This rotation technique is sometimes used to make paraboloidal mirrors for astronomical telescopes, and has also been used for solar cookers.
2.
Important developments in reflecting telescopes were John Hadley's production of larger paraboloidal mirrors in 1721; the process of silvering glass mirrors introduced by L�on Foucault in 1857; and the adoption of long-lasting aluminized coatings on reflector mirrors in 1932.
3.
Schmidt realized that by employing a large spherically shaped mirror ( instead of the normal paraboloidal mirror of a reflector telescope ) and a smaller apertured diaphragm placed at the center of curvature of the mirror, he could at a stroke eliminate coma and astigmatism.
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