In machine vision, industrial lenses, as the core components of machine vision systems, often need to be used in conjunction with industrial cameras. Industrial lens, belongs to a kind of optical system. An optical system is a system that consists of a variety of optical components such as lenses, mirrors, prisms and diaphragms combined in a certain order. So what are the types of industrial lenses?
I. Categorized according to the lens interface
1.C-Mount and CS-Mount
C interface is the current machine vision system is widely used in one of the lens interface, its thread parameters: diameter = 1, pitch: 32 teeth. It has the advantages of light weight, small volume, and economic diversity.
CS interface to add an adapter ring can be transformed into a C interface, CS interface flange distance is 12.5mm, C interface flange distance is 17.5mm. 5mm difference between them.
2. M12, M42, M58, M95 port
The number after M represents the diameter of the interface, M12 diameter is 12mm, M42 diameter is 42mm, M58 diameter is 58mm, M95 diameter is 95mm.
The above M and C/CS ports are all threaded ports.
3.F port and EF port
F port and EF port belongs to the snap interface, F port is the interface standard of many lens brands, usually the target surface of the industrial camera is larger than 1 inch when you need to use the F port of the lens.
4.V port
V interface lens is a well-known professional lens brand lens is the primary use of the standard, generally also used for industrial cameras target surface or special purpose lens.
5. Other interfaces
T2 interface, Leica interface is also used in the lens interface.
II. Industrial lenses in accordance with the focal length points
1. Fixed focal length lens: fixed focal length, generally adjustable aperture, with focus fine-tuning, only a small working distance, the field of view with the distance change.
According to the length of the focal length, fixed focal length lens can be divided into four categories: fisheye lens, short focal length lens, standard lens, telephoto lens. It should be noted that the length of the focal length of the division is not the absolute value of the focal length as the primary criterion, but the size of the image angle as the main basis for differentiation, so when the size of the target surface is not the same, the size of the focal length of the standard lens is also different.
2. Zoom industrial lens: the focal length can be continuously changed, the size is larger than the fixed focal length lens, suitable for object changes, the pixel quality is not as good as the fixed focal length lens.
Zoom lens on the zoom ring, adjust the ring can make the focal length of the lens value in a predetermined range of flexible change. The ratio of the longest focal length value and the shortest focal length value of the zoom lens is called the zoom magnification of the lens. Zoom lens can be divided into manual zoom and electric zoom two categories.
Zoom lens can be continuously changed due to the characteristics of the focal length value, in the need to frequently change the photographic field of view is very convenient to use, so in the field of photography is very widely used. However, due to the number of lenses of the zoom lens, complex structure, so the maximum relative aperture can not be made too large, resulting in lower image brightness, image quality deterioration, while in the design is also difficult for a variety of focal lengths, a variety of focusing distance to do the aberration correction, so its image quality can not be compared with the same grade of the fixed-focal-length lens.
III. Special Purpose Lenses
- Microscope head (Micro), generally refers to the imaging ratio greater than 10:1 shooting system used, but due to the current video camera pixel size has been achieved within 3 microns, so the general imaging ratio greater than 2:1 will be used when the microscope head.
- Macro lens (Macro), generally refers to the imaging ratio of 2:1 ~ 1:4 range of specially designed lenses. In the case of the image quality requirements are not very high, generally can be used between the lens and the camera with a proximity ring or in front of the lens with a proximity lens to achieve the effect of magnified imaging.
- Telecentric lens (Telecentric), mainly for the correction of parallax of traditional lenses and specially designed lenses, it can be in a certain range of object distance, so that the magnification of the image will not be obtained with the changes in the object distance changes, which is not in the same object surface of the measured object is very important application.
- Ultraviolet lens (Ultraviolet) and infrared lens (Infrared), the general lens is designed for the use of visible light range, due to the same optical system for different wavelengths of light refractive index of different, resulting in the same point of the different wavelengths of light issued by the imaging can not be converged into a point, resulting in chromatic aberration. Commonly used lens achromatic design is also for the visible light range, ultraviolet lens and infrared lens that is specifically designed for ultraviolet and infrared lens.
Telecentric lenses are divided into:
(1) object-side telecentric
In a certain depth of field range, even if the object distance changes, the size of the object imaging will not change. This type is most used in the field of industrial inspection.
2) Image-square telecentric
Even if the distance between the photoreceptor chip and the lens changes, the size of the image of the object does not change, but the object distance affects the size of the image. This type in the field of industrial inspection almost does not work, not to repeat.
3) Double telecenter
Objects and like the near and far will not affect the size of the imaging, often used in the field of machine vision inspection, the disadvantage is that the cost is higher.
Characteristics and application scope of telecentric lenses
Characteristics:
(1) no field angle, eliminating perspective, constant magnification
2) Low distortion
3) Only parallel light can be imaged
Application Scenarios:
(1) When the thickness of the object to be detected is large, need to detect more than one plane, typical applications such as food boxes, beverage bottles and so on.
(2) When the placement of the object to be measured is uncertain, may be with the lens at a certain angle.
(3) When the object under test jumps up and down during the detection process, such as the production line vibration up and down resulting in changes in the working distance.
(4) When the object to be measured with aperture, or three-dimensional objects.
(5) When the need for a low distortion rate, the brightness of the image effect is almost identical.
(6) When the defects to be detected can only be detected under parallel illumination in the same direction.
(7) When it is necessary to exceed the detection accuracy, such as the allowable error of 1um.