The lens is the eye of the camera. The correct selection of the lens and good installation and adjustment are the first steps for clear imaging. At present, 1/3" lens is the mainstream of application, auto iris lens has the most sales volume, and zoom lens is the trend of application development.

1) The focal length of the fixed focal lens (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 lenses, medium focal length standard lenses, and long focal length tele lenses. The focal length of the lens is usually expressed by a value, and the lens aperture is generally expressed by F. The value of F is measured by the ratio of the focal length of the lens to the clear aperture d, F=f/d, and each lens is marked with its maximum F value.

2) The lens specification of the camera should correspond to the size of the camera CCD target surface (1/2" is 6.4hX4.8υ, 1/3" is 4.8hX3.6υ, 1/4" is 3.2hX2.4υ). 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 vision of the camera have the following relationship with the camera CCD target surface size hXυ and the lens focal length f: horizontal vision = 2arctan (h/2f); vertical vision = 2arctan (υ/2f).

4) The lens has auto iris (auto iris) and manual iris (manual iris). The automatic iris is used for the occasions where the light of the illuminated object changes frequently, and the manual iris is used for the stable light of the illuminated object.

There are two 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 iris motor. The other type is called DC input type (DC driverno Amp), which uses the DC voltage on the camera to directly control the iris. Only the galvanometer type iris motor is included, and there is no amplifier circuit in the camera. The products of the two drive modes are not interchangeable, but a general-purpose automatic iris lens is now available.

5) There are two types of lens installation: C-type and CS-type. The C-type lens has an extra 5mm ring between the CCD camera and the lens to adjust the aperture value. C-mount cameras can use CS-type lenses, but CS-mount cameras cannot use C-type lenses. Philips launched a revolutionary Wizard lens installation guide 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 a lens, so it can enlarge or reduce the monitored target. Typical optical magnification specifications have different grades such as 6 to 20 times, and the most common application is a motorized zoom lens (Zoom Lens). The adjustable items according to the zoom lens parameters are divided into:

· Three variable lens-aperture, focus and focal length need to be adjusted manually.

· Two variable lens-usually an automatic iris lens, and the focus and focal length need to be adjusted manually.

· Single variable lens—usually an auto iris and auto focus lens, and the focal length needs to be adjusted manually.

7) Vari Focal Lens (Vari Focal Lens) is a zoom lens with zoom lens function. The focal length is continuously variable, which can magnify long-distance objects and provide a wide view to increase the monitoring width. Kowa of Japan provides wide-angle lenses ranging from 1.6 to 3.4mm to telephoto lenses ranging from 15.0 to 300mm.

8) In addition to the traditional spherical lens, the new generation of aspheric lens (Aspherical Lens), the shape of the lens grinding is parabola, quadratic curve, cubic curve or high-order curve, and the lens phase difference and chromatic aberration are considered in the design , Spherical aberration and other correction factors, usually one aspheric lens can achieve the effect of multiple spherical lenses to correct aberrations, so the number of lenses can be reduced, so that the lens has better precision, better definition, and more accurate color reproduction. The light reflection in the lens is reduced, and the lens volume is reduced accordingly. The aspheric lens has the characteristics of high zoom, short object distance and large aperture. The zoom height can simplify the types of lenses, the short object distance can be applied to the occasions of close-up photography, and the large aperture can adapt to the dark places, so the application field is becoming wider. Japan 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, and the zoom ratio can be up to ten times. It can be used in television monitoring and other fields.