| 摘要 |
A lens assembly (I) comprises a lens (2; 10, 11; 20) the focal length of which may be changed by application of an electric or magnetic field. A switching means (4, 15) provides a drive impulse to change the focal length of the lens (2; 10, 11; 20). An integral power source (4, 15) provides power for the switching means. A lens which can be switched between near and distance vision by the user is thereby provided.
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