Posted: May 22nd, 2023
As Borra (2009) puts it, the curvature of liquid mirrors follows equipotential surfaces, which can be shaped by rotation to yield paraboloidal surfaces. The liquid metal is held in a container which is rotated in a gravitational field. The rotation around a vertical axis is performed at a specific speed, and the shape of the container, which is perfectly horizontal, is very close to the desired shape of the liquid metal to reduce its amount. The shape of the liquid mirror is therefore created by the natural equilibrium of gravitational forces.
Another way to affect the shape of a liquid mirror involves applying magnetic fields ferrofluids to achieve the desired shape (Borra, 2009). In practice, Primary mirror focal ratio of The Large Zenith Telescope is f/1.50 with effective focal length of 10000 meters (The Large Zenith Telescope, 2004, para. 6). It uses 4-element refracting corrector lens with the diameter of the corrected field of 24 arcmin (The Large Zenith Telescope, 2004, para. 6). The liquid dish is rotated at seven times per minute, and this exact number distributes the mercury into a 1-millimeter-thick parabolic layer. Mirrorâ€™s outer edge has a velocity of just more than 2 meters per second (Schilling, 2003, para. 6). The telescope uses 2048 x 2048 pixel CCD as a detector with the width of 16.9 arcmin and 0.495 arcsec/pixel image scale (The Large Zenith Telescope, 2004).
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