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Concept and classification of industrial lens

Issuing time:2020-02-08 15:58

Concept and classification of industrial lens


Key words: machine vision lens


小草社区免费视频大全Concept and classification of industrial lens

小草社区免费视频大全Optical lens is generally called camera lens or photographic lens, which is called lens for short. Its function is optical imaging. Lens is an important component of machine vision system, which plays a key role in image quality. It has an impact on several main indexes of image quality, including resolution, contrast, depth of field and various aberrations. There are many kinds of lens, and the quality difference is also very big. But the general users often pay less attention to the choice of lens when they design the system, which leads to the failure of getting the ideal image and even the failure of system development. The purpose of this paper is to summarize the relationship between various factors by introducing the classification and main parameters of various common lenses, so that readers can master the skills of lens selection in machine vision system.


According to the size of effective image field


The camera lens is installed at the front end of a large expansion darkbox, and a large frosted glass is installed at the back end of the darkbox. When the lens aperture is turned to the maximum and the focus is focused on the infinite distant scene, the images on the frosted glass are all in a circular area, while the outside of the circular area is dark and there is no image. The circular area of the image is called the largest image field of the lens. In the center of the largest image field, there is an area that can make the scene in the infinite distance form a clear image. This area is called a clear image field. The camera or the target of the camera is usually located in the clear image field, which is called the effective image field. Because there are various types of camera's target size in the vision system, we must pay attention to that the effective image field of the lens should be greater than or equal to the camera's target size when choosing the lens, otherwise the edge and angle of the image will be blurred or even there is no image.


小草社区免费视频大全According to the size of the effective image field, it can be generally divided into the following categories:


Classification according to focal length


According to whether the focal length can be adjusted, it can be divided into fixed focal length lens and variable focal length lens. According to the length of focal length, fixed focal length lens can be divided into four categories: fish eye lens, short focal lens, standard lens and long focal lens. It should be noted that the division of focal length is not based on the absolute value of focal length, but on the size of image angle. Therefore, when the size of target surface is different, the focal length of standard lens is also different. There is a zoom ring on the zoom lens. Adjusting the ring can make the focal length of the lens change flexibly within a predetermined range. The ratio of the longest focal length value to the shortest focal length value of a zoom lens is called the zoom magnification of the lens. There are two kinds of zoom lens: manual zoom and electric zoom.


Zoom lens is widely used in the field of photography because it can continuously change the focal length value and is very convenient to use when the camera field of view needs to be changed frequently. However, due to the large number of lenses and complex structure of the zoom lens, the maximum relative aperture cannot be too large, resulting in low image brightness and poor image quality. At the same time, it is difficult to do aberration correction for various focal lengths and various focusing distances in the design, so the imaging quality of the zoom lens cannot be compared with that of the same level of the zoom lens.


小草社区免费视频大全In practice, the focal length of the commonly used lens ranges from 4mm to 300mm, and there are many levels. How to choose the appropriate focal length lens is a main problem to be considered in the design of machine vision system. The imaging law of optical lens can be derived from two basic imaging formulas Newton formula and Gauss formula. For the common design model of machine vision system, we generally select the lens with appropriate focal length according to the two conditions of imaging magnification and object distance. Here, we give a set of practical calculation formulas:


According to lens interface type


There are many different types of interfaces between lens and camera. Industrial camera commonly used include C interface, CS interface, f interface, V interface, T2 interface, Leica interface, M42 interface, M50 interface, etc. There is no direct relationship between the different interface types and lens performance and quality, only the different interface modes. Generally, we can also find the interfaces between various commonly used interfaces.


The C interface and CS interface are the most common international standard interfaces for industrial cameras. They are 1-32un British screw connection. The screw connection of C interface and CS interface are the same. The difference is that the back intercept of C interface is 17.5mm, and that of CS interface is 12.5mm. Therefore, the camera with CS interface can be connected with the lens of port C and port CS, only a 5mm ring is needed when using the lens of port C; the camera with C interface cannot use the lens of port CS.


小草社区免费视频大全F interface lens is the interface standard of Nikon lens, so it is also known as Nikon port. It is also a common type of industrial camera. Generally, when the camera target is greater than 1 inch, it needs f port lens.


V interface lens is the main standard used by Schneider lens, a famous professional lens brand. It is also generally used for lens with large target or special purpose.


小草社区免费视频大全Special purpose lens


Micro lens generally refers to the shooting system with an imaging ratio greater than 10:1. However, since the pixel size of the current camera has been within 3 microns, the micro lens will also be used when the imaging ratio is greater than 2:1.




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