Patent ID: 6522479
Filing Date: 2003-02-18
Classification: G02B

Abstract:
A zoom lens having both manual mode and auto focus mode of focus adjustment, said zoom lens comprising, in order from the object side:a focus portion; a zoom portion; and a main portion; wherein zooming is accomplished by moving some or all of the lens elements in the zoom portion along the optical axis; what would otherwise be a fluctuation of the image surface with change of object distance, is corrected as follows in manual mode, by manually moving some or all of the lens elements of the focus portion along the optical axis based on visual observation of the object through the zoom lens, and in auto focus mode, by micro-vibrating some or all of the lens elements of a lens group in the light path following the focus portion while detecting a signal that detects image quality variations caused by this micro-vibration, and by using the detected signal to automatically control the position of those lens elements in the focus portion that are manually moved in manual mode, so as to thereby automatically adjust the focus of the zoom lens; and wherein, in order from the object side, the first lens group has positive refractive power and comprises said focus portion; the second and third lens groups comprise the zoom portion, said third lens group having negative refractive power; the fourth and fifth lens groups comprise the main portion, and each of the fourth and fifth lens groups has positive refractive power; and the focal length of the zoom lens is changed by moving the second lens group and the third lens group along the optical axis, and some or all of the lens elements of the fourth lens group are micro-vibrated in the direction of the optical axis when in auto focus mode.