PRISM AND METHOD OF PRODUCING THE SAME

摘要

A prism is produced by the steps of feeding a glass base material into a heating furnace, the glass base material having surfaces to be prism surfaces after forming, the Ra value of the surface roughness of the surface being less than the Ra value corresponding to #170, the glass base material having a predetermined dimensional ratio, grasping the glass base material with feeding means, and feeding the glass base material into a heating furnace to heat the glass base material to a temperature so that a minimum viscosity of the glass base material becomes equal to or more than 10<4> Pa. s and less than 10<6> Pa. s, drawing and forming the lower portion of the glass base material, and then cutting the glass base material to obtain a longer body having a desired dimension and prism surfaces with the Ra value of the surface roughness equal to or less than a quarter of the wavelength of incident light, and cutting the longer body into desired length.