Optical coatings for cameras, lenses and imaging systems

Throughout the development of photography and imaging technology, optical coatings have always played the role of "invisible heroes". From the single lenses of early film cameras to the complex optical modules of today's professional single-lens reflex cameras, mirrorless cameras and industrial imaging systems, optical coatings have pushed the optical performance of lenses to the extreme by regulating the reflection, refraction and absorption characteristics of light. This special film covering the surface of optical components, although its thickness is often measured in nanometers, directly determines the clarity of the image, color reproduction and light utilization rate, and has become an indispensable core technology for modern imaging systems.

The core value of optical coatings lies in the precise control of inherent losses during the propagation of light. The surface of uncoated optical glass will suffer a reflection loss of approximately 4% due to the difference in refractive index between air and glass. A camera lens with multiple groups of lenses, without coating protection, can accumulate reflection loss of over 30%. This not only leads to insufficient image brightness but also causes "glare" and "ghosting" due to multiple reflections between the lenses, seriously damaging the quality of the picture. Optical coatings, through the principle of thin-film interference, make the reflected light cancel each other out while enhancing the intensity of the transmitted light, fundamentally solving this problem.

According to functional requirements, optical coatings in cameras and imaging systems have formed a diversified system, among which anti-reflection films, anti-reflective films, filter films and wear-resistant films are the most common. Anti-reflection coating is the most widely used type. Its design concept is to deposit multiple layers of dielectric films with different refractive indices (such as silicon dioxide, titanium dioxide) on the surface of the lens, so that the reflected light phases on the upper and lower surfaces of the film are opposite, thereby achieving interference cancellation. High-quality anti-reflection coatings can reduce the reflectivity of a single surface to below 0.1%. For telephoto lenses composed of multiple lenses, they can increase the total light transmittance from 70% to over 95%, making the images brighter and more detailed in low-light conditions. The common blue-purple or green anti-reflection films seen nowadays are precisely the visual presentation after multiple layers of media are superimposed.

Anti-reflection films and filter films play a role in meeting specific imaging requirements. In the viewfinder or distance measurement system of a camera, the anti-reflection film, through the superposition of high refractive index materials (such as zinc sulfide), makes the reflectivity of specific wavelengths of light exceed 90%, ensuring a clear viewfinder image. In color photography, the filter film precisely controls the luminous flux of the three primary colors - red, green and blue - through selective absorption and transmission, achieving realistic color reproduction. In imaging systems used for industrial inspection, dedicated filter films can also filter out stray light, allowing only the light of the target wavelength to pass through, thereby highlighting the subtle defects of the inspected object.

In addition to optical performance regulation, wear-resistant and protective coatings are also the "guardians" of lenses. Camera lenses are inevitably subject to friction, fingerprints and environmental erosion during use. Wear-resistant coatings containing fluorine or silicon dioxide can form a protective layer with a hardness of H or above on the surface of the lens, which not only can resist daily wear and tear, but also reduce fingerprint adhesion and facilitate cleaning. Imaging equipment used in extreme environments (such as outdoor exploration cameras and aerospace remote sensing lenses) also features special protective coatings that can resist high and low temperatures as well as chemical corrosion, ensuring the stable operation of the optical system.

The preparation technology of optical coatings has long evolved from the early vacuum evaporation to today's high-precision processes such as magnetron sputtering and ion beam-assisted deposition. Magnetron sputtering technology can prepare multilayer films with a thickness error of less than 1 nanometer by bombarting the target material with high-energy ions, causing the target material atoms to be uniformly deposited on the surface of the lens, meeting the requirements of complex optical design. Ion beam-assisted deposition can further enhance the density and adhesion of the film, making the coating less likely to fall off during long-term use. The application of these advanced processes enables modern lens coatings to simultaneously achieve multiple functions such as transparency enhancement, wear resistance, and water resistance, forming a "composite optical coating" system.

With the development of imaging technology towards high resolution, miniaturization and intelligence, optical coatings are also constantly making breakthroughs. In the periscope lenses of mobile phone cameras, the ultra-thin and light nano-coating has solved the optical loss problem of small-sized lenses. In the imaging system of professional astrophotography, a dedicated coating for the infrared or ultraviolet band enables the camera to capture cosmic light that is invisible to the human eye. In AI-assisted imaging devices, the collaborative optimization of coatings and algorithms further enhances the dynamic range and signal-to-noise ratio of images.

From the film era to the digital age, every advancement in optical coatings has driven a leap in imaging quality. Although it is hidden behind the lens, it uses nanometer-level precise control to make the light better serve the imaging requirements. In the future, with the development of new materials (such as two-dimensional materials) and new processes, optical coatings will achieve more precise spectral control and better environmental adaptability, opening up broader application Spaces for cameras, lenses and various imaging systems, and continue to write the legend of "invisibility" in the world of light and shadow.