Identify the advantages and disadvantages of the surveillance lens from the appearance, mainly pay attention to the following points: First, look at the delicateness of the appearance of the surveillance lens; second, feel the feel of the surveillance lens, and thirdly, look at the coating and feel the amount of light passing through the surveillance lens. These are just a look at the basics of the surveillance lens. Then, from the lens parameters, how should we interpret the surveillance lens? How to identify the monitor lens is the best surveillance lens?
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Everyone knows that engineering designers and construction personnel should always deal with the lens: the designer must calculate the focal length of the lens according to the object distance and imaging size, and the construction personnel need to perform on-site debugging and installation. The lens interface specifications, lens target size, amount of light, minimum object distance, and even temperature changes in the environment can affect the imaging performance of the lens. Today, the author and the engineers of the Shenzhen Supersonic AVENIR ETOKU Seiko lens talked about how to monitor the lens's advantages and disadvantages by monitoring these parameters.
Understand the matching degree of the surveillance lens from the basic parameters
Why do you need to consider the size of the imaging size 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 precision lens: "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 selected monitor lens size is smaller than the camera target size, the monitor screen will appear vignetting. If the monitor lens size is larger than the camera target surface, the monitoring angle of the monitor screen will become smaller. The best match is to match the size of the monitor lens to the size of the camera's target. â€
The standard interface of the monitoring lens is divided into C interface and CS interface. The interfaces of all cameras are threaded interfaces. The threaded parts of the C interface and the CS interface are the same, but the distance from the flange surface of the lens to the surface of the CCD/COMS. different. The distance between the lens of the CS interface and the photosensitive surface of the camera is 12.5mm, and the distance between the monitoring lens of the C interface and the photosensitive surface of the camera is 17.526mm. To install the monitoring lens of the C interface to the camera of the CS interface, a 5MM adapter ring is needed. .
The actual effect of the amount of light passing through the monitor lens
In the video surveillance engineering application, many users and engineers are very confused about how to choose an excellent lens. We all know that a good lens product can be combined with a good camera to show excellent imaging results. There is also a lot of knowledge about judging the F value of the surveillance lens.
The F value is the main indicator for judging the amount of light passing through the lens. It is the ratio of the focal length of the lens to the aperture of the light. In the case of a fixed focal length, the larger the aperture is, the smaller the F value is, indicating that the light passing capability of the monitoring lens is stronger. The smaller the F value of the monitor lens, the better the lens is. For example, in the case of a fixed focal length of the monitor lens, the F1.0 lens is compared with the F1.2 lens, it goes without saying that F1. The lens of 0 is better. However, it is true that the difference between F1.0 and F1.2 is only in the case of dark light. In a darker environment, a lens with a small F value may still see a little image, while a lens with a large F value can no longer see the image. However, in practical applications, both the construction personnel and Party A have found that the image observed at this time with a small F value does not achieve the purpose of monitoring. In actual engineering, it is necessary to add a fill light to meet the actual monitoring. Claim. In the case of sufficient light, the difference between the two is not obvious. At the same time, in the optical design process of the monitoring lens, in order to make the amount of light passing through it better, the depth of field of the monitoring lens is inevitably shortened, and the range that can be seen clearly is smaller than that of the monitoring lens of F1.2. To put it simply, in places where there is a large flow of people such as school gates and subway exits, it is necessary to see the characters in the range of the front and rear of the field of view at the same time. The effect of the F1.2 monitor lens is much better than that of F1.0. In terms of cost, the investment of the F1.0 surveillance lens and the F1.2 surveillance lens is not 1:1.2. In order to make the F value of the monitoring lens reach F1.0, the cost of the F1.2 monitor lens is at least double. The F value is the main cost of the lens.
At the same time, due to the application of infrared technology, the requirements of the night vision effect of the lens are improved, and the myth that the F value is smaller is better. In the actual monitoring project, to achieve real monitoring, the addition of infrared fill light can fully complement the problem caused by the slightly smaller F value of the monitoring lens. Therefore, we must remind everyone to pay attention not to blindly choose a lens with a small F value, and do not blindly think that a lens with a small F value can satisfy all requirements. Lens with a small F value is more expensive, so don't buy an inapplicable lens at an expensive price.
The effect of the driving method on the lens
In the auto iris lens, the aperture is driven by a motor. There are two kinds of aperture driving methods currently on the market, one is video driving, and the other is DC DC driving. The video-driven industry standards are consistent, but they are gradually fading out due to their high price, the slow penetration of high-definition surveillance, and the upgrade and transformation of traditional analog surveillance systems. The standards of DC DC drive are different. When selecting a DC-driven monitor lens, pay special attention to the matching of the current impedance to the camera impedance. For example, the AVENIR ETOKU Seiko lens of Shenzhen Supersonic Electronics Co., Ltd. has a braking impedance of most 500 Ω. The braking impedance of the Tamron lens is also 500 Ω. If the impedance of the monitoring lens is inconsistent with the camera impedance, the lens may flicker and whitish. , directly affect the monitoring screen. If this is the case, you can adjust the brightness level of the camera to adjust the brightness of the camera to achieve the best match between the camera and the lens.
Focal length, field of view and distortion
In optical design, the surveillance lens has two main points, one main main point and one secondary main point. The distance between the secondary main point and the focus determines the focal length of the lens. The size of the focal length determines the distance of the object monitored by the surveillance lens from the lens. The smaller the focal length, the larger the angle that the monitor lens can monitor. This monitoring angle is called the angle of view.
Focal length, field of view and distortion
According to AVENIR ETOKU Seiko lens engineer: "Because of the optical characteristics of the monitor lens, the zoom lens is generally large at its wide-angle end - even more than 50% distortion, any monitor lens is no exception. For example According to the theoretical value, the angle of view is only about 60°. However, due to distortion, the imaging angle of the monitor lens can reach more than 110 degrees. It is worth mentioning that the distortion of the monitor lens is not Affecting the sharpness of its imaging, it has the effect of a mirror, which makes the image within the distortion range of the edge of the field of view slightly deformed. If a large monitoring angle is required, proper distortion is acceptable. However, in practical applications, In the fields of intelligent transportation, machine vision, etc., because of the specific operation, it is required to see the number of license plate numbers, etc. The lens used is not allowed to have distortion or the distortion requirement is small."
From the parameters, we mainly use the above points as the main basis for identifying the surveillance lens. Selecting the surveillance lens is not blindly pursuing the optimal combination of all parameters. The optimal monitoring lens, such as the Japanese surveillance lens, is expensive, and the overall cost of the project is of course up. The right choice should be based on the engineering environment we use, our monitoring needs, choose the most suitable monitoring lens, enough for us to use, and to save engineering investment, is the best choice. The monitoring lens is ultimately attributed to the monitoring project. In the actual case of various projects, how should we choose the monitoring lens and how to look at the monitoring lens? In the next issue, we will continue to explore.
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