Fixed focus and zoom lens of camera
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, 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 of the lens f: 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 types of driving methods for automatic iris lenses: One 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 type of video input lens contains The amplifier circuit is used to convert the video signal from the camera into the control of the aperture motor. The other type is called DC input (DC driverno Amp). It uses the DC voltage on the camera to directly control the aperture. Only the galvanometer iris motor is included, 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. AVENIA Japan'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, and the magnification can be up to ten times, which can be used in TV monitoring and other fields.
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