- Detail

CCTV CCTV CCTV camera introduction

1) what is the meaning of CCTV

cctv is the abbreviation of closed circuit television in English, which means closed circuit television monitoring system

2) what is the focal length of a lens

in terms of optical principle, the focal length is the distance from the focus to the center of the lens. Focal length. For example, "f=mm,", which means that the focal length of the lens is mm

3) what is the relationship between the focal length and the size of the imaging angle

the length of the focal length is proportional to the size of the image. The longer the focal length, the larger the image, and the shorter the focal length, the smaller the image. The length of the lens focal length is inversely proportional to the size of the viewing angle. The longer the focal length, the smaller the viewing angle, and the shorter the focal length, the larger the viewing angle

4) what is the relationship between focal length and depth of field perspective

the length of focal length is inversely proportional to the depth of field. The longer the focal length, the smaller the depth of field, and the shorter the focal length, the greater the depth of field. The length of focal length is inversely proportional to the strength of perspective. The longer the focal length, the weaker the perspective, and the shorter the focal length, the stronger the perspective

5) what is the back focus adjustment of the camera

when a standard lens is installed, in order to make the image of the subject exactly on the target surface of the CCD image sensor, a fixed lens can be used, and adjusting the position of the CCD is an ideal detection device with simple operation, convenient use and stable performance. This method is called the rear focus bar adjustment of the camera

6) what is the lens F value

f value refers to the brightness of the lens. The F value is ＜ 1.2 ＞ of ＜ maximum aperture ratio 1:1.2 ＞ shown in the lens specification. The smaller the value of F should be adjusted, the higher the brightness of the lens. Every time the F value is reduced by one level, the brightness will increase by two times. The amount of light emitted by the lens is proportional to the sectional area of the beam [the square of the effective aperture of the lens [d], so the brightness of the image is the inverse ratio of the square of the F value. From this calculation, the brightness will increase by two times when the F value is reduced by one stage

7) what is the aperture of a lens

The function of the aperture is like the toad of our human eyes, which is mainly used to adjust the light input of the camera. F represents the aperture of the lens, and a smaller F value represents a larger aperture8) what is the depth of field

when an object is clearly focused, all the scenes from a certain distance in front of the object to a certain distance behind it are also clear. The distance from front to back with clear focus is called depth of field

9) what is a wide-angle lens? (wide, but the longer the time, the greater the damage caused by the circuit angle)

because the focal length of the wide-angle lens is very short, the scenery projected on the base film becomes smaller, and the shooting angle of the expanded lens is widened. In addition to shooting more scenery, it can shoot wide-angle images in a narrow environment. The viewing angle is more than 90 degrees, the observation range is large, and the near image is deformed

the pendulum and sample base can be replaced 10) what is a telephoto lens

the focal length can reach tens of millimeters or hundreds of millimeters within 20 degrees of viewing angle

11) what is a zoom lens

the focal length of the lens is continuously variable, and the focal length can be changed from wide-angle to telephoto. The longer the focal length, the larger the imaging

12) what is optical zoom

zoom is realized according to the optical lens structure, which is to enlarge and reduce the scene to be shot through the lens movement. The larger the optical zoom factor is, the farther the scene can be shot

13) what is a triple variable lens

aperture, focus and focal length need to be manually adjusted

14) what is a two variable lens

is usually an automatic aperture lens, and the focus and focal length need to be manually adjusted

15) what is the video drive of the lens? (video driver)

it transmits a video signal and power supply from the camera to the lens to control the aperture on the lens. This video input lens contains an amplifier circuit to convert the video signal from the camera into the control of the aperture motor

16) what is DC driverno amp?

it uses the DC voltage on the camera to directly control the aperture. This kind of lens only contains galvanometer aperture motor, and there is no amplifier circuit in the camera. The products of the two driving modes are not interchangeable, but universal automatic aperture lenses have been launched

17) what is the difference between C-type interface and CS type interface

there are two types of lens installed: C type and CS type. The lens installed in C type has an additional 5mm ring between the CCD camera and the lens to adjust the aperture value. C-type cameras can use CS lens, but CS installed cameras cannot use C-type lens

18) what is an aspheric lens? (aspheric lens)

the shape of lens grinding is parabola, quadratic curve, cubic curve or high-order curve, and the correction factors such as phase difference, color difference and spherical aberration of lens are considered in the design. Usually, one aspheric lens can achieve the effect of correcting the image difference of multiple spherical lenses, so the number of lenses can be reduced, making the lens more accurate, clearer and more accurate color restoration The reflection of light in the lens is reduced, and the volume of the lens is reduced accordingly. Aspheric lens has the characteristics of variable magnification, short object distance and large aperture. Zoom height can simplify the type of lens, short object distance can be applied to close-up camera occasions, and large aperture can adapt to dark places, so the application field is becoming wider and wider. The aspheric lens product ssv0770 from avenia in Japan has a close-up distance of 30cm

19) what is the relative aperture of the lens

in order to control the amount of luminous flux passing through the lens, aperture is set at the rear of the lens. Assuming that the effective aperture of the aperture is D, due to the relationship between light refraction, the actual effective aperture of the lens is D, which is larger than D. the ratio of D to focal length f is defined as the relative aperture a, that is, a=d/f. The relative aperture of the lens determines the illumination of the camera. The illumination of the image is proportional to the square of the relative aperture of the lens. Generally, it is customary to use f=f/d, that is, the reciprocal of the relative aperture to express the size of the lens aperture. The smaller the F value, the larger the aperture, and the greater the luminous flux reaching the CCD chip. Therefore, when the focal length f is the same, the smaller the F value, the better the lens

20) what is the field angle

we often use the field angle to represent the range of the observed scene. The so-called field of view angle means that all the objects in the field of view angle can fall into the imaging size, while the objects outside the field of view angle will not be captured. Therefore, the field angle of the lens is related to the target surface of the camera and the focal length of the lens

according to the geometric principle, the calculation formula of field angle can be obtained as follows:

α= 2tg-1（h/2f） β= 2 tg-1 (v/2f)

where α Is the horizontal field angle, β Is the vertical field angle, f is the focal length of the lens, h is the horizontal width of the camera target, and V is the vertical height of the camera target

when the imaging size is determined, the shorter the focal length, the larger the field angle. Therefore, the lens can be divided into Long-Angle lens (the field angle is less than 45 °), standard lens (the field angle is 45 ° ~ 50 °), wide-angle lens (the field angle is greater than 50 °), ultra wide-angle lens (the field angle is close to 180 °), fish eye lens (the field angle is greater than 180 °), etc. (end)

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