Assertion: camera lens's length | /r/HasProperty | determined
Facets:
value: by passing light
type: MANNER
Source sentences:
text: The focal length of a lens is determined when the lens is focused at infinity.
text: The focal length is determined whenever the lenses are focused at infinity.
text: No image is formed during such a test, and the focal length must be determined by passing light (for example, the light of a laser beam) through the lens, examining how much that light becomes dispersed/ bent, and following the beam of light backwards to the lens's focal point.