Raw Materials Coating, Barrel, Housing for the camera lens, Lens mounts The Manufacturing Process Grinding and polishing lens elements 1 Optical glass is supplied to lens manufacturers by specialized vendors. Usually, it is provided as a "pressed plate" or sliced glass plate from which the elements are cut. The glass elements are shaped to concave or convex forms by a curve generator machine that is a first-step grinder. To reach the specifications for its shape, a lens goes through a sequence of processes in which it is ground by polishing particles in water. The polishing particles become smaller in each step as the lens is refined. Curve generation and subsequent grinding vary in speed depending on the frailty, softness, and oxidation properties of the optical materials. After grinding and polishing, the elements are centered so that the outer edge of the lens is perfect in circumference relative to the centerline or optical axis of the lens. Lenses made of plastic or bonded glass and resin are produced by the same processes. Bonded materials are used to make lenses with non-spherical surfaces, and these lenses are called "hybrid aspherics." The aspherical surfaces of these lenses are completed during centering. Coating lenses 2 Formed lenses are coated to protect the material from oxidation, to prevent reflections, and to meet requirements for "designed spectrum transmission" or color balance and rendition. The lens surfaces are carefully cleaned before coating. Techniques for applying coatings and the coatings themselves are major selling points for a manufacturer's lenses and are carefully guarded secrets. Some types of coatings include metal oxides, light-alloy fluorides, and layers of quartz that are applied to lenses and mirrors by a vacuum process. Several layers of coating may be applied for the best color and light transmission, but excessive coating can reduce the light that passes through the lens and limit its usefulness. Producing the barrel 3 The barrel includes the chassis that supports the various lens elements and the cosmetic exterior. Metal mounts, grooves, and moving portions of the lens are critical to the performance of the lens, and are machined to very specific tolerances. Lens mounts may be made of brass, aluminum, or plastic. Most metal barrel components are die-cast and machined. Metal mounts last longer, maintain their dimensions, can be machined more precisely, and can be dismantled to replace elements, if necessary. Plastic mounts are less expensive and of lighter weight. If the barrel is made of engineering plastic, it is produced by a highly efficient and precise method of injection molding. The interior surfaces of the barrel are also coated to protect them and to prevent internal reflection and flare. Assembling the lens 4 Other parts of the lens, such as the diaphragm and auto focus module, are produced as subassemblies. The iris diaphragm is constructed of curved leaves cut out of thin sheets of metal. The metal leaves are held in place by two plates. One plate is fixed, the other moves, and has slots for sliding pins. These slide the leaves back toward the barrel to open the diaphragm or into the center to close the opening as the f-stop ring is turned. The diaphragm assembly is fastened into place when the lens mount is attached to the end of the barrel. The auto focus is also added, the optical elements are positioned, and the lens is sealed. After final assembly, the lens is adjusted and inspected rigorously. It must meet the design standards for optical resolution, mechanical function, and auto focus response. Lenses may also be tested by subjecting them to shocks, dropping, and vibration.