Assertion: eyepiece | /r/HasProperty | usable
Facets:
Source sentences:
text: Those eyepieces are usable until you can get something better, but their polish and coatings are noticeably inferior to those of eyepieces that don’t cost all that much more.
text: Small, cheap telescopes and microscopes are sometimes supplied with the eyepieces that give magnification far higher than is usable.