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After making that suggestion, I realize that Earth's gravity would make perfectly parabolic lenses if the suggestion was viable. That people aren't already get
by klyrs 4y ago
After making that suggestion, I realize that Earth's gravity would make perfectly parabolic lenses if the suggestion was viable. That people aren't already getting perfect(-enough) parabolic lenses from this technique suggests to me that it's probably not actually viable. Oh well.
Come to think of it, a film suspended from a ring would create a catenary[1] under constant gravity -- which is pretty darned close to a parabola but, I suspect, not good enough for astronomy.
[1] https://en.wikipedia.org/wiki/Catenary https://en.wikipedia.org/wiki/Catenary
- eesmith 4y agoI think the link you want is https://en.wikipedia.org/wiki/Liquid-mirror_telescope https://en.wikipedia.org/wiki/Liquid-mirror_telescope - "The liquid and its container are rotated at a constant speed around a vertical axis, which causes the surface of the liquid to assume a paraboloidal shape. This parabolic reflector can serve as the primary mirror of a reflecting telescope." This method in this article uses the same principle: “It has long been known that rotating liquids that are aligned with the local gravitational axis will naturally form a paraboloid surface shape,...“ See also https://en.wikipedia.org/wiki/Liquid-mirror_space_telescope https://en.wikipedia.org/wiki/Liquid-mirror_space_telescope .
- klyrs 4y agoI'm familiar with liquid mirror telescopes, but I was responding to some theorizing about using an inflated film. Without gravity, the film would produce a sphere; suspended in gravity, it would produce a catenary.