US 5,296,969 AGranted

Zoom lens system having a short total length

AssigneeOlympus Optical Co., Ltd.

InventorShinichi Mihara

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Abstract

The present invention provides a zoom lens system which comprises nine or less constituent lenses in all, has a short total length and a small front lens, is reduced in terms of size, weight and cost, has a high zoom ratio and a large aperture ratio, and is best suited for use with handy camcorders, and which comprises a first lens unit G1 having a positive refracting power, a second lens unit G2 having a negative refracting power and movable horizontally along the optical axis during zooming, a third lens unit G3 constantly remaining fixed and consisting of a positive lens in which the object-side surface has a stronger curvature and at least the object-side surface takes an aspherical configuration and a negative meniscus lens in which the image-side surface has a stronger curvature, two lenses in all, said third lens unit G3 having a positive refracting power as a whole, and a fourth lens unit G4 movable horizontally along the optical axis for focus regulation during zooming and moving the object point and consisting solely of a positive single lens in which the object-side surface assumes an aspherical configuration.

A zoom lens system which includes, in order from the object side, a first lens unit having a positive refracting power, a second lens unit having a negative refracting power, including a doublet, and movable along the optical axis for zooming, a third lens unit comprising, in order from the object side, a positive leans in which the object-side surface has a stronger curvature than the image-side surface and takes an aspherical configuration and a negative meniscus lens in which the image-side surface has a stronger curvature than the object-side surface, said third lens unit having a positive refracting power as a whole, and a fourth lens unit consisting of a positive single lens in which the object-side surface takes an aspherical configuration and movable along the optical axis for zooming and focusing,

wherein said third and fourth lens units satisfy the following conditions:
##EQU8## where:
f.sub.W and f.sub.T are the focal lengths of the total system at the wide angle and telephoto ends, respectively,
f.sub.34S is the composite focal length of the third and fourth lens units when the focal length of the total system lies at (f.sub.W f.sub.T).sup.1/2 and the object point at infinity is focused,
.beta..sub.4T is the magnification of the fourth lens unit when the object point at infinity is focused at the telephoto end,
r.sub.31 and r.sub.34 are the radii of curvature of the surfaces of the third lens unit proximate to the object and image sides, respectively,
n.sub.31 and n.sub.34 are the refractive indices of the positive and negative meniscus lenses of the third lens unit, respectively,
D.sub.III is the distance on the optical axis between the surfaces of the third lens unit proximate to the object and image sides, respectively,
D.sub.34T is the space on the optical axis between the third and fourth lens units, when the object point at infinity is focused at the telephoto end, and
n.sub.5 and n.sub.6 are the refractive indices of the respective lenses of the doublet of the second lens unit.

7 more elements

Abstract

Claims13