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Pioneered by Roger Angel at the Steward Observatory's mirror lab, this makes large (8.4 metres or 28 feet) thin parabolic mirrors by spinning the oven as the glass is melted and cooled. 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 ...
A parabolic reflector pointing upward can be formed by rotating a reflective liquid, like mercury, around a vertical axis. This makes the liquid-mirror telescope possible. The same technique is used in rotating furnaces to make solid reflectors. Parabolic reflectors are also a popular alternative for increasing wireless signal strength.
The primary mirror in most modern telescopes is composed of a solid glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is vacuum deposited onto the mirror, forming a highly reflective first surface mirror. Some telescopes use primary mirrors which are made differently.
Newtonian telescope design. A Newtonian telescope is composed of a primary mirror or objective, usually parabolic in shape, and a smaller flat secondary mirror.The primary mirror makes it possible to collect light from the pointed region of the sky, while the secondary mirror redirects the light out of the optical axis at a right angle so it can be viewed with an eyepiece.
The greatest advantage of a liquid mirror is its small cost, about 1% of a conventional telescope mirror. This cuts down the cost of the entire telescope at least 95%. The University of British Columbia’s 6-meter Large Zenith Telescope cost about a fiftieth as much as a conventional telescope with a glass mirror. [11]
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. The mirrors start as a flat disk of glass, typically plate glass or borosilicate glass (Pyrex). [ 4 ]
From top: Parabolic mirror showing Foucault shadow patterns made by knife edge inside radius of curvature R (red X), at R and outside R. Foucault testing is commonly used by amateur telescope makers for figuring primary mirrors in reflecting telescopes. [5] [6] The mirror to be tested is placed vertically in a stand. The Foucault tester is set ...
A telescope with only one curved mirror, such as a Newtonian telescope, will always have aberrations. If the mirror is spherical, it will suffer from spherical aberration. If the mirror is made parabolic, to correct the spherical aberration, then it must necessarily suffer from coma and off-axis astigmatism.