CCTV lens 1
1. The type of lens (classified according to application)
• Wide-angle lens: The angle of view is more than 90 degrees, the observation range is large, and the image in the vicinity is distorted.
• Standard lens: The angle of view is about 30 degrees, and the range of use is wide.
• Telephoto lens: The angle of view is within 20 degrees, and the focal length can reach tens of millimeters or hundreds of millimeters.
• Zoom lens: The focal length of the lens is continuously variable. The focal length can be changed from wide-angle to telephoto. The longer the focal length, the greater the imaging.
• Pinhole lens: used for covert observation, often installed in places such as ceilings or walls.
2. The relationship between the size, distance and focal length of the object
Let the height and width of the subject be H and W, the distance between the subject and the lens be D, and the focal length of the lens be f. The imaging height and width of the target surface are h and w, respectively, then the calculation formula is as follows: f = h × D / H f = w × D / W
According to the above formula, the field angle can also be easily calculated. The table below shows the target surface size and imaging size. The target surface specifications are 1 "2/3" 1/2 "1/3" h 9.6mm 6.6mm 4.8mm 3.6mm w 12.8mm 8.8mm 6.4mm 4.8mm
3. Relative aperture
In order to control the amount of light flux passing through the lens, apertures are set at the rear of the lens. Assuming that the effective aperture of the aperture is d, due to the refraction of light, the actual effective aperture of the lens is D, which is larger than d. The ratio of D to the focal length f is defined as the relative aperture A, that is, A = D / f. The illuminance of the image is proportional to the square of the relative aperture of the lens. It is customary to use F = f / D, that is, the reciprocal of the relative optical path to indicate the size of the lens aperture. The smaller the F value and the larger the aperture, the greater the luminous flux reaching the CCD chip. So with the same focal length f, the smaller the F value, the better the lens.
4. The focal length of the lens
1) Fixed focal length: The focal length is fixed and can be divided into two types with and without aperture.
• Aperture: The size of the lens aperture can be adjusted. According to the change of ambient light, the size of the aperture should be adjusted accordingly. The size of the aperture can be adjusted manually or automatically. Manually adjusting the iris manually is called manual iris; the lens comes with a micro motor to automatically adjust the iris, called automatic iris.
• No aperture: the fixed aperture, the light flux is fixed. It is mainly used when the light source is constant or the camera comes with an electronic shutter.
2) Zoom distance: The focal length can be adjusted as needed to enlarge or reduce the image of the subject.
Commonly used zoom lenses are 6x and 10x zoom.
Three variable lenses: adjustable focal length, focus adjustment, dimming circle.
Two variable lenses: adjustable focal length, focus adjustment, automatic iris.
5. Principle of optional lens
In order to obtain the expected camera effect, when selecting lenses, we should pay attention to six basic elements:
A) The size of the object
B) Detail size of the subject
C) Object distance
D) Focal length
E) CCD camera target size
F) Note on the resolution of the lens and camera system:
Zoom lens-an optical system where the position of the focal plane is fixed and the focal path can be adjusted continuously. Zooming is achieved by moving the lens inside the lens and changing the relative position between them. This can change the focal length and angle of view of the lens within a certain range.
Focal length--the distance from the center of the lens or its second principal plane to the point where the image is focused. The unit is generally millimeters or inches.
Aperture--An adjustable optical mechanical stop located inside the camera lens can also be used to control the amount of light passing through the lens.
Automatic iris-the diaphragm device in the lens can be adjusted according to the video signal from the TV camera to adapt to changes in light intensity. The aperture diaphragm controls the light transmitted through the lens by opening or closing the aperture. The typical compensation range is 1000-1 to 300,000-1.
CCTV lens 2
The lens is the eye of the camera. Proper lens selection and good installation and adjustment are the first steps in clear imaging. Currently, 1/3 "lenses are the mainstream of applications, auto iris lenses are the most sold, and zoom lenses are the trend of application development.
1) The focal length of the fixed focal lens should be selected according to the distance from the camera to the monitored target.
From the focal length, there are short focal length wide-angle lens, medium focal length standard lens, and long focal length far lens. The focal length of the lens is usually expressed by value, and the aperture of the lens is generally expressed by F. The value of F is measured by the ratio of the focal length of the lens and the clear aperture d, F = f / d, and each lens is marked with its maximum F value.
2) The camera lens specifications should correspond to the camera CCD target size (1/2 "is 6.4hX4.8Ï…, 1/3" is 4.8hX3.6Ï…, 1/4 "is 3.2hX2.4Ï…). If the lens size When the size of the CCD target surface of the camera is inconsistent, the observation angle will not meet the design requirements, or the picture will be out of focus.
3) The horizontal and vertical visual degrees of the camera have the following relationship with the size of the CCD target surface of the camera hXÏ… and the focal length f of the lens: horizontal visual degree = 2arctan (h / 2f);
Vertical visual power = 2arctan (Ï… / 2f).
4) The lens is divided into auto iris and manual iris. The automatic iris is used for occasions where the light of the object changes a lot, and the manual iris is used where the light of the object is stable.
There are two driving methods for the automatic iris lens:
One type is the video input type Video driver (with Amp), which transmits a video signal and power from the camera to the lens to control the aperture on the lens. This video input type lens contains an amplifier circuit to transmit the camera The video signal is converted into the control of the aperture motor,
The other type is called DC driverno Amp, which uses the DC voltage on the camera to directly control the iris. This lens contains only the galvanometer iris motor, and there is no amplifier circuit in the camera. The two driving methods are not interchangeable, but universal automatic iris lenses are now available.
5) The lens is installed in two types, C type and CS type. The C type mounted lens has a 5mm ring between the CCD camera and the lens to adjust the aperture value. Type C mounted cameras can use CS type lenses, but CS mounted cameras cannot use type C lenses. Philips introduced the revolutionary Wizard lens installation wizard to ensure that the lens is fully compatible with the camera, which makes it possible to get the best image in any environment.
6) The zoom lens can change the focal length of the lens within a certain range within one lens, so it can enlarge or reduce the monitored object. Typical optical magnification specifications have different grades, such as 6 to 20 times, and are most commonly used with electric zoom lenses (Zoom Lens). The items that can be adjusted according to the zoom lens parameters are:
• Three variable lenses-the aperture, focus, and focal length all need to be adjusted manually.
• Two variable lenses-usually auto-iris lenses, and the focus and focal length need to be adjusted manually.
• Single variable lens——generally the lens with auto iris and auto focus, and the focal length needs to be adjusted manually.
7) Zoom / Zoom Lens (Vari Focal Lens) is a zoom lens with zoom lens function. The focal length is continuously variable, which can magnify distant objects, and also provides a wide view, which increases the monitoring width. Kowa Japan provides wide-angle lenses from 1.6 to 3.4mm to 15.0-300mm telephoto lenses.
8) In addition to the traditional spherical lens, the new generation is an aspherical lens (Aspherical Lens), the shape of the lens grinding is parabolic, quadratic, cubic or high-degree curve, and the phase difference and chromatic aberration of the lens are taken into account in the design , Spherical aberration and other correction factors, usually a single aspheric lens can achieve the effect of correcting aberrations of multiple spherical lenses, so the number of lenses can be reduced, making the lens more accurate, better definition, more accurate color reproduction, The light reflection in the lens is reduced, and the lens volume is reduced accordingly. Aspheric lens has the characteristics of high magnification, short object distance and large aperture. The high magnification can simplify the types of lenses, the short object distance can be used in close-up camera applications, and the large aperture can adapt to the dark places, so the application field is becoming wider. Japan's AVENIA's aspheric lens product SSV0770, the close-up distance can reach 30cm, the aperture value can also reach F1.6, the zoom range can be from 7.0 to 70mm, the zoom ratio is up to ten times, and it can be used in TV monitoring and other fields.
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