Assertion: eyepiece's diameter | /r/HasProperty | last stop
Facets:
value: usually
type: DEGREE
Source sentences:
text: This can be either the desired widest angular width or linear dimension of full illumination produced at the field stop (which determines the radius dimensions necessary for all secondary mirrors, stops and baffles), or the secondary mirror minor axis (which controls the effective field of full illumination), or the internal diameter of a refractor or Cassegrain stop or baffle (in refractors, usually the last stop before the focal surface).