Zoom lens, and electronic imaging system using the same

#This application claims benefits of Japanese Application No. 2002-107711 filed in Japan on Apr. 10, 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) and 1(b) are illustrative in section of Example 1 of the zoom lens according to the present invention at the wide-angle end (a), and at the telephoto end (b), respectively, when the zoom lens is focused on an object point at infinity.

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

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

#Examples 1 to 3 of the zoom lens according to the present invention are now explained. Sectional lens configurations of Examples 1 to 3 at the wide-angle end (a), and at the telephoto end (b) upon focused on an object point at infinity are shown in FIGS. 1 to 3. Throughout FIGS. 1 to 3, the first lens group is indicated by G1, a stop by S, the second lens group by G2, the third lens group by G3, an optical low-pass filter by LF, a cover glass for an electronic image pickup device CCD by CG, and the image plane of CCD by I. A plane-parallel plate, that is, the taken-apart optical path-bending prism in the first lens group G1 is indicated by P. 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. 4 that is an optical path diagram for Example 2 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 FIGS. 1(a) and 1(b), Example 1 is directed to a zoom lens made up of a first lens group G1 composed of a double-concave negative lens element, an optical path-bending prism P and a positive meniscus lens element convex on its object side, an aperture stop S, a second lens group G2 composed of a double-convex positive lens element and a double-concave negative lens element and a third lens group G3 composed of one double-convex positive lens element. Upon zooming from the wide-angle end to the telephoto end of the zoom lens, the first lens group G1 remains fixed, and the second lens group G2 moves together with the aperture stop S toward the object side and then the image plane side of the zoom lens.