Bright wide-angle zoom lens

Claim 2

In a compact and high-performance bright wide-angle zoom lens comprising, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power, with a stop diaphragm being disposed between the front and rear groups, said front group, said stop diaphragm and said rear group being capable of independent mechanical movement in response to a change in the focal length of the overall system, the improvement wherein the rear group having a positive refractive power is composed, in order from the object side, of a positive lens unit, a negative lens unit, and a positive lens unit, with a lens element having a refractive index gradient profile along the optical axis being disposed in the positive lens unit on the image side of the rear group.

Claim 3

The zoom lens according to claim 1 wherein said lens element having a refractive index gradient profile along the optical axis satisfies the following relationship: 0.02<ΔN>0.06 where ΔN is the absolute value of the change in the refractive index of said lens element.

Claim 4

The zoom lens according to claim 1 wherein said front group having a negative refractive power is composed, in order from the object side, of a positive lens, negative lens, negative lens, positive lens, negative lens, and a positive lens.

Claim 5

The zoom lens according to claim 1, wherein said rear group having a positive refractive power is composed of a positive lens unit, a negative lens unit, and a positive lens unit, said first positive lens unit being composed, in order from the object side, of a positive cemented lens comprised of positive and negative lenses, a positive lens, and a positive lens having a surface with a smaller radius of curvature directed toward the object side, said negative lens unit being composed of a negative lens having a surface with a smaller radius of curvature directed toward the image side, said second positive lens unit being composed, in order from the object side, of a positive cemented lens comprised of negative and positive lenses and a positive lens, and the positive lens which is the closest to the image side being a lens element having a refractive index gradient profile along the optical axis.

Claim 6

The zoom lens according to claim 1, further satisfying the following chart: ______________________________________ Surface No. r d Na Nb Nc ______________________________________ 1 151.755 3.11 1.73654 1.73106 1.74504 2 921.764 0.20 3 106.300 1.20 1.83633 1.82814 1.84942 4 25.970 3.31 5 38.754 1.50 1.83633 1.82814 1.84942 6 27.450 5.54 7 317.405 2.58 1.72539 1.71847 1.73655 8 -200.000 1.80 9 -87.610 1.20 1.63975 1.63646 1.64638 10 71.800 0.20 11 39.010 4.24 1.80843 1.79712 1.82717 12 232.266 Variable 13 -254.587 3.57 1.83685 1.82965 1.84818 14 -33.124 1.15 1.85029 1.83768 1.87133 15 -70.680 0.20 16 110.000 2.46 1.80580 1.79941 1.81578 17 -525.000 0.20 18 22.910 4.60 1.83633 1.82814 1.84942 19 61.411 3.34 20 719.556 5.00 1.85029 1.83768 1.87133 21 21.273 2.42 22 83.484 1.00 1.83685 1.82965 1.84818 23 21.776 6.49 1.56968 1.56629 1.57482 24 -105.520 0.20 25 ∞ 3.00 varies as shown below 26 -34.055 ______________________________________ 28.8 35.0 48.0 ______________________________________ 18.36 12.41 2.93 d.sub.12 stop stop stop diaphragm diaphragm diaphragm 11.64 6.22 1.39 ______________________________________ ΔN = 0.0309 ______________________________________ where r is the radius of curvature of a specific lens surface; d is the thickness of a specific lens or the aerial distance between adjacent lenses; and Na, Nb and Nc represent the refractive indices of a specific lens at wavelengths of 0.5682 μm, 0.6471 μm, and 0.488 μm, respectively.

Claim 7

The zoom according to claim 1, further satisfying the following chart: ______________________________________ f = 28.8˜35.0˜48.0 F.sub.NO = 1:2.25˜2.55˜2.90 ω = 38.3°˜32.3°˜24.3° ______________________________________ Surface No. r d Na Nb Nc ______________________________________ 1 227.465 3.06 1.51718 1.51414 1.52177 2 -919.110 0.20 3 98.688 1.20 1.83633 1.82814 1.84942 4 25.119 3.93 5 43.799 1.50 1.73088 1.72170 1.74598 6 30.483 5.09 7 1081.085 2.18 1.74351 1.73396 1.75925 8 -230.069 1.98 9 -82.020 1.20 1.62149 1.61764 1.62740 10 80.646 0.20 11 42.367 4.28 1.80843 1.79712 1.82717 12 927.908 Variable 13 -368.365 3.74 1.78775 1.78120 1.79807 14 -33.324 1.15 1.85029 1.83768 1.87133 15 -67.654 0.20 16 93.816 2.50 1.80580 1.79941 1.81578 17 -1903.529 0.20 18 23.039 5.24 1.83633 1.82814 1.84942 19 55.039 2.99 20 319.618 5.00 1.85029 1.83768 1.87133 21 20.934 3.05 22 76.266 1.00 1.83685 1.82965 1.84818 23 21.619 6.04 1.56968 1.56629 1.57482 24 -111.609 0.20 25 ∞ 3.00 varies as shown below 26 -35.265 ______________________________________ 28.8 35.0 48.0 ______________________________________ 18.20 13.22 2.28 d.sub.12 stop stop stop diaphragm diaphragm diaphragm 11.15 4.72 1.31 ______________________________________ ΔN = 0.0309 ______________________________________ where r is the radius of curvature of a specific lens surface; d is the thickness of a specific lens or the aerial distance between adjacent lenses; and Na, Nb, and Nc represent the refractive indices of a specific lens at wavelengths of 0.5682 μm, 0.6471 μm, and 0.488 μm, respectively.

Claim 8

In a compact and high-performance bright wide-angle zoom lens comprising, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power, with a stop diaphragm being disposed between the front and rear groups, said front group, said stop diaphragm and said rear group being capable of independent mechanical movement in response to a change in the focal length of the overall system, the improvement wherein the rear group having a positive refractive power is composed, in order from the object side, of a positive lens unit, a negative lens unit, and a positive lens unit, with a lens element having a refractive index gradient profile along the optical axis being disposed in the positive lens unit on the image side of the rear group, and wherein said front group having a negative refractive power is composed, in order from the object side, of a positive lens, negative lens, negative lens, positive lens, negative lens, and a positive lens.

Claim 9

In a compact and high-performance bright wide-angle zoom lens comprising, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power, with a stop diaphragm being disposed between the front and rear groups, said front group, said stop diaphragm and said rear group being capable of independent mechanical movement in response to a change in the focal length of the overall system, the improvement wherein the rear group having a positive refractive power is composed, in order from the object side, of a positive lens unit, a negative lens unit, and a positive lens unit, with a lens element having a refractive index gradient profile along the optical axis being disposed in the positive lens unit on the image side of the rear group, and wherein said front group having a negative refractive power is composed, in order from the object side, of a positive lens, negative lens, negative lens, positive lens, negative lens, and a positive lens.

Claim 10

In a compact and high-performance bright wide-angle zoom lens comprising, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power, with a stop diaphragm being disposed between the front and rear groups, said front group, said stop diaphragm and said rear group being capable of independent mechanical movement in response to a change in the focal length of the overall system, the improvement wherein the rear group having a positive refractive power is composed, in order from the object side, of a first positive lens unit, a negative lens unit, and a second positive lens unit, said first positive lens unit being composed, in order from the object side, of a positive cemented lens comprised of positive and negative lenses, a positive lens, and a positive lens having a surface with a smaller radius of curvature directed toward the object side, said negative lens unit being composed of a negative lens having a surface with a smaller radius of curvature directed toward the image side, said second positive lens unit being composed, in order from the object side, of a positive cemented lens comprised of negative and positive lenses and a positive lens, the last-mentioned positive lens which is the closest to the image side being a lens element having a refractive index gradient profile along the optical axis.

Claim 11

In a compact and high-performance bright wide-angle zoom lens comprising, in order from the object side, a front group having a negative refractive power and a rear group having a positive refractive power, with a stop diaphragm being disposed between the front and rear groups, said front group, said stop diaphragm and said rear group being capable of independent mechanical movement in response to a change in the focal length of the overall system, the improvement wherein the rear group having a positive refractive power is composed, in order from the object side, of a first positive lens unit, a negative lens unit, and a second positive lens unit, said first positive lens unit being composed, in order from the object side, of a positive cemented lens comprised of positive and negative lenses, a positive lens, and a positive lens having a surface with a smaller radius of curvature directed toward the object side, said negative lens unit being composed of a negative lens having a surface with a smaller radius of curvature directed toward the image side, said second positive lens unit being composed, in order from the object side, of a positive cemented lens comprised of negative and positive lenses and a positive lens, the last-mentioned positive lens which is the closest to the image side being a lens element having a refractive index gradient profile along the optical axis.