Assertion: eyepiece's field stop | /r/DefinedAs | ring
Facets:
value: usually
type: TEMPORAL
value: inside the barrel
type: OTHER
value: at the entrance of the eyepiece
type: LOCATION
Source sentences:
text: For moderate to short-focal length eyepieces, the field stop is usually defined by a ring inside the barrel at the entrance of the eyepiece.