Learn the advantages and disadvantages of surveillance cameras from several important parameters

As we all know, engineering designers and construction workers must always deal with the lens: the designer needs to calculate the focal length of the lens according to the object distance and imaging size, and the construction personnel need to conduct on-site debugging and installation. The interface specifications of the lens, the size of the lens target surface, the amount of light passing, the minimum object distance, and even the temperature change of the environment in use will affect the imaging effect of the lens. This article will explain in detail how to monitor the lens parameters to understand the quality of surveillance cameras.

Understand the matching degree of monitoring lens from basic parameters

Why do I need to consider the size of the image when selecting the lens? Because the imaging size is one of the important parameters to determine whether the monitoring lens matches. According to the senior engineer of the supersonic AVENIRETOKU Seiko lenses, “The imaging size commonly used for surveillance cameras is generally 1/3” 1/2.7 “1/2.5”, 1/1.8”, 1/2”2/3 “1”, etc. specification. If the size of the monitoring lens selected is smaller than the target size of the camera, a hidden corner will appear on the monitoring screen. If the surveillance lens size is larger than the target of the camera, the monitoring angle of the surveillance screen will be smaller. The best match is that the size of the surveillance lens matches the size of the target of the camera. “

The standard interface for surveillance cameras is classified into two types: C interface and CS interface. The interfaces of all cameras are threaded interfaces. The threads of C interface and CS interface are the same, but the distance from the flange surface of the lens to the surface of the CCD/COMS is the same. different. The distance from the CS interface lens to the camera surface is 12.5mm, the distance from the C interface monitor lens to the camera surface is 17.526mm. .

The actual impact of the amount of light on the surveillance camera

In the application of video surveillance engineering, many users and contractors are confused about how to choose a good lens. We all know that good lens products and good cameras can show excellent imaging results. There is also a lot of knowledge about judging the F value of a surveillance camera.

The F value is the main indicator of the amount of light passing through the lens. It is the ratio of the focal length of the lens to the clear aperture. In the case of a fixed focal length, the larger the clear aperture, the smaller the F value, indicating that the monitoring lens has a stronger light transmission capability. The smaller the monitoring lens F, the better the lens is. For example, in the case of monitoring the focal length of the lens, F1.0 lens compared with F1.2 lens is self-evident, F1.0 lens light better. However, the real difference between F1.0 and F1.2 is only in the dark. In a dark environment, a lens with a small F value may still see a bit of an image, while a lens with a high F value cannot see the image. However, in practical applications, both construction workers and Party A have found that the little image observed by the lens with a low F value cannot achieve the monitoring purpose. To achieve real monitoring in the actual project, it is still necessary to add a light to meet the needs of monitoring. Claim. In the case of adequate light, the difference between the two is not obvious. At the same time, in the process of optical design of the monitoring lens, in order to allow better light transmission, the depth of field of the monitoring lens is inevitably shortened, and the range that can be seen is smaller than that of the F1.2 monitoring lens. Simply put, in areas where people's gates, subway exits, etc., have a large flow of people, it is necessary to see clearly the people in the front, rear, left, and right scopes at the same time. The effect of F1.2 surveillance cameras is much better than that of F1.0. In terms of cost, the input of F1.0 surveillance cameras and F1.2 surveillance cameras is not 1:1.2. In order to make the monitoring lens's F value reach F1.0, the cost of the F1.2 monitoring lens is at least doubled. The F value is the main cost input for the lens.

At the same time, due to the application of infrared technology, the night vision requirements of the lens increase, and the smaller the F value, the better the myth. In the actual monitoring project, to achieve true monitoring, the addition of infrared fill light can completely make up for the problem that the monitoring lens F value is slightly smaller. Therefore, we must remind everyone not to blindly choose a lens with a small F value. Do not blindly believe that a lens with a small F value can meet all requirements. A lens with a small F value is more expensive, so don't spend an expensive price on an unsuitable lens.

Drive effect on the lens

In an auto iris lens, the aperture is driven by a motor. There are two types of aperture driving methods available on the market. One is video drive, and the other is DC DC drive. Video-driven industry standards are the same, but gradually fade out of the market due to their high prices, slow penetration of high-definition monitoring, and the upgrading and transformation of traditional analog surveillance systems. The standards for DC-DC drives are not the same. When selecting a DC-DC monitor lens, special attention must be paid to the matching of the current impedance and the camera impedance. For example, Shenzhen Supersonic Electronics Co., Ltd. AVENIR ETOKU Seiko lens most of the braking impedance of 500Ω, Tamron lens braking impedance is mostly 500Ω, if the monitor lens impedance and camera impedance are inconsistent, easily lead to the lens screen flicker, white , directly affect the monitoring screen. If you encounter such a situation, you can adjust the camera's brightness level value to adjust the camera control brightness in order to achieve the best match between the camera and the lens.

Focal length, field angle and distortion

In the optical design, the surveillance lens has two main points, a main main point and a minor main point. The distance between the main main point and the focal point determines the focal length of the lens. The size of the focal length determines the distance that the surveillance camera monitors from the lens. The smaller the focal length, the larger the angle at which the surveillance lens can monitor. This surveillance angle is what we call the field angle.

According to the AVENIR ETOKU Precision Lens Engineer, "Because of the optical characteristics of the monitor lens, the zoom lens will generally be larger at its wide-angle end - even with a distortion of more than 50%, and any surveillance camera is no exception. For a lens with a focal length of 2.8mm, according to theoretical values, the viewing angle is only about 60°, but due to distortion, the resulting surveillance lens imaging angle can reach more than 110 degrees.It is worth mentioning that the distortion of the monitoring lens is not Affecting the sharpness of its imaging, it has the effect of a magic mirror, so that the picture in the distortion range of the edge of the visual field is slightly deformed.If a larger monitoring angle is required, appropriate distortion is acceptable, but in practical applications, Intelligent transportation, machine vision and other fields, because of their specific operations, require the need to see the license plate numbers, and the use of the lens does not allow distortion to exist or that the distortion requirements are small.

From the parameters, we mainly use the above points as the main basis for identifying surveillance cameras. Selecting the monitoring lens is not blindly pursuing the best combination of all the parameters of the monitoring lens, the optimal monitoring of the parameters of the lens, such as Japanese surveillance cameras, expensive, the overall cost of the project, of course, up. The correct choice should be based on the engineering environment we use, our monitoring needs, choosing the most suitable surveillance lens, enough for us to use, but also saving the project investment, is the best choice.