Metal and plastic matter but they aren't the most important materials in a lens. That's why many thousands square meters of the factory are dedicated to production and processing of glass elements.
Hoya company delivers glass to Aizu and elements have to be heavily processed before they can be put inside lenses. They are delivered as matt, unfinished pieces which need to be shaped, grounded, and polished.
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It is a three-stage process which starts with grinding. Grinding gives an element the desired shape. Even though the producer has roughly already shaped that element, now all the curves must be redefined and shaped with utmost precision.
Then on one of dozens of machines the polishing process starts. There are two phases of it, using different gradation. After the second polishing phase the element finally looks like the glass component you can find in your lens but the processing is not over.
Then the elements undergo a centering process because, at that point, a grinded and polished element is not perfectly circular yet. You have to put it in a lathe and process its edge in such a way that it becomes ideally round. Only such an element can be put inside the tube of a lens.
There are section in the factory dedicated to production of special elements. In one of them we saw special machines which are able to shape optical lenses in untypical way.
In other room glass molded aspherical elements are produced by heating and press-forming. Although these parts allow you to eliminate many aberrations in a lens without making the whole inner system overly complex, their production is very expensive. In order to create an element of such type you have to heat the glass to 600 degrees Centigrade and put it inside a press which will shape it according to your design. The process not only entails using expensive, specialist, glass-molding machinery but is also time-consuming. The production of just one element might take even two hours.
That's why hybrid aspherical elements are often used instead of heat-moulded ones. Their production is much easier and cheaper – an element is created by glueing two different parts, a glass and plastic one which comes with aspherical surface.
Finally the elements are coated by anti-reflective layers. All of them go to an all-female section of the factory. Why? It happens that an eye of a woman is able to notice all flaws and uneven areas on lenses better. When the quality of an element is beyond reproach, it is put on a special rack which then goes to a specialist machine responsible for covering it with more than a dozen layers on each side.
