JP2004102313A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exit pupil position sufficiently separated from an image plane, to reduce distortion while reducing the lens outer diameter with a small number of lenses, to be small, to have little aberration, and to have a zoom ratio of 3 or more. Get a zoom lens.
SOLUTION: A negative first lens group G1, a positive lens group G2, and a positive lens group G3 are sequentially arranged from an object side to an image side. During zooming from the wide-angle end to the telephoto end, on the optical axis, the lens group G1 moves to the image side, reverses and moves from the middle to the object side, and the lens group G2 moves monotonously to the object side. The aperture stop S moves integrally with the lens group G2. The focal length of the M lens group (M = 1 to 3) and _{f M,} the combined focal length of the entire system at the wide angle end as _{f W,} condition _{(1) 2.47 <| f 1} | / f W <2 .61 (f ₁ <0), condition (2) f ₃ / f _W <4.1, and condition (3) 0.52 <f ₂ / f ₃ <0.61 (f ₂ > 0, f ₃ >) 0) is satisfied.
[Selection diagram] Fig. 1

Description

The present invention relates to an optical system of a zoom lens, and more particularly to a zoom lens suitable as a telecentric small-sized wide-angle zoom lens for a digital still camera and a video camera using a solid-state imaging device as a light receiving element.

In a so-called video camera that captures moving images, a solid-state imaging device such as a CCD (charge coupled device) or a MOS (metal oxide semiconductor) has conventionally been 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 image sensor, 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 data on a video flexible disk or the like have been widely used. Some digital cameras can capture not only still images but also moving images (movie images).

By the way, the optical system of a camera using such a solid-state imaging device such as a CCD is required to have the exit pupil position sufficiently separated from the 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 beam 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.

The first lens group having a negative refractive power and the second lens group having a positive refractive power are sequentially arranged from the object side to the image side, and the first lens group and the second lens group are arranged. A zoom lens that performs zooming by changing the distance between the groups and the group is well known as a so-called two-group 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, it has been 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 second lens group, and many zoom lenses have been proposed. Have been. As described above, examples of a zoom lens in which a lens group having a positive refractive power is arranged behind the second lens group are described in, for example, Patent Document 1 (Japanese Patent Publication No. 3-20735) and Patent Document 2 (Japanese Patent Publication No. 7-52256) and Patent Document 3 (Japanese Patent Application Laid-Open No. 6-94996).

However, the zoom lenses described in Patent Document 1 and Patent Document 2 are designed mainly for single-lens reflex (single-lens reflex) still cameras. Therefore, in the configurations described in Patent Document 1 and Patent Document 2, 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 Patent Document 3, in order to keep the exit pupil position away from the image plane, the stop position is fixed at an intermediate position between the first lens unit and the second lens unit during zooming. I have. For this reason, the movement of the first lens group and the second lens group is restricted, so that the zoom ratio is less than twice.

In order to address the above-described problem, the present applicant can obtain a zoom ratio of about three times, and furthermore, the exit pupil position can be sufficiently separated from the image plane, and is suitable for a small digital still camera or the like. A wide-angle zoom lens has been proposed so far.
For example, Patent Document 4 (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% distortion at the wide-angle end. Such a 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 tend to pursue higher image quality, and small distortion of an image is also one of the important quality items in a digital still camera oriented to high image quality. For this reason, the zoom lens described in Patent Document 4 described above is considered to be unsuitable for recent digital still cameras with high image quality.

Japanese Patent Publication No. 3-20735 Japanese Patent Publication No. 7-52256 Japanese Patent Publication No. 6-94996

The present invention has been made in view of the above-described circumstances, and achieves a zoom ratio of 3 or more, can sufficiently separate the exit pupil position from the image plane, and suppresses distortion. It is an object of the present invention to provide a zoom lens that can be formed, is small, has little aberration, and can be configured as a bright wide-angle zoom lens suitable for a digital still camera or the like.

In particular, a first object of the present invention is to provide a zoom lens that is small in size and has aberrations well corrected.
A second object of the present invention is to provide a zoom lens which is configured with a small number of lenses, reduces the lens outer diameter, and effectively corrects the aberration generated in the second 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 that can prevent the spherical aberration from being insufficiently corrected.

In order to achieve the above object, particularly the first object, the zoom lens according to the first aspect of the present invention has a first lens group having a negative refractive power in order from the object side to the image side. A second group optical system having a positive refractive power, and a third group optical system having a positive refractive power. The second group optical system is disposed on the object side of the second group optical system during zooming. In addition to providing an aperture stop that moves integrally, 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 reverses the movement direction to the object side halfway. The second group optical system monotonously moves on the optical axis to the object side to perform zooming, thereby moving in a convex arc shape toward the image side and correcting the fluctuation of the focal position. The system has a negative lens provided with an aspheric surface, the second group optical system has a positive lens provided with an aspheric surface, The negative lens provided with the aspherical surface of the first group optical system has a meniscus shape having a convex surface facing the object side, the lens surface on the image side is aspherical surface, and the third group optical system includes one positive lens. It is characterized by comprising.

3. The zoom lens according to claim 2, wherein the positive lens provided with the aspheric surface of the second group optical system is disposed closest to the stop, and the lens surface on the object side is aspheric. The aspherical surface is characterized in that the positive refractive power decreases as the distance from the optical axis increases.

4. The zoom lens according to claim 3, wherein the first group optical system includes a meniscus negative lens having a convex surface facing the object side from the object side to the image side, and a convex surface facing the object side. , And three lenses each including a meniscus-shaped positive lens with a convex surface facing the object side.
In the zoom lens according to the present invention as set forth in claim 4, wherein the second group optical system includes, in order from the object side to the image side, a positive lens having a strong refractive surface facing the object side, and a convex surface facing the object side. It is characterized by including five lenses that are arranged with a positive meniscus lens directed toward the lens, 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. And
In the zoom lens according to the fifth aspect of the present invention, when the focal length of the M-th 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 , Is a condition;
f ₃ / f _W <4.1
It is characterized by satisfying.
In the zoom lens according to the present invention described in claim 6, when the focal length of the M-th 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 , conditions;
2.47 <| f ₁ | / F _W <2.61 (f ₁ <0)
_{0.52 <f 2 / f 3 <} 0.61 (f 2> 0, f 3> 0)
It is characterized by satisfying.

[Action]
That is, the zoom lens according to the present invention sequentially includes, from the object side to the image side, a first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a positive refractive power. A third-group optical system 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 when 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 in the middle, reverses the moving direction to the object side, thereby moving in a convex arc shape toward the image side to correct the fluctuation of the focal position. The second group optical system monotonously moves on the optical axis to the object side to perform zooming, and the third group optical system first moves on the optical axis to the object side and moves in the middle. Is inverted to the image side to move in an arc shape convex to the object side to perform zooming, and the M-th group optical system (M = The focal length f _M of _-3), when the combined focal length of the entire system at the wide angle end and f _W, these are conditions:
(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)
Is satisfied.

With such a configuration, the third group optical system is reciprocated in an arc shape convex toward the object side, thereby assisting the zooming while reducing the power burden on the second group optical system, and moving the second group. The size can be reduced and a small size and high zoom ratio can be realized. In particular, by setting the range of the focal length of the first group optical system to the range of the condition (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, by setting the distribution of the positive refractive power between the second group optical system and the third group optical system within the range of the condition (3), even with a small number of lenses, the lens is small and the aberration is favorably corrected.
Therefore, it is possible to obtain a zoom ratio of three times or more, 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.

In the zoom lens according to the present invention, the first lens group optical system includes a meniscus-shaped negative lens having a convex surface facing the object side and a meniscus-shaped negative lens having a convex surface facing the object side, sequentially from the object side to the image side. It has three lenses each including a negative lens and a meniscus-shaped positive lens having a convex surface facing the object side, and the second group optical system sequentially moves the object side from the object side to the image side. Positive lens with a strong refractive surface facing the lens, meniscus-shaped positive lens with a convex surface facing the object side, negative lens with a strong refractive surface facing the image side, positive lens, and meniscus-shaped positive lens with a convex surface facing the object side It is configured to have five lenses in which lenses are arranged.
With such a configuration, in particular, it is configured with a small number of lenses, the outer diameter of the lens is reduced, and the aberration generated in the second group optical system is effectively corrected.

In the zoom lens according to the present invention, of the three lenses of the first group optical system, the image-side lens surface of the meniscus-shaped negative lens located second from the object side becomes negatively refracted as the distance from the optical axis increases. It is configured as an aspherical surface with a shape that weakens the force.
With such a configuration, negative distortion that increases particularly on the short focal length side is effectively corrected.
The zoom lens according to the present invention has a shape in which a positive refractive power becomes weaker as the distance from the optical axis increases as the distance from the optical axis increases, with the lens surface on the object side of the most object side positive lens among the five lenses of the second group optical system. Configure as an aspheric surface.
With such a configuration, in particular, the spherical aberration is prevented from being insufficiently corrected.

According to the first aspect of the present invention, in order from the object side to the image side, the first group optical system having a negative refractive power, the second group optical system having a positive refractive power, and the positive refractive power are sequentially changed. A third-group optical system having an aperture stop that moves integrally with the second-group optical system during zooming on the object side of the second-group optical system;
When 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 in the middle of the movement, reverses the moving direction to the object side, thereby moving in an arc shape convex to the image side. To correct the fluctuation of the focal position, the second group optical system monotonously moves on the optical axis to the object side to perform magnification,
The first group optical system has a negative lens provided with an aspheric surface, the second group optical system has a positive lens provided with an aspheric surface,
The negative lens having an aspheric surface of the first group optical system has a meniscus shape with a convex surface facing the object side, the lens surface on the image side is aspheric, and the third group optical system is a single lens. Since it is composed of a positive lens, a zoom ratio of 3 times or more can be obtained, the exit pupil position can be sufficiently separated from the image plane, distortion can be suppressed, and the size is small and the aberration is small. The present invention can be configured as a bright wide-angle zoom lens suitable for a digital still camera or the like. In particular, it is possible to provide a zoom lens that is small and has aberrations well corrected.
In particular, since the 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 in claim 1, the movement of the second group optical system is prevented by the aperture stop. In particular, when the zooming is performed from the wide-angle end to the telephoto end, the first group optical system is moved along a convex arc-shaped trajectory toward the image side, thereby correcting the fluctuation of the focal position during the zooming. it can.

According to the zoom lens of the second aspect of the present invention, the positive lens provided with the aspheric surface of the second group optical system is disposed closest to the stop, and the lens surface on the object side is an aspheric surface. Since the aspherical surface has a shape in which the positive refractive power becomes weaker as the distance from the optical axis increases, in particular, it is possible to prevent the spherical aberration from being insufficiently corrected.
Further, according to the zoom lens of claim 3 of the present invention, the first group optical system includes a meniscus negative lens having a convex surface facing the object side in order from the object side to the image side, and The lens includes a meniscus-shaped negative lens with a convex surface facing the lens and a meniscus-shaped positive lens with a convex surface facing the object side. Can be reduced.

According to the zoom lens of claim 4 of the present invention, the second group optical system includes, in order from the object side to the image side, a positive lens having a strong refraction surface facing the object side, and a convex surface facing the object side. A positive lens having a meniscus shape directed toward the lens, a negative lens having a strong refraction surface facing the image side, a positive lens, and a positive lens having a meniscus shape having a convex surface facing the object side. Therefore, in particular, it is possible to configure the lens with a small number of lenses, to reduce the outer diameter of the lens, and to correct the aberration generated in the second group optical system.
According to the zoom lens of the present invention, when the focal length of the M-th 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 are the conditions:
(2) f ₃ / f _W <4.1
Is satisfied, it is possible to keep the exit pupil position away from the image plane and not to lose telecentricity.

According to the zoom lens of claim 6 of the present invention, when the focal length of the M-th 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 are the conditions;
(1) 2.47 <| f ₁ | / F _W <2.61 (f ₁ <0)
_{(3) 0.52 <f 2 /} f 3 <0.61 (f 2> 0, f 3> 0)
Among them, by satisfying the above expression (1), it is possible to reduce the size and satisfactorily correct aberrations. By satisfying the above expression (3), the spherical aberration is suppressed and the image flatness is also good. The size of the entire system can be reduced.
According to the zoom lens of the present invention comprising the above-described claims 1, 5 and 6, 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. It is possible to configure a bright wide-angle zoom lens that is small, has little aberration, and is suitable for a digital still camera, etc. it can.

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 includes a first lens group G1 as a first group optical system, a second lens group G2 as a second group optical system, and a third lens group from the object, that is, the object side to the image side. A third lens group G3, which is a group optical system, is disposed.
The first lens group G1 is composed of three lenses L1, L2 and L3, the second lens group G2 is composed of five lenses L4, L5, L6, L7 and L8, and the third lens group G3 Is composed of 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 G2 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 elements L1 to L9 are lenses, and the optical elements L10 and L11 are optical filters.

The first lens group G1 including the lenses L1 to L3 has a negative refractive power. The second lens group G2 including the lenses L4 to L8 has a positive refractive power. The third lens group G3 including the 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 moving direction from the middle to move to the object side. As described above, the first lens group G <b> 1 moves by drawing an 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 to 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 moving direction and moves to the image side halfway. As described above, the third lens group G3 moves while drawing an arc-shaped locus convex toward the object side. Zooming from the wide-angle end to the telephoto end is performed by the zoom 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 an arc shape convex toward the object side, so that the power burden on the second lens group G2 is reduced and the zoom lens is assisted in zooming. It is possible to realize a small size and high zoom ratio by reducing the moving amount of the lens.

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~G3 is the focal length of the first lens group G1 _{f 1,} a focal length of the second lens group G2 _{f 2,} and the focal length of the third lens group G3 _f 3, that the M lens the 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 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)
Condition (1) is a zoom lens is downsized, 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. However, since the negative refractive power of the first lens unit G1 becomes too strong, various aberrations such as spherical aberration deteriorate. Absent. If the upper limit of the condition (1) is exceeded, aberrations can be satisfactorily corrected, but it is 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 unit G3 becomes insufficient, the exit pupil position approaches the image plane, and the telecentric property 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 having 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, and the effect of the third lens group G3 decreases. Since the refractive power burden of the second lens group G2 becomes excessive, the spherical aberration is deteriorated and the flatness of the image is also deteriorated, which is not preferable.
When the value exceeds the upper limit of the condition (3), the refractive load of the third lens group G3 is large, so that the refractive load of the second lens group G2 is reduced, the spherical aberration is improved, and the flatness of the image is also improved. However, the negative refractive power of the first lens group G1 and the positive refractive power of the second lens group G2 both tend to be weak, and it is difficult to achieve the miniaturization of the entire system.

As shown in FIG. 1, the first lens group G1 includes a meniscus-shaped negative lens L1 having a convex surface facing the object side, a meniscus-shaped negative lens L2 having a convex surface facing the object side, and a convex surface facing the object side. It is composed of a meniscus-shaped positive lens L3, and these three lenses L1 to L3 are arranged in the order of L1-L2-L3 from the object side to the image plane side.
The second lens group G2 includes a positive lens L4 having a strong refractive surface facing the object side, a meniscus-shaped positive lens L5 having a convex surface facing the object side, a negative lens L6 having a strong refractive surface facing the image side, and a positive lens L6. A lens L7 and a meniscus positive lens L8 having a convex surface facing the object side. These five lenses L4 to L8 are sequentially arranged from the object side to the image side as L4-L5-L6-L7-L8. It is arranged in the order of.

The negative lenses L1 and L2 constituting the first lens group G1 are arranged on the object side in order to make up the lens with a small number of lenses and to reduce the lens outer diameter. Then, in order to correct spherical aberration, coma aberration, 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 so that positive refraction as a whole is obtained. The force is obtained, then the overcorrection is performed by the negative lens L6, and the field angle difference of each aberration is averaged by the two subsequent positive lenses L7 and L8.
The meniscus-shaped negative lens L2 disposed second from the object side of the first lens group G1 is configured such that the image-side lens surface is formed as an aspheric surface having a shape in which negative refractive power becomes weaker as the distance from the optical axis increases. I have.

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 forms an aspheric surface having a shape in which the negative refractive power becomes weaker as the distance from the optical axis increases. Thus, the negative distortion that increases particularly on the short focal length side is corrected.
The positive lens L4 disposed closest to the object side of the second lens group G2 has a lens surface on the object side formed as an aspheric surface in which the positive refractive power becomes weaker as the distance from the optical axis increases.
In this manner, the object-side lens surface of the positive lens L4 closest to the object side of the second lens group G2 forms an aspherical 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.

Next, Tables 1 to 3 show specific data of the zoom lens of Example 1 according to the above-described first embodiment. Table 1 shows lens data of an optical system constituting the zoom lens, Table 2 shows aspherical data, and Table 3 shows 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 mm and F / F respectively. No. = 2.8 to 5.1, ω = 32.3 to 11.7 deg, and 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 , the surface interval with the subsequent optical surface (optical surface adjacent to the image side) is _di , and the optical element The 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 Abbe number of the optical material of the optical element L _j as the [nu _j, shows lens data of the optical system constituting the zoom lens shown in Table 1.

The notation of the radius of curvature r _i as “0.000” in Table 1 means that the radius of curvature r _i is infinite (∞), and indicates that the optical surface is flat.
Therefore, both surfaces of the optical elements L10 and L11 constituting the filter F are flat, and these two optical elements L10 and L11 are closely joined.
Table 4 optical surface and the eighth optical surface in 1, i.e. the image side of the lens surface r ₄ and the second lens group G2 of a meniscus-shaped negative lens L2 which is disposed second outermost from the object side of the first lens group G1 the lens surface r ₈ of the object side of the positive lens L4, which is disposed closest to the object side, and an aspherical surface.
As is well known, when the Z coordinate axis is made coincident with the optical axis and the Y coordinate is taken perpendicular to the optical axis, the radius of curvature on the optical axis is r, the conic constant is K, and the higher order aspherical coefficient is A, B, and C are curved surfaces obtained by rotating the curves represented by Formula 1 around the optical axis.

　すなわち、非球面は、数１の非球面の式に、光軸上の曲率半径ｒ、円錐定数Ｋ、および高次の非球面係数Ａ、Ｂ、およびＣの各パラメータを与えて定義することにより、形状を特定する。

That is, the aspherical surface is defined by giving the parameters of the radius of curvature r on the optical axis, the conical constant K, and the higher order aspherical coefficients A, B, and C to the equation of the aspherical surface of Formula 1. , Specify the shape.

Therefore, the fourth optical surface in Table 1, 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 the eighth optical surface in Table 1, that lens surface r ₈ on the object side of the positive lens L4 is disposed on the most object side in the second lens group G2, curvature on the optical axis shown in Table 2 the radius r _4, r _8, the conic constant K, and higher order Are formed on the aspheric surface defined by the respective parameters of the aspheric surface coefficients A, B, and C.

In Table 1, the sixth optical surface r ₆ where the surface distance d _i "variable", the spacing of the next (surface number) optical surface of the 17 optical surfaces r ₁₇ and 19 optical surface r _19, At the wide-angle end where the focal length f of the entire system is 5.60 mm, the intermediate focal length where the focal length f is 9.70 mm, and the telephoto end where the focal length f is 16.79 mm, the values change as shown in Table 3.

In this case, the overall 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 42.1 mm.
2 to 4 show aberration diagrams in the first embodiment. 2 is an aberration diagram at the wide-angle end, FIG. 3 is an aberration diagram at the intermediate focal length, and FIG. 4 is an aberration diagram at the telephoto end.
In the aberration diagrams, SA indicates spherical aberration, SC indicates sine condition, Ast indicates astigmatism, and Dist indicates distortion. In each aberration diagram, “d” indicates an aberration with respect to the d-line, and “g” indicates an aberration with respect to the g-line. In the spherical aberration diagram, the spherical aberration is indicated by a solid line, and the sine condition is indicated by a broken line. 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 FIG. 2 to FIG. 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.
FIG. 5A shows a lens configuration in a state where the zoom lens is set at the wide-angle end of zooming, and FIG. 5B shows a lens configuration in a state where the zoom lens is set at the telephoto end of zooming. Is shown.
The zoom lens shown in FIG. 5 includes a first lens group G1 ′ as a first group optical system, a second lens group G2 ′ as a second group optical system, and a A third lens group G3 ', which is a 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', L7 'and L8'. The third lens group G3 'is composed of 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 G2' and the first lens group G1 '. Further on the image side of the third lens group G3 ', a filter F formed by combining a low-pass filter L10' and an infrared light cut filter L11 'is provided between the third lens group G3' and the image plane. That is, the optical elements L1 'to L9' are lenses, and the optical elements L10 'and L11' are optical filters.

The first lens group G1 'including the lenses L1' to L3 'has a negative refractive power. The second lens group G2 'including the lenses L4' to L8 '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 'thus moves while drawing a convex arc-shaped trajectory 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 'moves monotonically on the optical axis toward the object side during zooming from the wide-angle end to the telephoto end. When 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. Thus, the third lens group G3 'moves while drawing an 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'.
As described above, the third lens group G3 'is reciprocated in an arc shape convex toward the object side, so that the power burden on the second lens group G2' is reduced and the second lens group G3 'is assisted in zooming. It is possible to reduce the amount of movement of the group G2 'and 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 G1'～G3 ', as in the case of the first embodiment, the focal length of the M lens group (M = 1 to 3) and _{f M,} all at the wide angle end when the combined focal length f _W of the system, configured to satisfy the above conditions (1) to (3).

As shown in FIG. 5, the first lens group G1 ′ includes a meniscus negative lens L1 ′ having a convex surface facing the object side, a meniscus negative lens L2 ′ having a convex surface facing the object side, and a convex surface facing the object side. , And these three lenses L1 'to L3' are arranged in the order of L1'-L2'-L3 'from the object side to the image plane side. are doing.
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 having a strong refractive surface facing the image side. L6 ', a positive lens L7', and a meniscus-shaped positive lens L8 'having a convex surface facing the object side. '-L5'-L6'-L7'-L8'.

The meniscus-shaped negative lens L2 'disposed second from the object side of the first lens group G1' forms the lens surface on the image side into an aspheric surface having a shape in which the negative refractive power becomes weaker as the distance from the optical axis increases. are doing.
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. 5A and 5B, the signs of the radii of curvature and the distances between the surfaces of the lenses L1 'to L9' and the filter F 'are not shown, but are shown in FIGS. It assumed that is common with the reference numeral r ₁ ~r ₂₂ and d ₁ to d ₂₁ was subjected in b).
Next, Tables 4 to 6 show specific data of the zoom lens of Example 2 according to the above-described second embodiment. Table 4 shows lens data of the optical system constituting the zoom lens, Table 5 shows data of the aspherical surface, and Table 6 shows data of the variable amount of the variable portion.

A fourth optical surface in Table 4, that is, a lens surface r ₄ on the image side of the negative meniscus lens L2 ′ disposed second from the object side of the first lens group G1 ′, and an eighth optical surface in Table 4, That is, 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 the radius of curvature r on the optical axis shown in Table 5, the conic constant K, and the higher order non-linearity. An aspheric surface defined by the parameters of the spherical coefficients A, B, and C is formed.

　表１において、面間隔ｄ_iを「可変」とした第６光学面ｒ₆、第１７光学面ｒ₁₇および第１９光学面ｒ₁₉の次の（面番号の）光学面ｒ₇，ｒ₁₈およびｒ₂₀との面間隔は、全系の焦点距離ｆが５．６０mmの広角端、焦点距離ｆが９．７０mmの中間焦点距離、および焦点距離ｆが１６．８０mmの望遠端において、表６に示されるように変化する。

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 at the telephoto end of 16.80Mm, Table 6 Changes as shown.

　この場合も、広角端におけるレンズ全長、すなわち光学系の第１光学面ｒ₁から像面までの距離は、４２．１mmである。

Again, the total lens length at the wide angle end, that is, the distance from the first optical surface r ₁ of the optical system to the image plane is 42.1 mm.

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.
According to FIGS. 6 to 8, it was confirmed that the aberration was satisfactorily 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 includes a first lens group G1 ″ as a first group optical system, a second lens group G2 ″ as a second group optical system, and a A third lens group G3 ″, which is a three-group optical system, is arranged.
The first lens group G1 ″ is composed of three lenses L1 ″, L2 ″ and L3 ″, and the second lens group G2 ″ is composed of five lenses L4 ″, L5 ″, L6 ″, L7 ″ and L8 ″. The third lens group G3 ″ is composed of one 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 cut filter L11 "are combined is provided between the third lens group G3" and the image plane. "-L9" are lenses, and the optical elements L10 "and L11" are optical filters.
The first lens group G1 "including the lenses L1" to L3 "has a negative refractive power. The second lens group G2" including the lenses L4 "to L8" 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 then reverses the direction of movement from the middle to move to the object side. In this way, by moving along a convex arc-shaped trajectory toward the image side, a change in the focal position at the time of zooming from the wide-angle end to the telephoto end is corrected.
The second lens group G2 ″ moves monotonously on the optical axis toward the object side during 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, then reverses the direction of movement from the middle and moves to the image side. The third lens group G3 ″ moves in such a manner as to draw an arc-shaped locus convex toward the object side. The zoom operation by the movement of the second lens group G2 ″ and the third lens group G3 ″ causes the wide-angle end. Zooming from the telephoto end to the telephoto end.

As described above, the third lens group G3 ″ is reciprocated in an arc shape convex toward the object side, so that the power burden on the second lens group G2 ″ is reduced and the second lens group G3 ″ is assisted in zooming. The amount of movement of the group G2 ″ is reduced, and it is possible to realize a small size and 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 G1 ″ to G3 ″ have the focal length of the M-th lens group (M = 1 to 3) as f _M and the wide angle as in the first and second embodiments. When the combined focal length f _W of the entire system at the end is set, the configuration is such that the above-described conditions (1) to (3) are satisfied.

As shown in FIG. 9, the first lens group G1 ″ includes a meniscus negative lens L1 ″ having a convex surface facing the object side, a meniscus negative lens L2 ″ having a convex surface facing the object side, and a convex surface facing the object side. , And these three lenses L1 ″ to L3 ″ are arranged in the order of L1 ″ −L2 ″ −L3 ″ from the object side to the image plane side. are doing.
The second lens group G2 ″ includes a positive lens L4 ″ having a strong refractive surface facing the object side, a meniscus-shaped positive lens L5 ″ having a convex surface facing the object side, and a negative lens having a strong refractive surface facing the image side. L6 ", 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 by L4. They are arranged in the order of "-L5" -L6 "-L7" -L8 ".

"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 aspherical surface of the negative refractive power becomes weaker shape the distance from the optical axis Is formed.
The "positive lens L4 disposed nearest to the object side of the" second lens group G2, and forming 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. 6A and 6B, the signs of the curvature radii and the distances between the surfaces of the lenses L1 ″ to L9 ″ and the filter F ″ are not shown, but are shown in FIGS. It assumed that is common with the reference numeral r ₁ ~r ₂₂ and d ₁ to d ₂₁ was subjected in b).
Next, Tables 7 to 9 show specific data of the zoom lens of Example 3 according to the third embodiment described above. Table 7 shows lens data of an optical system constituting the zoom lens, Table 8 shows data of an aspheric surface, and Table 9 shows data of a variable amount of a variable portion.

A fourth optical surface in Table 7, that is, an 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 an eighth optical surface in Table 7, That is, 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 8, a conic constant K, and a higher order non-linearity. An aspheric surface defined by the parameters of the spherical coefficients A, B, and C is formed.

　表７において、面間隔ｄ_iを「可変」とした第６光学面ｒ₆、第１７光学面ｒ₁₇および第１９光学面ｒ₁₉の次の（面番号の）光学面ｒ₇，ｒ₁₈およびｒ₂₀との面間隔は、全系の焦点距離ｆが５．６０mmの広角端、焦点距離ｆが９．７０mmの中間焦点距離、および焦点距離ｆが１６．８１mmの望遠端において、表９に示されるように変化する。

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 at the telephoto end of 16.81Mm, Table 9 Changes as shown.

この場合は、広角端におけるレンズ全長、すなわち光学系の第１光学面ｒ₁から像面までの距離は、４２．０mmである。

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.

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. According to FIGS. 10 to 12, it is confirmed that the aberration is satisfactorily corrected at any of the wide-angle end, the intermediate focal length, and the telephoto end in the zoom range, and the performance is good.
The parameters | f ₁ | / f _W , f ₃ / f _W , f ₂ / f ₃ , and the distortion D _W at the wide-angle end at an image height ratio of 1.0 in Examples 1 to 3 described above. 1.0) is shown in Table 10.

　上述のように、本発明の第１〜第３の実施の形態によれば、変倍比が３倍で射出瞳位置を像面から充分に離間させて、しかも小型で且つ収差が良好に補正され、さらに、歪曲収差を２％以下に抑えたズームレンズとすることができる。このようなズームレンズは、ディジタルスティルカメラ等に好適な明るい広角ズームレンズとして構成することができる。

As described above, according to the first to third embodiments of the present invention, the magnification ratio is three times, the exit pupil position is sufficiently separated from the image plane, and the size is small and the aberration is satisfactorily 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.

FIG. 2 is an optical system layout diagram schematically illustrating the configuration of the optical system of the zoom lens according to the 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. 1. FIG. 2 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at an intermediate focal length of the zoom lens of FIG. 1. FIG. 2 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens of FIG. 1. FIG. 10 is an optical system layout diagram schematically illustrating an arrangement configuration of an optical system of a zoom lens according to a second embodiment of the present invention. FIG. 6 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens in FIG. 5. FIG. 6 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. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens in FIG. 5. FIG. 11 is an optical system layout diagram schematically illustrating 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. FIG. 10 is an aberration diagram showing a spherical aberration, an astigmatism, and a distortion at an intermediate focal length of the zoom lens of FIG. 9. FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens in FIG. 9.

Explanation of reference numerals

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 ' To L11 ', L1 "to L11" Optical element L1 to L9, L1' to L9 ', L1 "to L9" Lens L10, L10', L10 ", L11, L11 ', L11" Optical filter

Claims (6)

From the object side to the image side, a first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a third group optical system having a positive refractive power are sequentially arranged. An aperture stop that moves integrally with the second group optical system during zooming on the object side of the second group optical system;
When 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 in the middle of the movement, reverses the moving direction to the object side, thereby moving in an 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,
The first group optical system has a negative lens provided with an aspheric surface, the second group optical system has a positive lens provided with an aspheric surface,
The negative lens having an aspheric surface of the first group optical system has a meniscus shape with a convex surface facing the object side, the lens surface on the image side is aspheric, and the third group optical system is a single lens. A zoom lens comprising a positive lens. The positive lens provided with an aspheric surface of the second group optical system is disposed closest to the stop, and the lens surface on the object side is an aspheric surface. The aspheric surface becomes positively refracted as the distance from the optical axis increases. The zoom lens according to claim 1, wherein the zoom lens has a shape in which a force is weakened. 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, and an object side. The zoom lens according to claim 1, further comprising three lenses each including a meniscus positive lens having a convex surface. The second group optical system includes, in order from the object side to the image side, a positive lens having a strong refractive surface facing the object side, a meniscus-shaped positive lens having a convex surface facing the object side, and a strong refractive surface facing the image side. The zoom lens according to claim 1, further comprising five lenses each including a negative lens, a positive lens, and a meniscus-shaped positive lens having a convex surface facing the object side. When the focal length of the M-th 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:
f ₃ / f _W <4.1
The zoom lens according to claim 1, wherein the following condition is satisfied. When the focal length of the M-th 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:
2.47 <| f ₁ | / F _W <2.61 (f ₁ <0)
_{0.52 <f 2 / f 3 <} 0.61 (f 2> 0, f 3> 0)
The zoom lens according to claim 1, wherein the following condition is satisfied.

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