Assertion: effective focal ratio | /r/HasProperty | 18
Facets:
value: typically
type: DEGREE
Source sentences:
text: All Cassegrain designs are significantly limited by the front opening of the primary baffle and in some cases by the opening in the visual back; at large effective focal ratios (typically  > 18), depending on the diameter and magnification of the secondary mirror, no baffling solution may be possible that blocks all stray light without vignetting.