Assertion: newtonian telescope's mirror | /r/HasProperty | ground
Facets:
Source sentences:
text: Both internal mirrors, primary and secondary, are ground and polished under computer control for guaranteed diffraction limited performance then coated with 91% reflectivity enhanced aluminum, and then coated again with a protective layer of quartz for long life.
text: Both primary and diagonal mirrors are ground and polished under computer control for guaranteed diffraction limited performance, coated with 91% reflectivity aluminum, and overcoated with a protective layer of silicon dioxide (quartz) for long life.