Assertion: newtonian telescope's mirror | /r/HasProperty | concave ellipsoid
Facets:
Source sentences:
text: It travels to the secondary mirror (B) which is a concave ellipsoid.
text: The Gregorian telescope consists of two concave mirrors; the primary mirror (a concave paraboloid) collects the light and brings it to a focus before the secondary mirror (a concave ellipsoid) where it is reflected back through a hole in the centre of the primary, and thence out the bottom end of the instrument where it can be viewed with the aid of the eyepiece.