Optical coating on the lens of the optical coating is a very important part of the surface of the glass will reflect light, if more oblique angle of incidence, then, possible loss of more than 20% of the light! This is just a loss of face, in fact, even the camera lens is at least the early telescope has two heads, a total of four faces. As a loss of light is very impressive. If a known f2 lens, but not coated, then six or seven reflections off the surface, the aperture may be only 2.8. So many of the old lens glued lens was used as much as possible to reduce the reflection interface.
In addition to media exposure will be reduced to reach the light, the light reflected in the result of overlap between the lens will the image is unclear, contrast reduction; sometimes there will be a bunch of shooting against the light spot, or even a dead white. Although sometimes spot well-organized, then, is very pretty, but most will cause interference to the shooting, thus reducing the handy glass surface reflection has become an important technology. If the two materials of refractive index is closer to the smaller reflectivity, whereas the larger, so if the glass attached to the surface layer between the refractive index between air and glass material, you can reduce reflection and increase penetration. If the refractive index of air (nair) and the refractive index of glass (ng) does not change, coupled with a layer of coating material refractive index nc, were calculated at this time if the air → coating, the transmittance of the glass coating → , and then multiplying the coating will find the light transmittance increases. Therefore, the coating on the application of the concept of the anti-reflective top of the lens, at the outset using magnesium fluoride, calcium fluoride and the like of the components, when only single-layer coating. Steady progress in science and technology, the use of fluoride will gradually lead, titanium dioxide, silica, magnesia, etc. to the coating composition, and will last ten to twenty-plated layer coating. Such multi-layer coating will greatly increased light transmittance, so that the reflected light between the lens greatly reduced, yet even the plastic lens can be coated on the multilayer film. Also many major camera factory coating developed their own way, such as Pentax's super multi-layer coating (SMC), Carl Zeiss's T * coating, etc., ingredients should also be more complex, of course, most are confidential. Early is coated with chemically deposited on the glass surface, then is the vacuum pan, heat the coating material after evaporation of condensation on the glass surface.
After coating the reflected light actually prescribe. A reflection from the surface coating, a coating and the glass from the interface reflection, although the reflected light is greatly reduced, but there are still, will produce two-channel reflection light optical path difference, interference will occur, so some band will be destructive, it will send some colorful color. Because the human eye 555nm wavelength of the most sensitive to yellow-green light, it is generally old-fashioned single-layer coatings are coating thickness control and violet light reflected by the yellow-green light. Modern multi-layer coating is more for color reproduction, must balance the colors of the reflectivity, neodymium fluoride thus reflecting the color of the coating will be complementary shade most of the phenomenon, which is a blue reflective side of the other side is there will be with yellow reflective, there are red with green complementary; so multi-coated lens reflective color colorful. But we can not determine whether the color of reflective multi-layer coating, in general, single-layer reflective coating is a blue-violet, blue and purple but is not necessarily reflective layer coating. To determine if the coating is performing well, not to judge by the color, but the strength should be reflective of view, reflecting the stronger of course, the worse the effect. But sometimes the eyes will be allowed to determine the most direct is to take a front sun, but the strength of glare or ghosting know. Source:http://www.mhcocm.com