make a list of lenses and Mirrors used in making a powerful telescope
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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. The most important raw material used to make optical glass is silicon dioxide, which must not contain more than one-tenth of one percent (0.1%) of impurities.
Optical glasses are generally divided into crown glasses and flint glasses. Crown glasses contain varying amounts of boron oxide, sodium oxide, potassium oxide, barium oxide, and zinc oxide. Flint glasses contain lead oxide. The antireflective coating on telescope lenses is usually composed of magnesium fluoride.
A telescope mirror can be made from glass that is somewhat less pure than that used to make a lens, since light does not pass through it. Often a strong, temperature-resistant glass such as Pyrex is used. Pyrex is a brand name for glass composed of silicon dioxide, boron oxide, and aluminum oxide. The reflective coating for telescope mirrors is usually made from aluminum, and the protective coating on top of the reflective coating is usually composed of silicon dioxide.
Hardware components that are directly involved with the optical system are usually manufactured from steel or steel and zinc alloys. Less critical parts can be made from light, inexpensive materials such as aluminum or acrylonitrile-butadiene-styrene plastic, commonly called ABS.
