Lens material is transparent media, divided into two broad categories of inorganic and organic. In our daily lives will come across a natural medium crystal lens, which is made of quartz ore grinding lenses. Ancient crystal beauty eyesight can say, but in fact the main component is silicon dioxide crystal (sio2), the biggest advantage is hard and difficult to damp high, but the ultraviolet and infrared transmittance is high, and crystal density uneven, with impurities, striped and bubble until the produce, will form birefringence, which affects vision.
Glass is a very special amorphous materials at room temperature, showing solid, hard but fragile, with a viscosity at high temperatures. The chemical structure of the glass is not fixed, so there is no exact melting point. As the temperature increases, Zinc oxide the glass material will become soft and sticky to increase, and gradually from the solid into a liquid, which gradually changes the characteristics of what we call "glass state." This feature means that the glass can be processed at high temperatures and mold. Lenses made of glass material with good transparency, more transparent after polishing the surface of the benefits.
(1) ordinary glass materials (1.5 and 1.6): the refractive index of 1.523 crown glass is the traditional optical lens manufacturing materials, of which 60% to 70% of silica, the remainder from calcium oxide, sodium and boron and other substances mixed. The refractive index of 1.6 is sometimes classified as an ordinary lens of the lens. (2) high refractive index glass materials: After years of research, lens manufacturers have found in raising the refractive index while maintaining low dispersion method, that is added to the glass new chemical elements. Back in 1975 produced a titanium element of the lens, the refractive index of 1.7, Abbe number is 41; 15 years later produced a lanthanum element of the lens, the refractive index of 1.8, Abbe number is 34; 1995 refractive index of 1.9 years, there's material, adding the element niobium, Abbe number of 30, which is the highest refractive index lens material. Although the use of these materials created by the lens thinner, but it has not reduced the lens of the other important parameters: weight. In fact, with the refractive index increases, the proportion of materials have increased, so that offset the thinning of the lens because of the weight brought on relief.
(3) stained glass materials: glass materials mixed into some of the special nature of the metal salt absorption will show the effect of color, such as: Canadian nickel and cobalt (purple), cobalt and copper (blue), chromium (green ), iron, cadmium (yellow), gold, copper, Titanium dioxide and selenium (red), and so on. These materials are mainly used in large-scale dyeing lenses to produce plain sunglasses or protective lenses. Some of the special nature of the light filtering material (brown, gray, green or pink) is also used to produce refractive lenses, but as the material of this lens is not much demand now, mainly due to myopia or hyperopia lens center thickness and edge thickness, so that the color depth of the lens is inconsistent, the higher refractive error, the more obvious color difference.
(4) photochromic glass materials: Photochromic phenomenon is the absorption of light by changing the material properties of the material intensity of sunlight as a response to nature. Its basic principle is to make ordinary glass (including plastic photochromic materials) under the influence of UV radiation in the darker, and under the influence of high temperatures around the color fades, the two processes are reversible, and may persist . This phenomenon is mixed in the material through the activation of photochromic molecules and materials to complete. In 1962 appeared the first generation of photochromic glass, then constantly improve performance. The main material is added in the glass silver halide crystals. UV radiation in these crystals under attack from a chemical reaction, so that the lens darker. The first generation of photochromic materials, color glass works silver atoms and chlorine atoms of an electronic exchange, Nickel oxide through the silver chloride and the surrounding environment to performance. In the absence of light conditions, showed ionic silver chloride, silver ion is due to transparent, so the lens is transparent; in ultraviolet radiation, unstable electron left the chloride ions, and silver ions to metallic silver and absorption light, the lens is dark. When ultraviolet radiation weakened, mobile electronic chlorine atoms leave the silver atoms to return, the lens gradually restored the original clear state. General photochromic glass, color is also controlled by temperature, light intensity at constant temperature, the lower is darker. Photochromic materials are mostly gray and brown, graying and tea become known, other colors can also be achieved through a special process. All the glasses, including melting double-focus lens, progressive lenses are available photochromic materials. In recent years, photochromic lenses of the rapid development of the resin material in the continuous improvement of its refractive index is no longer limited to 1.50. Source:http://www.mhcocm.com