英和和英

出典:『Wikipedia』 (2009/12/18 22:16 UTC 版)

英語による解説

引用

A rotating furnace is a device used to create lenses or primary mirrors for optical telescopes. It was known already to Newton that the centrifugal-force-induced shape of a spinning liquid is a paraboloid, the same as the shape of a telescope's primary focusing mirror. So glass is placed in the furnace, the furnace is spun up and heated, the top surface of the melted glass takes on a concave shape, and the glass is cooled to solidification while still spinning. If the shape does not exactly represent a telescope mirror, it is then corrected by computer-controlled grinding machines. The net amount of grinding done, and the net mass of glass material used, is less than would have been required without spinning. Once solidified, the concave top surface can be silvered and used as a focusing mirror. (If centrifugal force & gravity are the main shaping forces, this would tend to create a concave top-surface of the lens, and the bottom surface would be shaped by the liquid's container much like a mold; only the top surface would be shaped by non-contact forces.)