The lens is the eye of the camera, and its performance is directly related to whether the camera image is clear. Therefore, in order to maximize the performance of the camera, in addition to the camera's own camera components and circuit design, you need to choose a suitable lens.
Security monitoring system lens selection
1. Lens focal length: When considering the lens index, the solution designer needs to comprehensively consider the position, distance, CCD specification of the monitoring target, and the image effect of the monitoring target on the monitor to select the lens with the most suitable focal length. . For example, production line monitoring generally requires monitoring of relatively close objects and requires high definition. In this case, the effect of the fixed-focus lens is generally better than that of the zoom, so a short focal length fixed-focus lens is usually selected. Such as 2.8mm, 4mm, 6mm, 8mm and so on.
Another example is to monitor the indoor target, the selected focal length will not be too large, generally choose a short focal length manual zoom lens, such as 3.0-8.2mm, 2.7-12.5mm, etc.; in road monitoring, multi-lane monitoring should use a shorter focal length For example, 6-15mm; traffic lights at intersections should be monitored with a correspondingly longer focal length, such as 6-60mm; urban surveillance should generally use a longer-focus motorized zoom lens, such as 6-60mm, 8-80mm , 7.5-120mm, etc.; highways, railways, rivers, environmental detection, forest fire prevention, airports, coastal defense, etc., generally use large variable power and long focal length motorized zoom lens, such as 10-220mm, 13-280mm, 10- 330mm, 15-500mm and 10-1100mm, etc.
2. Field of view angle range: There is a formula for calculating the angle of view of the field of view. Knowing the focal length of the lens, the size of the CCD, and the angle of view can be calculated. The lens has such a rule: the larger the focal length, the farther the monitoring is, the smaller the angle of view; the smaller the focal length, the closer the monitoring distance, the larger the angle of view, and the inverse relationship between the focal length and the angle of view. As in some projects with manual zoom lens requirements, the field of view angle is the first to be considered, so the selected focal length range is generally determined based on the field of view angle range. The motorized zoom lens can control the zoom and focus at any time according to the scene environment, so the field of view angle range is not too much to consider. However, when the starting focal length of the motorized zoom lens is too large (such as the starting focal length exceeds 20 mm), it is impossible to achieve wide-range monitoring.
3. Aperture of the lens: The amount of light passing through the lens is measured by the ratio of the focal length of the lens to the aperture of the light (F=f/D), marked with F. Each lens is marked with its maximum F value, and the smaller the F value, the larger the aperture. For constant lighting conditions, a fixed aperture lens can be used. This is generally a laboratory environment. For environments where the illuminance changes are not obvious, a manual iris lens is often used. After the aperture is adjusted to an ideal value, it can be fixed. If the illuminance changes a lot, 24 hours of all-weather outdoor monitoring is required, and an automatic iris lens should be used.
Monitoring lens application
Fixed aperture lens: fixed focus and fixed aperture, mainly used in places where ambient light is fixed;
Manual aperture lens: fixed focus but adjustable aperture, mainly used in places where ambient light is fixed but the brightness is uncertain;
Auto iris lens: fixed focal length, using DC voltage to drive a fixed range of places for ambient light variability;
Auto iris lens: fixed focal length, using a video signal to drive a fixed range of locations for ambient light variability;
Manual iris zoom lens: mainly used in indoor environments where the light level is variable and the range is different;
Auto iris zoom lens: mainly used in places where the ambient light level is variable and the range is different;
On-Board: It is mainly equipped with an infrared camera, suitable for indoor and outdoor use;
Fisheye panoramic lens: It is mainly used in indoor environment where the light level is variable and the range is specific;
Power zoom lens: remote focus depth and aperture can be remotely controlled. It is mainly used for indoor and outdoor environments where the light level is variable and the depth of field can be adjusted according to requirements.
Pin-Hole: It is mainly used for hidden surveillance and ambient light-specific and range-specific locations.
Test pace
1. clarity
When using multiple surveillance cameras for testing, the same lens should be used (recommended for fixed focus, two variable lenses), and the center circle of the test card appears on the left and right sides of the monitor screen, clearly and accurately counted out. The tick marks a total of 10 sets of vertical lines and 10 sets of horizontal lines. They represent vertical and horizontal resolution, respectively, and the corresponding set of lines has been given. If the vertical 350 line level is 800 lines, it is best to use a black and white monitor at this time. You can focus on the distant object during the test, or focus on the side. It is best to use both, and you can see the difference in this camera (convergence in the distance).
2. Color reduction
Test this parameter should choose a good color monitor. First, observe the characters and costumes from a distance, see if there is any color distortion, compare the objects with bright colors, look at the sensitivity of the camera response, put the color album in front of the camera, and see the picture is clear, too light or too thick, and respond to the movement again. The color object is photographed to see if there is color tailing, delay, blur, etc. The test condition is such that the maximum illumination of the camera should be measured at 50+10V illumination at 50V, that is, 10 volts is added to the maximum illumination of each camera, and the aperture should be kept in the closest state.
3. Illuminance
The camera is placed in the dark room, and the active room 220V is self-illuminating before and after the dark room. A voltage regulator is arranged to adjust the voltage of the dark room to adjust the voltage of the dark room. The voltage can be adjusted from 0V to 250V. The indoor illumination can also be adjusted from the darkest to the brightest. When the camera aperture is turned to the maximum during the test, the next minimum illumination value is recorded. (The active lamp is dimmed to the inside of the darkroom.) After hitting the minimum, the next minimum illuminance value is recorded, and the front and rear lights can be separately pressed and extinguished.
4. Backlight compensation
There are two ways to test this parameter: one is to open the front side of the camera in the dark room, adjust to the brightest, then place a picture or text below the light, the camera to the camera, see the image and Whether the text can be seen clearly, the picture is not glaring, and adjust the AL, AX pull switch to see if there is any change, which effect is best. The other is to take the camera out of the window in the sun, and see if the image and text can be seen clearly.
5. Spherical distortion
Look at the spherical distortion. Place the test card on the front of the camera so that the whole sphere appears on the screen. See if the sphere has an ellipse, move the camera forward, see if the center of the circle is enlarged, and then test the edge, corner, and frame with or without arc. Shape distortion and so on.
6. Power consumption
The minimum operating voltage, use a multimeter to measure the current, use a small regulator to adjust the voltage.
Lens common troubleshooting
The high performance of the monitoring system depends on the perfect combination of the camera and the lens. In the monitoring project, if the professional skills of the user or the construction personnel are insufficient, the camera and lens selection and installation are unreasonable, which will directly affect the overall effect of the system. . Summarize some common but easily overlooked issues during the lens installation process for your reference.
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