JP2003057547A - Zoom lens and optical apparatus having the same - Google Patents

Abstract

(57) [Problem] To provide a zoom lens composed of three groups suitable for an electronic still camera excellent in portability and shortening the entire length of the lens, and an optical apparatus having the same. SOLUTION: In order from an object side, a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a third lens unit L3 having a positive refractive power are provided. In a zoom lens that changes magnification by changing the interval, the first lens unit L2 includes one negative lens and one positive lens, and the second lens unit L2 includes a positive lens and a negative lens in order from the object side. The third lens unit L3 has a single positive lens, and has a cemented lens having a positive refractive power, a negative lens, and a positive lens as a whole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens suitable for a still camera, a video camera, a digital still camera and the like, and an optical device having the zoom lens.

[0002]

2. Description of the Related Art Recently, with the increasing functionality of image pickup devices (cameras) such as video cameras and digital still cameras using a solid-state image pickup device, the optical system used for them has a wide aperture ratio and a large aperture ratio zoom. A lens is needed. In this type of camera, between the rearmost part of the lens and the image sensor,
Since various optical members such as a low pass filter and a color correction filter are arranged, a lens system having a relatively long back focus is required for the optical system used therein. further,
In the case of a color camera that uses an image sensor for color images,
In order to avoid color shading, it is desired that the optical system used therefor has good telecentric characteristics on the image side.

Conventionally, there is a so-called short zoom type wide-angle lens system which is composed of two lens groups, a first lens group having a negative refractive power and a second lens group having a positive refractive power, in which zooming is performed by changing the distance between the two lens groups. Various two-group zoom lenses have been proposed. In these short zoom type optical systems, the second optical system having a positive refractive power is used.
Magnification is changed by moving the lens unit, and the image point position associated with the magnification change is corrected by moving the first lens unit having a negative refractive power. In the lens configuration consisting of these two lens groups,
The zoom magnification is about 2 times.

In order to combine the entire lens into a compact shape while having a high zoom ratio of 2 times or more, for example, Japanese Patent Publication No. 7-3507 and Japanese Patent Publication No. 6-40170 disclose a two-group zoom lens. A so-called three-group zoom lens has been proposed in which a third group having negative or positive refracting power is arranged on the image side to correct various aberrations caused by increasing the magnification.

However, since these three-group zoom lenses are mainly designed for cameras for 35 mm film photography, both the back focus length required for an optical system using a solid-state image sensor and good telecentric characteristics are achieved. It was hard to say.

[0006]

A three-group zoom lens system having a wide angle of view that satisfies back focus and telecentric characteristics is disclosed in, for example, Japanese Patent Laid-Open No. 63-135913.
It is proposed in Japanese Patent Laid-Open No. 7-261083. Further, in Japanese Patent Laid-Open No. 3-288113, in a three-group zoom lens, the first group having negative refractive power is fixed, and the second group having positive refractive power and the third group having positive refractive power are moved. An optical system for zooming is also disclosed.

However, in these conventional examples, the number of lenses in each lens group is relatively large, and the total lens length tends to be long.

Further, in recent years, in order to achieve both compactness of the camera and high zoom ratio of the zoom lens, the distance between the lens groups is reduced to a distance different from the photographing state when not photographing, and the distance from the camera body (front of the camera) is reduced. A so-called collapsible zoom lens in which the amount of protrusion of the lens system is reduced is widely used. However, as in the above-mentioned conventional example, the number of constituent lenses of each lens group is large, and as a result, the length on the optical axis of each lens group is If the length of the lens is long, or if the amount of movement of each lens unit during zooming and focusing is large and the total length of the lens is long, the desired retractable length may not be achieved.

Further, in the example disclosed in Japanese Patent Laid-Open No. 7-261083, a convex lens (positive lens) is arranged on the most object side of the first lens unit having a negative refractive power, and particularly when the angle of view is widened. The outer diameter of the lens tended to increase. further,
In this example, the first group having a negative refracting power is moved to perform focusing on a short-distance object, so that the mechanical structure tends to be complicated together with the movement during zooming.

Further, in US Pat. No. 4,999,007,
A three-group zoom lens is disclosed in which each of the first lens group and the second lens group is composed of one single lens.

However, the total length of the lens at the wide-angle end is relatively large, and the aperture is far apart from the first lens unit at the wide-angle end, so that the incident height of off-axis rays is large and the diameter of the lens forming the first lens unit is large. Since the number of lenses increases, the size of the entire lens system tends to increase.

In addition to this, as a problem peculiar to the wide angle zoom lens having a large angle of view at the wide angle end, there is a problem of insufficient correction of distortion. Further, a larger aperture ratio is required for use in a high-pixel image pickup device having a relatively low sensitivity.

It is an object of the present invention to provide a compact zoom lens having a small number of constituent lenses and excellent optical performance, and an optical apparatus having the zoom lens.

In addition to the above, the present invention is suitable for an image pickup system using a solid-state image pickup device, has a small number of constituent lenses, is compact,
An object of the present invention is to provide a zoom lens having a high zoom ratio and excellent optical performance, and an optical device having the zoom lens.

[0015]

A zoom lens according to a first aspect of the present invention comprises, in order from the object side, a first lens group having a negative refractive power,
In a zoom lens that has a second lens group having a positive refractive power and a third lens group having a positive refractive power, and performs zooming by changing the distance between the lens groups, the first lens group is a negative lens. The second lens group has a positive lens, the positive lens and the negative lens are cemented in order from the object side, and the second lens group has a cemented lens having a positive refractive power as a whole, a negative lens and a positive lens, and the third lens group has It is characterized by having one positive lens.

The invention of claim 2 is characterized in that, in the invention of claim 1, the first lens group comprises, in order from the object side, a negative lens and a positive lens.

According to a third aspect of the invention, in the invention of the second aspect, the refractive index of the material of the negative lens in the first lens group is nd1.
1. When the Abbe number is νd11, it is characterized in that the condition of nd11> 1.70 νd11> 35.0 is satisfied.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the material of the positive lens disposed closest to the object side in the second lens group has a refractive index of nd21 and an Abbe number of νd2.
When set to 1, it is characterized by satisfying the condition of nd21> 1.70 νd21> 35.0.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the cemented lens of the second lens group is
It consists of a positive lens with a convex surface facing the object side and a negative lens with a concave surface facing the image side, and the object-side lens surface of the positive lens is an aspherical surface, and the paraxial curvature of the object-side lens surface of the positive lens. When the radius is R21 and the radius of curvature of the image side lens surface of the negative lens is R23, -0.1 <(R21-R23) / (R21 + R23) <
It is characterized by satisfying the condition of 0.1.

According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the second lens group has, in order from the object side, a positive lens having a convex surface facing the object side and a concave surface facing the image side. It is characterized in that it consists of a cemented lens in which a negative lens is cemented, a meniscus-shaped negative lens with a convex surface facing the object side, and a positive lens with both lens surfaces convex.

The invention of claim 7 is characterized in that, in the invention of any one of claims 1 to 6, the third lens group comprises a single positive lens.

According to an eighth aspect of the present invention, in the zooming operation from the wide-angle end to the telephoto end in the invention according to any one of the first to seventh aspects, the first lens group has a part of a locus convex toward the image side. The second lens group monotonously moves to the object side, and the third lens group moves to the object side and then to the image side.

According to a ninth aspect of the present invention, in zooming from the wide-angle end to the telephoto end in the invention according to any one of the first to eighth aspects, the zoom lens is moved to the telephoto end of the third lens group with reference to the wide-angle end. It is characterized in that the condition of 0.1 <| X1 / X3 | <7.0 is satisfied when the movement amount of X is X3.

According to a tenth aspect of the invention, in the invention according to any one of the first to ninth aspects, at the telephoto end, the distance from the apex on the object side of the lens arranged closest to the object side of the first lens group to the image plane. DL, the distance from the object side vertex of the lens arranged closest to the object side of the first lens group to the image side vertex of the lens arranged closest to the image side of the first lens group is D
L1, the distance from the object side vertex of the lens arranged closest to the object side of the second lens group to the image side vertex of the lens arranged closest to the image side of the second lens group DL2, the third distance
When the distance from the object-side apex of the lens arranged closest to the object side of the lens group to the image-side apex of the lens arranged closest to the image side of the third lens group is DL3, 0.25 <(DL1 + DL2 + DL3 ) / DL <0.5.

The eleventh aspect of the present invention is the invention according to any one of the first to tenth aspects, wherein the sum of the thicknesses on the optical axis of the respective lenses forming the second lens group is ΣD2. It is characterized in that the condition that 0.05 <ΣA2 / ΣD2 <0.3 is satisfied, where ΣA2 is the total of the air gaps between the lenses.

The invention of claim 12 is characterized in that, in the invention of any one of claims 1 to 11, the first lens group and the second lens group each have an aspherical surface.

The thirteenth aspect of the present invention is characterized in that, in the invention according to any one of the first to twelfth aspects, the positive lens forming the third lens group has an aspherical surface.

According to a fourteenth aspect of the present invention, in the invention according to any one of the first to thirteenth aspects, the third group is moved to the object side to perform focusing from an object at infinity to a near object. .

The invention of claim 15 is from claim 1 or claim 3
In the invention of any one of 4 above, the first lens group is
A zoom lens that consists of two negative lenses and one positive lens.

A sixteenth aspect of the present invention is characterized in that, in the first to fifteenth aspects of the present invention, it is an optical system for forming an image on an image pickup device.

A camera according to a seventeenth aspect of the present invention is characterized by including the zoom lens according to any one of the first to sixteenth aspects and an image pickup device for receiving an image formed by the zoom lens. .

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a lens sectional view of a zoom lens at a wide-angle end according to a first embodiment of the present invention described later. Figure 2
4 is a wide-angle end of the zoom lens according to Embodiment 1 of the present invention,
FIG. 6 is an aberration diagram at a middle zoom position and at a telephoto end.

FIG. 5 is a lens sectional view at the wide-angle end of a zoom lens according to a second embodiment of the present invention which will be described later. 6 to 8 are aberration diagrams of the zoom lens of Embodiment 2 of the present invention at the wide-angle end, the intermediate zoom position, and the telephoto end.

FIG. 9 is a lens sectional view of a zoom lens according to a third embodiment of the present invention which will be described later. 10 to 12 are aberration diagrams of the zoom lens of Embodiment 3 of the present invention at the wide-angle end, the intermediate zoom position, and the telephoto end.

In the lens sectional view, L1 is a first lens group having a negative refractive power, L2 is a second lens group having a positive refractive power, and L3.
Is a third lens unit having a positive refractive power, SP is an aperture stop, and IP is an image plane. G is a glass block corresponding to a filter, a color separation prism or the like.

The zoom lens of each embodiment has, in order from the object side, a first lens unit L1 having a negative refractive power, a second lens unit L2 having a positive refractive power, and a third lens unit L3 having a positive refractive power.
In zooming from the wide-angle end to the telephoto end, the first lens group moves a part of the convex locus toward the image side, and the second lens group moves toward the object side. The third lens group once moves to the object side and then moves to the image side.

In the zoom lens of each embodiment, the main zooming is performed by moving the second lens unit L2, and the first lens unit L2 is moved.
The movement of the image point due to the magnification change is corrected by the substantially reciprocating movement of 1 and the convex movement of the third lens group once toward the object side in the image side direction.

The third lens unit L3 shares the increase of the refracting power of the photographing lens with the downsizing of the image pickup device, and reduces the refracting power of the short zoom system composed of the first and second lens units L1 and L2. In particular, this is used to suppress the occurrence of aberrations in the lenses that form the first lens unit L1 and achieve good optical performance. In addition, telecentric image formation on the image side, which is particularly necessary for a photographing apparatus using a solid-state image sensor or the like, is achieved by making the third lens unit L3 function as a field lens.

Further, the stop SP is placed on the most object side of the second lens unit L2, and the distance between the entrance pupil on the wide angle side and the first lens unit L1 is shortened, so that the lens outside the lenses forming the first lens unit L1 is closed. The number of constituent lenses is not increased by suppressing an increase in the diameter and canceling off-axis various aberrations between the first lens unit L1 and the third lens unit L3 with a diaphragm arranged on the object side of the second lens unit L2 being sandwiched. It has excellent optical performance.

In the zoom lens of each embodiment, the first lens unit L1 has at least one negative lens and one positive lens, and the second lens unit L2 has the positive lens and the negative lens in order from the object side. Has a cemented lens having a positive refractive power as a whole, a negative lens, and a positive lens, and the third lens group has at least one positive lens.

Next, a specific lens configuration of each embodiment will be described.

In the zoom lenses of Embodiments 1 and 2 of FIGS. 1 and 5, the first lens unit L1 having a negative refractive power is arranged in order from the object side, and the meniscus negative lens 11 having a concave surface facing the image side,
2 of meniscus-shaped positive lens 12 with convex surface facing the object side
It is composed of one lens. And the second of the positive refractive power
The lens unit L2 includes, in order from the object side, a positive meniscus lens 21 having a concave surface facing the image side, a negative meniscus lens 22 having a convex surface facing the object side, and a negative meniscus lens having a convex surface facing the object side. 23 and four positive lenses 24 each having a convex lens surface. The positive lens 21 and the negative lens 22 are cemented lenses. Also, the third of the positive refractive power
The lens unit L3 is composed of a positive lens 31 whose both lens surfaces are convex.

In the zoom lens according to the third embodiment of FIG. 9, the first lens unit L1 having a negative refractive power is arranged in order from the object side to a negative meniscus lens 11 having a concave surface facing the image side, and also to the image side. 3 of the meniscus negative lens 12 having a concave surface and the meniscus positive lens 13 having a convex surface facing the object side
It is composed of one lens. The second lens unit L2 having a positive refractive power is provided in order from the object side, such as a meniscus positive lens 21 having a concave surface facing the image side, a meniscus negative lens 22 having a convex surface facing the object side, and a convex surface facing the object side. Negative lens 23 in the form of a meniscus, positive lens 2 having convex lens surfaces on both sides
It consists of 4 lenses of 4 and the positive lens 21 and the negative lens 2
2 is used as a cemented lens. Further, the third lens unit L3 having a positive refractive power is composed of the positive lens 31 having both convex lens surfaces.

As described above, in the zoom lens of each embodiment, by making each lens group a lens configuration that achieves both a desired refractive power arrangement and aberration correction, the entire lens system is maintained while maintaining good performance. Has been made compact.

Next, general features of each embodiment will be described.

The first lens unit L1 has a role of focusing the off-axis chief ray to form a pupil in the center of the diaphragm. Especially, on the wide-angle side, since the off-axis chief ray has a large refraction amount, various off-axis aberrations, especially Astigmatism and distortion easily occur.

In Embodiments 1 and 2 of each embodiment, a negative lens and a positive lens that suppress the increase of the lens diameter on the most object side are used as in the case of a normal wide-angle lens.

If necessary, the image-side lens surface of the meniscus negative lens 11 is made an aspherical surface having a shape in which the negative refracting power is weakened around the lens, so that astigmatism and distortion are corrected in a well-balanced manner. In addition, the first lens group is configured with a small number of lenses, that is, two lenses, which contributes to downsizing of the entire lens.

Each lens constituting the first lens unit L1 has a shape close to a concentric sphere centered at a point where the stop and the optical axis intersect in order to suppress the generation of off-axis aberration caused by refraction of the off-axis chief ray. Is taking.

Next, in the second lens unit L2, the positive lens 21 having a convex surface stronger than the image surface side is arranged on the most object side to the object side in the second lens unit, and the first lens unit is emitted. The lens shape is such that the off-axis chief ray has a small refraction angle and various off-axis aberrations do not occur.

The positive lens 21 is a lens that has the highest height through which axial rays pass, and is a lens that is mainly involved in correction of spherical aberration and coma.

In each embodiment, the positive lens 21
It is preferable that the object-side lens surface of is an aspherical surface having a shape in which the positive refractive power is weakened around the lens. According to this, it becomes easy to favorably correct spherical aberration and coma.

Next, the negative lens 22 disposed on the image side of the positive lens 21 is provided with a concave surface on the image side, and the subsequent object side lens surface of the negative lens 23 on the image side is made negative by forming a convex surface. A lens is formed to correct spherical aberration that occurs when the aperture ratio is increased.

Further, in each of the embodiments, in order to cope with the reduction in the amount of chromatic aberration required in accordance with the increase in the number of pixels of the solid-state image pickup device such as CCD and the miniaturization of the cell pitch, the second embodiment is adopted.
By arranging the cemented lens on the object side of the lens group, axial chromatic aberration and lateral chromatic aberration are well corrected.

The positive lens 21 and the negative lens 22 are cemented together to form a cemented lens having a positive refracting power as a whole, a negative lens 23, and a positive lens 24. The advantage of this configuration is that the refractive power of the so-called triplet type negative lens component is separated into two components, and the degree of freedom in aberration correction is increased compared to the aberration correction method using a single negative lens component such as the triplet type. The triplet type eliminates the need to correct the off-axis flare that was corrected by increasing the glass thickness of the negative lens component and the spherical aberration correction by the two negative air lenses provided before and after the negative lens component. The second lens unit L2 compared to
It is possible to reduce the thickness on the optical axis, which contributes to shortening the total optical length and the total lens length when retracted.

Next, the third lens unit L3 is composed of a positive lens 31 having a convex surface on the object side, and also serves as a field lens for making the image side telecentric. In Embodiments 2 to 3 of each embodiment, an aspherical surface having a shape in which the positive refractive power is weakened around the lens is provided on the object-side lens surface of the positive lens 31, and correction of off-axis aberrations in the entire zoom range is performed. Contribute to.

Now, the back focus is sk ', the focal length of the third lens group is f3, and the imaging magnification of the third lens group is β.
When 3, the relationship of sk '= f3 (1-β3) is established.

However, 0 <β3 <1.0 Is.

Here, if the third lens unit L3 is moved to the image side during zooming from the wide-angle end to the telephoto end, the back focus sk 'will decrease, and the imaging magnification β3 of the third lens unit L3 will change to the telephoto end. Increase on the side.

Then, as a result, the third lens unit L3 can share the variable magnification, the moving amount of the second lens unit L2 is reduced, and the space therefor can be saved, which contributes to downsizing of the lens system.

When shooting from an object at infinity to a near object using the zoom lens of each embodiment, good performance can be obtained by moving the first lens unit L1 toward the object side. Desirably, the third lens unit L3 may be moved to the object side.

This is because the front lens diameter increases and the load of the actuator caused by moving the first lens unit L1 having the heaviest lens weight occurs when the first lens unit L1 arranged closest to the object is focused. This is because it is possible to prevent the increase and further to move the first lens unit L1 and the second lens unit L2 in a simple manner by a cam or the like during zooming, thereby simplifying the mechanical structure and improving accuracy.

When focusing is performed by the third lens unit L3, the third lens unit is used for zooming from the wide-angle end to the telephoto end.
By moving the lens unit L3 to the image side, it is possible to arrange the telephoto end, which has a large focusing movement amount, on the image plane side. Therefore, all the movement amounts of the third lens unit 13 required for zooming and focusing are minimized. It has become possible to achieve a compact lens system.

The zoom lens of each embodiment satisfies the following conditions in order to obtain good optical performance and to downsize the entire lens system. In the zoom lens of the present invention, by satisfying at least one of these various conditions, it is possible to obtain the effect of improving the optical performance by satisfying the respective conditional expressions or downsizing the entire lens system.

(A-1) When the refractive index and the Abbe number of the material of the positive lens 21 arranged closest to the object in the second lens unit L2 are nd21 and νd21, respectively, the following conditions must be satisfied. .

Nd21> 1.70 (1) νd21> 35.0 (2) When the lower limit of conditional expression (1) is exceeded, the Petzval sum increases in the negative direction and field curvature correction is performed. It will be difficult.

If the lower limit of conditional expression (2) is exceeded, it becomes difficult to correct axial chromatic aberration at the telephoto end, which is not preferable.

Conditional expressions (1) and (2) are more preferably set as follows.

Nd21> 1.72 (1a) νd21> 38 (2a) (a-2) In order to shorten the total length of the optical system and the total lens length when retracted, the following conditions are satisfied. It is good to let

0.1 <| X1 / X3 | <7.0 (3) Here, X1 is at the time of zooming from the wide-angle end to the telephoto end.
The maximum amount of movement of the first lens unit L1 in the image plane direction with the wide-angle end as a reference (here, the movement to the image plane side is a positive sign and the object side is a negative code. The same applies hereinafter) X3. , Is the amount of movement to the telephoto end with respect to the wide-angle end of the third lens unit L3 when focusing on an object at infinity.

When the upper limit of conditional expression (3) is exceeded, the amount of movement of the third lens unit L3 on the optical axis increases, and the third lens unit L3
3 requires a long motor shaft to move, which makes it difficult to shorten the entire retractable length, which is not preferable.

When the lower limit of conditional expression (3) is exceeded, the moving condition of the convex locus of the first lens unit L1 toward the image side due to zooming becomes tight, and the first lens unit L1 moves from the wide-angle end to the telephoto end. Since the angle of the cam locus to the end becomes large, this is also a factor that increases the total retractable length, which is not preferable.

Conditional expression (3) is more preferably set as follows.

0.15 <| X1 / X3 | <5 (3a) (a-3) In order to reduce the total length of the optical system and the total lens length when retracted, the following conditions must be satisfied. good.

0.25 <(DL1 + DL2 + DL3) / DL <0.5 (4) Here, DL is from the object-side apex of the lens arranged closest to the object side of the first lens unit L1 at the telephoto end to the image plane. (When there is a plane-parallel plate such as a filter between the final lens surface and the image surface, the length is taken as the air-equivalent length), DL1 is arranged on the most object side of the first lens unit L1. DL2, the distance from the apex of the lens on the object side to the image-side point of the lens arranged closest to the image side in the first lens unit L1;
Is the distance from the object-side apex of the lens arranged closest to the object side of the second lens unit L2 to the image-side apex of the lens arranged closest to the image side of the second lens unit L2, and DL3 is the third lens unit L3. Is the distance from the object side vertex of the lens arranged closest to the object side to the image side vertex of the lens arranged closest to the image side of the third lens unit L3.

When the value exceeds the upper limit of conditional expression (4), the total optical length at the telephoto end becomes short, but the total length on the optical axis of each lens group becomes large.

If the lower limit of conditional expression (4) is exceeded, the total length on the optical axis of each lens group will be small, but the optical total length at the telephoto end will be long, and the optical axis of each lens group will inevitably be long. Since the amount of upward movement is increased, the length of the cam ring or the like for moving each lens group becomes long, and as a result, the total retractable length is not shortened, which is not preferable.

Conditional expression (4) is more preferably set as follows.

0.28 <(DL1 + DL2 + DL3) / DL <0.48 (4a) (A-4) The total thickness of the lenses constituting the second lens group on the optical axis is D2, and the total thickness of the lenses in the second lens group is D2. When the total air space between the lenses is A2, it is preferable that the condition of 0.05 <A2 / D2 <0.3 (5) is satisfied. According to this, it is possible to achieve both compactness and achievement of excellent imaging performance.

If the upper limit of conditional expression (5) is exceeded, the length of the second lens group on the optical axis becomes long, which makes it difficult to achieve compactness, which is not preferable.

If the lower limit of conditional expression (5) is exceeded, the power of the air lens becomes small and it becomes difficult to correct spherical aberration, which is not preferable.

Conditional expression (5) is more preferably set as follows.

0.1 <A2 / D2 <0.2 (5a) (A-5) When the first lens unit has a two-lens configuration, the negative lens of the first lens unit L1 The refractive index of the material is n
When d11 and Abbe number are νd11, it is preferable that the following conditions are satisfied.

Nd11> 1.70 (6) νd11> 35.0 (7) When the upper limit of conditional expression (6) is exceeded, the Petzval sum of the first lens unit L1 becomes positive. And the curvature of field becomes difficult to correct.

If the upper limit of conditional expression (7) is exceeded,
In particular, it becomes difficult to correct lateral chromatic aberration at the wide-angle end, which is not preferable.

Conditional expressions (6) and (7) are more preferably set as follows.

Nd11> 1.75 (6a) νd11> 38 (7a) (A-6) The cemented lens arranged on the most object side of the second lens unit L2 satisfies the following conditions. It is good to

−0.1 <(R21−R23) / (R21 + R23) <0.1 (8) Here, R21 is the paraxial radius of curvature of the lens surface of the positive lens 21 on the object side, and R23 is negative. It is the radius of curvature of the image side lens surface of the lens 22.

If the upper limit of conditional expression (8) is exceeded, the Petzval sum of the second lens unit L2 increases in the negative direction, making it difficult to correct the field curvature.

If the lower limit of conditional expression (8) is exceeded, it becomes difficult to correct spherical aberration and coma, which is not preferable.

Conditional expression (8) is more preferably set as follows.

-0.08 <(R21-R23) / (R21 + R23) <0.09 (8a) Next, numerical examples of the respective embodiments of the present invention will be shown. In each numerical example, i represents the order of surfaces from the object side, and r
i is the radius of curvature of the lens surface, di is the lens thickness and air gap between the i-th surface and the (i + 1) -th surface, and ni and νi are the refractive index and Abbe number for the d-line, respectively.

The two surfaces closest to the image side are parallel plane plates corresponding to face plates and the like. f is the focal length, fno
Is the F number, and ω is the half angle of view. K is the eccentricity,
B, C, D, E and F are aspherical coefficients. The aspherical shape is x = (h ² / R) / [1+ {1− (1 + k) (h), where x is the displacement in the optical axis direction at the position of height h from the optical axis with respect to the surface vertex. /
R) ² } ^1/2 ] + Bh ⁴ + Ch ⁶ + Dh ⁸ + Eh ¹⁰ + Fh ¹² . However, R is a radius of curvature. “D-X” means “10 ^−X ”.

Table 1 shows the relationship between each conditional expression and each numerical example.

[0095]

[Outer 1]

Numerical Embodiment 1 is a zoom lens having a zoom ratio of 2.9 and an aperture ratio of about 2.8 to 4.8.

[0097]

[Outside 2]

Numerical Embodiment 2 has a variable power ratio of 2 and an aperture ratio of 2.8.
It is a zoom lens of about 4.0.

In this embodiment, during zooming from the wide-angle end to the telephoto end, the first lens group reciprocates in a convex locus toward the image side, the second lens group moves toward the object side, and the third lens group moves. It has moved to the image side.

[0100]

[Outside 3]

Numerical Example 3 has a variable power ratio of 2 and an aperture ratio of 2.9.
It is a zoom lens of about 4.0.

In this embodiment, during zooming from the wide-angle end to the telephoto end, the first lens group moves back and forth along a convex locus to the image side, the second lens group moves to the object side, and the third lens group moves. It has moved to the image side.

[0103]

[Table 1]

According to the zoom lens of each practical form described above, it is possible to achieve high performance and compactness while increasing the angle of view at the wide-angle end.

Astigmatism and distortion, especially on the wide-angle side, can be satisfactorily corrected.

It is possible to reduce the sharing of aberrations of the moving lens group, reduce the performance deterioration due to the eccentricity between the lens groups due to the manufacturing error, etc., and to make the manufacturing easy while taking the minimum lens configuration.

A large aperture ratio suitable for a high-pixel image pickup device having low sensitivity can be achieved.

A good image-side telecentric image formation suitable for a photographing system using a solid-state image pickup device can be achieved while minimizing the number of constituent lenses.

The length of each lens unit on the optical axis required for the retractable zoom lens and the amount of movement of each lens unit on the optical axis due to zooming and focusing can be shortened.

Distortion aberration can be satisfactorily corrected not only at the wide-angle end but also over the entire zoom range.

It is possible to reduce the fluctuation of the image-side telecentric image formation due to zooming.

It is possible to further reduce the size by reducing the amount of movement of the variable power lens group while maintaining telecentric imaging.

The focusing mechanism for a short-distance object can be simplified. Such various effects can be obtained. Next, an embodiment of a digital still camera using the zoom lens of the present invention as a photographic optical system (note: this is a DSC lens, will be changed) (optical device) will be described with reference to FIG.

In FIG. 13, reference numeral 20 denotes a camera body, and 21
Is a photographing optical system constituted by the zoom lens of the present invention, 22 is a strobe built into the camera body, 23 is an external viewfinder, and 24 is a shutter button.

By thus applying the zoom lens of the present invention to an optical device such as a digital still camera, an optical device having a small size and high optical performance is realized.

As described above, by appropriately setting each element constituting the zoom lens, the number of constituent lenses is small and the size is compact, and the chromatic aberration is particularly good, which is particularly suitable for an image pickup system using a solid-state image pickup element. A zoom lens having excellent optical performance corrected to the above and an optical device having the same can be achieved.

Besides, by effectively introducing an aspherical surface into each lens group, various off-axis aberrations, particularly astigmatism / distortion aberration and spherical aberration when a large aperture ratio is made, can be effectively corrected. A zoom lens and an optical device having the same can be achieved.

[0118]

According to the present invention, it is possible to achieve a compact zoom lens having a small number of constituent lenses and excellent optical performance, and an optical apparatus having the zoom lens.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view at a wide-angle end according to Numerical Example 1.

FIG. 2 is an aberration diagram at the wide-angle end according to Numerical Example 1.

FIG. 3 is an aberration diagram at an intermediate zoom position of Numerical Example 1.

FIG. 4 is an aberration diagram at a telephoto end according to Numerical Example 1.

FIG. 5 is a lens cross-sectional view of a wide-angle end according to Numerical Example 2.

FIG. 6 is an aberration diagram at the wide-angle end according to Numerical Example 2.

FIG. 7 is an aberration diagram at a middle zoom position in Numerical Example 2.

8 is an aberration diagram at a telephoto end according to Numerical Example 2. FIG.

FIG. 9 is a lens cross-sectional view of a wide-angle end according to Numerical Example 3.

FIG. 10 is an aberration diagram at a wide-angle end according to Numerical Example 3.

FIG. 11 is an aberration diagram at an intermediate zoom position in Numerical Example 3.

FIG. 12 is an aberration diagram at a telephoto end according to Numerical Example 3.

FIG. 13 is a schematic view of a main part of an optical device of the present invention.

[Explanation of symbols]

L1 first group L2 second group L3 third group SP aperture IP image plane G glass block d d line g g line ΔS sagittal image plane ΔM meridional image plane

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA02 KA03 MA14 PA06 PA07                       PA18 PB07 PB08 QA02 QA07                       QA17 QA21 QA22 QA25 QA34                       QA41 QA46 RA05 RA12 RA36                       RA42 SA14 SA16 SA19 SA62                       SA63 SA64 SB03 SB04 SB15                       SB22                 2H101 BB07                 5C022 AA00 AB21 AB66 AC54

Claims (17)

[Claims] 1. A first lens unit having a negative refracting power, a second lens unit having a positive refracting power, and a third lens unit having a positive refracting power are arranged in this order from the object side. In a zoom lens that performs variable power by changing, the first lens group has a negative lens and a positive lens, and the second lens group has a positive lens as a whole in which a positive lens and a negative lens are cemented in order from the object side. A cemented lens having a refractive power, a negative lens, and a positive lens,
A zoom lens characterized in that the lens group has a positive lens. 2. The first lens group, in order from the object side,
The zoom lens according to claim 1, comprising a negative lens and a positive lens. 3. When the refractive index of the material of the negative lens in the first lens group is nd11 and the Abbe number is νd11, the condition of nd11> 1.70 νd11> 35.0 is satisfied. The zoom lens according to claim 2. 4. The refractive index of the material of the positive lens disposed closest to the object in the second lens group is nd21 and the Abbe number is ν
When it is d21, it satisfies the condition that nd21> 1.70 νd21> 35.0.
Zoom lens. 5. The cemented lens of the second lens group includes a positive lens having a convex surface directed toward the object side and a negative lens having a concave surface directed toward the image side, and the object-side lens surface of the positive lens is an aspherical surface. R21 is the paraxial radius of curvature of the object-side lens surface of the positive lens, and R2 is the radius of curvature of the image-side lens surface of the negative lens.
When set to 3, -0.1 <(R21-R23) / (R21 + R23) <
The zoom lens according to any one of claims 1 to 4, wherein the condition of 0.1 is satisfied. 6. The second lens group, in order from the object side,
It consists of a cemented lens in which a positive lens with a convex surface facing the object side and a negative lens with a concave surface facing the image side are cemented together, a meniscus negative lens with a convex surface facing the object side, and a positive lens with both lens surfaces convex. The zoom lens according to claim 1, wherein the zoom lens is a zoom lens. 7. The zoom lens according to claim 1, wherein the third lens group is composed of a single positive lens. 8. Upon zooming from the wide-angle end to the telephoto end, the first lens group moves along a part of a convex locus toward the image side, and the second lens group monotonously moves toward the object side. 8. The zoom lens according to claim 1, wherein the third lens group moves to the object side and then to the image side. 9. When zooming from the wide-angle end to the telephoto end, the maximum amount of movement of the first lens unit in the image plane direction when the wide-angle end is the reference is X1, and when the wide-angle end is the reference, 9. When the amount of movement of the third lens group to the telephoto end is X3, the condition of 0.1 <| X1 / X3 | <7.0 is satisfied. Zoom lens. 10. At the telephoto end, the distance from the object-side apex of the lens arranged closest to the object side of the first lens group to the image plane is DL, and the lens arranged closest to the object side of the first lens group The distance from the object-side apex of the first lens group to the image-side apex of the lens disposed closest to the image side is DL1,
The distance from the object-side vertex of the lens arranged closest to the object side of the second lens group to the image-side vertex of the lens arranged closest to the image side of the second lens group is DL2, and the distance of the third lens group is the maximum. When the distance from the object-side apex of the lens arranged on the object side to the image-side apex of the lens arranged on the most image side of the third lens group is DL3, 0.25 <(DL1 + DL2 + DL3) / DL <0 The zoom lens according to any one of claims 1 to 9, wherein the zoom lens satisfies the following condition. 11. When the total of the thicknesses on the optical axis of the respective lenses constituting the second lens group is ΣD2 and the total of the air gaps between the respective lenses in the second lens group is ΣA2, 0.05: 11. The zoom lens according to claim 1, wherein the condition <ΣA2 / ΣD2 <0.3 is satisfied. 12. The zoom lens according to claim 1, wherein each of the first lens group and the second lens group has an aspherical surface. 13. The zoom lens according to claim 1, wherein the positive lens forming the third lens group has an aspherical surface. 14. The zoom lens according to claim 1, wherein the third lens unit is moved to the object side to perform focusing from an object at infinity to a near object. 15. The zoom lens according to claim 1, wherein the first lens group includes two negative lenses and one positive lens. 16. An optical system for forming an image on an image pickup device according to any one of claims 1 to 15.
Item zoom lens. 17. A camera comprising: the zoom lens according to claim 1; and an image pickup device that receives an image formed by the zoom lens.