Manufacturing a Telescope

Input A telescope consists of an optical system (the lenses and/or mirrors) and hardware components to hold the optical system in place and allow it to be maneuvered and focused. Lenses must be made from optical glass, a special kind of glass which is much purer and more uniform than ordinary glass. Hardware components that are directly involved with the optical system are usually manufactured from steel or steel and zinc alloys.

Process (hardware components) Metal hardware components are manufactured using standard metalworking machines such as lathes and drill presses. Components made from ABS plastics (usually the external body of the telescope) are produced using a technique known as injection molding. In this process the plastic is melted and forced under pressure into a mold in the shape of the final product. The plastic is allowed to cool back into a solid, and the mold is opened to allow the component to be removed.

Process (optical glass) The glass manufacturer mixes the proper raw materials with waste glass of the same type as the glass to be made. This waste glass, known as cullet, acts as a flux; that is, it causes the raw materials to react together at a lower temperature than they would without it. This mixture is heated in a glass furnace until it has melted into a liquid. The temperature needed to form molten glass varies with the type of glass being made, but it is typically about 2550°F The temperature of the molten glass is raised to about 2820°Fto force air bubbles to come to the surface. It is then allowed to cool while being stirred constantly until it has reached about 1830°Fat which point it is an extremely thick fluid.

Process (optical glass) After the glass has cooled to about 570°F it must be reheated to about 1020°F to remove internal stresses that form during the initial cooling period and which weaken the glass. It is then allowed to cool slowly to room temperature.

lenses First a high-speed, rotating cylindrical cutter with a round diamond blade, known as a curve generator, shaves the surface of the lens until a close approximation of the desired curve is achieved. Several cut blanks are placed on a curved block in such a way that their surfaces line up as if they were all part of one large spherical curve. The polishing machine is similar to the grinding machine, but the tool is made from pitch—a thick, soft, resinous substance derived from coal tar or wood tar

output Tolerances vary with the type of lens being manufactured, but a typical acceptable variation might be plus or minus inches For a flat lens, generally one destined to become a flat mirror, the tolerance is much smaller, usually about plus or minus inches

feedback The techniques used to produce excellent lenses and mirrors have been well under-stood for many years, and major innovations in this area are unlikely. One area of active research is in coating technology. New coating substances may be developed to provide better protection for mirrors and better prevention of loss of light through reflection for lenses.