JPH08327906A - Zoom lens - Google Patents

Abstract

PURPOSE: To obtain a compact zoom lens which is a three-component zoom lens of positive, positive and negative and of which zoom ratio is 3 to 4 and which is made higher in magnification and smaller in the number of constituting elements by constituting lens groups of distributed refractive index lenses of a specific radial type and forming the faces of the distributed refractive index lenses as aspherical faces. CONSTITUTION: This three-component zoom lens consists, successively from an object side, a first lens group having positive refracting power, a second lens group having positive refracting power and a third lens group having negative refracting power. At least one lens groups consist of the distributed refractive index lenses of the radial type expressed by the equation N(r)=N0 +N1 .r<2> + N2 .r<4> +N3 .-r<6> +N4 .r<8> +.... At least one faces of the distributed refractive index lenses of the radial type are the aspherical faces. In the equation, (r) denotes height in the direction perpendicular to the optical axis; N0 denotes the refractive index on the optical axis; N1 denotes a refractive index distribution coefft. of second order; N2 denotes a refractive index distribution coefft. of fourth order; N3 denotes a refractive index distribution coefft. of sixth order and N4 denotes a refractive index distribution coefft. of eighth order.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a small zoom lens having three positive, positive and negative components suitable for lens shutter cameras, video cameras and the like.

[0002]

2. Description of the Related Art Most of the conventionally known positive / positive / negative three-component zoom lenses have a first lens group consisting of at least two lenses and a second lens group consisting of at least four lenses. The third lens group is composed of two or three lenses.

On the other hand, there has been proposed a positive / positive / negative three-component zoom lens in which aberration is corrected by using an aspherical surface in the optical system, thereby reducing the number of lenses. For example, Japanese Patent Laid-Open No. 4-95912 discloses that each lens group is composed of one lens. In Japanese Patent Laid-Open No. 4-260016, the first lens group is composed of one lens, the second lens group is composed of two lenses, and the third lens group is composed of one lens.
It is shown in pieces. JP-A-5-188296
In the publication, the second lens group includes one or two lenses and a third lens group.
It is shown that the lens group is composed of one lens, and the total number of optical systems is four or five. JP-A-6
In Japanese Patent Laid-Open No. 123835, the first lens group is referred to as lens 2
In the figure, the second lens group includes one lens, the third lens group includes one lens, and the total number of optical systems is four. In Japanese Patent Laid-Open No. 4-78810,
It is shown that each lens group is composed of two lenses, and the total number of optical systems is six.

In Japanese Patent Laid-Open No. 4-67114,
By using a gradient index lens for the second lens group, the second lens group is composed of two lenses, and a positive / positive / negative three-component zoom lens in which the total number of constituent elements of the optical system is six is shown. ing.

The above-mentioned gradient index lens, that is, a GRIN lens, has optical characteristics.
(That is, the property that light travels while bending in the lens medium) and the possibility of dispersion control have been attracting attention for a long time as they have a great effect on reducing the number of lenses forming an optical system and making the lenses compact. It is an optical element. In particular, since it is possible to control chromatic aberration and Petzval's sum which could not be achieved with an aspherical surface, an effect superior to that of an aspherical surface is expected.

[0006]

In the conventional zoom lens having the above-mentioned aspherical surface, it is impossible to reduce the number of constituent elements of the entire optical system while making the optical system compact and achieving high magnification. . For example, even if the first lens group (that is, the lens group closest to the object side) is made up of one lens, correction of chromatic aberration and Petzval sum generated in the lens group will be insufficient with only a homogeneous lens, so However, it is impossible to achieve compactness and high magnification of the optical system (especially, high magnification cannot be achieved). In addition, in the conventional positive / positive / negative three-component zoom lens, the number of constituent elements of the lens group becomes large especially when trying to correct the aberration generated in the second lens group, so that the number of constituent elements of the entire optical system is reduced. Is very difficult. The details will be described below.

Japanese Unexamined Patent Publication Nos. 4-95912 and 4-
In the zoom lenses disclosed in Japanese Patent No. 260016 and Japanese Patent Laid-Open No. 5-188296, correction of various aberrations (particularly chromatic aberration and Petzval sum) is insufficient because the lens is a homogeneous lens, and as a result, the zoom ratio is small. Only things and dark F-numbers have been achieved. Japanese Patent Laid-Open No. 6-1
The zoom lens disclosed in Japanese Patent No. 23835 achieves a high-power zoom of 2.6 times with a small number of lenses by using an aspherical surface, but the zoom lens shown cannot be said to have high performance. It has become a thing.

Further, in the zoom lens disclosed in Japanese Patent Laid-Open No. 4-78810, at least two lenses are required in each lens group because the aspherical surface has no ability to correct chromatic aberration and Petzval sum. Has become. This is because, in the zoom lens, when trying to correct aberrations in the entire zoom range, it is necessary to correct at least chromatic aberration and Petzval's sum in each lens unit that constitutes the zoom.

In the zoom lens disclosed in Japanese Patent Laid-Open No. 4-67114, the number of constituent lenses is reduced by using a GRIN lens in the second lens group.
Since the GRIN lens is composed of only spherical lenses, the degree of freedom in aberration correction is insufficient, and in the end, the number of lenses in the second lens group is only two.

When a single-focus lens is composed of a spherical GRIN lens, the degree of freedom for third-order aberration correction is insufficient, so it is impossible to compose it with one lens.
(LGAtkinson et al., "Design of a gradient-index p
hotographic objective ", Appl.Opt.Vol.21,1982,993-9
98). The same applies to the zoom lens. In other words, if each lens group constituting the zoom lens is configured with one lens, it is impossible to correct the aberration because the degree of freedom of the third-order aberration is insufficient, and eventually each lens group of the zoom lens is changed to the lens 1 It is impossible to compose with one sheet.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a positive, positive, and negative three-component zoom lens with a high zoom ratio of about 3 to 4 times and the number of constituent lenses. It is to provide a compact zoom lens in which the reduction of

[0012]

To achieve the above object, a zoom lens according to a first aspect of the present invention comprises, in order from the object side, a first lens group having a positive refractive power and a first lens group having a positive refractive power. A three-component zoom lens including two lens units and a third lens unit having a negative refractive power, wherein at least one lens unit is a radial type represented by the following formula (A) of the refractive index distribution. Of the gradient index lens, wherein at least one surface of the radial type gradient index lens is an aspherical surface. N (r) = N ₀ + N ₁ · r ² + N ₂ · r ⁴ + N ₃ · r ⁶ + N ₄ · r ⁸ + ... (A) where r is the height in the direction perpendicular to the optical axis N ₀ : refractive index on the optical axis N ₁ : second-order refractive index distribution coefficient N ₂ : fourth-order refractive index distribution coefficient N ₃ : sixth-order refractive index distribution coefficient N ₄ : 8th-order refractive index distribution coefficient is there.

According to the structure of the first aspect of the invention, the lens has a radial type refractive index distribution, so that it is possible to correct chromatic aberration and Petzval sum generated in the lens group. Further, by using the aspherical surface, the degree of freedom for aberration correction is secured, so that each lens group of the zoom lens can be configured with one lens. The formula (A)
As you can see, the radial type refractive index profile is
The direction of the refractive index distribution is the refractive index distribution in the direction perpendicular to the optical axis.

The zoom lens according to the second invention is
A first lens group having positive refractive power in order from the object side;
A three-component zoom lens including a second lens group having a positive refracting power and a third lens group having a negative refracting power, each lens group being composed of one lens, and
It is characterized in that the following conditional expression (1) is satisfied. 0.15 <φ ₁ / φ ₂ <1.0 (1) where φ _{1 is} the refractive power of the first lens group φ ₂ is the refractive power of the second lens group.

According to the structure of the second invention, the positive / positive / negative three-component zoom lens satisfies the conditional expression (1), so that each lens group can have a well-balanced aberration correction function. Therefore, it becomes possible to increase the zoom magnification.

If the upper limit of conditional expression (1) is exceeded, the second
The lateral magnification of the lens group increases, and the burden on the aberration correction becomes very large. As a result, it becomes difficult to correct various aberrations generated therein, especially chromatic aberrations, so that the configuration becomes undesired for increasing the zoom magnification (for example, the three-component zoom disclosed in Japanese Patent Laid-Open No. 4-95912). In that case, the only option was to reduce the zoom ratio or darken the F number.) On the other hand, if the lower limit of conditional expression (1) is exceeded, the refractive power of the first lens group becomes too weak, and the amount of movement of the first lens group increases, which is not desirable.

As in the case of the zoom lens according to the first aspect of the invention, in the zoom lens according to the second aspect of the invention, at least one lens group is of the radial type represented by the formula (A). It is preferably composed of a gradient index lens.

In the zoom lens according to the second aspect of the present invention, the first lens group has a positive lens shape having a convex surface with a strong curvature on the object side, and the second lens group has a convex surface with a strong curvature on the image side. It is preferable that the third lens group has a positive lens shape, and the third lens group has a negative lens shape having a concave surface with a strong curvature on the object side.

By constructing the first lens group by one positive lens having a convex surface having a strong curvature on the object side, the image side principal point position of the first lens group becomes relatively front (object side), Two
By forming the lens unit with a positive lens having a convex surface having a strong curvature on the image side, the object-side principal point position of the second lens unit is relatively on the rear side (image side). Therefore, it is possible to reduce the distance between the first lens group and the second lens group, and thus configuring the first and second lens groups in this way
It is effective in making the optical system compact.

Further, by constructing the second lens group by one positive lens having a convex surface having a strong curvature on the image side, the image side principal point position of the second lens group is relatively rearward (image side). Therefore, by constructing the third lens group with a negative lens having a concave surface with a strong curvature on the image side, the object-side principal point position of the second lens group is relatively on the front side (object side). Therefore, it is possible to secure a sufficient distance between the second lens group and the third lens group at the zoom telephoto end. As a result, it is possible to prevent the second lens group and the third lens group from colliding with each other at the telephoto end when the magnification of the optical system is increased, and eventually it becomes impossible to achieve the high magnification of the zoom. it can.

The desirable conditions in the first and second inventions will be described below. First, regarding the movement of the lens groups, during zooming from the wide angle to the telephoto, each lens group moves toward the object side, the distance between the first lens group and the second lens group increases, and the distance between the second lens group and the second lens group increases. It is desirable that the distance to the third lens group moves so as to decrease. This makes it possible to achieve compactness at the wide-angle end.

When a radial type GRIN lens is used for a lens unit having a positive refractive power, the conditional expression shown below is used.
It is desirable to satisfy (2). ^{_{-30 <N 1d / φ p 2}} <20 ...... (2) where, N _1d: refractive index distribution coefficient of the secondary with respect to the d-line of the GRIN lens phi _p: a refractive power of the positive lens group.

Conditional expression (2) represents a condition for controlling the Petzval sum in the lens group.
If the lower limit of conditional expression (2) is exceeded, the Petzval sum becomes negatively large, which is not desirable. On the other hand, when the upper limit of conditional expression (2) is exceeded, the Petzval sum becomes positively large, and it becomes difficult to correct the Petzval sum in the optical system as a whole.

When a radial type GRIN lens is used for a lens unit having a negative refractive power, the following conditional expression
It is desirable to satisfy (3). -20 <N _1d / φ _m ² <30 (3) where φ _m is the refractive power of the negative lens group.

This conditional expression (3) shows the condition for controlling the Petzval sum in the lens group.
If the lower limit of conditional expression (3) is exceeded, the Petzval sum becomes positively large, which is not desirable. On the other hand, when the upper limit of conditional expression (3) is exceeded, the Petzval sum becomes negatively large, and it becomes difficult to correct the Petzval sum in the total optical system.

The refractive index distribution of the GRIN lens preferably satisfies the following conditional expression (4). | N _2d / φ _G ⁴ | <1000 (4) where N _{2d is the} fourth-order refractive index distribution coefficient φ _{G of the} GRIN lens with respect to the d-line: the refractive power of the GRIN lens.

Conditional expression (4) represents a condition relating to the refractive index distribution of the GRIN lens. If the range of conditional expression (4) is exceeded, the refractive index distribution of the lens becomes too large,
Higher-order aberration correction becomes very difficult.

When an aspherical surface is used for the GRIN lens, the aspherical surface has the following conditional expression when 0 <H <H _max .
It is desirable to satisfy (5). -6.0 <(φ _a −φ _0a ) / φ _G <5.0 (5) where H: height in the lens radial direction H _max : effective diameter of the lens φ _a : local refractive power of the aspheric surface φ _0a : It is the refractive power due to the reference curvature of the aspherical surface, and φ _a and φ _0a are _expressed by the following equations (B) and (C). φ _a = C _alo (n _(H) '−n _(H) ) …… (B) φ _0a = C ₀ (n ₀ ' −n ₀ ) …… (C) where C _alo is each aspherical surface. Local curvature at height C ₀ : Reference curvature of aspheric surface n _(H) ': Refractive index at each height of aspherical image side medium n _(H) : At each height of aspherical object side medium Refractive index n ₀ ': Refractive index of the aspherical image side medium on the optical axis n ₀ : Refractive index of the aspherical object side medium on the optical axis.

Conditional expression (5) represents a desirable condition that should be satisfied when an aspherical surface is used for the GRIN lens. If the upper limit of conditional expression (5) is exceeded, various aberrations occurring in the spherical system within the group will be further deteriorated by the aspherical surface, which is not desirable. On the other hand, when the value goes below the lower limit of conditional expression (5), the correction by the aspherical surface becomes excessive. For example, even when a plurality of aspherical surfaces are used, it is difficult to cancel the excessive correction by another aspherical surface, which is not desirable. .

When an aspherical surface is used for the GRIN lens, it is highly desirable that the GRIN lens has aspherical surfaces on both sides. If both aspherical surfaces are used, the degree of freedom increases due to the increase in aspherical surfaces, and the aberration that is overcorrected by one aspherical surface can be compensated for by the other aspherical surface, so that a further aberration correction effect can be obtained. Obtainable. In that case, it is desirable that the aberration that is overcorrected on one aspherical surface is corrected on the other aspherical surface.

When an aspherical surface is used for the first lens group, the aspherical surface satisfies the following conditional expression (6) when 0 <H <H _max .
It is desirable to satisfy. -6.0 <(φ _a −φ _{0 a} ) / φ ₁ <5.0 …… (6)

This conditional expression (6) shows a desirable condition that should be satisfied when an aspherical surface is used for the first lens group. If the upper limit of conditional expression (6) is exceeded, it is desirable that the spherical aberration and the coma aberration occurring in the spherical system are further deteriorated on the aspherical surface because the aspherical surface is a direction in which the positive refractive power is strengthened. Absent. On the other hand, if the lower limit of conditional expression (6) is exceeded,
On the contrary, the positive refracting power is weakened too much and the correction by the aspherical surface becomes excessive. For example, even when a plurality of aspherical surfaces are used, it is difficult to cancel the excessive correction by other aspherical surfaces, which is not desirable.

When a double-sided aspherical lens is used in the first lens group, one aspherical surface has at least 0.8H _max.
Condition (φ _a −φ _{0 a} ) / φ ₁ <0.0 in the region of <H <H _max
(Aspherical surface in the direction of weakening the positive refracting power) and the other aspherical surface satisfies the condition (φ _a −φ _0a ) / φ ₁ > 0.0 (positive aspherical surface) in a region of at least 0.8H _max <H <H _max . It is desirable to satisfy the aspherical surface (direction of strengthening the refractive power).

Further, in that case, the aspherical surfaces are 0.8
In the region of H _max <H <H _max , the following conditional expression (7)
It is desirable to meet. _{│A m1} │> A _p1 (7) where A _m1 is (φ _a −φ _0a ) / of the aspherical surface that weakens the positive refractive power.
Value of φ ₁ A _p1 : (φ _a −φ _0a ) / of the aspherical surface that strengthens the positive refractive power
It is the value of φ ₁ .

This conditional expression (7) shows a desirable condition that both aspherical surfaces in the first lens group should satisfy. If this condition is satisfied, a double-sided aspherical surface is generated in the first lens group.
Various aberrations (due to the positive refracting power) were corrected by the aspherical surface in the direction that weakens one of the positive refracting powers, resulting in overcorrection.
It means that (especially higher order) aberration is corrected by the aspherical surface in the direction that strengthens the other positive refractive power.

When an aspherical surface is used for the second lens group, the aspherical surface satisfies the following conditional expression (8) when 0 <H <H _max .
It is desirable to satisfy. -3.0 <(φ _a −φ _{0 a} ) / φ ₂ <2.0 …… (8)

This conditional expression (8) shows a desirable condition that should be satisfied when an aspherical surface is used for the second lens group. If the upper limit of conditional expression (8) is exceeded, it is desirable that the spherical aberration and coma generated in the spherical system will be further deteriorated on the aspherical surface because the aspherical surface is in the direction of strengthening the positive refractive power. Absent. On the other hand, if the lower limit of conditional expression (8) is exceeded,
On the contrary, the positive refracting power is weakened too much and the correction by the aspherical surface becomes excessive. For example, even when a plurality of aspherical surfaces are used, it is difficult to cancel the excessive correction by other aspherical surfaces, which is not desirable.

When a double-sided aspherical lens is used in the second lens group, one aspherical surface has at least 0.8H _max.
Condition (φ _a −φ _0a ) / φ ₂ <0.0 in the region of <H <H _max
(Aspherical surface in the direction of weakening the positive refracting power), and the other aspherical surface satisfies the condition (φ _a −φ _0a ) / φ ₂ > 0.0 (positive aspherical surface) in a region of at least 0.8H _max <H <H _max . It is desirable to satisfy the aspherical surface (direction of strengthening the refractive power).

Furthermore, in that case their aspherical surface is 0.8
In the region of H _max <H <H _max , the following conditional expression (9)
It is desirable to meet. _{│A m2} │> A _p2 (9) where A _m2 : (φ _a −φ _0a ) / of the aspherical surface that weakens the positive refractive power
Value of φ ₂ A _p2 : (φ _a −φ _0a ) / of the aspherical surface that strengthens the positive refractive power
It is the value of φ ₂ .

This conditional expression (9) shows a desirable condition that both aspherical surfaces in the second lens group should satisfy. If this condition is satisfied, a double-sided aspherical surface is generated in the second lens group.
Various aberrations (due to the positive refracting power) were corrected by the aspherical surface in the direction that weakens one of the positive refracting powers, resulting in overcorrection.
It means that (especially higher order) aberration is corrected by the aspherical surface in the direction that strengthens the other positive refractive power.

When an aspherical surface is used for the negative lens of the third lens group, it is desirable that the aspherical surface satisfy the following conditional expression (10) in 0 <H <H _max . -6.0 <(φ _a −φ _0a ) / φ ₃ <5.0 (10) where φ ₃ is the refractive power of the third lens group.

This conditional expression (10) shows a desirable condition that should be satisfied when an aspherical surface is used for the negative lens of the third lens group. If the upper limit of conditional expression (10) is exceeded, the spherical aberration and coma produced in the spherical system (especially at the telephoto end) will be further reduced by the aspherical surface because it is an aspherical surface that strengthens the negative refractive power. This is not desirable because it will worsen the correction of distortion at the wide-angle end. On the other hand, if the lower limit of conditional expression (10) is exceeded, conversely, the negative refracting power will be weakened too much, resulting in excessive correction by the aspherical surface. Is difficult to counteract, which is not desirable.

When a double-sided aspherical lens is used as the negative lens of the third lens group, one aspherical surface satisfies the condition (φ _a −φ _0a ) in at least 0.8H _max <H <H _max.
/ Φ ₃ <0.0 (aspherical surface in the direction of weakening the negative refracting power), and the other aspherical surface is at least 0.8H _max <H <H
_It is desirable to satisfy the condition (φ _a −φ _{0 a} ) / φ ₃ > 0.0 (aspherical surface in the direction of increasing the negative refracting power) in the _max region.

Furthermore, in that case, their aspherical surface is 0.8
In the region of H _max <H <H _max , the following conditional expression (11)
It is desirable to meet. _{│A m3} │> A _p3 (11) where A _m3 : (φ _a −φ _0a ) / of the aspherical surface that weakens the negative refracting power
Value of φ ₃ A _p3 : (φ _a −φ _0a ) / of the aspherical surface that strengthens the negative refracting power
It is the value of φ ₃ .

This conditional expression (11) shows a desirable condition that both aspherical surfaces of the negative lens in the third lens group should satisfy. If conditional expression (11) is satisfied, various aberrations (due to the negative refracting power) generated by the double-sided aspherical surface in the third lens group will be corrected by the aspherical surface in the direction that weakens one negative refracting power. That is, the aberration (in particular, higher order) is corrected by the aspherical surface in the direction of strengthening the other negative refractive power.

Furthermore, when a double-sided aspherical lens is used as the negative lens of the third lens group, one of the double-sided aspherical lenses has at least 0.8H _max <H <H _max.
In the region of (φ _a −φ _{0 a} ) / φ ₃ <0.0 (aspherical surface in the direction of weakening the negative refracting power), and the other aspherical surface is at least 0.8 H _max <H <H _max The shape may satisfy the condition (φ _a −φ _{0 a} ) / φ ₃ <0.0 (aspherical surface in the direction of weakening the negative refracting power).

Further, when an aspherical surface is used for the positive lens of the third lens group, it is desirable that the aspherical surface satisfy the conditional expression (10) at 0 <H <H _max . Where the conditional expression
(10) shows a desirable condition that should be satisfied when an aspherical surface is used for the positive lens of the third lens group. Conditional expression
When the value exceeds the upper limit of (10), the spherical aberration and coma generated in the spherical system (especially at the telephoto end) are worsened by the aspherical surface because the aspherical surface is in the direction of strengthening the negative refractive power. In addition, the correction of the distortion aberration at the wide-angle end becomes insufficient, which is not desirable. On the other hand, if the lower limit of conditional expression (10) is exceeded, conversely, the negative refracting power will be weakened too much, resulting in excessive correction by the aspherical surface. Is difficult to counteract, which is not desirable.

When a double-sided aspherical lens is used as the positive lens of the third lens group, one aspherical surface satisfies the condition (φ _a
−φ _0a ) / φ ₃ <0.0 (aspherical surface in the direction of weakening negative refracting power)
And the other aspherical surface satisfies the condition (φ _a −φ _0a ) / φ ₃
It is desirable to satisfy> 0.0 (aspherical surface in the direction of increasing negative refractive power).

When the first lens group is a GRIN lens, the dispersion satisfies the conditional expression (12) shown below in the region of 0 <H <0.5H _max , and the condition shown below in 0 <H <H _max . It is desirable to satisfy the equation (13). dν _d (H) / dH <0 …… (12) -1.0 <{ν _d (H) −ν _d (0)} / ν _d (0) ≦ 0.0 …… (13) where ν _d (H) Is a dispersion value at a point separated by a height H in the direction perpendicular to the optical axis in the GRIN lens, and this v _d (H) is expressed by the following equation (D). _{ν d (H) = {N} d (H) -1} / {N F (H) -N C (H)} ...... (D) , where, N _d (H): _d line of the height H Refractive index N _F (H): F-line refractive index at height H N _C (H): C-line refractive index at height H

Conditional expressions (12) and (13) are defined as follows when the first lens group for positive / positive / negative three-component zoom is a GRIN lens.
It shows the desired distribution of dispersion that the GRIN lens should satisfy. If the ranges of conditional expressions (12) and (13) are exceeded, color correction in the entire optical system becomes extremely difficult due to chromatic aberration occurring in the first lens group.

When the second lens group is a GRIN lens, the dispersion satisfies the conditional expression (12) in the region of 0 <H <0.5H _max , and the conditional expression (0) in the case of 0 <H <H _max . It is desirable to satisfy 13). Here, the conditional expression (1
2) and (13) show desirable distributions of dispersion that should be satisfied by the GRIN lens when the second lens group for positive / positive / negative three-component zoom is a GRIN lens. Conditional expression (1
If the ranges (2) and (13) are exceeded, color correction (especially axial chromatic aberration) in the entire optical system becomes very difficult due to chromatic aberration occurring in the second lens group.

When the third lens group is a GRIN lens, the dispersion satisfies the conditional expression (14) shown below in the region of 0 <H <0.5H _max , and the condition shown below in 0 <H <H _max . It is desirable to satisfy the formula (15). dν _d (H) / dH> 0 (14) 0.0 ≦ {ν _d (H) −ν _d (0)} / ν _d (0) <1.0 (15)

Conditional expressions (14) and (15) are defined as follows when the third lens group for positive / positive / negative three-component zoom is a GRIN lens.
It shows the desired distribution of dispersion that the GRIN lens should satisfy. If the ranges of conditional expressions (14) and (15) are exceeded, chromatic aberration in the third lens group causes chromatic aberration in the entire optical system (especially lateral chromatic aberration and axial chromatic aberration at the telephoto end). Becomes difficult.

When the first lens group is composed of one lens, it is desirable that the lens satisfies the following conditional expression (16). 0.0 <(R ₁₂ + R ₁₁ ) / (R ₁₂ −R ₁₁ ) <5.0 (16) where R _{11 is the} radius of curvature of the object side surface of the first lens group R ₁₂ is the radius of curvature of the image side surface of the first lens group .

This conditional expression (16) represents a condition relating to aberration correction in the case where the first lens group includes one lens. If the upper limit of conditional expression (16) is exceeded, spherical aberration in particular tends to fall to the over side, which is not desirable. On the other hand, if the lower limit of conditional expression (16) is exceeded, spherical aberration will fall to the under side, which is not desirable.

Similarly, the first lens group is made up of one GRI.
When it is composed of N lenses, it is the conditional expression shown below.
It is desirable to satisfy (17). 0.02 ≦ T ₁ / f ₁ ≦ 0.4 (17) where f _{1 is} the focal length of the first lens group T ₁ is the core thickness of the first lens group.

This conditional expression (17) represents the condition regarding the lens core thickness when the first lens group is composed of one GRIN lens. If the upper limit of conditional expression (17) is exceeded,
The lens core thickness becomes too large, and the thickness as a group becomes too large, and it becomes impossible to achieve a compact system. On the other hand, if the lower limit of conditional expression (17) is exceeded, the refractive index distribution of the GRIN lens becomes large in order to control the Petzval sum of the system, and the curvature of the rear surface of the lens becomes tight, which makes manufacturing difficult. Become. Further, in this case, since the refractive index distribution is large, high-order aberrations are also generated, which is not desirable.

When the second lens group is composed of one lens, it is desirable that the lens satisfies the following conditional expression (18). -5.0 <(R ₂₂ + R ₂₁ ) / (R ₂₂ −R ₂₁ ) <0.0 (18) However, R ₂₁ : radius of curvature of the object side surface of the second lens group R ₂₂ : of the image side surface of the second lens group Is the radius of curvature.

This conditional expression (18) shows the condition relating to the aberration correction in the case where the second lens group is composed of one lens. If the upper limit of conditional expression (18) is exceeded, spherical aberration particularly falls to the over side, which is not desirable. On the other hand, if the lower limit of conditional expression (18) is exceeded, the spherical aberration falls to the under side and the R ₂₂ surface (image side surface of the second lens group)
Is not desirable because it causes a large curvature and makes manufacturing difficult.

Similarly, the second lens group is made up of one GRI.
When it is composed of N lenses, it is the conditional expression shown below.
It is desirable to satisfy (19). 0.08 ≦ T ₂ / f ₂ ≦ 1.0 (19) where f _{2 is} the focal length of the second lens group T ₂ is the core thickness of the second lens group.

This conditional expression (19) represents the condition relating to the lens core thickness when the second lens group is composed of one GRIN lens. If the upper limit of conditional expression (19) is exceeded,
The lens core thickness becomes too large, and the thickness as a group becomes too large, and it becomes impossible to achieve a compact system. On the other hand, if the lower limit of conditional expression (19) is exceeded, the refractive index distribution of the GRIN lens becomes large and the curvature of the rear surface of the GRIN lens becomes particularly large in order to control the Petzval sum of the system, which makes manufacturing difficult. Become. Further, in this case, since the refractive index distribution is large, high-order aberrations are also generated, which is not desirable.

When the third lens unit is composed of one lens, it is desirable that the lens satisfies the following conditional expression (20). 0.0 <(R ₃₂ + R ₃₁ ) / (R ₃₂ −R ₃₁ ) <5.0 (20) where R _{31 is the} radius of curvature of the object side surface of the third lens group R ₃₂ is the radius of curvature of the image side surface of the third lens group .

This conditional expression (20) represents the condition relating to the aberration correction in the case where the third lens group is composed of one lens. If the upper limit of conditional expression (20) is exceeded, spherical aberration particularly at the telephoto end falls to the over side, which is not desirable. On the other hand, if the lower limit of conditional expression (20) is exceeded, the spherical aberration will fall to the under side, which is not desirable. Further, if these limits are exceeded, coma will also deteriorate, which is not desirable.

Similarly, the third lens group is made up of one GRI.
When it is composed of N lenses, it is the conditional expression shown below.
It is desirable to satisfy (21). 0.02 ≦ T ₃ / | f ₃ | ≦ 0.7 (21) where f _{3 is} the focal length of the third lens group T ₃ is the core thickness of the third lens group.

This conditional expression (21) represents the condition regarding the lens core thickness when the third lens group is composed of one GRIN lens. If the upper limit of this conditional expression (21) is exceeded, the lens core thickness will become too large, and the thickness of the lens group will become large, making it impossible to achieve a compact system. On the other hand, when the lower limit of conditional expression (21) is exceeded, the refractive index distribution of the GRIN lens becomes large and the curvature of the rear surface of the GRIN lens becomes large in order to control the Petzval sum of the system, which makes the manufacturing difficult. Become. Also in this case,
Since the refractive index distribution is large, high-order aberrations are also generated, which is not desirable.

In the positive / positive / negative three-component zoom lens, it is desirable that the first lens group satisfy the following conditional expression (22). 0.1 ≦ φ ₁ / φ _W ≦ 1.0 (22) where φ _W is the refractive power at the wide-angle end of the entire optical system.

This conditional expression (22) represents the condition relating to the refractive power of the first lens group. If the upper limit of conditional expression (22) is exceeded, the refractive power of the group becomes too strong, and it becomes difficult to correct various aberrations (particularly spherical aberration and coma). On the other hand, the conditional expression
When the value goes below the lower limit of (22), the refracting power of the group becomes too weak, which leads to an increase in the optical system and an amount of movement of the group during zooming, which is not desirable.

In the positive / positive / negative three-component zoom lens, it is desirable that the third lens group satisfy the following conditional expression (23). 0.4 ≦ | φ ₃ / φ _W | ≦ 2.5 …… (23)

This conditional expression (23) shows the condition relating to the refractive power of the third lens group. If the upper limit of conditional expression (23) is exceeded, the refracting power of the group becomes too strong, and it becomes difficult to correct various aberrations (particularly spherical aberration at the telephoto end and distortion aberration at the wide-angle end). On the other hand, when the value goes below the lower limit of the conditional expression (23), the refractive power of the group becomes too weak, which causes an increase in the optical system.
This is not desirable because the amount of movement of the group during zooming increases.

Next, paraxial ray tracing in a radial type GRIN lens will be described. If the refractive index distribution is expressed by the above-mentioned refractive index distribution formula (A), the optical path in the radial type refractive index distribution medium is expressed by the following equation (1) for each of the cases (a) and (b) below. , Is expressed by the paraxial ray-tracing equation of Equation 2. As can be seen from the equations (1) and (2), in the GRIN lens, the light ray does not travel linearly as in a homogeneous medium, but gradually travels while curving due to its refractive index distribution. Therefore, even if the GRIN lens is a flat lens, it becomes a lens having a refractive power.

[0071]

[Equation 1] Here, k ² = −2N ₁ / N ₀ .

[0072]

[Equation 2] Here, k ² = 2N ₁ / N ₀ .

Here, α ′: direction of light ray (tilt) α: incident inclination H ₀ : incident height z: distance from the lens object side surface vertex in the direction parallel to the optical axis.

Next, the effect of the radial type GRIN lens on Petzval sum correction will be described. The Petzval sum PT in the case of using the radial type GRIN lens is represented by the following formula (E) when the optical system is approximated by a thin wall. PT = (φ _S / N ₀ ) + (φ _M / N ₀ ² ) ... (E) where φ _S : refractive power of the surface (refractive power when the lens is homogeneous) φ _M : medium Refractive power φ = φ _S + φ _M (where φ: is the refracting power of the system) …… (F).

From the above equations (E) and (F), the refracting powers φ _S and φ _M are given by the following equations (G) and (H), respectively (that is, from the refracting power φ of the system and the Petzval sum PT, The respective refracting powers φ _S and φ _M are obtained using the refractive index N ₀ on the axis as a parameter.) φ _S = (N ₀ ² · PT−φ) / (N ₀ −1) …… (G) φ _M = {N ₀ (N ₀ · PT−φ)} / (1-N ₀ ) …… (H )

Here, assuming that the lens core thickness is t, the refractive power φ _M is expressed by the formula: φ _M ≈−2N ₁ · t (I) Therefore, φ _M obtained by the above equation (H)
Therefore, when the Petzval sum PT is given with the refractive index N ₀ on the optical axis and the lens core thickness t as parameters, the second-order refractive index distribution coefficient N ₁ is uniquely determined by the formula (I). From this, when the target of the Petzval sum PT of the system is determined, it can be said that the Petzval sum PT of the system has been corrected by using the second-order refractive index distribution coefficient N ₁ obtained by the above calculation. .

Next, the handling of chromatic aberration will be described. The axial chromatic aberration PAC of the thin type is represented by the following formula (J). This formula
From (J), the quadratic coefficient of the refractive index distribution of each wavelength is important for correcting chromatic aberration of the system (that is, ν ₁ is important).
I understand. PAC ∝ (φ _S / ν ₀ ) + (φ _M / ν ₁ ) ... (J) where ν ₀ : Abbe number when the lens is homogenous ν ₁ : Abbe number because the medium is a GRIN lens Yes, and they are represented by the following equations (K) and (L), respectively. ν ₀ = (N _0d −1) / (N _0F −N _0C ) …… (K) ν ₁ = N _1d / (N _1F −N _1C ) …… (L) where N _0d : lens for d line Refractive index on optical axis N _0F : Refractive index on lens optical axis for F line N _0C : Refractive index on lens optical axis for C line N _1d : Second-order refractive index distribution coefficient N _1F for d line : Second order refractive index distribution coefficient for F line N _1C : second order refractive index distribution coefficient for C line

Next, the third-order aberration coefficient of the GRIN lens will be described. As described above, light travels while bending inside the GRIN lens, which is an effect of the medium of the GRIN lens having a refractive index distribution. Therefore, the effect of the medium also contributes to the aberration coefficient.
PJ Sands paper (PJ Sands, "Third-Order Aberrations
of Inhomogeneous Lenses ", J.Opt.Soc.Am, Vol.60, No.1
1,1970,1436-1443), the aberration coefficient of a lens including a GRIN lens is discussed.
The aberration coefficient of the N lens is expressed by the sum of four terms as follows. [Aberration coefficient of GRIN lens] = [Contribution of spherical surface] + [Contribution of aspherical surface] + [Contribution of surface by GRIN lens] + [GRIN
Contribution of lens medium]

The terms of [spherical surface contribution] and [aspherical surface contribution] are the same as the aberration coefficient of a conventional homogeneous lens, and in addition, an aspherical contribution due to the fact that the lens is a GRIN lens. And the contribution of light being bent in the medium of the GRIN lens are added to give a total aberration coefficient. This total aberration coefficient is expressed by the following equation (3).

[0080]

(Equation 3)

However, S _i : Third-order aberration coefficient of GRIN lens (Seidel's 5 aberrations) S _0i : [Contribution of spherical surface] + [Contribution of aspherical surface] a _ij : [Contribution of surface by GRIN lens] a _ij ^* : [Contribution by medium of GRIN lens] of j-th surface k: number of surfaces of optical system

[Contribution of surface by GRIN lens] a _ij
Is represented by the following formula. a _1j = κ _j · y _aj ⁴ a _2j = κ _j · y _aj ³ · y _bj a _3j = κ _j · y _aj ² · y _bj ² a _4j = 0 a _5j = κ _j · y _aj · y _bj ³ However, κ _j = −C _j · Δ {4N ₁ + C _j (dN ₀ / dz)} (in the case of a radial type GRIN lens, dN ₀ / dz
≡ 0 [z is the optical axis direction]. ) C _j : Curvature of j-th surface Δ: Difference between various amounts before and after refraction on lens surface y _aj : Height of paraxial chief ray on j-th surface y _bj : Height of paraxial marginal ray on j-th surface Is.

[Contribution by medium of GRIN lens] a
_ij ^* is represented by the following formula. In the formula, 'indicates a value after refraction on that surface (for example, the j-th surface), and the subscript j is omitted. ^{_{a 1j * = ∇ (N 0}} · y a · v a '3) + ∫ 0 t (8N 2 · y a 4 + 4N 1 · y a
² · v _a ' ^{2 −} N ₀ v _a ' ⁴ ) dz a _2j ^* = ∇ (N ₀ · y _a · v _a ' ² · v _b ') + ∫ ₀ ^t (8N ₂ · y _a ³ · y <sub>b
+ 2N 1 · y a · v</sub> a '[y a · v b' + y b v a '] -N 0 · v a' 3 ·
v _b ') dz a _3j ^* = ∇ (N ₀ · y _a · va _a ′ · v _b ' ² ) + ∫ ₀ ^t (8N ₂ · y _a ² · y _b ²
_{+ 4N 1 · y a · y} b · v a '· v b' -N 0 · v a '2 · v b' 2) dz a 4j * = ∫ 0 t (N 1 / N 0 2) dz a 5j * _{= ∇ (N 0 · y a} · v b '3) + ∫ 0 t (8N 2 · y a · y b 3 + 2N 1
_{· Y b · v b '[} y a · v b' + y b v a '] -N 0 · v a' · v b '3) dz where, ∇: quantities before and after the propagation starting-end of the medium of the difference y _a: is the angle of the paraxial marginal ray paraxial height axis principal ray y _b: height of the paraxial marginal ray v _a: angle of the paraxial chief ray v _b.

[0084]

According to the structure of the first invention, since the radial type gradient index lens is used, it is possible to satisfactorily correct chromatic aberration and Petzval's sum, and further, this gradient index lens is provided. Since the aspherical surface ensures the degree of freedom in aberration correction, each lens group of the zoom lens can be configured with one lens.

According to the structure of the second invention, even if each lens group is composed of one lens, by satisfying the conditional expression (1) regarding the refractive power of the first and second lens groups, each lens group It is possible to satisfactorily correct the aberration.

[0086]

EXAMPLES Examples of zoom lenses according to the present invention will be shown below. In each example, ri (i = 1,2,3, ...) indicates the radius of curvature of the i-th surface Si (i = 1,2,3, ...) counted from the object side,
di (i = 1,2,3, ...) indicates the i-th axial top surface distance from the object side, and Ni (i = 1,2,3, ...), νi (i = 1, 2,3, ...) indicates the refractive index and Abbe number of the i-th lens for the d-line counting from the object side. Further, the focal length f of the entire system and the F number FNO at the wide end [W], the intermediate focal length [M], and the tele end [T] are also shown.

In each of the embodiments, the surface marked with * on the surface Si indicates that the surface is an aspherical surface, and is defined by the following formula 4 which represents the surface shape of the aspherical surface. And

[0088]

[Equation 4]

However, in the equation (4), X: displacement from the reference surface in the optical axis direction Y: height in the direction perpendicular to the optical axis C: paraxial curvature ε: quadric surface parameter Ai: i It is an aspherical coefficient.

For each example, Table 1 to Table 3; Table 7, Table 8; Table 12 to Table 14; Table 18 to Table 20; Table 24 to
Table 26 shows the refractive index distribution coefficient of radial distribution of GRIN lenses (GRIN1 to GRIN3), and Tables 4 to 6; Tables 9 to 1
1; Table 15 to Table 17; Table 21 to Table 23; Table 27 to Table 29
Shows the values corresponding to the conditional expressions (1) to (23).

Example 1 f = 38.9 to 75.5 to 133.0 FNO = 3.60 to 5.91 to 9.18 [plane] [curvature radius] [axis upper surface spacing] [GRIN lens] {Gr1} S1 * r1 35.214 d1 6.000 GRIN1 S2 * r2 182.059 d2 4.902 ~ 17.320 ~ 25.192 {Gr2} S3 * r3 -38.891 d3 13.766 GRIN2 S4 * r4 -14.094 d4 25.325 ~ 14.551 ~ 8.520 {Gr3} S5 * r5 -22.237 d5 2.817 GRIN3 S6 * r6 58.823 Σd = 52.809 ~ 52.809 ~ ~ 56.295

[Aspherical data] S1: ε = 1.0000 A4 = -0.13708 × 10 ^-4 A6 = -0.29259 × 10 ^-7 A8 = -0.12399 × 10 ^-9 A10 = -0.75694 × 10 ^-13 A12 = 0.12456 × 10 ^-16 S2: ε = 1.0000 A4 = -0.13611 × 10 ^-4 A6 = -0.34 168 × 10 ^-7 A8 = -0.47310 × 10 ^-10 A10 = 0.28331 × 10 ^-13 A12 = 0.13843 × 10 ^-16 S3: ε = 1.0000 A4 = -0.68634 × 10 ^-4 A6 = 0.62144 × 10 ^-7 A8 = -0.850 42 × 10 ^-8 A10 = 0.19116 × 10 ^-9 A12 = -0.14989 × 10 ^-11 S4: ε = 1.0000 A4 = 0.56337 × 10 ^{-5 A6 = -0.92913 × 10 -8 A8 =} -0.49274 × 10 -8 A10 = 0.35667 × 10 -10 A12 = -0.27362 × 10 -13 S5: ε = 1.0000 A4 = 0.72812 × 10 -4 A6 = -0.50640 × 10 - ⁶ A8 = 0.24029 × 10 ^-8 A10 = 0.15908 × 10 ^-11 A12 = -0.22905 × 10 ^-13 S6: ε = 1.0000 A4 = 0.78956 × 10 ^-5 A6 = -0.25503 × 10 ^-6 A8 = 0.75480 × 10 ^-9 A10 = -0.80557 × 10 ^-13 A12 = -0.22267 × 10 ^-14

[0093]

[Table 1]

[0094]

[Table 2]

[0095]

[Table 3]

[0096]

[Table 4]

[0097]

[Table 5]

[0098]

[Table 6]

Example 2 f = 38.9 to 75.5 to 133.0 FNO = 3.60 to 5.93 to 9.24 [plane] [curvature radius] [axis upper surface spacing] [GRIN lens] {Gr1} S1 * r1 35.214 d1 6.000 GRIN1 S2 * r2 182.059 d2 4.902 to 17.320 to 25.192 {Gr2} S3 * r3 -38.891 d3 13.766 GRIN2 S4 * r4 -14.094 d4 20.034 to 9.260 to 3.229 {Gr3} S5 * r5 -41.554 [Refractive index] [Abbe number] d5 4.300 N3 1.58340 ν3 30.23 S6 * r6 -21.599 d6 3.100 S7 r7 -13.226 d7 1.200 N4 1.61800 ν4 63.39 S8 r8 208.332 Σd ＝ 53.301〜54.946〜56.787

[0100] [Aspherical Data] S1: ε = 1.0000 A4 = -0.56592 × 10 -5 A6 = -0.89214 × 10 -8 A8 = -0.96609 × 10 -10 A10 = 0.99980 × 10 -14 A12 = 0.36852 × 10 - ¹⁵ S2: ε = 1.0000 A4 = -0.67805 × 10 ^-5 A6 = -0.15083 × 10 ^-7 A8 = -0.20319 × 10 ^-10 A10 = 0.71035 × 10 ^-13 A12 = 0.11265 × 10 ^-15 S3: ε = 1.0000 A4 = -0.49905 × 10 ^-4 A6 = 0.45911 × 10 ^-7 A8 = -0.56389 × 10 ^-8 A10 = 0.11205 × 10 ^-9 A12 = -0.36621 × 10 ^-12 S4: ε = 1.0000 A4 = -0.77066 × 10 ^-5 A6 = -0.73209 × 10 ^-7 A8 = -0.42058 × 10 ^-8 A10 = 0.140 64 × 10 ^-10 A12 = 0.46336 × 10 ^-12 S5: ε = 1.0000 A4 = 0.21158 × 10 ^-4 A6 = -0.63080 × 10 ^-6 A8 = 0.10295 × 10 ^-7 A10 = -0.22328 × 10 ^-10 A12 = -0.43 167 × 10 ^-12 A14 = 0.13292 × 10 ^-14 A16 = 0.38291 × 10 ^-17 S6: ε = 1.0000 A4 = -0.17555 × 10 ^-4 A6 = -0.53307 × 10 ^-6 A8 = 0.56899 × 10 ^-8 A10 = -0.32546 × 10 ^-10 A12 = 0.30347 × 10 ^-12 A14 = -0.32467 × 10 ^-14 A16 = 0.88590 × 10 ^-17

[0101]

[Table 7]

[0102]

[Table 8]

[0103]

[Table 9]

[0104]

[Table 10]

[0105]

[Table 11]

Example 3 f = 39.0 to 75.6 to 133.2 FNO = 3.60 to 5.76 to 8.73 [plane] [radius of curvature] [axis upper surface spacing] [GRIN lens] {Gr1} S1 * r1 19.236 d1 3.376 GRIN1 S2 * r2 31.690 d2 3.826 ~ 15.158 ~ 22.338 {Gr2} S3 * r3 -38.660 d3 10.371 GRIN2 S4 * r4 -13.723 d4 25.419 ~ 14.673 ~ 8.500 {Gr3} S5 * r5 -14.854 d5 2.500 GRIN3 S6 * r6 -143.032 Σd = 45.492 46.077 ~ 47.084

[Aspherical data] S1: ε = 1.0000 A4 = -0.11101 × 10 ^-4 A6 = -0.31213 × 10 ^-7 A8 = -0.25714 × 10 ^-9 A10 = -0.21090 × 10 ^-11 A12 = -0.10704 × 10 ^-13 S2: ε = 1.0000 A4 = -0.92959 × 10 ^-5 A6 = -0.70696 × 10 ^-7 A8 = -0.71400 × 10 ^-9 A10 = -0.25534 × 10 ^-11 A12 = 0.22470 × 10 ^-13 S3: ε = 1.0000 A4 = -0.72892 × 10 ^-4 A6 = 0.18671 × 10 ^-6 A8 = -0.10447 × 10 ^-7 A10 = 0.21617 × 10 ^-9 A12 = -0.19349 × 10 ^-11 S4: ε = 1.0000 A4 = -0.79424 × 10 ^-5 A6 = -0.25155 × 10 ^-6 A8 = -0.19348 × 10 ^-8 A10 = -0.59649 × 10 ^-10 A12 = 0.11942 × 10 ^-11 S5: ε = 1.0000 A4 = 0.14140 × 10 ^-3 A6 = -0.34045 × 10 ^-6 A8 = 0.16645 × 10 ^-8 A10 = -0.11636 × 10 ^-10 A12 = 0.53017 × 10 ^-13 S6: ε = 1.0000 A4 = 0.33472 × 10 ^-5 A6 = -0.12069 × 10 ^-6 A8 = 0.44230 × 10 ^-9 A10 = -0.160 35 × 10 ^-11 A12 = 0.31384 × 10 ^-14

[0108]

[Table 12]

[0109]

[Table 13]

[0110]

[Table 14]

[0111]

[Table 15]

[0112]

[Table 16]

[0113]

[Table 17]

Example 4 f = 39.0 to 75.3 to 132.2 FNO = 3.60 to 5.84 to 9.26 [plane] [curvature radius] [axis upper surface spacing] [GRIN lens] {Gr1} S1 * r1 19.763 d1 4.546 GRIN1 S2 * r2 28.143 d2 1.000 ~ 17.320 ~ 25.192 {Gr2} S3 * r3 -54.468 d3 13.000 GRIN2 S4 * r4 -14.545 d4 25.348 ~ 14.551 ~ 8.520 {Gr3} S5 * r5 -20.519 d5 1.107 GRIN3 S6 * r6 68.036 Σd = 45.000 ~ 50.523. ~ 52.365

[Aspherical data] S1: ε = 1.0000 A4 = -0.14605 × 10 ^-4 A6 = -0.38770 × 10 ^-7 A8 = -0.20976 × 10 ^-9 A10 = -0.85100 × 10 ^-12 A12 = -0.56174 × 10 ^-14 S2: ε = 1.0000 A4 = -0.12474 × 10 ^-4 A6 = -0.46235 × 10 ^-7 A8 = -0.40022 × 10 ^-9 A10 = -0.32334 × 10 ^-11 A12 = 0.14197 × 10 ^-13 S3: ε = 1.0000 A4 = -0.72911 × 10 ^-4 A6 = 0.94527 × 10 ^-7 A8 = -0.92016 × 10 ^-8 A10 = 0.17892 × 10 ^-9 A12 = -0.92520 × 10 ^-12 S4: ε = 1.0000 A4 = 0.57695 × 10 ^-5 A6 = -0.47917 × 10 ^-7 A8 = -0.54778 × 10 ^-8 A10 = 0.24387 × 10 ^-11 A12 = 0.64533 × 10 ^-12 S5: ε = 1.0000 A4 = 0.37359 × 10 ^-4 A6 = -0.38061 × 10 ^-6 A8 = 0.22097 × 10 ^-8 A10 = 0.30354 × 10 ^-11 A12 = -0.29399 × 10 ^-13 S6: ε = 1.0000 A4 = -0.45821 × 10 ^-4 A6 = -0.58353 × 10 ^-7 A8 = 0.69408 × 10 ^-9 A10 = -0.11 103 × 10 ^-11 A12 = -0.115 18 × 10 ^-14

[0116]

[Table 18]

[0117]

[Table 19]

[0118]

[Table 20]

[0119]

[Table 21]

[0120]

[Table 22]

[0121]

[Table 23]

Example 5 f = 38.9 to 75.5 to 133.2 FNO = 3.60 to 5.79 to 8.94 [surface] [curvature radius] [axial upper surface spacing] [GRIN lens] {Gr1} S1 * r1 17.338 d1 2.723 GRIN1 S2 * r2 29.975 d2 2.364 ~ 11.673 ~ 17.187 {Gr2} S3 * r3 -28.504 d3 8.473 GRIN2 S4 * r4 -12.202 d4 23.204 ~ 13.876 ~ 8.500 {Gr3} S5 * r5 -13.226 d5 2.500 GRIN3 S6 * r6 -77.123 Σd = 39.264 39.244 ~ 39.382

[Aspherical data] S1: ε = 1.0000 A4 = -0.82445 × 10 ^-5 A6 = -0.58420 × 10 ^-7 A8 = -0.66920 × 10 ^-9 A10 = -0.77340 × 10 ^-11 A12 = -0.74900 × 10 ^-13 S2: ε = 1.0000 A4 = -0.89565 × 10 ^-5 A6 = -0.113 64 × 10 ^-6 A8 = -0.14265 × 10 ^-8 A10 = -0.79825 × 10 ^-11 A12 = 0.15285 × 10 ^-13 S3: ε = 1.0000 A4 = -0.92407 × 10 ^-4 A6 = 0.12823 × 10 ^-6 A8 = -0.10094 × 10 ^-7 A10 = 0.35499 × 10 ^-9 A12 = -0.57203 × 10 ^-11 S4: ε = 1.0000 A4 = -0.88335 × 10 ^-5 A6 = -0.32982 × 10 ^-6 A8 = -0.58897 × 10 ^-8 A10 = -0.18343 × 10 ^-9 A12 = 0.31830 × 10 ^-11 S5: ε = 1.0000 A4 = 0.16591 × 10 ^-3 A6 = -0.74943 × 10 ^-6 A8 = 0.45270 × 10 ^-8 A10 = -0.25022 × 10 ^-10 A12 = 0.10431 × 10 ^-12 S6: ε = 1.0000 A4 = -0.46558 × 10 ^-4 A6 = 0.10056 × 10 ^-6 A8 = -0.24196 × 10 ^-9 A10 = 0.22951 × 10 ^-12 A12 = 0.10685 × 10 ^-14

[0124]

[Table 24]

[0125]

[Table 25]

[0126]

[Table 26]

[0127]

[Table 27]

[0128]

[Table 28]

[0129]

[Table 29]

1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 are lens configuration diagrams corresponding to Examples 1 to 5, respectively.
The lens arrangement at the wide end [W] is shown. The loci m1, m2, m3 in these figures are the first lens group (G
r1), second lens group (Gr2), third lens group (Gr3)
The respective movements during zooming from the wide end [W] to the tele end [T] are schematically shown.

Examples 1 to 5 are, in order from the object side,
Three-component zoom consisting of a first lens group (Gr1) having a positive refractive power, a second lens group (Gr2) having a positive refractive power, and a third lens group (Gr3) having a negative refractive power It is a lens. The first lens group (Gr1) has a positive lens shape having a convex surface having a strong curvature on the object side, and the second lens group
(Gr2) has a positive lens shape having a convex surface having a strong curvature on the image side, and the third lens group (Gr3) has a negative lens shape having a concave surface having a strong curvature on the object side.

In Examples 1 and 4, the first lens group
(Gr1) is a positive meniscus lens convex to the object side, the second lens group (Gr2) is a positive meniscus lens convex to the image side, and the third lens group (Gr3) is a biconcave negative lens. Made of lenses. In Example 2, the first lens group
(Gr1) is a positive meniscus lens convex to the object side, the second lens group (Gr2) is a positive meniscus lens convex to the image side, and the third lens group (Gr3) is convex to the image side. It consists of a positive meniscus lens and a biconcave negative lens. In Example 3 and Example 5, the first lens group (Gr
1) is composed of a positive meniscus lens convex to the object side, the second lens group (Gr2) is composed of a positive meniscus lens convex to the image side, and the third lens group (Gr3) is concave to the object side. Made of negative meniscus lenses.

2, FIG. 4, FIG. 6, FIG. 8 and FIG. 10 are aberration charts corresponding to Examples 1 to 5, respectively. In these figures, [W] indicates the aberration at the wide end, [M] indicates the intermediate focal length (middle), and [T] indicates the aberration at the tele end. Also, the solid line
(d) shows the spherical aberration for the d line, the broken line (SC) shows the sine condition, and the broken line (DM) and the solid line (DS) show the astigmatism for the d line on the meridional surface and the sagittal surface, respectively. There is.

[0134]

As described above, according to the zoom lens according to the first aspect of the present invention, since the GRIN lens is an aspherical surface in the positive / positive / negative three-component zoom lens, the number of constituent lenses is increased. While being compact,
Moreover, it is possible to realize a high-magnification zoom lens having a zoom ratio of about 3 to 4 times.

According to the zoom lens of the second invention, in the positive / positive / negative three-component zoom lens, each lens group is composed of one lens and the conditional expression (1) is satisfied. Therefore, it is possible to realize a compact and high-magnification zoom lens having a zoom ratio of about 3 to 4 while reducing the number of constituent elements.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment of the present invention.

FIG. 2 is an aberration diagram of Example 1 of the present invention.

FIG. 3 is a lens configuration diagram of a second embodiment of the present invention.

FIG. 4 is an aberration diagram of Example 2 of the present invention.

FIG. 5 is a lens configuration diagram of a third embodiment of the present invention.

FIG. 6 is an aberration diagram for Example 3 of the present invention.

FIG. 7 is a lens configuration diagram of Example 4 of the present invention.

FIG. 8 is an aberration diagram for Example 4 of the present invention.

FIG. 9 is a lens configuration diagram of a fifth embodiment of the present invention.

FIG. 10 is an aberration diagram of Example 5 of the present invention.

[Explanation of symbols]

 Gr1 ... 1st lens group Gr2 ... 2nd lens group Gr3 ... 3rd lens group

Claims (2)

[Claims] 1. A first lens having a positive refractive power in order from the object side.
A three-component zoom lens including a lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, wherein at least one lens group has a refractive index distribution shown below. A zoom lens comprising a radial type gradient index lens element represented by the following formula, wherein at least one surface of the radial type gradient index lens element is an aspherical surface; N (r) = N ₀ + N ₁ · r ² + N ₂ · r ⁴ + N ₃ · r ⁶ + N ₄ · r ⁸ +, where r: height in the direction perpendicular to the optical axis N ₀ : refractive index on the optical axis N ₁ : 2 following the refractive index distribution coefficient N _2: 4-order refractive index distribution coefficient N _3: 6-order refractive index distribution coefficient N _4: 8 is a primary refractive index distribution coefficients. 2. A first lens element having a positive refractive power in order from the object side.
A three-component zoom lens including a lens group, a second lens group having a positive refracting power, and a third lens group having a negative refracting power, each lens group being composed of one lens. And a zoom lens characterized by satisfying the following conditions: 0.15 <φ ₁ / φ ₂ <1.0 where φ _{1 is} the refractive power of the first lens group φ ₂ is the refractive power of the second lens group .