Assertion: reflecting telescope's mirror | /r/HasAspect | shape
Facets:
value: precisely
type: MANNER
Source sentences:
text: This design, with two hyperbolic mirrors, is known for good imaging performance over a wide field of view, with the disadvantage that the mirrors have shapes that are hard to fabricate and test.
text: A mirror the size of Keck's cast of a single piece of glass could not be made rigid enough to hold its shape precisely; it would sag microscopically under its own weight as it was turned to different positions, causing aberrations in the optical path.