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Will lens continue to be the decisive factor?

2021-04-29 22:56:20Source:CIOE

Optical lens as an essential part of the machine vision system, directly affects the quality of imaging, as well as the realization and the effect of the algorithm. Optical lens from the focal length can be divided into short focal length lens, medium, telephoto lens; from the field of view size points have a wide-angle, standard, telephoto lens; structure points have a fixed aperture fixed focus lens, manual aperture fixed focus lens, automatic aperture fixed focus lens, manual zoom lens, automatic zoom lens, automatic aperture electric zoom lens, electric three variable (aperture, focal length, focus are variable) lens, etc..


Optical Lens Supply Chain


The R&D and manufacturing process of optical lens are in the midstream of the industry chain. Optical lens is a necessary component of the optical imaging system, and is the key factor affecting the quality of imaging. The lens is mainly composed of lens, spacer, and lens barrel. 


The most extensive application area of glass-plastic hybrid lens


The application areas of different types of optical lens vary widely, including:


  • Plastic lenses are mainly used in the field of smart phones.


  • Glass lenses are mainly used in high-end security video surveillance, vehicle-mounted imaging systems, machine vision and high-end emerging consumer electronics.


  • Glass-plastic hybrid lenses are more widely used, and almost all of the above areas can be covered.


A common indicator to measure the resolution of the lens is the MTF (Modulation Transfer Function), which measures the reduction of the contrast of the lens.  


The ideal lens can achieve 100% restoration, the worst lens cannot restore contrast, so the MTF value is located in the range of 0-1. The larger the MTF value, the better the resolution of the lens.  


For example, in the picture below, the contrast of the black and white bar is originally 100%, but after the processing of the lens, the middle of the black and white bar will be gray due to the crosstalk of light, which is the case of incomplete restoration of contrast.


Modulation and Contrast Transfer Functions


In this example, this lens has an MTF value of 90%, indicating that it can restore 90% of the contrast.


In mobile phone visible light camera, although the light transmission of glass is better than that of plastic lens, plastic is easy to mold and can be composed of various combinations needed, and the control of light is also better, so the MTF of plastic lens will be larger than that of glass lens instead. Then, we believe that plastic lenses will still be the mainstream of mobile phone visible lenses in the coming period, but glass lenses or glass-plastic hybrid lenses will probably also have a place.


In general, the more the number of lenses, the higher the imaging quality of the lens. Plastic lens and glass lens have different application areas due to the difference in materials, processing technology, light transmittance, and other aspects.


Plastic lenses are lenses composed of optical plastic lenses, which are widely used in mobile phones, digital cameras, and other devices due to their high plasticity, easy to make aspherical shapes, and convenient miniaturization.


Glass lens is made of glass lens assembly, due to the high requirements of molding technology, coating technology, precision processing and its high light transmission characteristics, more used in high-end imaging field, such as SLR cameras, high-end scanners, and other equipment.


Glass-plastic hybrid lens, composed of glass lens and plastic lens, combines the characteristics of both, with high refractive index optical performance and stability, widely used in surveillance cameras, digital cameras, car cameras and other lens modules.


Comparison of the three main types optical lens


Key processing technology of optical lens


The difficulty of optical lens mainly lies in the design and manufacturing process.


Design process


The design process requires years of experience and imagination, and is not only an engineering process, but also an art.


Each design of the optical lens can be specifically patented to protect the designer's hard work. The design process directly determines whether the manufacturer can produce a certain specification of the lens, also is the ticket to enter the industry.  


When light passes through a lens, it undergoes a very complex refraction process to reach the image sensor. The complex refraction process causes the image on the image sensor to differ from the theoretical results obtained according to Gaussian optics, which is aberration. Aberrations cannot be completely eliminated, so there is no perfect lens in the world.  


Optical design is to achieve the control of these aberrations by combining different shapes, different numbers of lenses, so as to obtain the as perfect an imaging effect as possible.  


However, because there are so many aberrations, it is impossible to achieve complete aberration control, but only through optical design to achieve a balance among the many aberrations. Optical design is not engineering, but is an art, and an understanding of beauty, testing the experience, talent and inspiration of the optical designer.


Leica and Zeiss, as the best optical manufacturers, are proud of their accumulation in optical design. The main cooperation between Huawei and Leica is that Leica helps Huawei improve the optical design.


Optical design

Manufacturing process


If the design solution solves the problem of whether the lens manufacturer can produce, then the manufacturing process is the key to determine the production yield and consistency.  


In the process of mold making, molding, and assembly, there are very high requirements for production accuracy, and any error in any one process will have a very large impact on the final imaging effect.      


manufacturing process


The mold making process is the most critical part of plastic lens manufacturing.  


The quality of the molds directly affects the molding of the lens, so a very high precision mold is required. Molds require not only experienced designers for the design, but also manufacturing personnel with a foundation in precision machining and inspection.  


During the molding process, the material undergoes phase changes, density changes, temperature changes, and pressure changes, and these variables must be strictly and precisely controlled in order for the lens to have good optical properties.  


This places extremely high demands on the manufacturer's production, requiring not only high-precision instruments, but also experienced and skilled workers to complete the operation, and any errors will affect the final imaging quality.


Assembly process is the process of completing the assembly of the lens, spacer, compression ring and other components to complete the assembly and to achieve optical performance, which is mainly achieved through automation.


Lens assembly technology is very complex, the accuracy of the processing of components, assembly accuracy has very high requirements, the overall tolerance is generally not more than 3 microns, but Largan and other companies even can reach 2 microns.


Optical lens design is very complex, there are hundreds of known aberrations, there are still a large number of unknown aberrations continue to be discovered and need to be taken into account in the design.


There are countless paths of refraction and reflection paths of light that require constant calculations and trade-offs by the designer. The shape, position, and material of the lens can be combined in countless ways, allowing designers to continually explore better designs.


There is never an end to progress in the optical lens industry, and there is room for exploration. Although the production of mobile phone lens is not as difficult as camera lens, time and experience are still important.


For example, Taiwan's Largan is one of the first manufacturers to start researching plastic lenses, which has been established for nearly 40 years.


Although the plastic lens began to flourish after the rise of smart phones, Largan had accumulated nearly 20 years of experience before that. Therefore, it has always been difficult for other manufacturers to reach lens quality and production yields of Largan, which also has created the dominant position of Largan in the field of mobile phone lens.


In summary, with the rapid emergence of the end-use product market, the development of the downstream industry has put forward higher requirements for the design level and precision production and processing capabilities of optical lenses, while the increasing market demand also provides a valuable opportunity for the sustainable and healthy development of the optical lens industry.


Optical lenses determine the imaging effect


In addition to the sensor, the quality of the optical lens is also an important factor in determining the picture. The camera is generally composed of multiple lenses, spacing circle, and lens barrel. Theoretically, if the more lenses, the stronger the convergence of light. Also, the higher the resolution and contrast of the lens, the better the imaging effect, but the mobile phone lens will also be thicker, light loss will also be more serious.


Most mobile phone lenses on the market today are made up of 4-5 lenses, and some high-end smartphones have adopted a configuration of 6 or more lenses. The emergence of periscopic lens technology makes the number of lenses no longer limited by the thickness of the phone, and it is expected that the average pivot of the number of lenses will continue to move up in the future, and the penetration rate of 6P+ lenses is expected to super reach 28% in the second half of 2019. 


3D lens industry chain


By disassembling and analyzing the mainstream 3D camera products that have been listed, the 3D camera industry chain can be divided into:


Upstream: infrared sensor, infrared light source, optical components, optical lens and CMOS image sensor;

Midstream: sensor module, camera module, light source foundry, light detection and image algorithm;

Downstream: terminal manufacturers and applications.

CIOE 2021 - Precision Optics, Lens & Camera Module Expo will be held on September 1-3, 2021, covering the latest optical components, lens, camera module, and industrial applications. Concurrent CIOEC Optics Forum will focus on the latest development and trends in optics industry. TSR has already confirmed its presentation in our optics forum. Meet them and other industrial professionals onsite at Shenzhen World Exhibition and Convention Center in September.

CIOE-Precision Optics, Lens & Camera Module Expo


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