Clears Glass

Abstract

This paper describes the progress made in lens making for telescopes. The use of rotating equipment was an important innovation in lens making, although it is possible to grind lenses entirely by hand. After grinding, the lens was polished, sometimes using the same lap that had been used to shape it. It required preparing the lap surface to remove roughness. In some cases, it was done by overlaying the surface of the lap with a specially prepared paper. Pitch was poured on the lens surface and, when it hardened, was removed, creating a tool exactly matching the curvature of the lens. When it became possible to make generalizations about the performance of telescopes, it became obvious that the spherical aberration due to the shape of simple lenses was a factor that limited optical quality. The vast majority of amateur-made telescopes are reflectors.