In machine vision, industrial lenses, as the core components of machine vision systems, often need to be used in conjunction with industrial cameras. Industrial lenses belong to an optical system. An optical system is a system composed of a variety of optical elements such as lenses, mirrors, prisms, and diaphragms in a certain order. So what are the types of industrial lenses?
1. Classification according to lens mount.
1. C-mount and cs-mount
C-mount is one of the most widely used lens mounts in machine vision systems, its thread parameters: diameter = 1, pitch: 32 teeth. It has the advantages of light weight, small size, and economic diversity.
Add an adapter ring to the CS interface to convert to the C interface, and the flange distance of the CS interface is 125mm, the flange distance of the C mount is 175mm。There is a difference of 5mm between them.
2. M12, M42, M58, M95 ports.
The number after M represents the interface diameter, M12 diameter is 12mm, M42 diameter is 42mm, M58 diameter is 58mm, and M95 diameter is 95mm.
The above M port, C port and CS port are all threaded ports.
3. F port and EF port.
The F port and EF port belong to the snap interface. F-mount is the interface standard of many lens brands, and usually industrial cameras need to use F-mount lenses when the target surface is larger than 1 inch.
4. V-port. V-mount lenses are the primary standard used by well-known professional lens brands, and are generally used for industrial cameras with large target areas or special purpose lenses.
5. Other interfaces.
The T2 mount and Leica mount are also used in the lens.
2. Industrial lenses are divided according to focal length.
1. Fixed focal length lens: fixed focal length, generally adjustable aperture, with focus fine-tuning, only a small working distance, and the field of view changes with distance.
According to the length of the focal length, fixed focal length lenses can be divided into four categories: fisheye lenses, short-throw lenses, standard lenses, and telephoto lenses. It should be noted that the length of the focal length is not based on the absolute value of the focal length as the primary criterion, but on the size of the image angle as the main criterion, so when the size of the target surface is different, the focal length of the standard lens is also different.
2. Zoom industrial lens: the focal length can change continuously, the size is larger than the prime lens, suitable for object changes, and the pixel quality is not as good as the prime lens.
Zoom lenses have zoom rings on them, and adjusting the ring allows the focal length of the lens to be flexibly changed 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 that lens. There are two types of zoom lenses: manual zoom and power zoom.
The zoom lens is widely used in the field of photography because it can continuously change the focal length value, and it is very convenient to use when it is necessary to change the field of view frequently. However, due to the large number of lenses and complex structure of the zoom lens, the maximum relative aperture can not be too large, resulting in low image brightness and poor image quality, and it is difficult to make aberration correction for various focal lengths and various focusing distances in the design, so its imaging quality cannot be compared with the fixed focal length lens of the same grade.
3. Special-purpose lenses.
Microscope lens (micro) generally refers to the imaging ratio greater than 10:1 for the shooting system, but because the current camera pixel size has been within 3 microns, the microscope lens is generally used when the imaging ratio is greater than 2:1.
A macro lens generally refers to a specially designed lens with an imaging ratio of 2:1 1:4. In the case that the image quality requirements are not very high, the effect of magnifying imaging can generally be achieved by adding a close-up lens between the lens and the camera or adding a close-up lens in front of the lens.
Telecentric lens is mainly a lens specially designed to correct the parallax of traditional lenses, which can make the image magnification not change with the change of object distance within a certain object distance, which is a very important application for the situation that the measured object is not on the same object surface.
Ultraviolet lenses (ULR**IOLET) and infrared lenses (Infrared), general lenses are designed for use in the visible light range, due to the different refractive indices of different wavelengths of light emitted by the same optical system, resulting in different wavelengths of light emitted at the same point can not converge into a point when imaging, resulting in chromatic aberration. The achromatic design of commonly used lenses is also for the visible light range, and ultraviolet lenses and infrared lenses are lenses specifically designed for ultraviolet and infrared rays.
Telecentric lenses are divided into:
1) Object side telecentricity.
Within a certain depth of field, the size of the object image does not change even if the object distance changes. This type is the most widely used in the field of industrial inspection.
2) Like Fang Yuanxin.
Even if the distance between the sensor and the lens changes, the size of the object image does not change, but the object distance affects the image size. This type has little effect in the field of industrial inspection, so I won't go into details.
3) Bitelecentric.
The distance of the object and the image will not affect the size of the imaging, which is often used in the field of machine vision inspection, and the disadvantage is that the cost is higher.
Characteristics and range of applications of telecentric lenses.
Features: 1) No field of view, eliminate perspective, constant magnification.
2) Low distortion.
3) Only collimated light can be imaged.
Application scenarios: 1) When the thickness of the detected object is large and more than one plane needs to be detected, typical applications such as food boxes, beverage bottles, etc.
2) When the position of the measured object is uncertain and may be at a certain angle to the lens.
3) When the measured object jumps up and down during the detection process, such as the working distance changes due to the vibration up and down of the production line.
4) When the object to be measured has an aperture or is a three-dimensional object.
5) When low distortion rate is required, the brightness of the image effect is almost exactly the same.
6) When the defect to be detected can only be detected under parallel illumination in the same direction.
7) When the detection accuracy needs to be exceeded, such as the allowable error is 1um.
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