Assertion: eyepiece's field | /r/CapableOf | approach 15 degrees
Facets:
Source sentences:
text: 4 - Monocentric - shown is the modern form of this eyepiece, but performance level is similar to the original - maintains excellent correction even at f/5, but field is limited by secondary astigmatism, exploding as field approaches 15 degrees; since it has a significant higher order aberration component, as well as primary coma, its aberration load diminishes more quickly with slower focal ratios than in eyepiece types limited mainly by primary astigmatism.