Assertion: telescope's lens | /r/HasAspect | high f-ratio
Facets:
value: very
type: DEGREE
Source sentences:
text: Considerably higher magnifications can be reached with this design, but to overcome aberrations the simple objective lens needs to have a very high f-ratio (Johannes Hevelius built one with a 46-metre (150 ft) focal length, and even longer tubeless "aerial telescopes" were constructed).