JPH1195103A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small zoom lens capable of sufficiently separating the position of an exit pupil from the image plane and suppressing the distortion aberration and having a small aberration and the variable power ratio of more than three times. SOLUTION: In order from the object side to the image side, a negative lens group G1, a positive lens group G2 and a positive lens group G3 are arranged. At the time of zooming from the wide-angle end to the telescopic end, the lens group G1 is moved to the image side and reversely moved to the object side on the way, the lens group G2 is monotoniously moved to the object side and the lens group G3 is moved to the object side and reversely moved to the image side on the way. An aperture diaphragm S is integrally moved with the lens group G2. By representing the focal distance of the Mth (M=1-3) lens group by fM and the composite focal distance of the whole system at the wide-angle end by fW, the conditions: (1) 2.47<|f1 |/fW<2.61 (f1 <0), (2) f3 /fW<4.1, and (3) 0.52<f2 /f3 <0.61 (f2 >0, f3 >0) are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of a zoom lens, and more particularly to a zoom lens suitable as a small telephoto wide-angle zoom lens for digital still cameras and video cameras using a solid-state image sensor as a light receiving element. It is about.

[0002]

2. Description of the Related Art In a so-called video camera for capturing moving images, a CCD (charge coupled device) or an M
2. Description of the Related Art A solid-state imaging device such as an OS (metal oxide semiconductor) is used as a light-receiving device for imaging. In recent years, a digital still camera or simply a digital camera or the like is used. An image of a subject is captured by a solid-state imaging device, and image data of a still image (still image) of the subject is obtained.
2. Description of the Related Art Cameras of the type that digitally records on a C (integrated circuit) card or a video floppy disk have been widely used. Some digital cameras can capture not only still images but also moving images (movie images).

Incidentally, the optical system of a camera using such a solid-state image pickup device such as a CCD is required to have an exit pupil position sufficiently separated from an image plane. This is for the following reasons. Since the color filter of the solid-state imaging device is located at a position slightly distant from the imaging surface, the substantial aperture efficiency is reduced when the light flux is obliquely incident. It is required that the effective thickness of the crystal filter for preventing the moire phenomenon caused by the periodic structure of the solid-state imaging device does not fluctuate much on and around the axis. In particular, recent high-sensitivity small solid-state imaging devices have a microlens array immediately before the imaging surface. Even in such a case, if the exit pupil is not sufficiently separated from the image surface, the aperture efficiency is reduced. Drops around.

A first lens group having a negative refractive power and a second lens group having a positive refractive power are sequentially arranged from the object side to the image side. By changing the distance between the group and the second lens group,
A zoom lens that performs zooming is well known as a so-called two-unit zoom. Most of such two-unit zooms have an exit pupil position close to the image plane, which is not preferable for application to a camera using a solid-state imaging device such as a CCD. Therefore, the second
It is considered that the position of the exit pupil is moved away from the image plane by disposing a fixed lens group or a moving lens group having a positive refractive power behind the lens group, and many zoom lenses have been proposed. As described above, an example of a zoom lens in which a lens group having a positive refractive power is arranged behind the second lens group is described in, for example, Japanese Patent Publication No. 3-2073.
No. 5, JP-B-7-52256, and JP-A-6-94996.

[0005] However, the zoom lenses described in Japanese Patent Publication No. 3-20735 and Japanese Patent Publication No. 7-52256 mainly use a single-lens reflex (single-lens reflex).
It is designed for still cameras. For this reason, Japanese Patent Publication No. 3-20735 and Japanese Patent Publication No. 7-5
In the configuration described in Japanese Patent No. 2256, the positive refractive power of the third lens group is extremely weak, and the exit pupil cannot be sufficiently moved away from the image plane. Further, in the zoom lens described in JP-A-6-94996, in order to keep the exit pupil position away from the image plane, the stop position is fixed during zooming to an intermediate position between the first lens group and the second lens group. Are arranged. For this reason, the movement of the first lens group and the second lens group is restricted, and the zoom ratio is only slightly less than twice.

[0006]

SUMMARY OF THE INVENTION In order to address the above-described problems, the present applicant has obtained a zoom ratio of about three times, and has a sufficient distance between the exit pupil and the image plane. A bright wide-angle zoom lens suitable for a small digital still camera or the like has been proposed. For example, Japanese Patent Application No. 8-237672 describes an example of such a zoom lens. However, these zoom lenses have large distortion and generate about 6% of distortion at the wide-angle end. Such distortion is large compared to a photographic lens of a conventional camera using a silver halide film of a 35 mm version, so-called Leica version, and it is difficult to obtain an accurate image.

On the other hand, recent digital still cameras are
There is a tendency to pursue higher image quality, and the small distortion of the image is also one of the important quality items in a digital still camera oriented for higher image quality. For this reason, the zoom lens described in Japanese Patent Application No. 8-237672 is considered to be unsuitable for recent high-quality digital still cameras. The present invention has been made in view of the above-described circumstances, and achieves a zoom ratio of three times or more so that an exit pupil position can be sufficiently separated from an image plane and distortion can be suppressed. It is an object of the present invention to provide a zoom lens which can be formed as a bright wide-angle zoom lens which is small, has little aberration, and is suitable for a digital still camera or the like.

[0008] In particular, a first object of the present invention is to provide a zoom lens which is small and whose aberration is well corrected. A second object of the present invention is to provide a lens having a small number of lenses, a small lens outer diameter,
It is an object of the present invention to provide a zoom lens that effectively corrects aberration generated in a lens group. A third object of the present invention is to provide a zoom lens that can correct negative distortion that increases particularly on the short focal length side. A fourth object of the present invention is to provide a zoom lens capable of preventing spherical aberration from being insufficiently corrected.

[0009]

According to the first aspect of the present invention, there is provided a zoom lens according to the present invention, in order to achieve the above-mentioned object, in particular, the first object, from the object side to the image side. A first group optical system having a positive refractive power, a second group optical system having a positive refractive power, and a third group optical system having a positive refractive power are provided, and on the object side of the second group optical system, In addition to providing an aperture stop that moves integrally with the second group optical system during zooming, when zooming from the wide angle end to the telephoto end, the first group optical system first moves on the optical axis to the image side, and By inverting the moving direction to the object side, the lens moves in a convex arc shape convex to the image side to correct the change in the focal position, and the second group optical system monotonously moves on the optical axis to the object side. Do the magnification,
The third group optical system first moves on the optical axis to the object side, and in the middle, reverses the moving direction to the image side, moves in a convex arc shape convex to the object side, and performs zooming. Assuming that the focal length of the M group optical system (M = 1 to 3) is f _M and the combined focal length of the entire system at the wide angle end is f _W , these conditions are as follows: (1) 2.47 <| f ₁ | / f _W <2.61 (f ₁ <
0) (2) f ₃ / f _W <4.1 (3) 0.52 <f ₂ / f ₃ <0.61 (f ₂ > 0,
f ₃ > 0).

According to a second aspect of the present invention, there is provided a zoom lens according to the present invention, wherein the first group optical system has a meniscus negative lens having a convex surface facing the object side in order from the object side to the image side. A second meniscus negative lens having a convex surface facing the lens side and a meniscus positive lens having a convex surface facing the object side. Towards, sequentially, a positive lens with a strong refractive surface facing the object side, a meniscus-shaped positive lens with a convex surface facing the object side, a negative lens with a strong refractive surface facing the image side,
It is characterized by including five lenses each having a positive lens and a meniscus-shaped positive lens having a convex surface facing the object side.

According to a third aspect of the present invention, in the zoom lens according to the first aspect, the meniscus-shaped negative lens located second from the object side among the three lenses of the first group optical system is replaced with an image-side lens surface. Is an aspheric surface having a shape in which the negative refractive power becomes weaker as the distance from the optical axis increases. The zoom lens according to the present invention described in claim 4 is the zoom lens according to claim 2, wherein
The positive lens closest to the object among the five lenses of the group optical system is characterized in that the lens surface on the object side is an aspherical surface whose positive refractive power becomes weaker as the distance from the optical axis increases.

[0012]

In the zoom lens according to the first aspect of the present invention, the first group optical system having a negative refractive power and the second group optical system having a positive refractive power are sequentially arranged from the object side to the image side. And a third group optical system having a positive refractive power is provided, and an aperture stop that moves integrally with the second group optical system during zooming is provided on the object side of the second group optical system, and from the wide-angle end. Upon zooming to the telephoto end, the first group optical system first moves to the image side on the optical axis, and in the middle, reverses the moving direction to the object side, thereby moving in a convex arc shape convex to the image side. The second group optical system monotonously moves on the optical axis to the object side to perform magnification change, and corrects the change in the focal position.
The group optical system first moves to the object side on the optical axis, and in the middle, reverses the moving direction to the image side to move in a convex arc shape convex to the object side to perform zooming. When the focal length of (M = 1 to 3) is f _M and the combined focal length of the entire system at the wide-angle end is f _W , these conditions are as follows: (1) 2.47 <| f ₁ | / f _W <2 .61 (f ₁ <
0) (2) f ₃ / f _W <4.1 (3) 0.52 <f ₂ / f ₃ <0.61 (f ₂ > 0,
f ₃ > 0).

With such a configuration, by moving the third group optical system back and forth, the power burden on the second group optical system can be reduced and the zooming can be assisted while reducing the moving amount of the second group. And a high zoom ratio can be realized. In particular, the condition of the range of the focal length of the first group optical system (1)
, The size is reduced and the aberration is reduced. By setting the positive refractive power of the third group optical system in the range of the condition (2), the position of the exit pupil is separated from the image plane, and telecentricity is provided. Further, the second group optical system and the third group optical system
By setting the distribution of the positive refractive power to the group optical system in the range of the condition (3), even with a small number of lenses, the lens can be small and the aberration can be corrected well. Therefore, it is possible to obtain a zoom ratio of 3 times or more, and to sufficiently separate the exit pupil position from the image plane, to suppress distortion, and to be suitable for a digital still camera and the like with a small size and little aberration. It can be configured as a bright wide-angle zoom lens.

A zoom lens according to a second aspect of the present invention comprises:
The first group optical system includes, in order from the object side to the image side, a meniscus negative lens having a convex surface facing the object side, a meniscus negative lens having a convex surface facing the object side, and a convex surface facing the object side. And the second group optical system has a positive refracting surface with a strong refracting surface facing the object sequentially from the object side to the image side. A lens, a positive meniscus lens with a convex surface facing the object side, a negative lens with a strong refractive surface facing the image side, a positive lens, and a positive meniscus lens with a convex surface facing the object side It has a configuration having a lens. With such a configuration, in particular, the configuration is configured with a small number of lenses, the lens outer diameter is reduced, and aberrations generated in the second group optical system are effectively corrected.

A zoom lens according to a third aspect of the present invention includes:
2 from the object side of the three lenses of the first group optical system
The image side lens surface of the second meniscus negative lens is formed as an aspherical surface having a negative refractive power that becomes weaker as the distance from the optical axis increases. With such a configuration, particularly, the negative distortion that increases on the short focal length side is effectively corrected. In the zoom lens according to a fourth aspect of the present invention, the positive refracting power of the positive lens closest to the object side of the positive lens closest to the object among the five lenses of the second group optical system decreases as the distance from the optical axis increases. It is configured as an aspherical surface having the following shape. Such a configuration prevents the spherical aberration from being insufficiently corrected.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a zoom lens according to the present invention will be described in detail based on embodiments with reference to the drawings. FIG. 1 shows a configuration of a zoom lens according to a first embodiment of the present invention. FIG. 1A shows a lens configuration in a state where the zoom lens is set at a wide-angle end of zooming, and FIG. 1B shows a lens configuration in a state where the zoom lens is set at a telephoto end of zooming. Is shown.

The zoom lens shown in FIG. 1 has a first lens group G1 as a first group optical system and a second lens group G2 as a second group optical system sequentially from the object, that is, from the object side to the image side. And a third lens group G3, which is a third group optical system. The first lens group G1 includes three lenses L
1, L2 and L3, and the second lens group G2 is
The third lens group G3 includes five lenses L4, L5, L6, L7, and L8, and the third lens group G3 includes one lens L9. An aperture stop S is arranged on the object side of the second lens group G2, that is, between the second lens group G1 and the first lens group G1. Further on the image side of the third lens group G3, a filter F in which a low-pass filter (LPF) L10 and an infrared light cut filter (IRCF) L11 are combined is provided between the third lens group G3 and the image plane. That is, the optical element L1
L9 is a lens, and the optical elements L10 and L11 are optical filters.

First lens group G composed of lenses L1 to L3
1 has a negative refractive power. The second lens group G2 including the lenses L4 to L8 has a positive refractive power. Lens L9
Has a positive refractive power. When zooming from the wide-angle end to the telephoto end, the first lens group G1 first moves on the optical axis to the image side, and reverses the direction of movement from the middle to move to the object side. As described above, the first lens group G1 moves while drawing a convex arc-shaped trajectory convex on the image side, thereby correcting a change in the focal position when zooming from the wide-angle end to the telephoto end.

The second lens group G2 monotonously moves on the optical axis toward the object side during zooming from the wide-angle end to the telephoto end. In zooming from the wide-angle end to the telephoto end, the third lens group G3 first moves on the optical axis to the object side, and reverses the moving direction and moves to the image side halfway. Third lens group G3
Moves in such a manner as to draw a locus of a convex arc that is convex toward the object side. The second lens group G2 and the third lens group G
The zooming from the wide-angle end to the telephoto end is performed by the zooming operation by the movement of No. 3. Thus, the third lens group G3
By reciprocating in a convex arc shape convex to the object side,
By reducing the power burden on the second lens group G2 and assisting the zooming, the amount of movement of the second lens group G2 is reduced, and it is possible to realize a compact and high zooming.

The aperture stop S located on the object side of the second lens group G2 moves integrally with the second lens group G2. Therefore, the movement of the second lens group G2 is not hindered by the aperture stop S. The first to third lens groups G1 to G3
Is, f ₁ the focal length of the first lens group G1, the focal length of the second lens group G2 f _2, and the focal length of the third lens group G3 f _3, i.e. the M lens group (M = 1 to 3 the focal length of) the f _M, when the combined focal length f _W of the entire system at the wide angle end, configured to satisfy the following respective conditions.

Condition (1): 2.47 <| f ₁ | / f _W <2.61 (f ₁ <0) Condition (2) f ₃ / f _W <4.1 Condition (3) 0.52 < f ₂ / f ₃ <0.61 (f ₂ > 0, f ₃
> 0) conditions (1), the zoom lens is compact, is a condition for restricting the range of the focal length f ₁ of the first lens group G1 to favorably correct aberrations. When the value is less than the lower limit of the condition (1), it is advantageous for miniaturization of the entire lens system, but the first lens group G1
Is too strong, and various aberrations such as spherical aberration are deteriorated. When the value exceeds the upper limit of the condition (1), aberrations can be satisfactorily corrected, but it becomes difficult to reduce the size of the entire lens system.

Condition (2) is a condition for regulating the positive refractive power of the third lens group G3. When the value exceeds the upper limit of the condition (2), the positive refractive power of the third lens group G3 becomes insufficient, and
The exit pupil position approaches the image plane, and the telecentricity is lost. The condition (3) is a condition for regulating the distribution of the refractive power between the second lens group G2 and the third lens group G3, both of which have a positive refractive power. The condition (3) is for reducing the number of the second lens group G2 and the third lens group G3 to a small number, facilitating miniaturization, and favorably correcting aberrations.

When the value is less than the lower limit of the condition (3), the refractive power of the third lens group G3 becomes insufficient, so that the effect of the third lens group G3 is reduced and the refractive power of the third lens group G3 is compensated. In addition, since the refractive power burden of the second lens group G2 becomes excessive,
It is not preferable because the spherical aberration deteriorates and the flatness of the image deteriorates. When the value exceeds the upper limit of the condition (3), the third lens unit G3
Is large, the refractive load of the second lens group G2 is reduced, the spherical aberration is improved, and the flatness of the image is improved. However, the negative refractive power of the first lens group G1 and the negative This also matches the tendency that both the positive refractive powers of the two lens groups G2 become weak, and it is difficult to achieve the miniaturization of the entire system.

(The above corresponds to claim 1 of the present invention.) As shown in FIG. 1, the first lens group G1 includes a meniscus negative lens L1 having a convex surface facing the object side, and a convex surface facing the object side. And a positive meniscus lens L3 having a convex surface facing the object side. These three lenses L1 to L3 are sequentially arranged as L1 from the object side toward the image surface side. They are arranged in the order of -L2-L3.
The second lens group G2 includes a positive lens L4 having a strong refractive surface facing the object side, a meniscus positive lens L5 having a convex surface facing the object side, and a negative lens L5 having a strong refractive surface facing the image side.
6, a positive lens L7, and a meniscus-shaped positive lens L8 having a convex surface facing the object side. These five lenses L4 to L8 are sequentially moved from the object side to the image side as L4-
They are arranged in the order of L5-L6-L7-L8.

To reduce the number of lenses and reduce the outer diameter of the lens, negative lenses L1 and L2 constituting the first lens group G1 are arranged on the object side.
Then, in order to correct spherical aberration, coma, and astigmatism generated in the second lens group G2, first, generation of spherical aberration is suppressed as much as possible by the two positive lenses L4 and L5, and positive refraction as a whole is performed. Power, followed by the negative lens L6
Is overcorrected, and the two positive lenses L7 and L8 average the difference in the angle of view of each aberration. (The above corresponds to claim 2 of the present invention.) The meniscus-shaped negative lens L2 disposed second from the object side of the first lens group G1 moves the lens surface on the image side more negatively away from the optical axis. Are formed on an aspherical surface having a shape in which the refracting power of the light is weakened.

As described above, the image-side lens surface of the second meniscus negative lens L2 from the object side of the first lens group G1 has an aspheric surface whose negative refractive power becomes weaker as the distance from the optical axis increases. By forming, the negative distortion which increases especially on the short focal length side is corrected. (The above corresponds to claim 3 of the present invention.) The positive lens L disposed closest to the object side in the second lens group G2.
Reference numeral 4 indicates that the lens surface on the object side is formed as an aspherical surface having a shape such that the positive refractive power becomes weaker as the distance from the optical axis increases. As described above, the object-side lens surface of the positive lens L4 closest to the object side of the second lens group G2 forms an aspheric surface having a shape in which the positive refractive power becomes weaker as the distance from the optical axis increases, so that the main surface is mainly spherical. The aberration is prevented from being insufficiently corrected.

(The above corresponds to claim 4 of the present invention.) Tables 1 to 3 show specific data of the zoom lens of Example 1 according to the first embodiment. Table 1
Is lens data of an optical system constituting the zoom lens, Table 2 is data of an aspheric surface, and Table 3 is data of a variable amount of a variable portion. When the focal length of the entire system is f, the F number is F / No., The half angle of view is ω, and the image height is Y ′, f = 5.6 to 16.8, respectively.
mm, F / No. = 2.8-5.1, ω = 32.3-11.7
deg, Y '= 3.47.

The surface number of the optical surface constituting the optical system from the object side is i, the radius of curvature of each optical surface is r _i , and the distance between the subsequent optical surface (the optical surface adjacent to the image side) is _di. , The optical element number is j [that is, each optical element is represented by L _j (j = 1 to natural number of 1 to 11)], the refractive index of the optical material of the optical element L _j is n _j , and the optical material of the optical element L _j is Table 1 shows the lens data of the optical system that constitutes the zoom lens, where the Abbe number of ν _j is ν _j .

[0029]

[Table 1]

In Table 1, the description of the radius of curvature r _i as “0.000” means that the radius of curvature r _i is infinity (∞), which indicates that the optical surface is flat.
Therefore, both surfaces of the optical elements L10 and L11 constituting the filter F are flat, and both optical elements L1 and L11 are flat.
0 and L11 are tightly joined. The fourth optical surface and the eighth optical surface in Table 1, that is, the first lens group G1
Of the lens surface r ₈ of the object side of the positive lens L4, which is arranged on the most object side lens surface r ₄ and the second lens group G2 on the image side of the meniscus-shaped negative lens L2 arranged from the object side in the second , And an aspheric surface. As is well known, when the Z coordinate axis is made coincident with the optical axis and the Y coordinate is taken orthogonal to the optical axis, the radius of curvature on the optical axis is r, the conic constant is K, and the higher order aspheric coefficient is A, B, and C are curved surfaces obtained by rotating the curves represented by Equation 1 around the optical axis.

[0031]

(Equation 1) That is, the aspherical surface is obtained by adding the radius of curvature r on the optical axis, the conical constant K, and the higher order aspherical coefficient A to
The shape is specified by giving and defining each parameter of B and C.

Therefore, the fourth optical surface in Table 1, that is, the image-side lens surface r _{4 of} the meniscus negative lens L2 disposed second from the object side of the first lens group G1, and the eighth optical surface in Table 1 Optical surface, that is, the second lens group G2
The object-side lens surface r ₈ of the positive lens L4 disposed closest to the object side has radii of curvature r ₄ , r ₈ on the optical axis shown in Table 2,
Conic constant K, and higher order aspheric coefficients A, B, and C
Are formed on an aspheric surface defined by the following parameters.

[0033]

[Table 2]

[0034] In Table 1, the sixth optical surface r ₆ where the surface distance d _i "variable", the face of the next (surface number) optical surface of the 17 optical surfaces r ₁₇ and 19 optical surface r ₁₉ The interval is the wide-angle end where the focal length f of the entire system is 5.60 mm, and the focal length f is 9.7.
An intermediate focal length of 0 mm and a focal length f of 16.79 mm
At the telephoto end of the camera as shown in Table 3.

[0035]

[Table 3]

In this case, the total length of the lens at the wide-angle end,
That is, the distance from the first optical surface of the optical system to the image plane is 4
2.1 mm. 2 to 4 show aberration diagrams in the first embodiment. 2 shows the aberration at the wide-angle end, FIG. 3 shows the aberration at the intermediate focal length, and FIG. 4 shows the aberration at the telephoto end. In the aberration diagrams, SA indicates spherical aberration, SC indicates a sine condition, Ast indicates astigmatism, and Dist indicates distortion. In each aberration diagram, "d" indicates an aberration with respect to d-line, and "g" indicates an aberration with respect to g-line. In the spherical aberration diagram, the spherical aberration is indicated by a solid line, the sine condition is indicated by a broken line, and in the astigmatism diagram, the sagittal ray is indicated by a solid line, and the meridional ray is indicated by a broken line. According to FIGS. 2 to 4, aberrations are satisfactorily corrected at any of the wide-angle end, the intermediate focal length, and the telephoto end in the zoom range, and it is confirmed that the performance is good.

FIG. 5 shows a configuration of a main part of a zoom lens according to a second embodiment of the present invention. (A) of FIG.
FIG. 5 shows a lens configuration in a state where the zoom lens is set at a wide-angle end of zooming, and FIG. 5B shows a lens configuration in a state where the zoom lens is set at a telephoto end of zooming. The zoom lens shown in FIG.
From the object, that is, the object side, to the image side, the first
A first lens group G1 'as a group optical system, a second lens group G2' as a second group optical system, and a third lens group G3 'as a third group optical system are arranged.

The first lens group G1 'includes three lenses L
1 ′, L2 ′ and L3 ′, and the second lens group G
2 'denotes five lenses L4', L5 ', L6', L7 '
And L8 ', and the third lens group G3' is composed of one lens L9 '. Second lens group G
An aperture stop S is disposed on the object side of 2 ', that is, between the first lens group G1'. Third lens group G3 '
Further on the image side, a low-pass filter L
A filter F is provided which is a combination of 10 'and the infrared light cut filter L11'. That is, the optical elements L1 'to L9' are lenses and the optical elements L1
0 'and L11' are optical filters.

The first lens group G1 'composed of the lenses L1' to L3 'has a negative refractive power. Lens L4'-L
The second lens group G2 'composed of 8' has a positive refractive power. The third lens group G3 'including the lens L9' has a positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens group G1 'first moves on the optical axis to the image side, and reverses the direction of movement from the middle to move to the object side. The first lens group G1 'moves in such a manner as to draw a convex arc-shaped locus convex toward the image side, thereby correcting a change in the focal position when zooming from the wide-angle end to the telephoto end.

The second lens group G2 'monotonously moves on the optical axis toward the object side during zooming from the wide-angle end to the telephoto end. During zooming from the wide-angle end to the telephoto end, the third lens group G3 'first moves on the optical axis to the object side, and reverses the direction of movement from the middle to move to the image side. The third lens group G3 'moves in such a manner as to draw a convex arc-shaped locus convex toward the object side. Zooming from the wide-angle end to the telephoto end is performed by the zooming operation by the movement of the second lens group G2 'and the third lens group G3'. In this way, by moving the third lens group G3 'back and forth in a convex arc shape convex toward the object side, the power burden on the second lens group G2' is reduced and the second lens group G2 'is assisted in zooming. The movement amount of the lens group G2 'is reduced, and it is possible to realize a small size and a high zoom ratio.

The aperture stop S located on the object side of the second lens group G2 'moves integrally with the second lens group G2'. Therefore, the aperture stop S does not hinder the movement of the second lens group G2 '. The first to third lens groups G
1 ′ to G3 ′ are the focal length of the M-th lens unit (M = 1 to 3) as f _M, and the combined focal length f _W of the whole system at the wide-angle end, as in the case of the first embodiment. Then, it is configured to satisfy the above-mentioned conditions (1) to (3).

As shown in FIG. 5, the first lens group G1 '
Is a negative meniscus lens L having a convex surface facing the object side.
1 ', meniscus negative lens L with the convex surface facing the object side
2 'and a meniscus-shaped positive lens L3' having a convex surface facing the object side.
3 ′ are sequentially shifted from the object side to the image plane side by L1′−
They are arranged in the order of L2'-L3 '. The second lens group G2 'includes a positive lens L having a strong refractive surface facing the object side.
4 ', meniscus-shaped positive lens L with the convex surface facing the object side
5 ', a negative lens L6' having a strong refracting surface facing the image side, a positive lens L7 ', and a meniscus-shaped positive lens L8' having a convex surface facing the object side.
4 ′ to L8 ′, sequentially from the object side to the image side,
4'-L5'-L6'-L7'-L8 '.

The meniscus-shaped negative lens L2 'disposed second from the object side of the first lens group G1' has a non-uniform shape in which the negative refractive power becomes weaker as the distance from the optical axis increases as the distance from the optical axis increases. It is formed on a spherical surface. The positive lens L4 'located closest to the object side of the second lens group G2' has a lens surface on the object side formed as an aspheric surface having a shape such that the positive refractive power becomes weaker as the distance from the optical axis increases.

In FIGS. 5 (a) and 5 (b), the radii of curvature of the respective surfaces of the lenses L1 'to L9' and the filter F 'and the signs of the surface intervals are not shown.
Symbols r _{1 to} r ₂₂ and d given in (a) and (b)
_{1 to} d ₂₁ are common. Next, the second
Tables 4 to 6 show specific data of the zoom lens of Example 2 according to the embodiment. Table 4 shows lens data of an optical system constituting the zoom lens, Table 5 shows data of an aspheric surface, and Table 6 shows data of a variable amount of a variable portion.

[0045]

[Table 4]

The fourth optical surface in Table 4, that is, the lens surface r ₄ on the image side of the meniscus-shaped negative lens L2 'disposed second from the object side of the first lens group G1', and Table 4
, The object-side lens surface r ₈ of the positive lens L 4 ′ disposed closest to the object side of the second lens group G 2 ′ has a radius of curvature r on the optical axis shown in Table 5 and a conic constant K ,
And higher order aspherical coefficients A, B, and C are formed on an aspherical surface defined by parameters.

[0047]

[Table 5] In Table 1, the sixth optical surface r ₆ where the surface distance d _i "variable", the following (surface number) the optical surface r ₇ of the 17 optical surfaces r ₁₇ and 19 optical surface r _19, r ₁₈ and spacing of the r ₂₀ is the wide angle end focal length f of the entire system 5.60 mm, an intermediate focal length of the focal length f 9.70 mm, and the focal length f 1
At the telephoto end of 6.80 mm, it changes as shown in Table 6.

[0048]

[Table 6] Again, the distance of the total lens length at the wide angle end, i.e. from the first optical surface r ₁ of the optical system to the image plane, 42.1 mm
It is.

FIGS. 6 to 8 show aberration diagrams in the second embodiment. 6 is an aberration diagram at the wide-angle end, FIG. 7 is an aberration diagram at the intermediate focal length, and FIG. 8 is an aberration diagram at the telephoto end. 6 to 8, it was confirmed that the aberration was well corrected at any of the wide-angle end, the intermediate focal length, and the telephoto end in the zoom range, and the performance was good.
FIG. 9 shows a configuration of a main part of a zoom lens according to a third embodiment of the present invention. FIG. 9A shows a lens configuration in a state where the zoom lens is set at a wide-angle end of zooming, and FIG. 9B shows a lens configuration in a state where the zoom lens is set at a telephoto end of zooming. Is shown.

The zoom lens shown in FIG. 9 has a first lens group G1 ″ as a first group optical system and a second lens group G2 as a second group optical system sequentially from the object, that is, the object side to the image side. "And the third lens group G3 as the third group optical system"
Is arranged. The first lens group G1 "includes three lenses L1", L2 ", and L3", and the second lens group G2 "includes five lenses L4", L5 ", L6", L5.
7 "and L8", and the third lens unit G
Reference numeral 3 "denotes a single lens L9".

An aperture stop S is arranged on the object side of the second lens group G2 ", that is, between the first lens group G1". Further on the image side of the third lens group G3 ", a filter F in which a low-pass filter L10" and an infrared light cut filter L11 "are combined is provided between the third lens group G3" and the image plane. "-L9" is a lens, and the optical elements L10 "and L11" are optical filters. The first lens group G1 "including the lenses L1" -L3 "has a negative refractive power. Lens L4 ″ -L
The second lens group G2 ″ composed of 8 ″ has a positive refractive power. The third lens group G3 "including the lens L9" has a positive refractive power.

During zooming from the wide-angle end to the telephoto end, the first lens group G1 ″ first moves on the optical axis to the image side.
The direction of movement is reversed halfway and moves toward the object side. The first lens group G1 ″ corrects a change in the focal position during zooming from the wide-angle end to the telephoto end by moving while drawing a convex arc-shaped locus that is convex toward the image side.
The lens group G2 ″ moves monotonously on the optical axis toward the object side when zooming from the wide-angle end to the telephoto end. The third lens group G3 ″ moves along the optical axis when zooming from the wide-angle end to the telephoto end. First, it moves to the object side, and in the middle, reverses the moving direction and moves to the image side. The third lens group G3 ″ moves in such a manner as to draw a locus that is convex toward the object side.
Zooming from the wide-angle end to the telephoto end is performed by the zooming operation by the movement of the second lens group G2 ″ and the third lens group G3 ″.

As described above, the third lens group G3 "is reciprocated in a convex arc shape convex toward the object side, so that the power load on the second lens group G2" is reduced and the zooming assist is performed. To reduce the amount of movement of the second lens group G2 ″,
It is possible to realize a small size and a high zoom ratio.
The aperture stop S located on the object side of the second lens group G2 ″ is
It moves integrally with the second lens group G2 ". Therefore, the aperture stop S does not hinder the movement of the second lens group G2". The first to third lens groups G1 "to G3"
Is the same as that of the first and second embodiments.
Lens focal length of (M = 1 to 3) and f _M, when the combined focal length f _W of the entire system at the wide angle end, configured so as to satisfy the above conditions (1) - (3) .

As shown in FIG. 9, the first lens group G1 ″
Is a negative meniscus lens L having a convex surface facing the object side.
1 ″, meniscus negative lens L with the convex surface facing the object side
2 "and a meniscus-shaped positive lens L3" having a convex surface facing the object side, and these three lenses L1 "-L
3 ″ sequentially from the object side to the image plane side, L1 ″ −
L2 "-L3" are arranged in this order. The second lens group G2 ″ is a positive lens L having a strong refractive surface facing the object side.
4 ″, meniscus-shaped positive lens L with the convex surface facing the object side
5 ", a negative lens L6" having a strong refractive surface facing the image side, a positive lens L7 ", and a meniscus positive lens L8" having a convex surface facing the object side. These five lenses L
4 ″ to L8 ″ sequentially from the object side to the image side,
4 "-L5" -L6 "-L7" -L8 ".

[0055] "negative lens L2 meniscus shape which is disposed second outermost from the object side of the" first lens group G1, the lens surface r ₄ of the image side, a negative refractive power with distance from the optical axis becomes weaker shape Are formed on the aspheric surface. Second lens group G
"Positive lens L4 disposed nearest to the object side of the" 2 forms a lens surface r ₈ of the object side, an aspherical positive refractive power becomes weaker shape the distance from the optical axis.

In FIGS. 6 (a) and 6 (b), the radii of curvature of the respective surfaces of the lenses L1 "to L9" and the filter F "and signs of the surface intervals are not shown, but FIG.
Symbols r _{1 to} r ₂₂ and d given in (a) and (b)
_{1 to} d ₂₁ are common. Next, the third
Tables 7 to 9 show specific data of the zoom lens of Example 3 according to the embodiment. Table 7 shows lens data of the optical system constituting the zoom lens, Table 8 shows aspherical data, and Table 9 shows data of the variable amount of the variable portion.

[0057]

[Table 7]

The fourth optical surface in Table 7, that is, the image-side lens surface r _{4 of} the meniscus-shaped negative lens L2 ″ disposed second from the object side of the first lens group G1 ″, and Table 7.
, The lens surface r ₈ on the object side of the positive lens L 4 ″ disposed closest to the object side of the second lens group G 2 ″ has a radius of curvature r and a conic constant K on the optical axis shown in Table 8. ,
And higher order aspherical coefficients A, B, and C are formed on an aspherical surface defined by parameters.

[0059]

[Table 8] In Table 7, the sixth optical surface r ₆ where the surface distance d _i "variable", the following (surface number) the optical surface r ₇ of the 17 optical surfaces r ₁₇ and 19 optical surface r _19, r ₁₈ and spacing of the r ₂₀ is the wide angle end focal length f of the entire system 5.60 mm, an intermediate focal length of the focal length f 9.70 mm, and the focal length f 1
It changes as shown in Table 9 at the telephoto end of 6.81 mm.

[0060]

[Table 9] In this case, the distance of the total lens length at the wide angle end, i.e. from the first optical surface r ₁ of the optical system to the image plane is 42.0 mm
It is.

FIGS. 10 to 12 show aberration diagrams in the third embodiment. 10 is an aberration diagram at the wide-angle end, FIG. 11 is an aberration diagram at the intermediate focal length, and FIG. 12 is an aberration diagram at the telephoto end. FIG.
According to FIGS. 0 to 12, aberrations were corrected well at any of the wide-angle end, the intermediate focal length, and the telephoto end in the zoom range, and it was confirmed that the performance was good. Each parameter | f ₁ | in the above-described first to third embodiments
/ F _W , f ₃ / f _W , f ₂ / f ₃ , and image height ratio: 1.
Table 10 shows the distortion D _W (1.0) at the wide-angle end at 0.

[0062]

[Table 10] As described above, according to the first to third embodiments of the present invention, the zoom ratio is three times, the exit pupil position is sufficiently separated from the image plane, and the size is small and the aberration is well corrected. Further, it is possible to provide a zoom lens in which distortion is suppressed to 2% or less. Such a zoom lens can be configured as a bright wide-angle zoom lens suitable for a digital still camera or the like.

[0063]

As described above, according to the first aspect of the present invention, from the object side to the image side, the first group optical system having a negative refractive power and the positive group have a positive refractive power. A second group optical system and a third group optical system having a positive refractive power are provided, and an aperture stop that moves integrally with the second group optical system during zooming is provided on the object side of the second group optical system. At the same time, during zooming from the wide-angle end to the telephoto end, the first group optical system first moves on the optical axis to the image side, and reverses the moving direction to the object side on the way, so that the convex on the image side is formed. The second group optical system monotonously moves on the optical axis to the object side to perform zooming by moving in an arc shape to correct the change of the focal position.
The group optical system first moves to the object side on the optical axis, and in the middle, reverses the moving direction to the image side to move in a convex arc shape convex to the object side to perform zooming. When the focal length of (M = 1 to 3) is f _M and the combined focal length of the entire system at the wide-angle end is f _W , these conditions are as follows: (1) 2.47 <| f ₁ | / f _W <2 .61 (f ₁ <
0) (2) f ₃ / f _W <4.1 (3) 0.52 <f ₂ / f ₃ <0.61 (f ₂ > 0,
f ₃ > 0), a zoom ratio of three times or more can be obtained, the exit pupil position can be sufficiently separated from the image plane, and distortion can be suppressed. In addition, the zoom lens can be configured as a bright wide-angle zoom lens which is small, has little aberration, and is suitable for a digital still camera or the like. In particular, it is possible to provide a zoom lens which is small and whose aberration is well corrected.

In particular, according to the zoom lens of the second aspect of the present invention, the first group optical system includes a meniscus-shaped negative lens having a convex surface facing the object side in order from the object side to the image side; It has a meniscus negative lens with a convex surface facing the object side, and three meniscus positive lenses with a convex meniscus lens facing the object side, and the second group optical system is arranged from the object side. Towards the image side, in turn, a positive lens with a strong refractive surface facing the object side, a meniscus-shaped positive lens with a convex surface facing the object side, a negative lens with a strong refractive surface facing the image side,
With a configuration having five lenses in which a positive lens and a meniscus-shaped positive lens with the convex surface facing the object side are arranged, in particular, the configuration is made with a small number of lenses, and the lens outer diameter is reduced. The aberration generated in the second lens group can be effectively corrected.

According to the zoom lens of the third aspect of the present invention, the image side lens surface of the meniscus negative lens located second from the object side among the three lenses of the first group optical system is By configuring the aspherical surface so that the negative refractive power becomes weaker as the distance from the optical axis increases, negative distortion that increases particularly on the short focal length side can be effectively corrected. According to the zoom lens of the fourth aspect of the present invention, the object side lens surface of the most object side positive lens among the five lenses of the second group optical system has a positive refractive power as the distance from the optical axis increases. In particular, it is possible to prevent the spherical aberration from being insufficiently corrected by configuring as an aspherical surface having a shape in which the spherical aberration becomes weak.

[Brief description of the drawings]

FIG. 1 is an optical system layout diagram schematically showing an arrangement configuration of an optical system of a zoom lens according to a first embodiment of the present invention.

FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens of FIG.

FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion at an intermediate focal length of the zoom lens of FIG. 1;

FIG. 4 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens of FIG. 1;

FIG. 5 is an optical system layout diagram schematically showing an arrangement configuration of an optical system of a zoom lens according to a second embodiment of the present invention.

6 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens in FIG.

7 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at an intermediate focal length of the zoom lens of FIG. 5;

8 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens in FIG.

FIG. 9 is an optical system layout diagram schematically showing an arrangement configuration of an optical system of a zoom lens according to a third embodiment of the present invention.

FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens of FIG. 9;

11 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion of the zoom lens of FIG. 9 at an intermediate focal length.

12 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens in FIG.

[Explanation of symbols]

G1, G1 ', G1 "First lens group G2, G2', G2" Second lens group G3, G3 ', G3 "Third lens group S Aperture stop F, F', F" Filters L1 to L11, L1 ' ~ L11 ', L1 "~ L11"
Optical elements L1 to L9, L1 'to L9', L1 "to L9" Lenses L10, L10 ', L10 ", L11, L11', L1
1 "optical filter

Claims (4)

[Claims] 1. A first group optical system having a negative refractive power and a second optical system having a positive refractive power in order from the object side to the image side.
A group optical system and a third group optical system having a positive refractive power are provided, and an aperture stop that moves integrally with the second group optical system during zooming is provided on the object side of the second group optical system, Upon zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and reverses the moving direction to the object side in the middle, thereby forming a convex arc convex to the image side. The second group optical system moves monotonically on the optical axis toward the object side to perform zooming, and the third group optical system first moves along the optical axis. By moving to the object side and reversing the moving direction to the image side in the middle, the lens moves in a convex arc shape convex to the object side to perform zooming, and the focal length of the M-th group optical system (M = 1 to 3) Is f _M and the combined focal length of the whole system at the wide-angle end is f _W. These conditions are as follows: (1) 2.47 <| f ₁ | / f _W <2.61 (f ₁ <
0) (2) f ₃ / f _W <4.1 (3) 0.52 <f ₂ / f ₃ <0.61 (f ₂ > 0,
zoom lens satisfies the f _3> 0). 2. The first group optical system includes: a meniscus negative lens having a convex surface facing the object side, a meniscus negative lens having a convex surface facing the object side, in order from the object side to the image side; The second group optical system includes three lenses each including a meniscus positive lens having a convex surface facing the object side, and the second group optical system sequentially has a strong refractive surface on the object side from the object side to the image side. A positive lens with a positive surface, a meniscus-shaped positive lens with a convex surface facing the object side, a negative lens with a strong refractive surface facing the image side, a positive lens, and a positive meniscus lens with a convex surface facing the object side. The zoom lens according to claim 1, comprising five lenses. 3. A negative meniscus lens located second from the object side among the three lenses of the first group optical system has a weak negative refractive power as the lens surface on the image side moves away from the optical axis. 3. The zoom lens according to claim 2, wherein the zoom lens has an aspherical shape. 4. The positive lens closest to the object among the five lenses of the second group optical system is an aspheric surface having a shape such that the positive refractive power becomes weaker as the lens surface on the object side moves away from the optical axis. The zoom lens according to claim 1, wherein: