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Parsons improved the techniques of casting, grinding and polishing large telescope mirrors from speculum metal, and constructed steam-powered grinding machines for parabolic mirrors. His 3 foot (91 cm) mirror of 1839 was cast in smaller pieces and then fitted together before grinding and polishing; its 1840 successor was cast in a single piece.
Grinding a mirror using an abrasive and a smaller tool over 300 mm mirror ("ATM Korenica 2006", in Korenica, Croatia) Since the Newtonian reflector is the most common telescope built by amateur telescope makers, large sections of the literature on the subject are devoted to fabrication of the primary mirror .
Generally, a spin-cast paraboloid is not sufficiently accurate to permit its immediate use as a telescope mirror or lens, so it is corrected by computer-controlled grinding machines. The amount of grinding done, and the mass of glass material wasted, are much less than would have been required without spinning.
The term is applied to the fabrication of large telescope mirrors, where the natural paraboloid curve followed by the molten glass greatly reduces the amount of grinding required. Rather than being cast by pouring glass into a mold (with top and bottom), an entire turntable containing the peripheral mold, and the back pattern (a honeycomb ...
The telescope main-frame was built by members from scaffold tubing and mounted on an equatorial fork driven by DC electrical motors for tracking the stars. The main mirror was ground at the observatory by a home-made mirror grinding machine over a period of four years, however this piece of glass was damaged when sent away for aluminising.
Fifteen people signed up for that class; 14 men, most of whom were workers from Jones & Lamson, and one woman, a school teacher. Porter showed them how to make Newtonian reflectors, teaching all the aspects of mirror making including grinding, polishing, and testing their own mirrors, and designing and constructing telescope mounts. The members ...
Although speculum metal mirror reflecting telescopes could be built very large, such as William Herschel's 126-cm (49.5-inch) "40-foot telescope" of 1789 and Lord Rosse 183-cm (72-inch) mirror of his "Leviathan of Parsonstown" of 1845, impracticalities in using the metal made most astronomers prefer their smaller refracting telescope ...
This limits Hubble's performance as an infrared telescope. [35] The backup mirror, by Kodak; its inner support structure can be seen because it is not coated with a reflective surface. Perkin-Elmer (PE) intended to use custom-built and extremely sophisticated computer-controlled polishing machines to grind the mirror to the required shape. [33]