Principle of zoom and zoom of camera lens

zoom-refers to the change of focal length of zoom lens when shooting; Zoom-refers to the zoom multiple of a zoom lens. For example, a zoom lens with a wide-angle end of 28mm and a telephoto end of 28mm is called a 1-fold zoom lens.

The lens is the eye of the surveillance camera. Correct lens selection and good installation and adjustment are the * steps for clear imaging. At present, 1/3 "lens is the mainstream of application, and the sales volume of automatic aperture lens is zui, and zoom lens is the trend of application development.

1. the focal length of the fixed-focus lens should be selected according to the distance from the surveillance 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 a lens is usually represented by a value, and the aperture of the lens is generally represented by f, and the value of f is measured by the ratio of the focal length of the lens/to the aperture d of light, F=f/d, and each lens is marked with a value of f with a larger zui.

2. The lens specification of the surveillance camera should correspond to the CCD target size of the surveillance camera (1/2 "is 6.4hX4.8υ, 1/3" is 4.8hX3.6υ and 1/4 "is 3.2hX2.4υ). If the lens size is inconsistent with the CCD target size of the surveillance camera, the observation angle will not meet the design requirements, or the picture will be out of focus.

3. There are the following relationships between the horizontal vision and vertical vision of the surveillance camera and the CCD target size hXυ and the lens focal length F of the surveillance camera: horizontal vision = 2 arctan (h/2f); Vertical vision =2arctan(υ/2f).

4. The lens can be divided into automatic aperture and manual aperture. Automatic aperture is used in situations where the light of the illuminated object changes a lot, and manual aperture is used in places where the light of the illuminated object is stable.

there are two driving modes of automatic aperture lens: one is video input type Videodriver, which transmits a video signal and power supply from the monitoring camera to the lens to control the aperture on the lens. This video input type lens contains an amplifier circuit to convert the video signal from the camera into the control of the aperture motor, and the other is called DC input type, which uses the DC voltage on the camera to directly control the aperture. This lens only contains the galvanometer aperture motor, but there is no one in the camera. The two driving methods are not interchangeable, but now there are universal automatic aperture lenses.

5. There are two types of surveillance camera lenses: C-type and CS-type. The lens installed in C-type has a 5mm ring for adjusting the aperture value between the CCD surveillance camera and the lens. C-type cameras can use CS-type lenses, but CS-type surveillance cameras cannot use C-type lenses.

6. the zoom lens can make the focal length of the lens change within a certain range, so it can enlarge or reduce the monitored object. Typical optical magnification specifications have different grades, such as 6-2 times, etc., and zui is widely used in electric zoom lens. The items that can be adjusted according to the zoom lens parameters are:

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

two variable lenses-usually automatic aperture lenses, and the focus and focal length need to be adjusted manually.

Single variable lens-usually an automatic aperture lens and an automatic focusing lens, and the focal length needs to be adjusted manually.

7. Zoom/zoom lens is the function of zoom lens matching zoom lens. The focal length can be changed continuously, which can enlarge distant objects and provide a wide view to increase the monitoring width.

8. In addition to the traditional spherical lens, the new generation of surveillance cameras is aspheric lens. The grinding shape of the lens is parabola, quadratic curve, cubic curve or high-order curve, and the correction factors such as lens phase difference, chromatic aberration and spherical aberration are taken into account in the design. Usually, one aspheric lens can achieve the effect of correcting aberration of multiple spherical lenses, so the number of lenses can be reduced, and the lens accuracy, clarity and color reproduction can be improved. Aspheric lens has the characteristics of zoom height, short object distance and large aperture. Zooming in height can simplify the types of lenses, short object distance can be used in close-range surveillance cameras, and large aperture can adapt to dark places, so the application field is increasingly broad.