Zoom lens system

Abstract

A zoom lens system has a first lens unit located closest to an object side and moves in an optical axis direction during both zooming and focusing and a light shielding plate which moves in a same direction and by same amount as the first lens unit during zooming, while the light shielding plate being stationary during focusing. As a result, adequate light is secured for peripheral areas when the lens system is in focus on a close-range object and the occurrence of flaring is prevented when the lens system is in focus on an object located at infinity.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a zoom lens system, and more particularly to a zoom lens system suited for a silver halide film cameras and a digital cameras.

2. Description of the Related Art

A zoom lens systems in which the first lens unit located closest to the object has a positive refractive power and said first lens unit moves during zooming and focusing are conventionally known. This conventional zoom lens system, however, has a problem that it is difficult to ensure adequate light for peripheral areas when it is in focus on a close-range object. Because of this problem in, light for peripheral areas have been conventionally secured while the lens system is in focus on a close-range object by means of increasing the effective diameter of the first lens unit.

However, with a conventional zoom lens system, flaring occurs when the lens system is in focus on an object located at infinity.

OBJECT AND SUMMARY

The present invention was made in view of the problems described above. Its object is to provide a zoom lens system when it is possible to ensure adequate light for peripheral areas when the lens system is in focus on a close-range object and when the occurrence of flaring is also prevented when the lens system is in focus on an object located at infinity.

In order to attain the object described above, the zoom lens system of the present invention comprises multiple lens units, wherein the first lens unit which among said multiple lens units is located closest to the object has a positive refractive power and moves along the optical axis during zooming and focusing, and wherein said zoom lens system also has a light shielding plate that moves in the same direction and by the same amount as the first lens unit during zooming but does not move during focusing.

These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following description, like parts are designated by like reference numbers throughout the several drawings.

FIG. 1 shows the lens construction of embodiment 1 of the present invention.

FIG. 2 shows the lens construction of embodiment 2 of the present invention.

FIG. 3 shows the lens construction of embodiment 3 of the present invention.

FIG. 4 shows the optical paths of embodiment 1 of the present invention when the lens system is in focus on an object located at infinity.

FIG. 5 shows the optical paths of embodiment 1 of the present invention when the lens system is in focus on a close-range object.

FIG. 6 shows the optical paths of comparison example 1 when the lens system is in focus on an object located at infinity.

FIG. 7(a) to FIG. 7(c) show the aberrations of embodiment 1 of the present invention.

FIG. 8(a) to FIG. 8(c) show the aberrations of to comparison example 1.

FIG. 9(a) to FIG. 9(e) show the aberrations of to embodiment 2 of the present invention.

FIG. 10(a) to FIG. 10(e) show the aberrations of comparison example 2.

FIG. 11(a) to FIG. 11(e) show the aberrations of example 3 of the present invention.

FIG. 12(a) to FIG. 12(e) show the aberrations of comparison example 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are explained below with reference to the drawings.

FIG. 1 shows the lens construction of embodiment 1, with the locations of lenses when the lens system is in focus on an object located at infinity using the shortest focal length. FIGS. 2 and 3 show embodiments 2 and 3, respectively, and show the locations of lenses when the lens system is in focus on an object located at infinity using the longest focal length. Arrows m1 through m4 in FIG. 1 indicate the loci of the movement of first lens unit Gr1 through fourth lens unit Gr4 from the shortest focal length condition (W) to the longest focal length condition (T) Arrows m1 through m4 in FIGS. 2 and 3 show the loci of the movement of first lens unit. Gr1 through fourth lens unit Gr4 from the longest focal length condition (T) to the shortest focal length condition (W).

In the explanation below, the constructions of embodiments 1 through 3 described above excluding light shielding plate S will be called comparison examples 1 through 3, respectively.

In FIG. 1, embodiment 1 comprises, from the object side, first lens unit Gr1 having a positive refractive power, second lens unit Gr2 having a negative refractive power, third lens unit Gr3 having a positive refractive power and fourth lens unit Gr4 having a negative refractive power.

First lens unit Gr1 comprises, from the object side, negative meniscus lens L1 having a convex surface on the object side and lens L2 with convex surfaces on both sides. Second lens unit Gr2 comprises, from the object side, lens L3 having concave surfaces on both sides and positive meniscus lens L4 having a concave surface on the object side. Third lens unit Gr3 comprises, from the object'side, lens L5 having concave surfaces on both sides, lens L6 having convex surfaces on both sides and lens L7 having convex surfaces on both sides. Fourth lens unit Gr4 comprises, from the object side, positive meniscus lens L8 having a concave surface on the object side and lens L9 having concave surfaces on both sides. Aperture stop A is located on the object side of third lens unit Gr3 and moves together with third lens unit Gr3 during zooming.

In FIG. 1, S is a light shielding plate having a fixed aperture diameter. Light shielding plate S is located on the image side of first lens unit Gr1 and moves together with first lens unit Gr1, or in other words, in the same direction and by the same amount as first lens unit Gr1, during zooming. Focusing in embodiment 1 is attained by zooming out first lens unit Gr1, but light shielding plate S is not moved during focusing.

In FIG. 2, embodiment 2 comprises, from the object side, first lens unit Gr1 having a positive refractive power, second lens unit Gr2 having a negative refractive power, third lens unit Gr3 having a positive refractive power and fourth lens unit Gr4 having a positive refractive power.

First lens unit Gr1 comprises, from the object side, a combination lens consisting of negative meniscus lens L1 having a convex surface on the object side and lens L2 having convex surfaces on both sides, and positive meniscus lens L3 having a convex surface on the object side. Second lens unit Gr2 comprises, from the object side, negative meniscus lens L4 having a convex surface on the object side, lens L5 having concave surfaces on both sides, positive meniscus lens L6 having a convex surface on the object side and lens L7 having concave surfaces on both sides. Third lens unit Gr3 comprises, from the object side, lens L8 having convex surfaces on both sides, a combination lens consisting of lens L9 having convex surfaces on both sides and lens L10 having concave surfaces on both sides, and lens L11 having convex surfaces on both sides. Fourth lens unit Gr4 comprises combined aspherical lens L12 having concave surfaces on both sides, said lens L12 comprising spherical lenses s25 and s26 having concave surfaces on both sides and aspherical surface s24 attached to the object side surface of spherical lenses s25 and s26. Aperture stop A is located on the object side of third lens unit Gr3 and moves together with third lens unit Gr3 during zooming.

In FIG. 2, S is a light shielding plate having a fixed aperture diameter which is used in the present invention. Shielding plate S is located on the image side of first lens unit Gr1. It moves together with first lens unit Gr1, or in other words, in the same direction and by the same amount as first lens unit Gr1, during zooming. Focusing in embodiment 2 is attained by zooming out first lens unit Gr1, but light shielding plate S is not moved during focusing.

In FIG. 3, embodiment 3 comprises, from the object side, first lens unit Gr1 having a positive refractive power, second lens unit Gr2 having a negative refractive power and third lens unit Gr3 having a positive refractive power.

First lens unit Gr1 comprises, from the object side, a combination lens consisting of negative meniscus lens L1 having a convex surface on the object side and lens L2 having convex surfaces on both sides, and positive meniscus lens L3 having a convex surface on the object side. Second lens unit Gr2 comprises, from the object side, a combination lens consisting of positive meniscus lens L4 having a concave surface on the object side and lens L5 having concave surfaces on both sides, and a combination lens consisting of lens L6 having concave surfaces on both sides and lens L7 having convex surfaces on both sides. Third lens unit Gr3 comprises, from the object side, lens L8 having convex surfaces on both sides, a combination lens consisting of lens L9 having convex surfaces on both sides and lens L10 having concave surfaces on both sides, a combination lens consisting of negative meniscus lens L11 having a convex surface on the object side and positive meniscus lens L12 having a convex surface on the object side, positive meniscus lens L13 having a con cave surface on the object side, negative meniscus lens L14 having a concave surface on the object side, and positive meniscus lens L15 having a convex surface on the object side. A is located on the image side of second lens unit Gr2 and moves together with second lens unit Gr2 during zooming.

In FIG. 3, S is a light shielding plate having a fixed aperture diameter which is used in the present invention. Light shielding plate S is located on the image side of first lens unit Gr1. It moves together with first lens unit Gr1, or in other words, in the same direction and by the same amount as first lens unit Gr1, during zooming. Focusing in embodiment 3 is attained by moving out first lens unit Gr1, but light shielding plate S is not moved during focusing.

FIG. 6 shows the optical paths when focusing has been performed on an object located at infinity in comparison example 1. Since this comparison example does not have a light shielding plate, the lower extra-axial light rays are regulated by the effective diameter of first lens unit Gr1. In the case of the comparison example, flaring occurs due to the lower extra-axial light rays.

On the other hand, in embodiments 1 through 3 described above, the lower extra-axial light rays, which are the cause of flaring in comparison example 1, are shielded by light shielding plate S. With regard to embodiment 1, FIG. 4 clearly shows how the lower extra-axial light rays are shielded by light shielding plate S. As shown in this drawing, the lower extra-axial light rays are shielded by light shielding plate S in embodiments 1 through 3, and therefore flaring is prevented from occurring.

FIG. 5 shows the optical paths when focusing has been performed in embodiment 1 on a close-range object using the longest focal length (this corresponds to close-range distance 1.1 in embodiment 1 described below). As is clear from this drawing, adequate light is secured for peripheral areas when the lens system is in focus on a close-range object as well in the present invention.

Tables 1 through 3 show embodiments, i.e., specific representations of the embodiments described above. Embodiment 1 in Table 1 is a specific representation corresponding to embodiment 1, embodiment 2 in Tables 2 is a specific representation corresponding to embodiment 2, and embodiment 3 in Table 3 is a specific representation corresponding to embodiment 3. In each embodiment, ri (i=1, 2, 3, . . . ) represents the radius of curvature of the ith lens surface from the object side; di (i=1, 2, 3, . . . ) represents the ith axial distance from the object side; and Ni (i=1, 2, 3, . . . ) and .nu.i (i=1, 2, 3, . . . ) represent the refractive index and the Abbe number with regard to the d-line of the ith lens from the object side, respectively. Focal length f and F-number FNO of the entire lens system in the shortest focal length condition (W), middle focal length condition (M) and longest focal length condition (T) are also shown.

In embodiment 2, the surfaces marked with asterisks in the radius of curvature column are aspherical. The configuration of an aspherical surface is defined by equation shown below. ##EQU1## Where, x: height in a direction vertical to the optical axis;

y: amount of displacement from the reference spherical surface along the optical axis; C: paraxial curvature; .epsilon.: quadratic surface parameter; and Ai: ith aspherical coefficient. TABLE 1______________________________________(1st Embodiment)f = 57.4 to 98.7 to 165.8 Fno. = 4.61 to 5.38 to 5.55 AbbeRadius of Curvature Axial Distance Refractive ouIndex number______________________________________r1 59.535 d1 1.850 N1 1.84666 .nu.1 23.82r2 40.872 d2 0.250r3 43.289 d3 5.500 N2 1.69680 .nu.2 56.47r4 -1011.542 d4 1.000r5 .infin. d5 1.129 to 22.582 to 45.635r6 -48.633 d6 1.000 N3 1.69680 .nu.3 56.47r7 56.720 d7 5.200r8 -341.045 d8 1.800 N4 1.83350 .nu.4 21.00r9 -71.385 d9 25.791 to 12.985 to 1.350r10 .infin. d10 9.000r11 -155.628 d11 1.000 N5 1.76182 .nu.5 26.55r12 46.061 d12 0.370r13 86.703 d13 2.750 N6 1.69680 .nu.6 56.47r14 -41.957 d14 0.150r15 29.741 d15 3.500 N7 1.48749 .nu.7 70.44r16 -66.045 d16 20.587 to 11.940 to 0.522r17 -343.007 d17 2.300 N8 1.75000 .nu.8 25.17r18 -40.930 d18 0.700r19 -42.274 d19 1.000 N9 1.77250 .nu.9 49.77r20 36.932______________________________________ TABLE 2______________________________________(2nd Embodiment)f = 36.0 to 66.5 to 102.0 Fno. = 3.60 to 4.80 to 4.65 AbbeRadius of Curvature Axial Distance Refractive Index number______________________________________r1 115.469 d1 2.100 N1 1.84666 .nu.1 23.82r2 44.489 d2 7.350 N2 1.67000 .nu.2 57.07r3 -343.699 d3 0.100r4 29.399 d4 3.250 N3 1.69680 .nu.3 56.47r5 50.429 d5 5.750r6 .infin. d6 -4.900 to 5.498 to 12.043r7 67.068 d7 1.150 N4 1.77250 .nu.4 49.77r8 14.318 d8 3.950r9 -684.360 d9 1.100 N5 1.67000 .nu.5 57.07r10 36.228 d10 0.280r11 19.738 d11 2.600 N6 1.84666 .nu.6 23.83r12 111.064 d12 1.620r13 -29.167 d13 1.100 N7 1.58913 .nu.7 61.11r14 70.766 d14 14.488 to 6.683 to 1.360r15 .infin. d15 1.000r16 24.604 d16 3.150 N8 1.67000 .nu.8 57.07r17 -71.587 d17 0.150r18 -36.391 d18 6.000 N9 1.51680 .nu.9 64.20r19 -15.033 d19 2.500 N10 1.80741 .nu.10 31.59r20 91.766 d20 4.700 to 2.107 to to 0.886r21 59.139 d21 3.000 N11 1.72000 .nu.11 42.02r22 -22.069 d22 0.400r23 .infin. d23 3.210 r24* -25.829 d24 0.035 N12 1.51790 .nu.12 52.31r25 22.819 d25 1.800 N13 1.80500 .nu.13 40.97r26 438.400______________________________________Asphrical coefficientr24* .epsilon. 0.10000 .times. 10 A4 -0.65989 .times. 10.sup.-4 A6 -0.64604 .times. 10.sup.-7 A8 -0.64909 .times. 10.sup.-8 A10 0.11842 .times. 10.sup.-9 A12 -0.83160 .times. 10.sup.-12______________________________________ TABLE 3______________________________________(3rd Embodiment)f = 61.6 to 154.0 to 234.0 Fno. = 4.6 to 5.0 to 5.7 AbbeRadius of Curvature Axial Distance Refractive Index number______________________________________r1 148.425 d1 2.064 N1 1.80518 .nu.1 25.43r2 71.954 d2 6.191 N2 1.60311 .nu.2 60.68r3 -392.957 d3 0.079r4 88.647 d4 3.175 N3 1.49831 .nu.3 65.03r5 1042.916 d5 3.175r6 .infin. d6 -2.254 to 44.173 to 54.761r7 -1559.892 d7 2.381 N4 1.76182 .nu.4 26.55r8 -42.910 d8 1.191 N5 1.83400 .nu.5 37.17r9 39.045 d9 2.246r10 -35.060 d10 1.191 N6 1.77250 .nu.6 49.60r11 27.813 d11 2.381 N7 1.84666 .nu.7 23.89r12 -803.368 d12 1.254r13 .infin. d13 21.082 to 10.462 to 1.262r14 61.199 d14 3.969 N8 1.51680 .nu.8 64.20r15 -31.132 d15 0.079r16 36.148 d16 5.239 N9 1.48749 .nu.9 70.21r17 -27.226 d17 1.572 N10 1.80610 .nu.10 40.94r18 68.120 d18 0.079r19 20.003 d19 2.318 N11 1.76182 .nu.11 26.55r20 16.923 d20 4.199 N12 1.51633 .nu.12 64.15r21 106.133 d21 21.241r22 -75.629 d22 2.802 N13 1.56732 .nu.13 42.82r23 -34.616 d23 2.215r24 -13.740 d24 0.873 N14 1.77250 .nu.14 49.60r25 -29.099 d25 6.723r26 101.990 d26 3.000 N15 1.78472 .nu.15 25.75r27 3859.961______________________________________

In embodiment 1 shown above, during focusing on a close-range object (object distance 1.1 m), distance d4 between first lens unit Gr1 and light shielding plate S is increased to 12.08 m.

In embodiments 2 shown above, during focusing on a close range object (object distance 1.2 m), distance d5 between first lens unit Gr1 and light shielding plate S is increased to 9.745 mm.

In embodiment 3 shown above, during focusing on a close-range object (object distance 1.2 m), distance d5 between first lens unit Gr1 and light shielding plate S is increased to 16.218 mm.

FIGS. 7(a) through 7(c), 9(a) through 9(e) and 11(a) through 11(e) show Gaussian plane transverse aberration in the meridional direction regarding embodiments 1 through 3, respectively. FIGS. 8(a) through 8(c), 10(a) through (e) and 12(a) through 12(e) show Gaussian plane transverse aberration in the meridional direction regarding comparison examples 1 through 3, which are equivalent to the embodiments mentioned above excluding light shielding plate S. In the drawings, the solid line, dotted line and chain line represent aberration with regard to the d-line, g-line and c-line, respectively. Also, in the drawings, the values of tangent represent values of tangent of half angles of view of incident light.

As explained above, a light shielding plate that moves in the same direction and by the same amount as the first lens unit during zooming but does not move during focusing is used in the present invention. As a result, adequate light is secured for peripheral areas when the lens system is in focus on a close-range object and the occurrence of flaring is prevented when the lens system is in focus on an object located at infinity.

Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be as included therein.

Claims

1. A zoom lens system comprising:

a first lens unit located closest to an object side and moves in an optical axis direction both during zooming and focusing; and

a light shielding plate which moves in a same direction and by same amount as the first lens unit during zooming, while the light shielding plate being stationary during focusing.

2. A zoom lens system as claimed in claim 1, wherein said first lens unit has a positive refractive power.

3. A zoom lens system as claimed in claim 1, wherein said zoom lens system has a aperture stop other than said light shielding plate.

4. A zoom lens system as claimed in claim 1, comprising, from an object side, the first lens unit having a positive refractive power and a second lens unit having a negative refractive power.

5. A zoom lens system as claimed in claim 4, comprising, from an object side, the first lens unit having a positive refractive power, the second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a negative refractive power.

6. A zoom lens system as claimed in claim 4, comprising, from an object side, the first lens unit having a positive refractive power, the second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a positive refractive power.

7. A zoom lens system as claimed in claim 4, comprising, from an object side, the first lens unit having a positive refractive power, the second lens unit having a negative refractive power and a third lens unit having a positive refractive power.

8. A zoom lens system as claimed in claim 1, wherein said first lens unit moves in a same direction both during zooming and focusing.

9. A zoom lens system comprising:

a plurality of movable lens units including a first lens unit located closest to an object side, the first lens unit is movable during a zooming mode of operation and also is movable during a focusing mode of operation;

a light shielding member mounted adjacent the first lens unit for movement with the first lens unit during the zooming mode of operation and for being held stationary during the focusing mode of operation when the first lens unit is moved; and

an aperture stop located on the image side of the light shielding member.

10. The zoom lens system of claim 9 wherein the light shielding member has a fixed aperture diameter.

11. The zoom lens system of claim 9 wherein a second lens unit and a third lens unit are provided on the image side of the first lens unit and the aperture stop moves with the third lens unit during the zooming mode of operation.

12. The zoom lens system of claim 11 wherein a fourth lens unit is provided on the image side of the third lens unit.

13. The zoom lens system of claim 11 wherein the first lens unit has the light shielding member mounted on its image side.

14. The zoom lens system of claim 11 wherein the first lens unit comprises, from the object side, a doublet including a negative meniscus lens and a positive meniscus lens on the image side of the doublet having a convex surface on the object side.

15. A zoom lens system comprising, from the object side:

a first lens unit of a positive power that is movable in a zooming mode of operation and also is movable during a focusing mode of operation;

a second lens unit of a negative power;

a third lens unit of a positive power that is movable during a zooming mode of operation;

a fourth lens unit of a negative power;

a light shielding member mounted adjacent the first lens unit for movement with the first lens unit during the zooming mode of operation and for being held stationary during the focusing mode of operation when the first lens is moved during a focusing mode of operation; and

an aperture stop mounted adjacent the third lens unit and movable during a zooming mode of operation.