Varifocal lens
A varifocal lens is a camera lens with variable focal length in which focus changes as focal length changes, as compared to parfocal zoom lens, which remains in focus as the lens zooms. Many so-called "zoom" lenses, particularly in the case of fixed lens cameras, are actually varifocal lenses, which give lens designers more flexibility in optical design trade-offs than parfocal zoom. These are practical because of auto-focus, and because the camera processor can automatically adjust the lens to keep it in focus while changing focal length making operation practically indistinguishable from a parfocal zoom. Varifocal lenses can be used for image display as well as capture, and Oculus VR has confirmed developing a varifocal display for virtual reality.
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