes clear . Thus , the role of the lens in the closed-circuit surveillance system is very important. Engineering design and construction personnel must often deal with the lens : the designer according to the object distance , the image size is calculated lens focal length , construction workers often perform on-site commissioning , part of the lens is adjusted to the optimum state. 1 , the classification of the lens Press the function of the shape according to the size of the aperture points by pressing the zoom focal length according to the type of moments of Spherical Lens 1 "25mm auto iris motorized zoom lens focal length Aspherical lens 1/2 "3mm standard manual iris manual zoom lens Pinhole Lens 1/3 "8.5mm fixed focus wide-angle lens fixed iris Fisheye 2/3 "17mm ( 1 ) to the lens mount Category: All camera lenses are threaded port , CCD camera 's lens mount , there are two industry standards , namely C mount and CS mount . Both the threaded portion of the same , but both the distance from the lens to a different photosensitive surface . C mount : mounting reference to the distance from the lens focus is 17.526mm. CS mount : special C installation , then the washer should remove the front part of the camera before installing the lens. Its lens mount to the focal plane distance is 12.5mm. If you want to install a C mount lens to CS mount a camera on , you need to use the lens converter. ( 2 ) to the camera lens specifications Category: camera lens specifications should be considered depending on the size of a CCD camera , the two should correspond. That camera 's CCD target surface size is 1 / 2 inches , the lens should be selected 1 / 2 inches . CCD camera target surface size is 1/ 3 inches , the lens should be selected 1 /3 inch . CCD camera target surface size is 1 / 4 inches , the lens should be selected 1 / 4 inches. If the size of the lens and CCD camera the size of the target surface is inconsistent , the viewing angle will not meet the design requirements, or the occurrence of the picture out of focus and other issues. ( 3 ) to the lens aperture Category: lens with manual iris (manual iris) and auto- iris (auto iris) of the points , with the camera using manual iris lens is suitable for applications where constant brightness , auto iris lens brightness changes due also as its aperture is automatically adjusted so the brightness changes applicable occasions . Auto Iris lens has two types: one is a video signal and the power delivered to the lens from the camera to control the aperture on the lens , called the video input type , and the other on the use of a DC voltage to the direct control of camera iris , called DC input type . ALC ( automatic camera control ) is used to set the metering system automatically adjust the aperture on the lens , the average brightness of the entire screen can also be the brightest part of the picture (peak ) to set the reference signal strength , the supply of auto iris adjustment use . Generally , ALC has been through in the factory settings may be adjusted , but for shooting a scene contains a high brightness of the target , the image of a bright object may result in " white level clipping " phenomenon, and making the entire screen turns white , then you can adjust the ALC to transform the screen. In addition, the auto iris lens equipped with an aperture ring , when you turn the aperture ring will change through the lens of the luminous flux, luminous flux that aperture , usually with F that its value is more than the lens focal length of the lens Aperture , namely : F = f ( focal length ) / D ( real effective aperture of the lens ), F value is smaller, the larger the aperture . Automatic iris lens, is ideal for the following applications of choice , they are: in the case of such a very bright direct sunlight , etc., with automatic iris lens has a wide dynamic range. Requires a good focus throughout the field of view when using auto iris lens has a greater depth of field than a fixed aperture lens . Fuzzy minimum requirements on light caused by light signals , use automatic iris lens. ( 4 ) to the lens field of view size categories : Standard Lens: 30 degrees left and right perspective , in 1/2 inch CCD camera , the standard set for the lens focal length 12mm, 1 /3 inch CCD camera , a standard lens focal length as 8mm. Wide-angle lens: angle 90 degrees above , the focal length can be less than a few millimeters , can provide a wider perspective. Telephoto lens: angle less than 20 degrees , the focal length of up to several meters or tens of meters , the object affected by this lens can be taken in the case of long-range zoom , but the observation range smaller. Zoom lens (zoom lens): also known as telescopic lens, manual zoom lens and motorized zoom lens types. Variable focus lens (vari-focus lens): It is between the standard lens with wide-angle lens , the focal length of a continuous variable , distant objects can be enlarged , while at the same providing a broad visual , so that the monitoring range is increased. Auto focus zoom lens focal length to the minimum and maximum focal length by setting two positions , but the focal length from the minimum to the maximum focal length between the focus , the focus is required to achieve manually . Pinhole Lens : Lens few millimeters in diameter , can be concealed installation. ( 5 ) of the short focal length of the lens from the lens focal length : Due to a wide angle of incidence , can provide a broader perspective. The focal length of the lens : CCD length depending on the size of the standard lens , the focal length may be. Long focal length of the lens : Due to narrow the angle of incidence , it can only provide a narrow visual , suitable for long distance monitoring. Zoom : usually electric, can be used for wide-angle , standard, or afar , such as lenses. 1 ) Fixed Focal Length: fixed focal length , aperture and can be divided into two kinds of non- iris . There Aperture : The size of the lens aperture can be adjusted. According to changes in ambient light , the aperture size should be adjusted accordingly . Size of the aperture can be adjusted automatically or manually through . Artificially manually adjust the aperture , called manual iris ; lens comes with micro motor automatically adjusts the aperture , called auto iris . No Aperture : the fixed aperture , the amount of light is fixed . The main case comes with an electronic shutter with a constant light source or camera . 2 ) Variable Focus: Focus can be adjusted as needed , so that the subject of the picture to zoom in or out. The zoom lens is used six times , ten times zoom. Three variable lens : adjustable focus , adjusting focus, adjust the aperture. Two variable lens : adjustable focus , adjust the focus , auto iris . Notes: Focal plane of a fixed position , and the focal path of the optical system can be adjusted continuously - zoom lens. By moving the zoom lens within the lens , change the relative position therebetween achieved . This can change the focal length of the lens and viewing angle within a certain range . Focal Length - the distance image gathering point or center of the lens to the second principal plane . Units typically millimeters or inches. Aperture - located in the part of the camera lens , you can adjust the optical mechanical Lanna also be used to control by how much light the lens . Auto iris - diaphragm device inside the lens , you can adjust itself according to the video signal coming from the television cameras , to adapt to changes in light intensity . Iris diaphragm by opening or closing the aperture to control the transmission of light through the lens . The typical range is compensated to 300000-1 10000-1 . 2, choose the lens technical basis ( A ) the size of the imaging lens should be consistent with the size of the camera CCD plane , as described above , there is 1 inch , 2/3 inch, 1 /2 inch, 1 / 3 inch, 1 /4 inch, 1 / 5 inches and other specifications. ( 2 ) describe the resolution of the lens camera image quality index is intrinsic optical transfer function and the lens distortion , but the support , the need to understand the spatial resolution of the lens is just to be able to distinguish each millimeter number of black and white stripes units of measurement, calculated as follows: N = the height of the lens resolution 180 / frame format. Due to the size of the target surface CCD cameras have been standardized , such as 1 /2 inch camera , which is the target surface height width 6.4mm * 4.8mm, 1/3英寸camera to wide 4.8mm * height 3.6mm. Therefore, the CCD target surface 1 /2 inch format , the lens should be a minimum resolution of 38 pairs of lines / mm, for 1/3 inch format camera , lens resolution should be greater than 50 pairs of lines, the camera target surface , the higher the resolution of the lens . ( 3) The first lens focal length and angle of view is based on distance from camera to monitor the target , select the focal length of the lens , the lens focal length f determined by the camera determines the target surface horizons . ( 4 ) the amount of light aperture or amount of light through the lens to the lens focal length and aperture ratio measured with F marked , are marked with the maximum F value on each lens, the amount of light and the F value to the square inverse relationship , F value is smaller , the larger the aperture . Therefore, the light should be monitored according to the degree of change section to select manual or automatic iris lens aperture . 3 , lens (zoom lens) zoom lens with manual and automatic retractable telescopic lens into two categories. Since a zoom lens in the lens focal length of the lens can be within a certain range, the target can be enlarged or reduced to be monitored , it is often said to be the zoom lens. Typical specifications are six times optical zoom (6.0 ~ 36mm, F1.2), 8 -fold (4.5 ~ 36mm, F1.6), 10 times (8.0 ~ 80mm, F1.2), 12 times (6.0 ~ 72mm, F1 .2 ) , 20 times (10 ~ 200mm, F1.2) and other grades, and the most common electric telescopic lens . To increase the magnification , in addition to the optical zoom can also be subjected to external electronic digital zoom . Electric telescopic lens , adjust the aperture , there are three , namely: auto iris , auto iris DC drive , electric adjust the aperture . Adjust its focus and zoom , only the electric adjustment and preset two electric adjustment is driven by a motor inside the lens , while the preset count is pre-set by a potentiometer to adjust the stop bit inside the lens , so that imaging can be exempted successive adjustment process , accurate and rapid positioning. Integrated camera system in the dome cover , most with preset using telescopic lens. Another so interested users are fast -focus function , which consists of measuring the power zoom -focus system with a feedback control system structure. 4 , the relationship between the camera lens and CCD size 1 / 2 " lens used for both 1/ 2" cameras can also be used for 1/ 3 " cameras, but the perspective will be reduced by about 25%. 1 /3" lenses can not be used for 1 / 2 " camera , only for 1 /3" cameras. 5, the application of different types of lenses * Manual , auto iris lens manual iris lens is the scope of application of the easiest shot , under suitable lighting conditions relatively stable condition , manual iris constituted by several pieces of metal foil . Flux by a ring on the outside diameter of the lens to adjust . This ring can rotate or enlarge small aperture closed . Large changes in lighting conditions or environments not used to monitor a fixed target , auto iris lens should be used , such as outdoors or in artificial lighting often switch places, auto iris lens aperture movement driven by a motor , the motor is controlled by the camera video signal. Manual iris lens and auto iris lenses have fixed focal length ( aperture ) lens auto iris lens and motorized zoom points. * Fixed focal length ( aperture ) lens, generally with electronic shutter camera supporting role for indoor monitor places a fixed target . Fixed focal length lens is generally divided into long focal length lens , the focal length of the lens and short focal length lens. The focal length of the lens focal length is similar to the size of the lens and imaging ; focal length is less than the image size is called a short-range shot , short focal length lens , also known as a wide-angle lens, the focal length of the lens is usually less than 28mm lens, the short focal length lens mainly for ambient lighting conditions poor monitoring requirements of a wide range of occasions , the focal length is greater than the image size is called a telephoto lens , telephoto lens , also known as a telephoto lens , the focal length of these lenses typically 150mm or more, mainly used to monitor more distant scenery . * Manual iris lens can be used with electronic shutter camera support, can be used in a variety of light. * Auto Iris Lens , (EF) can be used with any CCD camera supporting , can be used in a variety of light, especially for the monitored surface brightness changes, a wider range of places. In order to avoid the halo phenomenon and burn the target surface , usually with automatic iris lens. * Motorized zoom lens , CCD camera can be used with any matching can be used in a variety of light, zoom through a remote control device for optical focus, aperture opening, changing the focal length size. 6, the key performance indicators of the lens are the following: ( 1 ) Focus: Size focal length determines the size of the viewing angle , the focal length value is small, a large field of view , the observed range is also large, but the distance is not very clear to distinguish objects ; focal length value large, small FOV , a small observation range , just select the appropriate focal length , even very far away objects can be seen clearly. As the focal length and field of view is one to one , one to determine the focal length of the field would mean a certain angle , so the choice of lens focal length , should give full consideration to detail is an important observation , there are still a large range of important observations , If you look at the details on the choice of long focal length lens ; If you look close scenes , on the choice of a small focal length wide angle lens. ( 2 ) aperture factor : the luminous flux, represented by F to the lens focal length f and aperture D ratio to measure . Each lens is marked with the maximum F value, such 6mm/F1.4 represents the maximum aperture of 4.29 mm . Inversely proportional to the square of the flux and F value , F value is smaller , the greater the flux. The lens aperture value 1.4,2,2.8,4,5.6,8,11,16,22 standard index series , with its exposure before the law is a scalar value happens to be a scalar value corresponding to the amount of exposure after 2 times . That is the lens aperture are 1/1.4 and 1/ 2 , 1/2.8 and 1/ 4 , 1/5.6 , 1 / 8, 1 / 11, 1 / 16, 1 / 22 , the previous value is root of 2 times the value of the latter , so the smaller the aperture of the index , the larger the aperture , the imaging illumination target surface is greater. In addition there is the lens aperture manually (MANUAL IRIS) and auto- iris (AUTO IRIS) points. With the camera to use , suitable for manual iris little change in brightness of the occasion, it 's the amount of light by adjusting the aperture ring on the lens , one-time adjustment appropriate date . With auto iris lens will automatically adjust to changes in light , for outdoor use , such as changing light entrance large and frequent occasions. ( 3 ) Auto Iris Lens: Auto Iris Lens is currently divided into two categories: one is called Video (VIDEO) driven lens itself contains the amplifier circuit for video surveillance cameras came amplitude signals translate into aperture motor control . Another known direct current (DC) drive type , the imaging head using the direct control of the DC voltage to the aperture . This lens aperture contains only galvanometer motors require amplifier circuit inside the camera . For all types of auto iris lens, usually there are two adjustable knobs , one ALC adjustment ( metering adjustment ) , there are at peak and average metering Metering two options depending on the target emitting conditions, generally averaging metering files ; another is the LEVEL control ( sensitivity ) can be output image becomes bright or dim. ( 4 ) Zoom Lens : Zoom lens into manual (MANUAL ZOOM LENS) and electric (AUTO ZOOM LENS) two kinds , manual zoom lens is generally used for research rather than in closed-circuit surveillance system . When monitoring a lot of scenes, usually with an electric camera lens and pan to use. Benefits motorized lens zoom range is large , you can see both a wide range of situations , you can focus on certain details , plus the head can be rotated up and down around the viewing area is very big. Motorized lens 6 times, 10 times , 15 times, 20 times magnification other , if we know the basis of focal length, you can determine the variable range of the lens focal length . For example, a six -fold power of the lens , the focal length of 8.5 mm benchmark , its zoom range is continuously adjustable from 8.5 to 51 mm , depending on the angle of 31.3 to 5.5 degrees. Control voltage DC power lens is generally 8V ~ 16V, maximum current of 30 mA . So when choosing a controller , to fully consider the transmission cable length , if the distance is too far , the line voltage drop will cause the lens to produce uncontrollable need to improve or replace the video input control voltage with the host matrix decoder control . |
