Zoom lens, and electronic imaging system using the same

#This application claims benefits of Japanese Application No. 2002-106378 filed in Japan on 4.9, 2002, the contents of which are incorporated herein by this reference.

#The present invention relates generally to a zoom lens and an electronic imaging system using the same, and more particularly to an electronic imaging system such as a video camera or a digital camera, the depth dimension of which is diminished by providing some contrivances to an optical system portion such as a zoom lens.

#In recent years, digital cameras (electronic cameras) have received attention as the coming generation of cameras, an alternative to silver-halide 35 mm-film (usually called Leica format) cameras. Currently available digital cameras are broken down into some categories in a wide range from the high-end type for commercial use to the portable low-end type.

#FIGS. 1(a), 1(b) and 1(c) are illustrative in section of Example 1 of the zoom lens according to the present invention at the wide-angle end (a), in an intermediate state (b) and at the telephoto end (c), respectively, when the zoom lens is focused on an object point at infinity.

#FIGS. 2(a), 2(b) and 2(c) are illustrative in section of Example 2 of the zoom lens, similar to FIGS. 1(a) to 1(c).

#FIGS. 3(a), 3(b) and 3(c) are sections in schematic illustrative of Example 3 of the zoom lens, similar to FIGS. 1(a) to 1(c).

#Examples 1 to 5 of the zoom lens according to the present invention are now explained. Sectional lens configurations of Examples 1 to 5 at the wide-angle end (a), in the intermediate state (b) and at the telephoto end (c) upon focused on an object point at infinity are shown in FIGS. 1 to 5. Throughout FIGS. 1 to 5, the first lens group is indicated by G1, the second lens group by G2, a stop by S, the third lens group by G3, the fourth lens group by G4, an optical low-pass filter by LF, a cover glass for an electronic image pickup device CCD by CC, and the image plane of CCD by I. A plane-parallel plate or the taken-apart optical path-bending prism in the first lens group G1 is indicated by P. The maximum thickness of the optical low-pass filter LF used in these examples will be explained later. It is noted that instead of the near-infrared sharp cut coat, it is acceptable to use an optical low-pass filter LF coated directly with a near-infrared sharp cut coat, an infrared cut absorption filter or a transparent plane plate with a near-infrared sharp cut coat applied on its entrance surface.

#As shown typically in FIG. 6 that is an optical path diagram for Example 1 of the zoom lens upon focused on an infinite object point at the wide-angle end, the optical path-bending prism P is configured as a reflecting prism for bending the optical path through 90°.

#As shown in FIG. 1(a), 1(b) and 1(c), Example 1 is directed to a zoom lens made up of a first lens group G1 composed of a negative meniscus lens element convex on its object side, an optical path-bending prism P and a double-convex positive lens element, a second lens group G2 composed of a double-concave negative lens element and a positive meniscus lens element convex on its object side, an aperture stop S, a third lens group G3 composed of a doublet consisting of a double-convex positive lens element and a double-concave lens element and a fourth lens group G4 composed of one positive meniscus lens element convex on its object side. Upon the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 and the aperture stop S remain fixed, the second lens group G2 moves toward the image plane side of the zoom lens, the third lens group G3 moves toward the object side of the zoom lens, and the fourth lens group G4 moves toward the image plane side. For focusing on a nearby subject, the fourth lens group G4 moves toward the object side.