Assertion: lens's length | /r/HasProperty | changed
Facets:
Source sentences:
text: Lenses of this kind are now called varifocal lenses, since when the focal length is changed, the position of the focal plane also moves, requiring refocusing of the lens after each change.
text: The first true zoom lens, which retained near-sharp focus while the effective focal length of the lens assembly was changed, was patented in 1902 by Clile C. Allen (U.S. Patent 696,788).
text: Whereas lenses used in cinematography and video applications are required to maintain focus while the focal length is changed, there is no such requirement for still photography and for zoom lenses used as projection lenses.
text: In early varifocal lens lenses, the focus also shifted as the lens focal length was changed.
text: However, rectangular or square lens hoods should not be used with zoom lenses whose front elements rotate as the focal length is changed, as the hood will rotate as well, blocking parts of the angle of view.
text: The power or focal length of adjustable or variable focus can be changed to suit the needs of the wearer.
text: This lens is not parfocal - you will need to re-focus if the focal length is changed (this complicates the gravity-zoom attribute).