Zoom lens system for use with a compact camera

Claim 2

A zoom lens system comprising, in order from the object side, a first lens group having a positive focal length and a second lens group having a negative focal length and which achieves zooming between a wide angle position and a narrow angle position by changing the distance between the first and second lens groups, said first lens group having a positive focal length and being composed of a lens unit (a) having a negative focal length that is positioned on the object side of said first lens group and which comprises at least one positive lens element and at least one negative lens element, a lens unit (b) having a positive focal length that is positioned on the image side of said first lens group and which comprises at least one negative lens element and at least one positive lens element, and a lens unit (m) that is positioned between the lens units a and b and which comprises at least one positive lens element having its convex surface directed toward the image side, said lens system satisfying the following conditions: (1) 1.35<f s /f 1 <1.7; (2) 1.69<N 1an ; (3) 34<ν 1an ; (4) -2.0<f s /f 1bn <-0.7; (5) 9<ν 1bp -ν 1bn ; (6) 0.23<f Bs /f s <0.5; and (7) 0.3<f s /f 1m <1.0 where f s : the focal length of the overall system at the wide angle position; f 1 : the focal length of the first lens group; N 1an : the refractive index at d-line of the negative lens element in the lens unit a; ν 1an : the Abbe number of the negative lens element in the lens unit a; f 1bn : the focal length of the negative lens element in the lens unit b; ν 1bp : the Abbe number of the positive lens element in the lens unit b; ν 1bn : the Abbe number of the negative lens element in the lens unit b; f Bs : the back focus at the wide angle position; and f 1m : the focal length of the lens unit m.

Claim 3

A zoom lens system according to claim 1, wherein said second lens group has a negative focal length being composed of, in order from the object side, a positive meniscus lens element which has a large curvature and which has its convex surface directed toward the image side and at least two negative meniscus lens elements which have a large curvature and each of which has its concave surface directed toward the object side, said second lens group satisfying the following condition: (8) 1.7<N 2n where N 2n : the average of the refractive indices at d-line of the negative lens elements in the second lens group.

Claim 4

A zoom lens system according to claim 2 wherein said lens unit a having a negative focal length comprises, in order from the object side, a positive lens element with a large curvature which has its convex surface directed toward the object side and a negative lens element with a large curvature which has its concave surface directed toward the object side, said lens unit b having a positive focal length and comprising, in order from the object side, a bioconvex positive lens element and a negative meniscus lens element cemented thereto which has its concave surface directed to the object side.

Claim 5

A zoom lens system according to claim 3, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 20.136 2.109 1.69680 55.5 2 38.230 1.795 3 -26.135 1.300 1.83400 37.2 4 387.577 1.719 5 -153.126 3.500 1.77250 49.6 6 -43.752 3.421 7 27.155 4.210 1.65016 39.4 8 -9.493 1.300 1.80518 25.4 9 -21.878 8.90-1.699 10 -32.888 2.682 1.80518 25.4 11 -15.811 1.254 12 -19.112 1.500 1.83400 37.2 13 -37.330 2.865 14 -11.967 1.500 1.83400 37.2 15 -47.652 ______________________________________

Claim 6

A zoom lens system according to claim 3, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 23.002 1.963 1.69680 55.5 2 44.778 1.899 3 -23.164 1.300 1.83481 42.7 4 -2384.334 1.259 5 -90.174 6.000 1.74400 44.7 6 -29.728 2.124 7 28.961 3.928 1.58267 46.3 8 -10.344 2.244 1.80518 25.4 9 -19.955 11.05-3.388 10 -37.145 2.972 1.80518 25.4 11 -15.613 1.631 12 -14.904 1.500 1.83400 37.2 13 -34.696 2.369 14 -14.343 1.500 1.83400 37.2 15 -56.214 ______________________________________

Claim 7

A zoom lens system according to claim 3, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 20.091 2.130 1.69680 55.5 2 46.182 1.755 3 -24.112 1.300 1.83400 37.2 4 126.183 2.374 5 -55.460 1.885 1.76200 40.1 6 -22.881 3.755 7 27.881 3.857 1.54814 45.8 8 -11.400 1.300 1.80518 25.4 9 -20.767 11.12-2.773 10 -35.550 2.860 1.80518 25.4 11 -16.324 2.217 12 -14.398 1.500 1.83400 37.2 13 -35.945 1.996 14 -16.707 1.500 1.83400 37.2 15 -53.051 ______________________________________

Claim 8

A zoom lens system according to claim 3, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 24.834 1.81 1.69680 55.5 2 45.134 1.99 3 -22.474 1.41 1.83481 42.7 4 -151.988 0.34 5 -54.518 7.00 1.74950 35.3 6 -25.252 3.65 7 27.066 4.24 1.51112 60.5 8 -11.617 2.50 1.80518 25.4 9 -20.160 12.57-7.78-3.83 10 -52.175 3.21 1.80518 25.4 11 -17.297 1.87 12 -15.240 1.63 1.83481 42.7 13 -57.266 2.53 14 -16.722 1.63 1.83400 37.2 15 -59.282 ______________________________________

Claim 9

A zoom lens system according to claim 3, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 29.587 1.77 1.69680 55.5 2 66.847 1.89 3 -20.327 1.41 1.83481 42.7 4 -103.024 0.32 5 -49.000 6.69 1.72342 38.0 6 -22.896 2.99 7 31.605 4.25 1.51454 54.7 8 -11.453 2.50 1.80518 25.4 9 -19.530 13.84 - 7.99 - 3.84 10 -60.655* 3.43 1.80518 25.4 11 -17.536 1.37 12 -15.251 1.63 1.83400 37.2 13 -34.886 2.47 14 -15.036 1.63 1.83400 37.2 15 -91.810 ______________________________________ *r.sub.10 surface is aspherical ##STR9## a.sub.4 y.sup.4 + a.sub.6 y.sup.6 + a.sub.8 y.sup.8 + a.sub.10 y.sup.10 c = 1/r.sub.10 a.sub.4 = 0.17199 × 10.sup.-4 a.sub.6 = -0.64881 × 10.sup.-7 a.sub.8 = 0.19095 × 10.sup.-8 a.sub.10 = -0.96176 × 10.sup.-11 k = 0.0 where y is the height from the optical axis, and k is the aspherical coefficient.

Claim 10

A zoom lens system according to claim 3, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 30.072 1.74 1.69680 55.5 2 64.653 1.94 3 -19.914 1.41 1.83481 42.7 4 -104.190 0.32 5 -49.065 7.00 1.72342 38.0 6 -22.868 2.52 7 31.048 4.38 1.51454 54.7 8 -11.289 2.50 1.80518 25.4 9 -19.137 13.62-7.89-3.84 10 -67.801 3.41 1.80518 25.4 11 -17.895 1.51 12 -16.677 1.63 1.83400 37.2 13 -75.103 2.91 14 -16.113 1.63 1.83400 37.2 15 -65.812 ______________________________________

Claim 11

A zoom lens according to claim 2 wherein said lens unit a having a negative focal length comprises, in order from the object side, a positive lens element with a large curvature which has its convex surface directed toward the object side and a negative lens element with a large curvature which has its concave surface directed toward the object side, said lens unit b having a positive focal length and comprisng, in order from the object side, a negative meniscus lens element which has its convex surface directed toward the object side and a bioconvex positive lens cemented thereto.

Claim 12

A zoom lens system according to claim 10, wherein an i-th one of said lens elements having radii of curvature r i and r i+1 , a thickness d i , a refractive index N i , an Abbe number ν i and an aerial distance d i-1 between separated adjacent lens elements satisfies all parts of the following table: ______________________________________ i r.sub.i d.sub.i N.sub.i ν.sub.i ______________________________________ 1 19.352 2.153 1.69680 55.5 2 48.677 1.618 3 -24.350 1.300 1.83400 37.2 4 113.517 1.247 5 -29.243 3.293 1.76200 40.1 6 -20.314 2.499 7 15.672 1.300 1.80518 25.4 8 8.802 6.000 1.56732 42.8 9 -32.874 8.730-2.102 10 -38.845 2.929 1.80518 25.4 11 -16.322 1.459 12 -17.543 1.500 1.83400 37.2 13 -68.469 3.102 14 -12.735 1.500 1.83400 37.2 15 -30.797 ______________________________________

Claim 13

A zoom lens system according to claim 1 wherein said lens unit a having a negative focal length comprises, in order from the object side, a positive lens element with a large curvature which has its convex surface directed toward the object side and a negative lens element with a large curvature which has its concave surface directed toward the object side, said lens unit b having a positive focal length and comprising, in order from the object side, a bioconvex positive lens element and a negative meniscus lens element cemented thereto which has its concave surface directed to the object side.

Claim 14

A zoom lens according to claim 1 wherein said lens unit a having a negative focal length comprises, in order from the object side, a positive lens element with a large curvature which has its convex surface directed toward the object side and a negative lens element with a large curvature which has its concave surface directed toward the object side, said lens unit b having a positive focal length and comprisng, in order from the object side, a negative meniscus lens element which has its convex surface directed toward the object side and a bioconvex positive lens cemented thereto.