Assertion: newtonian telescope's mirror | /r/HasProperty | elliptical
Facets:
value: usually
type: DEGREE
value: in shape
type: OTHER
Source sentences:
text: The secondary mirror in the Newtonian is usually elliptical in shape and is orientated such that its minor axis minimizes the size of the central obstruction that is all too important in producing images rich in contrast.
text: The secondary mirror is an elliptical shape but when presented to the focuser at the correct angle will appear as a perfect circle.
text: Modern variants may have a hyperbolic primary for increased performance (for example, the Ritchey–Chrétien design); and either or both mirrors may be spherical or elliptical for ease of manufacturing.