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The choice of lens and main parameters
Name:admin  time2011.09.27  Read:

 Installation and debugging the camera:

 
Installation of lens: C type and CS type two kinds, both threads are 1 inches 32 teeth, 1 inches in diameter, the difference is the lens distance from target surface of different CCD, C mounting seat from the datum to the focal distance of 17.562 mm, than the CS distance CCD target face one more special loop length, CS distance focal distance of 12.5 mm. Don't look down on this a connecting ring, without it, the lens and camera can not normally focus, image blur. So in the installed in front of the camera, take a look at the camera and lens is it right? The same interface mode, if not, we need according to the specific circumstances or connecting ring. Some camera without connecting ring, and the afterimage adjusting ring (such as Panasonic products), regulation, use a screwdriver to loosen the adjustment ring screw, turn adjusting ring, the CCD target surface will be relatively fixed base backward (front) movement, also play a connecting ring. In addition (such as SONY, JVC) in a manner similar after adjusting ring, fixing screws it generally in the camera side, unscrew rear, a top gear adjustment, also can make the image clear without addition and subtraction connecting ring.
 
AGC ON/OFF (automatic gain control): the camera has a signal from the CCD amplifier to use video amplifier level, which is equivalent to the amount of gain, higher sensitivity, but in the light of the environment amplifier overload, the video signal distortion. When the switch is in the ON, fully open the lens aperture in low light conditions, automatically increase the gain to obtain clear image. The switch in the OFF, access to natural and low noise images in low light.
 
ATW ON/OFF (auto white balance): switch to the ON, through the lens to detect light character / color temperature, thus continuously and automatically set the white level, gain even features / color temperature change can also control the red and blue signals.
 
ALC/ELC (automatic brightness control / electronic brightness control): when choosing a ELC, electronic shutter according to the brightness of light and continuously and automatically change the exposure time of CCD image sensor (from 1/50 to 1/10000 seconds continuous regulation). This way, we can use fixed or manual zoom lens to replace the ALC auto iris lens.
 
Note: outdoors or in bright environment, because the ELC control is limited, should choose ALC lens; in some unique lighting conditions, may be any of the following circumstances:
 
There is a strong tailing or fuzzy phenomenon in the spotlight or windows of high brightness objects
 
The image was flash and color reproducibility instability
 
A periodic change in the white balance, if this happens, you should use the ALC lens.
 
To fix the lens aperture using ELC way, image depth may be less than the use of ALC type lens the depth of field. Therefore, the camera in the fully open fixed iris lens using ELC mode, the depth of field than using the ALC lens is small, but the image of distant objects may not be in focus.
 
When the lens is auto iris lens, will need to switch to ALC mode.
 
BLC ON/OFF (backlight compensation switch): when the background lighting powerful and useless affect central important object definition, should put the switch to the ON position.
 
Note: when the Haeundae and matched or lighting change rapidly, suggested that the switch is in the OFF position, because in the ON position, the lens aperture is slow;
 
If the required object images not in the middle, backlight compensation may not give full play to the role of.
 
LL/INT (synchronized switch): this switch is used to select the camera synchronization mode, INT as internal synchronous 2:1 interlaced synchronization; LL power synchronization. Some cameras and a LL PHASE power supply phase synchronization controller, when the camera is used in a power synchronization status, this device can adjust the output video signal phase, the adjustment range is probably a frame. (adjustment need professionals)
 
VIDEO/DC (camera control signal selection switch): the ALC control signal auto iris lens is two, when the auto iris lens DC control signal is arranged on the camera when, should choose the location of DC;
 
Need auto iris lens installed video control signal, should choose VIDEO position.
 
When choosing the ALC auto iris lens video driver, there will be a video level control (VIDEO LEVEL L/H) may need to be adjusted, control level of the controller output to the auto iris lens, is used to control the lens aperture opening and reduced (i.e., the amount of light).
 
In the camera accessories, a small plug of a black, plug has four pins, black socket connected with a camera. If auto iris lens driven by DC, the lens is ready to plug, as long as it is inserted in the socket, the selection switch to the DC; if the auto iris lens with the video driver, user needs according to the instructions on the label, with a soldering iron. Because manufacturers definition is different, so the welding method also has difference, attention please install.
 
SOFT/SHARP (detail level switch): the switch to regulate the output image is clear (SHARP) or smooth (SOFT), usually set in the SHARP position.
 
FLICKERLESS (no flashing mode): when the power supply frequency of 50 Hz area, CCD accumulation time is 1/50 seconds, if you use the NTSC camera, the vertical synchronization frequency is 60Hz, this will cause visual image is not synchronous, appear on the monitor flashing; otherwise, PAL camera in the power supply for the 60Hz region will this phenomenon. To overcome this phenomenon, in the electronic shutter set no flashing mode, the NTSC camera with 1/100 seconds, providing a fixed shutter speed of 1/120 sec of PAL camera, can prevent the emergence of the monitor image flicker. Manual electronic shutter: some users use CCD uptake velocity faster object, if taken with 1/50 seconds, will produce the tailing phenomenon, serious impact on image quality. Some cameras are manual electronic shutter, the charge coupling speed of CCD is fixed at a value, such as 1/500, 1/1000, 1/2000 second, then charge coupled CCD speed increase, so the captured image is relatively less tailing phenomenon, but also for the observation of a high-speed moving or electric spark a class object, you must use the set. So, some special camera gives manual electronic shutter, provided to the special user. Manual electronic shutter adjustments needed to see random instructions, will not repeat them here.
 
Note: there are a lot of user requirements with no light environment in the evening under control, please note: due to the CCD camera is also relies on light reflection to imaging, if there is no light, the image will only be dark with a lot of snow. How to get the image? A method is visible light, such as street lights, searchlights; one is combined with infrared light (especially requirements cannot install visible light occasions), for color CCD camera, not in response to infrared light, there are some day and night color camera at night will automatically turn into black and white pattern. So, monitoring system to your request to use at night, must adopt a monochrome CCD camera.
 
Infrared light is indoor, outdoor, short and long distances of the points, the commonly used laboratory 10~20 meters range of infrared light, because of the wall reflection, the image effect is good; in the room of long distance of infrared light effect is not very ideal, but the price is expensive, not necessary in general do not use.
 
The choice of lens and main parameters:
 
The camera lens is the key equipment of video surveillance system, its quality directly influences the whole (index) index, the camera so, camera lens selection is appropriate not only relates to the quality of the system, but also related to the project cost.
 
The lens is equivalent to the human eye lens, if there is no lens, the eye can not see any object; if no lens, then the camera image output is a vast expanse of whiteness, no image output clearly, this principle and we home video camera and the camera is the same. When the eye muscles not lens stretching to the normal position, it is often said that the myopia, the scene is blurred; with the camera and lens has a similar phenomenon, when the image is not clear, the focus can be adjusted after the camera, changing the distance of CCD chip and the lens (a reference surface to adjust the human lens position), can be fuzzy image becomes clear.
 
Thus, lenses in closed-circuit monitoring system is very important. Engineering design and construction personnel must often deal with lens: designers to calculate the focal length of the lens according to the object distance, image size, construction personnel often carries on the scene debugging, part of which is to adjust to the best state of lens.
 
Classification of 1, lens
 
According to the shape function
 
According to the size of division
 
Press the aperture is divided
 
Press the zoom type
 
Focal length divided by the moment
 
Spherical lens
 
1 "25mm
 
Automatic aperture
 
Electric zoom
 
Telephoto lens
 
Aspheric lens
 
1/2 "3mm
 
Manual Iris
 
Manual zoom
 
Standard lens
 
Pinhole lens
 
1/3 "8.5mm
 
Fixed aperture
 
Fixed focal length
 
Wide-angle lens
 
Fisheye lens
 
2/3 "17mm
 
(1) to the lens mounting classification of camera lens all are threaded, CCD camera lens is provided with two kinds of industry standard, namely C and CS mounting seat mounting seat. Both threads are part of the same, but both to the photosensitive surface of the distance from the lens of different. C installation: installation datum from the lens to the focal distance is 17.526mm. CS installation seat: special C installation, this should be the washer camera front removed to install the lens. The lens installation datum to the focal distance is 12.5mm. If you want to put a C mount lens mounted to a CS installation seat on camera, you need to use a lens converter. (2) the camera lens specifications classification
 
Camera lens specifications should be considered camera CCD size and decide, the two should be corresponding. That is
 
The CCD target surface size camera is 1 / 2 inches, the lens should be 1 / 2 inch.
 
The CCD target surface size camera is 1 / 3 inches, the lens should be 1 / 3 inch.
 
The CCD target surface size camera is 1 / 4 inches, the lens should be 1 / 4 inch.
 
If the size of lens and camera CCD target size is inconsistent, point of view will not comply with the design requirements, or the picture in focus outside of.
 
(3) the classification to the lens aperture
 
Lens with manual aperture (Manual Iris) and automatic aperture (auto iris) points, with the camera, manual zoom lens is suitable for applications in the same brightness, auto iris lens for brightness changes the aperture or automatic adjustment, which is suitable for the occasions brightness change. Auto iris lens has two kinds: one kind is a video signal and power from the camera is transported to the lens to control the lens aperture, known as the input for the video, the other is the utilization of the DC voltage on camera to directly control the aperture, known as the input for DC.
 
Auto iris lens on the ALC (automatic camera control) to adjust the settings for metering system, can the average brightness of the picture, can screen the brightest part (peak) to set the reference signal strength, supply automatic aperture adjustment. Generally speaking, ALC has been in the factory setting, can not be adjusted, but for the shooting scene contains a high brightness goals, images of a bright object may cause "white clip" phenomenon, and that all the screen turns white, at this time can be adjusted to change the picture ALC. In addition, auto iris lens with the aperture ring, turning the aperture ring, the luminous flux of the lens will change, the luminous flux is aperture, general F, the value of the focal length of the lens and the lens aperture ratio, namely: F = f (focal length) / D (real effective aperture lens), the F value is smaller, the larger the aperture.
 
Using auto iris lens, for the following applications is the ideal choice, they are:
 
In such as the sun is very bright, with auto iris lens can have a wide dynamic range.
 
Requires a good focus on the horizon, with auto iris lens have greater than fixed iris lens depth of field.
 
In light of fuzzy because of the light signal causes the most hours, should use the auto iris lens.
 
(4) with field size classification of lens
 
Standard lens: from the angle of 30 degrees, in the 1 / 2 inch CCD camera, standard lens focal length is set to 12mm, in the 1 / 3 inch CCD camera, lens focal length is set to 8mm standard.
 
Wide-angle lens: from the angle of 90 degrees, the focal length is less than a few mm, can provide visual wide.
 
Telephoto lens: from the angle of 20 degrees, the focal length can reach several meters or tens of meters, this lens objects can be amplified in remote camera case, but that the observation is smaller.
 
Zoom lens (zoom lens): also known as the telescopic lens, a manual zoom lens and electric zoom two.
 
The variable focus lens (vari-focus lens): it is between the standard camera with wide-angle lens, focal length continuously variable, distant objects can be amplified, but also can provide a broad vision, the monitoring range increased. Zoom lens can be set through the automatic focusing on minimum focal length and maximum focal length two position, but from the minimum to maximum focal length between the focal length of focus, will be achieved by manual focus.
 
Pinhole lens: lens of a few millimeters in diameter, can be concealed installation.
 
(5) from the focal length of the lens.
 
Short focal length lens: because the incident angle is wide, can provide a wide field of vision.
 
In focal length lens: standard lens, focal length as the size of the CCD.
 
Telephoto lens: because the angle of incidence is relatively narrow, so it can only provide a narrow view, suitable for long distance monitor.
 
Zoom: usually electric type, can be used for wide-angle, standard or Yuanwang, lens.
 
2, choose the technical basis of lens
 
(1) the size of the imaging lens
 
Should be consistent with the camera CCD target size, as mentioned before, there are 1 inches, 2 / 3 inch, 2 inch, 1 / 1 / 3 inch, 4 inch, 1 / 1 / 5 inch size.
 
(2) the lens resolution
 
Internal index to describe the imaging quality of lens is a lens of the optical transfer function and distortion, but to support, need to know is only the space resolution of the lens, to the number of black and white striped per mm can identify as the units of measurement, the formula for the calculation of the lens resolution: N = 180 / format height. Because of the size of camera CCD target surface have been standardized, such as 1 / 2 inch camera, the target face is 6.4mm wide * high 4.8mm, 1 / 3 inch camera width 4.8mm * 3.6mm. So the CCD target of 1 / 2 inch format, the minimum resolution of the lens should be 38 line / mm, 1 / 3 inch format camera, camera resolution should be greater than 50 on the line, the target surface camera is smaller, the higher resolution of the lens.
 
(3) the focal length of the lens and the angle of view
 
According to the camera to the monitored object distance, choice of the focal length of the lens, the focal length of the lens f is determined, the camera target plane determines the view.
 
(4) the aperture or the amount of light
 
The amount of light to measure the ratio of lens with focal length of the lens and aperture, with F as the marker, each shot is marked with its largest F value, the amount of light is inversely proportional to the square of the F value, F value is smaller, the larger the aperture. It should be to choose aperture manual or auto iris lens light changes degree of partial monitored.
 
3, the zoom lens (zoom lens)
 
Zoom lens with manual zoom lens and automatic telescopic lens two categories. Telescopic lens makes the focal length of the lens changes within a certain range in a single shot, it can make the monitored target zoom in or out, so it is often called the zoom lens. Typical optical amplifier specifications are 6 times (6.0~36mm, F1.2), 8 times (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 the like, and the electric telescopic lens is the most widely used. In order to increase the magnification, besides the optical amplification may also impose electronic digital amplification. In the electric telescopic lens, aperture adjustment has three kinds, namely: automatic aperture, DC drive automatic aperture, electric adjustment aperture. The focus and zoom adjustment, only the electric adjustment and preset two, electric adjustment is driven by the motor in the lens, and the preset is through the potentiometer lens setting adjustment stop bit, this eliminates imaging process must be gradual adjustment, accurate and fast positioning. In the spherical cover integrated camera system, most of the telescopic lens preset.
 
Another so that users are interested in fast focusing function, comprising focus measurement system and electric zoom feedback control system.
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