Assertion: newtonian telescope's mirror | /r/HasProperty | thin
Facets:
value: very
type: DEGREE
value: usually
type: DEGREE
value: in this generation of telescopes
type: LOCATION
value: unlike a lens
type: OTHER
Source sentences:
text: Unlike a lens, a mirror can be very thin.
text: In this generation of telescopes, the mirror is usually very thin, and is kept in an optimal shape by an array of actuators (see active optics).