Four key points to identify video surveillance HD lens

The high-definition lens with high-definition camera has become an obvious product application trend in the past two years. The function and application capability of the surveillance application market for the lens is also getting higher and higher, and the development of the camera in HD has been faster than the development of the lens. HD and megapixel lenses still have a lot of room for upward development.

What kind of lens is the HD lens?

For high-definition cameras, it can be equipped with a common lens called megapixel, or with a million high-definition lens, or with a 3 million high-definition lens. In the case of the same camera, the final performance of the picture, the resolution of the lens A decisive role.

According to the technical indicators published by some products, the general "megapixel lens" has a central portion of the resolution of only 1 million pixels, and the periphery will be attenuated to only 500,000 to 600,000 pixels. At present, the mainstream "megapixel high-definition" lens on the market, the published technical indicators are usually 70% of the field height as the radius of the imaging circle, the resolution of 3 million pixels, 70% of the field height of the imaging circle can reach the resolution More than 1 million pixels.

Nowadays, only a very small number of "HD" lens products can be achieved: 80% of the field height is the radius of the imaging circle, the resolution is 3 million pixels, and the resolution around the image circle of 80% of the field height remains. More than 2 million pixels. Therefore, it is not difficult to see that due to the huge price difference between the high-definition lens and the ordinary lens, there are more and more definitions of the concept of confusion in the market, which makes consumers look at the fog. However, after the veil of these "beautiful" is removed, the high price is not necessarily the high quality product.

Nowadays, with the development and maturity of high-definition cameras, high-definition monitors, network transmission and other technologies, the CCTV security market is also entering the high-definition era. In such a wave of technological upgrading, the lens should not become a stumbling block for the high-definition development of the CCTV market. Therefore, the clear and unified "high-definition lens" indicator has become a top priority nowadays.

Identify the four main points of HD lens

It seems that as long as the monitoring system is mentioned, what people immediately think of is HD. So can HD monitoring really bring us a high-definition experience? Lenses that play a key role in the imaging process, and those that are easy to ignore? Please look down.

First, the lens is the key to using ED lenses

In the commonly used security surveillance market, we use more fixed-focus or manual zoom lenses, because the monitoring distance is closer, and the lens focal length is generally less than 50mm. This kind of scene has almost no requirement for the anti-dispersion performance of the lens. However, once a motorized zoom lens is used to monitor distant targets, the dispersion problem is highlighted (dispersion is the shift of the light of various wavelengths in visible light after being refracted by the lens, and the image is blue on the edge of the object. Color or red color strip). Originally in the analog monitoring system, due to the large size of the pixel, the problem of dispersion is not very prominent, and it will only be manifested when the 300mm focal length is configured. In the high-definition era, the commonly used 120mm focal length motorized zoom lens has been more obvious to see this problem. This has higher requirements on the lens in terms of material and coating accuracy. The higher the clarity of the matched camera, the more obvious the effect of the lens material on the imaging effect.

Second, large diameter design is the key

So is it possible to completely solve the problem of remote monitoring with the lens of ED lens? Usually we turn the image of 720p or more sharpness into a high-definition image. According to the free choice of the market, most of them use the 1080p output format. In the field of remote monitoring, users want to use high-definition surveillance systems to improve the pixels of the picture, so as to more clearly view long-distance targets. According to our actual experience, watching in HD system not only does not make the picture sharpness, but the color reproduction ability and sharpness of the picture are greatly attenuated. The sharpness of the output image is even worse than that of D1, even worse than the analog camera. .

When the focal length is elongated, the picture becomes a black and white picture, the sharpness is seriously degraded, and the image effect is worse than that of the same lens with the Hitachi ultra-low illumination camera. It is not difficult to understand this situation. Most of the HD cameras we use now use CMOS chips, and the illumination performance can only reach 0.5Lux. In the process of the focal length change of the telephoto lens, the luminous flux will also change, and the longer the focal length, the worse the luminous flux. When the focal length is extended to the maximum, the luminous flux is reduced to the weakest. Although it is daytime, for the camera, it is equivalent to being blocked in front, leaving only a small hole to transmit light. In this case, the normal high-definition camera will have a picture quality degradation due to insufficient illumination. To solve this problem, we can start from two aspects:

1. Adopt high-definition camera designed for long-distance monitoring. For example, high-definition SDI cameras, in addition to the minimum illumination of 0.3Lux, also added color reproduction and low illumination image enhancement technology for remote monitoring. This allows a clear picture to be obtained when the luminous flux is lowered.

2. Improve the luminous flux of the lens when the focal length is elongated. Once the lens is produced, the range of luminous flux is determined and cannot be changed. Therefore, we must select those products with better luminous flux performance at long focal lengths when selecting lenses. According to the optical relationship of the lens, F (inverse ratio of luminous flux) = f (focal length) / D (effective aperture before the lens). The F value is the inverse ratio of the luminous flux. The smaller the value, the better the luminous flux performance. Then, in the case of the same f, the lens with the larger effective aperture is selected, and the obtained picture effect is better.

Third, the IR function is easily overlooked

Users pay attention to high-definition systems, not only pay attention to whether they can get clear pictures during the day, but also monitor performance at night. In high-definition systems, IR functions are generally forgotten. However, with the improvement of the photographic performance of the high-definition system, the IR function is gradually recognized by users in the all-weather monitoring system. Especially for the power zoom system, the IR function is crucial. For systems with auxiliary light sources such as laser illuminators, the availability of IR functions will directly affect the ease of use and usability of the system.
 

Fourth, the large target design has a high degree of adaptability to the camera

In order to improve the picture performance, high-definition products often use a large-sized sensor chip. Often these cameras encounter a lot of confusion when configuring the lens. The lens produced by most lens manufacturers still uses the dimensional standards of the past analog era, namely 1/2" and 1/3" products. The actual specifications of the cameras on the market are mostly the following two:

1. Use products larger than 1/3" and less than 1/2", such as 1/2.5", 1/2.7", 1/2.8". These cameras use 1/3" lens when configuring HD lens. Will cause the picture to produce a "dark corner". Therefore, the current 1/3" high-definition lens, especially the motorized zoom lens, has almost become a chicken rib. In this application, the user uses 1/2" or more. For example, KOWA's 7.5-127mm product.

2. Use products larger than 1/2", such as 1/1.8", 2/3". Cameras with 1/1.8" sensor chip are more or less 1/2" when configuring HD lens. Vignetting may occur, so the customer chooses to use a 1/1.8" mirror' head as much as possible. This will ensure that there will be no vignetting. For specifications larger than 1/1.8", you should choose products with 2/3" or 1" specifications.

In short, for high-definition imaging systems, there are many technical details that are not worthy of attention compared to mature analog monitoring systems. The details determine success or failure, and excellent imaging systems will consider more. With the gradual popularization of high-definition systems, the choice of high-definition lenses will be more rational, and with the strong demand, it will in turn promote the continuous upgrading and development of products.